Reviews and Comments

• Data Assimilation for Soil Hydraulic Parameter Estimation：Progress and Perspectives

  MAN Jun, ZHANG Jiangjiang, ZHENG Qiang, YAO Yijun, ZENG Lingzao

  2023,60(6):1543-1554, DOI: 10.11766/trxb202203040090

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  Abstract:

  The characterization of soil hydraulic parameters and their heterogeneity is related to many scientific problems in soil and groundwater fields. Due to the limitation of time and sampling cost, the traditional experimental approaches cannot address this issue adequately. With the development of Internet of Things technology, the state variables related to soil water movement (such as water content and pressure head) can be acquired in real time through sensors. This has sparked some debates about how to estimate the soil hydraulic parameters using these measurements. Data assimilation methods can estimate the soil hydraulic parameters by integrating the measurements into numerical models. This paper systematically analyzes the uncertainty sources and measurement approaches of soil hydraulic parameters, expounds on the basic principles of several common data assimilation methods and their applications in soil hydraulic parameter inversion, and discusses the latest advances in data assimilation methods from aspects of computational efficiency and accuracy. Finally, the development direction of data assimilation methods is provided. The results show that the data assimilation methods can break through the limitation of the traditional experimental approach, and thus are suitable for the characterization of soil hydraulic parameters and their heterogeneity. However, limitations such as the strong nonlinearity of the unsaturated flow model, spatial heterogeneity of soil and sparsity of in-situ measurements do exist. It is, therefore, essential for us to unfold in-depth research on soil hydraulic parameter inversion from the aspects of supervised dimension reduction method, multi-source and multi-scale data fusion, and coupling of machine learning with physical mechanisms, thereby assisting agricultural soil and water management as well as the prevention, control, and remediation of pollution in agroecosystems.

• Functions of Plant Growth-Promoting Bacteria and Their Application in Sustainable Agriculture

  MA Ying, CAO Mengyuan, SHI Xiaojun, LI Zhenlun, LUO Yongming

  2023,60(6):1555-1568, DOI: 10.11766/trxb202203160112

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  Abstract:

  Global climate change and population growth exacerbate various biotic (e.g., infection of pathogens) and abiotic (e.g., drought, salinity, high temperature, etc.) stress in agricultural production, which impede plant growth, development and productivity by affecting plant morphology, physiological and biochemical characteristics as well as metabolic functions. Consequently, this affects crop yield and quality and seriously threatens agricultural sustainability. With the vigorous development of modern agriculture, beneficial microorganisms have attracted much attention due to their ability to improve soil quality and fertility, stress tolerance in crops, and their yield and quality. Besides, the proper use of microbial inoculum in agricultural production can achieve the effects of reducing the amounts of agrochemicals, reducing production costs, improving the quality of agricultural products, and protecting the ecological environment, which is also in line with the agricultural production goal of harmonious coexistence between humans and nature. In this review, the types and application effects of plant growth-promoting bacteria (PGPB) were briefly summarized, with emphasis on the analysis of PGPB's ability to produce phytohormone, fix nitrogen, facilitate the absorption and utilization of nutrients (phosphate and potassium solubilization and siderophore production), alleviate biotic and abiotic stress, regulate plant root architecture and rhizosphere microbial community structure. Moreover, the frontier science and technology of PGPB inoculum preparation and application methods in modern agriculture in recent years were systematically explored, and the application prospect and research direction of PGPB in future agricultural production were further discussed.

Research Articles

• Soil Organic Matter Prediction Research on the Integrating Models with Reduction of Residual Autocorrelation

  SONG Jie, WANG Siwei, ZHAO Yanhe, YU Dongsheng, CHEN Yang, WANG Xin, FENG Kaiyue, MA Lixia

  2023,60(6):1569-1581, DOI: 10.11766/trxb202111020591

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  Abstract:

  【Objective】Improving the spatial prediction accuracy of soil attributes is of great significance for achieving accurate fertilization of farmland and protecting the ecological environment. 【Method】Soil organic matter (SOM) data was collected from 1773 samples from soil surface layer (0-20cm) of cultivated land in Luanping County, Hebei Province. The optimal environmental variables were screened through a stepwise regression analysis method. Multiple linear regression (MLR), ordinary kriging (OK), random forest (RF), Bayesian regularized neural network (BRNNBP), and the corresponding three integrated models combined with a geostatistical model (MLR-OK, RF-OK and BRNNBP-OK) were utilized to predict SOM content via the training set including 1426 sampling points. Also, the prediction accuracy of each method was compared with 347 sampling points of the testing set. Autocorrelation analysis was carried out based on the residual of the integrated model to evaluate the fitting effect of the model. 【Result】Results showed that the range of SOM content in the study area was 8.62～35.64 g·kg^-1, and the coefficient of variation was 20.26%, which showed a moderate spatial variation. High concentrations of SOM were mainly distributed in the northeast and southeast areas with higher altitudes, while relative low concentrations of SOM were mostly observed in the southwest and central valleys of the study area. Elevation, slope and temperature selected by stepwise regression were closely related to SOM content (P<0.001). The lowest average absolute error and the root mean square error of the BRNNBP-OK model were 2.162 g·kg^-1and 2.801 g·kg^-1, respectively. Compared with the OK, MLR, RF, BRNNBP, MLR-OK and RF-OK models, the goodness of fit of the BRNNBP-OK model increased by 1.84%～43.72%, making it an optimal model for SOM spatial prediction. Compared with the single model, the nugget coefficient of the integrated model residual was greater than 0.75, and the Moran's I was less than 0 and numerically closer to 0, indicating that the spatial autocorrelation of the integrated model residual was weakened and the residual presented a more discrete spatial distribution. At the same time, the accuracy of all models was significantly correlated with Moran's index of model residuals. 【Conclusion】In this study, the integrated model fitted more trends and the spatial aggregation of model residuals decreased and even tended to be discrete. Thus, the overall prediction accuracy of the integrated models was improved.

• Soil Quality Change and Spatial Differentiation Characteristics of Greenhouses Land Soil in Lhasa River Valley

  GONG Dianqing, WANG Zhaofeng, ZHANG Yili, HU Xiaoyang, GU Changjun, WEI Bo

  2023,60(6):1582-1594, DOI: 10.11766/trxb202109300537

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  Abstract:

  【Objective】Soil quality problems often arise in the process of greenhouse agriculture pursuing economic benefits. There are also signs of soil quality changes in the Tibet Plateau greenhouse land, and the regional differentiation pattern of soil quality changes in the Lhasa Valley. The Lhasa Valley is the main distribution area of greenhouse plots on the Tibet Plateau. Nevertheless, there is limited research that integrates the physical and chemical properties of its soil to reflect overall soil quality changes in the facility farmland with a comprehensive index, and the overall soil quality changes and their regional differentiation patterns are not yet clear. 【Method】Taking the arable land soil samples as the references, this study collected 240 soil samples of greenhouse land and 112 soil samples of arable land. The texture, pH value, water-soluble total salt content, organic matter, total nitrogen, alkali-hydro nitrogen, total phosphorus, available phosphorus, total potassium, available potassium, and soil heavy metals elements (Cr, Ni, Cu, Zn, Pb, Cd, As, Hg) were determined. The comprehensive soil quality index and factor detector methods were used to study the soil quality changes and spatial differentiation characteristics of the greenhouse land soil in Lhasa Valley, and the main factors of soil quality changes in the greenhouse land soil were identified.【Result】The comprehensive soil quality indices of the Lhasa valley greenhouse land and the arable land soil were 0.36, and 0.43, respectively. The soil quality grades of 80% of both samples were distributed in V～III. The soil quality of the greenhouse land was relatively high on the sunny slopes within 930 m from the river at an altitude of 3, 700～3, 750 m in the area. Secondly, there were spatial differences in the degree of soil quality variation in the study area. The SQI of the greenhouse land decreased by 16.28% on average compared to that of the larger field farmland. Among them, soil quality in the Doilungdeqen county decreased most significantly, with an average decrease of 74.46%. At different depths, soil quality decreased most significantly in the range of 0～10 cm, in which the average decline was 6.5%, and the highest percentage of declining sample plots, at 66.67. Thirdly, there was spatial heterogeneity in soil quality changes in the greenhouse land affected by altitude and slope direction. With the increase of elevation and the change of soil quality from sunny slope to shady slope, the change of soil quality in the agricultural land facilities showed a significant trend of increase. Finally, analysis of the soil quality change factors in greenhouse land found that the soil quality change in the whole region was generally affected by changes in salt content, available potassium and cadmium content, and the explanatory power of all three could reach 20%.【Conclusion】Under the changing influence of salt accumulation, available potassium and cadmium content changes, the overall soil quality of the study area's greenhouse land showing a decreasing trend and varied significantly in different regions. This could provide a theoretical basis for the layout and development of greenhouse agriculture in the region.

• Impact of Sample Size and Sampling Method on Accuracy of Topsoil pH Prediction on a Regional Scale

  SUN Yueqi, SUN Xiaomei, WU Zhenfu, YAN Junying, ZHAO Yanfeng, CHEN Jie

  2023,60(6):1595-1609, DOI: 10.11766/trxb202112010651

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  Abstract:

  【Objective】Under the background of high-intensity soil resource utilization, digital soil mapping has become an effective method to obtain and characterize soil information quickly, efficiently and accurately. The accuracy and reliability of soil spatial prediction and digital mapping are restricted by multiple factors, such as soil sample size, sampling strategy, prediction model, the complexity of geomorphology and soil-forming environment in the target region, and quality of covariate data. 【Method】Choosing Henan Province as the study region, we applied five of the most representative machine learning (ML) algorithms to spatially predict and digitally map the topsoil pH of croplands. Afterwards, the impact of different sample sizes and sampling methods on the performance of the chosen ML models and the prediction accuracy of topsoil pH were compared. 【Result】The results showed that: (1) When the soil sample size increased from 200 to 2 000, the performance of all ML models and prediction accuracy of topsoil pH showed a general trend of rapid increase regardless of the sampling method. When sample size reached and exceeded 2 000, the performance of most ML models tended to be stable, and the prediction accuracy of topsoil pH increase rapidly slowed down, suggesting that a soil sample size of 2 000 might be the sample size threshold for these ML models to predict the topsoil pH of croplands in this area. (2) The performance of the five ML models and their topsoil pH prediction accuracy was significantly different. The tree-based ML models, namely Random forests (RF) and Cubist performed best. No matter which sampling method was used, when the sample size was more than 2 000, the archived coefficient of determination (R²) of the two models could be stable between 0.75 and 0.80, and the RMSE could be kept below 0.50. (3) When the soil sample size was large enough, the sampling method had little impact on the ML model performance. Also, the topsoil pH prediction accuracy and the sampling method gradually highlighted when the soil sample size was less than 2 000. Comparatively, Conditioned Latin hypercube sampling (clhs) had advantages when the sample size was small. When the sample size was 1 000, clhs sampling method could still keep the R² of random forest and Cubist prediction at about 0.80. Even when the sample size was as small as 200, the R² archived by all five ML models under the clhs sampling method was above 0.55. (4) The uncertainty analysis showed that 73.9% of the observed values of topsoil pH of the validation samples fell into the 90% Prediction Interval (PI) of the random forest model, indicating that the reliability of the model was slightly overconfident, but it was within the acceptable range. In addition, the data indicated that the uncertainty of model prediction was not significantly correlated with sample size. 【Conclusion】Tree-structured machine learning models Random Forest and Cubist stand out in this case. Improving the spatial prediction and digital mapping accuracy of soil target variables cannot be achieved simply by expanding the scale of sample points and increasing the density of sample points. It is necessary to improve the model prediction performance and covariate data quality at the same time. When the sample size is large enough, the sampling strategy has little effect on the performance of the ML model and the prediction accuracy of surface soil pH; when the sample size is smaller than a certain threshold, the sampling method has a significant impact on the model performance and prediction results.

• Effects of Biocrusts on Dustfall Retention and Soil Fixation and Their Influencing Factors in the Chinese Loess Plateau

  CAO Yousong, XIAO Bo, LI Shenglong, WANG Yanfeng, YU Xingxing

  2023,60(6):1610-1625, DOI: 10.11766/trxb202112150675

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  Abstract:

  【Objective】 Wind activity and aeolian dust transportation are key terrestrial processes in dryland ecosystems. Biocrusts are photoautotrophic communities that consist of cyanobacteria, actinomycetes, mosses, green algae, fungi, and other organisms. As an important living skin and pioneer communities developing on surface soil in drylands, biocrusts strongly influence most soil processes (hydrological, ecological, biological, and chemical processes) and have a variety of essential ecological functions. Although biocrusts are usually relatively thin (a few millimeters or centimeters at most), these organisms have unique micro-structures which could positively influence the formation of aeolian soil parent material. In order to further explore the aeolian sedimentary effects of biocrusts on soil parent material, we conducted this study to understand the effects of biocrusts on dustfall retention and soil fixation, as well as their influencing factors.【Method】 In the north of Chinese Loess Plateau, the biocrusts developed on aeolian and loessal soils were sampled, and the analyses and simulated experiments were carried out in the laboratory. The amount of dustfall retention and soil fixation of biocrusts at different developmental stages (cyano crust, mixed crust, and moss crust) were measured. The variations of dustfall retention amount under different wind speeds, dustfall grain sizes, and dustfall amount were explored. We also explored the key influencing factors.【Result】 The dustfall retention amount of biocrusts was 1.1～4.8 times higher than that without biocrusts, and it increased with the developmental stages of biocrusts from cyano crust to moss crust. On average, the erosion reduction of biocrusts was 19.5～4892 t·km^-2·a^-1under 1～8 m·s^-1 wind speeds. Moreover, the dustfall retention amount increased with increasing soil water content, and these increases were positively correlated with wind speed. It was found that the dustfall retention amount was increased by 4.9%, 53.1%, 59.6%, and 72.3%, respectively, under 5～8 m·s^-1 wind speeds when relative water content increased from 0 to 80%. Additionally, the dustfall retention amount was also significantly and positively correlated with the surface roughness of biocrusts. Similarly, the soil fixation amount of biocrusts also increased along with their developmental stages from cyano crust to moss crust. The soil fixation amount of moss crust was 1.4 times higher than that of cyano crust. At the same developmental stage, the soil fixation amount of biocrusts on aeolian sandy soil was significantly (F=30.74, P<0.003) higher than that on loessal soil. Furthermore, the soil fixation amount was positively correlated with the thickness of biocrusts and negatively correlated with the surface roughness. It firstly increased and then decreased with increasing soil water content.【Conclusion】 These findings show that biocrusts can significantly retain dustfall and fix soil due to their root, mycelium, exudates, and pore structures, and these biocrust functions are of great significance for the aeolian sedimentary process of soil parent material, the pedogenic process of primitive soil, and the primary succession of dryland ecosystem in the Chinese Loess Plateau. Additionally, this study demonstrates the important effects of biocrusts on the formation of aeolian soil parent material, and their key influencing factors are surface roughness, developmental stages, and water content of biocrusts. Therefore, it is essential to pay attention to the biocrust effects on dust retention and soil fixation in arid and semiarid climate regions.

• Isotopic Characteristics of Soil Water from Deep Vadose Zone of Different Typical Land Use Patterns in the North China Plain

  JIANG Pengju, WU Huawu, MIN Leilei, SHEN Yanjun, TIAN Lihui, ZHANG Zhihua, BI Huitao

  2023,60(6):1626-1636, DOI: 10.11766/trxb202110180561

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  Abstract:

  【Objective】The mechanisms of evaporation and infiltration during the processes of precipitation on soil layers is still not clear. Thus, this study was designed to investigate the spatial variations of soil water isotopes from deep vadose zones(>18 m)of pear orchard and farmland plots in the North China Plain. 【Method】Stable isotopes(δD and δ¹⁸O)in soil water, soil water content and soil texture were explored in the pear orchard and farmland plots of the North China Plain. 【Result】Results showed that the local meteoric water line(LMWL)was established as δD = 6.07δ¹⁸O-5.76(R²=0.86). The δD and δ¹⁸O of soil water from different soil layers fell below the LMWL, indicating that soil water replenished from precipitation experienced strong evaporation. Except for pear orchard(I), the coefficient of variation(CV)of soil water isotopic values was in the order of shallow layer>middle layer> deep layer, indicating that the δD and δ¹⁸O of shallow soil water fluctuated greatly. This implies that shallow soil water was more impacted by precipitation and evaporation compared with other soil layers. As the profile depth increased, the effect of precipitation and evaporation gradually became weaker. The larger isotopic CV of deep soil water in pear orchard(I)indicated deep soil water was affected by groundwater at this sampling site. The d-excess values of shallow soil water were greater in pear orchard plots than those in farmland plots, indicating that the evaporation intensity of shallow soil layers was less in the pear orchard plots than in farmland plots. The obvious isotopic enrichment(δD and δ¹⁸O)was observed in the soil layer of 0.25-0.5 m, which was associated with soil texture stratification and hindered infiltration into deep soil layers. This resulted in enriched soil water accumulating in the soil layer. The phenomenon of isotopic depletion was found in the soil layers(2-5 m)from the pear orchard plots and resulted from preferential flow induced by pear roots. 【Conclusion】The remarkable spatial differences of isotopic variations in soil layers were observed in the pear orchard and farmland plots, indicating that the infiltration processes of soil water differed in various land-use patterns of the North China Plain. The preferential flow of soil water during the infiltration processes was dominated in the pear orchard plots. These findings provide a theoretical basis for understanding the relationship between water movement, nitrogen migration and transformation, and groundwater quality in the deep vadose zone of the North China Plain.

• Evolution of Iron Oxides in Aggregates of Paddy Soil under Long-term Returning of Chinese Milk Vetch and Combined Application of Chemical Fertilizers

  XIE Kun, GENG Mingjian, NIE Jun, LU Yanhong, LIAO Yulin, HUANG Li

  2023,60(6):1637-1649, DOI: 10.11766/trxb202111110611

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  【Objective】Iron oxides are important cementitious substances in soil aggregates, which mainly exist in soil clay particles. This study aimed to reveal the transformation of iron oxides in soil aggregates and their enrichment characteristics in clay fractions of different particle sizes under the conditions of returning Chinese milk vetch to the field and applying chemical fertilizers.【Method】Four treatments including a single application of Chinese milk vetch (MV), a single application of chemical fertilizer (F100), Chinese milk vetch applied with chemical fertilizer(MV+F100)and Chinese milk vetch combined with 80% of chemical fertilizer (MV+F80) were selected. Soil aggregates (>250, 53～250 and 2～53 μm) and clay particles (<2 μm) were separated by wet sieving and centrifugation, and the content of iron oxides in soil aggregates and their clay particles with different treatments was determined. Also, the relationship between iron oxides and the stability of aggregates was analyzed.【Result】(1) Compared with MV and F100, the content of >250 μm aggregate was increased and the content of 53-250 μm aggregate was decreased, and the mean weight diameter (MWD) and geometric mean diameter (GMD) were increased by 8.2% to 20.5% and 4.1% to 8.5%, respectively. (2) Compared with MV, the combined application of Chinese milk vetch and chemical fertilizer significantly increased the contents of amorphous iron(12.7%-55.6%, 52.4%-54.9% and 45.9%-48.6%)in aggregates of various sizes, clay particles of 2～53 μm and free clay particles. The enrichment rates of amorphous iron in >250 and 53～250 μm aggregates were decreased (32.8%～36.8% and 17.2%～28.4%). Compared with F100, the content and enrichment rate of amorphous iron in 2～53 μm aggregates and clay of aggregates were significantly reduced (3.5%～21.3%, 29.2%～30.4% and 10.9%～26.9%). (3) The content of >250 μm aggregates was positively correlated with the content of non-crystalline iron and activation degree of iron in the clay of aggregates, and positively correlated with the enrichment rate of amorphous iron and the content of free iron in aggregates. The MWD and GMD were significantly positively correlated with the content of >250μm aggregates, and significantly negatively correlated with the content of <2μm aggregate. The free iron in the clay of >250 and 2～53μm aggregates and free clays was the most important factor influencing the MWD and GMD.【Conclusion】Combined application of Chinese milk vetch with chemical fertilizer could increase the content of iron oxide in the clay of different aggregates and promote the formation of >250μm aggregates, thus, enhancing the stability of aggregates.

• Effects and Mechanisms of Different Kinds of Catch Crops on Reducing Nitrogen and Phosphorus Leaching Loss in Protected Vegetable Field

  JU Shengrong, MIN Ju, DONG Gangqiang, LI Jianbin, SHI Weiming

  2023,60(6):1650-1661, DOI: 10.11766/trxb202112010590

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  Abstract:

  【Objective】Planting catch crops in a protected vegetable field during the fallow season is an important practice to reduce the leaching loss of important nutrients. However, few studies have been done on catch crops with high nitrogen and phosphorus leaching control efficiency in frequent rainfall areas.【Method】This research set up five planting catch crop treatments(sorghum treatment, maize treatment, ryegrass treatment, purslane treatment and collard treatment)and a fallow treatment to study the effect of different kinds of catch crops on nitrogen and phosphorus leaching, NO₃^--N and NH₄⁺-N content and soil microorganism.【Result】The results showed that compared with fallow treatment, sorghum, maize, ryegrass, purslane and collard treatments significantly reduced nitrogen leaching by 12.6, 26.6, 27.4, 28.9 and 26.8 kg·hm^-2 and phosphorus by 0.10, 0.05, 0.04, 0.04 and 0.13 kg·hm^-2, respectively. The nitrogen and phosphorus control efficiency was as follows; purslane＞ryegrass＞collard＞maize＞sorghum, and collard＞sorghum＞maize＞purslane＞ryegrass, respectively. The nitrogen control rates of ryegrass, purslane and collard reached 52.3%, 55.1% and 51.2%, respectively, which were nearly twice higher than the nitrogen control rates of sorghum and maize. This may be because the ryegrass, purslane and collard treatments had a certain coverage in the early fallow period(21 days), which reduced the leaching volume by 23.5%, 17.1% and 26.7% compared with fallow treatment. In contrast, sorghum and maize treatments had poor coverage in the early fallow period, hence there was no significant difference in leaching volume between sorghum and maize treatments and fallow treatment. In addition, the NO₃^--N content in the surface soil(0-20 cm)of ryegrass, purslane and collard treatments was 40.1-52.8 mg·kg^-1, while in the surface soil of sorghum and maize treatments it was 67.8-72.7 mg·kg^-1. Besides, compared with sorghum and maize treatments, ryegrass, purslane and collard treatments also significantly increased the abundance of nirS type denitrifying bacteria in surface soil and nosZ type denitrifying bacteria in rhizosphere soil, which may enhance the denitrification process in soil. This may be one of the mechanisms for high nitrogen leaching control efficiency.【Conclusion】In general, ryegrass, purslane and collard as the catch crops of protected vegetable field in areas with frequent rainfall can significantly reduce nitrogen and phosphorus leaching, and collard has the best effect on nitrogen and phosphorus comprehensive control.

• Research and Practice on Sustainable and Safe Utilization of Soil in Agricultural Land—A Case Study of Cadmium Contaminated Farmland in Zhejiang Province

  WANG Jie, ZHU Youwei, YANG Xiaoe, GUO Bin, WANG Yulei

  2023,60(6):1662-1675, DOI: 10.11766/trxb202205120170

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  【Objective】The sustainable and safe utilization of agricultural soil is of great significance to effectively improve the quality of the agricultural soil environment, and to ensure the quality and safety of agricultural products and human health.【Method】Taking Zhejiang Province, one of the most developed areas in the Yangtze River Delta, as an example, the main problems and development trends of agricultural land soil environment were analyzed, and the theory and method of sustainable and safe utilization of agricultural land soil were studied. During the 13th Five-year Plan period, based on the survey results of agricultural land soil pollution in Zhejiang Province at a scale of 1: 50 000 over the years, provincial pilot demonstrations focusing on the control of heavy metal cadmium pollution in agricultural land were carried out in Wenling City and Tonglu County. The methods of pollution source analysis and prevention, multi-dimensional agricultural safety utilization technology screening and application, and safe disposal of over-standard crop straws were comprehensively adopted to form a batch of agricultural land soil pollution comprehensive treatment technology models with significant regional characteristics, high-efficiency control effects, and independent intellectual property rights, which are suitable for mild to moderate and moderate to severe cadmium pollution.【Result】The main results were as follows: (1)Atmospheric deposition source is one of the main external input sources of Cd in the agricultural land ecosystem, accounting for about 24%-59% of the total input.(2)58 varieties with low accumulation(mainly Yongyou 538)were screened out, 20 passivation materials with calcareous substances as the main, and 10 leaf resistance control materials with silicon and selenium as the main were selected.(3)The safe utilization technology mode of rice/wheat rotation, which is suitable for light and moderate Cd polluted agricultural land can effectively reduce the available state of Cd in soil by more than 20%-50%. The production and remediation technology mode which is suitable for moderate and severe Cd polluted agricultural land, mainly with hyperaccumulators, can effectively reduce the total amount of Cd in soil by more than 30% and the available state of Cd in soil by more than 50%.【Conclusion】This paper innovatively puts forward the general idea and technical route of sustainable and safe utilization of heavy metal polluted agricultural land soil. It also summarizes the experience and strategy of sustainable and safe utilization of heavy metal polluted agricultural land soil, to provide a demonstration model and technical reference for the safe utilization of contaminated agricultural land soil in China.

• Remediation of Lead-contaminated Soil by Superparamagnetic Micro-nano MFH Functional Materials

  LI Jie, WANG Qiang, LUO Meng, JIANG Xiangting, SUN Yuanpeng, ZHANG Lizhi

  2023,60(6):1676-1687, DOI: 10.11766/trxb202204290220

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  Abstract:

  【Objective】This study aimed to effectively, rapidly, and cost-effectively purify wastewater and repair soil from lead pollution.【Method】The remediation effect of a lead-remediation material(superparamagnetic micro nano Fe₃O₄@ Ca₁₀(PO₄)₆(OH)₂functional material, MFH)on Pb²⁺ in wastewater and polluted soil was studied in terms of dosage, initial concentration of Pb²⁺, adsorption time, pH, ionic strength and organic matter concentration.【Result】The results showed that the adsorption of Pb²⁺ in solution by MFH satisfies the pseudo-second-order kinetic model. The adsorption equilibrium was reached in about 10 min, and the maximum adsorption capacity was 181.6 mg·g^-1; at pH 2.00～5.00. Also, the removal rate of Pb²⁺ in the pH range decreased with the increase of pH while an increase in ionic strength of the solution inhibited the removal rate of Pb²⁺ by MFH. Nevertheless, an increase in the organic matter content in the reaction system effectively improved the removal rate of Pb²⁺ by MFH. MFH showed a good lead-removal effect when applied to lead-contaminated soils in farmland and industrial parks. The addition of heavy metal activator EDTA can significantly improve the removal effect of MFH on lead in soil. In slightly lead-contaminated farmland soil, the total amount of lead removed was 102.74 μg·g^-1. After experimentation, the recovery rate of MFH from soil was over 88% by using a magnetic rod, while the recovery rate of MFH regeneration performance was 89.49%. Importantly, the magnetic properties and specific surface area of the regenerated MFH recovered well, suggesting that MFH had a good recovery and regeneration ability.【Conclusion】Therefore, MFH is a good material for the decontamination of lead- contaminated wastewater and soils and its usage is promising given that it can easily be recovered with its basic properties intact.

• Effects of Plough Layer Thickness on the Transformation and Fate of Fertilizer Nitrogen in Fluvo-aquic Soils with Different Textures

  DING Shijie, YANG Wenliang, XIN Xiuli, ZHANG Xianfeng, ZHU Anning, YANG Jiao, REN Guocui, LI Mengrou

  2023,60(6):1688-1699, DOI: 10.11766/trxb202204060097

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  Abstract:

  【Objective】Soil fertility is significantly influenced by plough layer thickness. However, it is still not clear how the transformation and fate of fertilizer nitrogen (N) in fluvo-aquic soils would be affected by plough layer thickness. 【Method】In this study, a soil column simulation experiment in the field was conducted throughout three crop cultivations. The experiment was performed in a completely randomized design with six treatments including two plough layer thicknesses (15 and 25 cm) and three soil textures (sandy loam, sandy clay loam and loamy clay). A ¹⁵N-labeled tracer technique was used to evaluate the dynamics of fertilizer-derived organic N, fixed NH₄⁺ and mineral N in 0-40 cm soil layer and the fate of fertilizer N in soil-crop systems. 【Result】 The transformation of fertilizer N in soil-crop systems was significantly affected by plough layer thickness, and showed the same varying tendency among different textural soils. The residual fertilizer N existed mainly in the form of organic N, which accounted for more than 83% of the total residual fertilizer N and played a pivotal role in the storage and supply of fertilizer N. Increasing plough layer thickness degraded the conversion of fertilizer N to fixed NH₄⁺ pool, while increased the stocks of fertilizer-derived organic N in 0-40 cm soil layer. In the current season after fertilizer N was applied, the average value of fertilizer-derived organic N stock in soils with 25 cm plough layer thickness (PLT-25) was averagely 8.9% higher than that in soils with 15 cm plough layer thickness (PLT-15). The stocks of fertilizer-derived mineral N under PLT-25 treatments were also higher than that under PLT-15 treatments in the current and subsequent crop cultivations; promoting the fertilizer N uptake by crops. The N use efficiency under PLT-25 treatments in the first two crop cultivations was about 8.0% higher than that of PLT-15 treatments, while the current seasonal loss rate and cumulative loss rate of fertilizer N were 12.3% and 9.1% lower, respectively. The stocks of fertilizer-derived organic N in sandy clay loam and loamy clay were significantly (P < 0.05) higher than that in sandy loam, while the trend was the opposite for the stocks of fertilizer-derived fixed NH₄⁺. And the fertilizer-derived mineral N stock was usually to be higher in sandy loam. Overall, the percentage of recovery of applied fertilizer N in crops and soil under sandy loam treatment was significantly (P < 0.05) lower than that in sandy clay loam and loamy clay. Also, the percentage of cumulative loss of fertilizer N in sandy loam was 20.4% and 18.2% higher than that in sandy clay loam and loamy clay, respectively. 【Conclusion】The fluvo-aquic soils with higher sand content have lower fertilizer N storage capacity, restricting the enhancing of N use efficiency. For fluvo-aquic soils with different textures, increasing plough layer thickness could improve the annual N use efficiency and the residual amount of applied fertilizer N in the current season. This, could be released for crop uptake in the subsequent crop cultivation. In typical fluvo-aquic soil areas, increasing the plough layer thickness may be a potential means for regulating the transformation and fate of applied fertilizer N, increasing fertilizer N retention, enhancing the fertilizer N uptake by crops and minimizing fertilizer N loss in soil-crop systems.

• Coupling Effects of Straw and Woody Peat on Rapidly Increasing Soil Organic Matter and Crop Yield Under Different Application Ratios

  ZHOU Tantan, LI Dandan, QIU Lili, XU Jisheng, ZHOU Yunpeng, TAN Jun, ZHAO Bingzi

  2023,60(6):1700-1713, DOI: 10.11766/trxb202112030656

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  【Objective】The combined application of woody peat and straw has the potential to rapidly increase soil organic matter (SOM) and crop yield. However, how the application proportion of woody peat and straw affects crop yield and its microbiological mechanism remains unclear. 【Method】A field experiment was designed, based on the application of straw and activator (RJ). Then, a was comparative analysis of the effects of the ratio of woody peat and straw at 2: 1 (RJM1), 3: 1 (RJM2), and 4: 1 (RJM3) on soil physicochemical properties, bacterial community composition and rice yield was carried out, and compared with the control (CK) without any organic matter. At the same time, based on co-occurrence networks, the path analysis model was used to elucidate the potential relationship between specific bacterial flora and crop yield under different treatments. 【Result】The results showed that the rice yield of RJM1, RJM2, and RJM3 was similar, and their average yield was 16.09% and 31.46% higher than that of RJ and CK, respectively. The soil physicochemical properties of the five treatments were divided into three different groups (P < 0.01). The first group was RJM2+RJM3, which was characterized by remarkably increased pH, SOM, dissolved organic carbon (DOC), available phosphorus (AP) and available potassium (AK) contents. The second group was RJ+RJM1, which was characterized by significantly increased nitrate-nitrogen (NO₃^--N) and dissolved organic nitrogen (DON). The third group was CK. The average content of SOM, DOC, and AP in RJM2+RJM3 was 29.69%, 22.65%, and 23.95% higher than those of RJM1, respectively, which indicates that RJM2+RJM3 has the potential of rapidly increasing the content of soil organic matter. The bacterial community composition between RJM2 and RJM3 was similar, and was mainly influenced by soil pH, SOM and DOC, while they were significantly different from RJM1. Module 1 of key ecological clusters within the bacterial co-occurrence network had a direct and significant positive effect on rice yield, in which soil physicochemical properties indirectly affected crop yield by directly and significantly affecting module 1 properties. The improvement of yield was mainly affected by the relative abundance and community composition of module 1, while module 2 and module 3 had no significant effect on rice yield. RJM2+RJM3 significantly increased the abundance of Gaiellaceae unidentified, Nocardioidaceae unidentified, Terracoccus, Comamonadaceae unidentified, WD2101 unidentified, and Sphingobacteriales unidentified, which were positively correlated with rice yield. Also, RJM1 significantly increased the abundance of the other five species mentioned above, except Sphingobacteriales unidentified, which indicates that RJM2+RJM3 could stimulate more dominant species that were positively correlated with crop yield than RJM1. Meanwhile, the sustainability of increasing rice yield in RJM1 was lower than RJM2+RJM3 because the SOM content of RJM1 was not significantly different from that of CK and RJ. 【Conclusion】Combining the above results with economic benefits, RJM2, the application ratio of woody peat to straw 3: 1, is recommended as an appropriate ratio that can rapidly improve SOM and crop yield at the same time.

• Characteristics of Fertilizer Inputs and Soil Nutrient Accumulation in Yangshan Juicy Peach Orchard with Different Cultivation Years

  YANG Guang, WANG Yu, WANG Shenqiang, ZHAO Xu

  2023,60(6):1714-1725, DOI: 10.11766/trxb202204060091

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  【Objective】The objective of this study was to clarify the status of soil nutrient accumulation in the peach orchard of Taihu Watershed. It aimed to provide a guide for the green production mode of peach orchard. 【Method】In this study, a total of 66 soil samples were collected from 33 juicy peach orchards, with different cultivation years in the four main planting towns. Combined with field research and laboratory analysis, the fertilizer input status, soil nutrient content and ecological stoichiometry characteristics were analyzed. 【Result】The results showed that the average total nutrient inputs was N 527 kg·hm^-2, P₂O₅ 362 kg·hm^-2 and K₂O 545 kg·hm^-2, and the proportion of organic inputs were 27.8%, 15.4% and 15.6% respectively. Here chemical fertilizer was mainly NPK compound fertilizer, while the types of organic fertilizer applied mainly included rapeseed cake, livestock manure, and composting straw. Over-application of fertilizer could aggravate soil acidification and nutrient accumulation, soil pH in 0-20 cm and 20-40 cm soil layers of planted >10 years peach orchard both decreased by more than 1.5 units, which belonged to strongly acidic soil (4.5<pH<5.5). According to the 2^nd National Soil Survey of soil fertility classification standards, soil organic matter, total nitrogen, phosphorus and potassium in 0-20 cm and 20-40 cm soil layers reached level 3 or above, and the C: N, C: P and N: P ratios in 0-20 cm soil layer decreased with an increase of cultivation years. Soil alkali-hydrolytic nitrogen, available phosphorus and potassium of planted >10 years peach orchard reached level 1. The soil NO₃^--N concentration of the peach orchard was up to 19.3-33.1 mg·kg^-1. The annual apparent surplus of N, P₂O₅, K₂O were 343 kg·hm^-2, 238 kg·hm^-2 and 240 kg·hm^-1, respectively. 【Conclusion】The excessive nutrient input in the peach orchard has aggravated soil acidification and nutrient accumulation. A high concentration of nitrogen and phosphorus accumulated in the soil might increase the environmental loss risk. Therefore, it is necessary to put forward a green production model for the peach production.

• Retention Capacity and Release Potential of Soil Phosphorus in Paddy Red Soil Pedogenic Horizons with Different Planting Years

  NIU Ben, WANG Yanling

  2023,60(6):1726-1738, DOI: 10.11766/trxb202205160257

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  【Objective】This study aimed to analyze the change of phosphorus fixation capacity and release potential in different occurrence layers of red paddy soil, to clarify the release mechanism of fixed phosphorus (P), and to evaluate the loss risk of P in red paddy soil with different planting years.【Method】Soil samples were collected from the bottom to the top of three typical red paddy fields in Yingtan, Jiangxi Province. These paddies included a mid-phase paddy field (MP), a new paddy field (NP) and an old paddy field (OP). Based on the adsorption-desorption experiment and structural equation model, the variation differences and influencing factors of phosphorus retention capacity (PSI), maximum capacity of soil fixed phosphorus (MCSP) and the release potential of the soil were analyzed.【Result】With the increase of pedogenic horizons depth, PSI and MCSP of red paddy soil gradually increased, and the order of their changes were: MP > NP > OP and NP > MP > OP. The desorption capacity of electrostatically adsorbed state P (CaCl₂-P) of OP, MP and NP profiles and the desorption capacity of specific adsorbed state P (EDTA-P) in the OP profile gradually decreased with the increasing profile depth. Also, the EDTA-P in MP (except Ap₁ layer) and NP profiles and residual P (Red-P) in soil pedogenic horizons followed an opposite trend. With the increase of profile depth, the CaCl₂-P/EDTA-P in the pedogenic horizons of the OP profile increased, which was significantly higher than that in the MP and NP profiles. The adsorption-desorption capacity of phosphorus in red paddy soil is mainly affected by SOM (soil organic matter), TP (total phosphorus), pH and iron-aluminum oxides. The interaction between SOM, TP, pH and iron-aluminum oxides jointly regulates the number of phosphorus adsorption sites and the strength of adsorption-desorption capacity in red paddy soil.【Conclusion】In this research, it was found that the Ap layer of red paddy soils was characterized by the weak capacity of the soil P sorption and strong capacity of P desorption and a high risk of soil P loss. Meanwhile, Br and C layers showed a stronger soil P sorption capacity and a weaker P desorption capacity, and a higher soil P fixation capacity than the Ap layer. Compared with the profile of OP, the exogenous P adsorbed in pedogenic horizons of NP and MP was more easily converted to the specialized adsorption state and residual state P, thus, resulting in a reduced risk of soil P loss. The risk of P loss in the OP profile was relatively higher than its counterparts, and timely regulatory measures are needed.

• Application Zoning of Magnesium Fertilizer in Bijie Tobacco Growing Area Based on Soil Calcium-Magnesium Ratio

  ZHANG Zhongqi, ZHU Liang, WANG Meiyan, SHI Xuezheng, SUN Weixia

  2023,60(6):1739-1750, DOI: 10.11766/trxb202201100014

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  【Objective】A reasonable supply of magnesium is an important guarantee for high-quality tobacco production. The current soil magnesium fertilizer application in tobacco growing areas is mainly determined according to the level of soil available magnesium content and its spatial distribution. However，the practical impact of the ratio of soil available calcium content to available magnesium content（Ca/Mg ratio）on magnesium supply is rarely considered. 【Method】Taking Bijie tobacco growing area as an example，the level of available magnesium content，Ca/Mg ratio and spatial distribution contours were obtained based on a large number of soil samples. Then，the suitable grade zoning of magnesium fertilizer was delimited through graphic superposition and grid operation. 【Result】The results showed that the average content of soil available magnesium in Bijie tobacco growing area was 278.1 mg· kg^-1. The content shows great fluctuation in space，which was caused by the parent rock，soil type，elevation and topographic location. Also，the average Ca/Mg ratio in this area was 14.5，and was at a high level. Moreover，the spatial fluctuation of the ratio was also large，and mainly related to the spatial distribution of soil-forming parent rock and soil types. From spatial interpolation contours of available magnesium content，the areas with high content were mainly concentrated in the east and southwest，while areas with low content were mainly distributed in the middle north and northwest. The available magnesium content was dominated by the suitable grade，which accounted for 69% of the whole area. Moreover，the area of lacking and rich grades accounted for 19.0% and 10.5% respectively，and the areas of extremely lacking and extremely rich grades were both small. From the distribution of soil Ca/Mg ratio，the study area was dominated by two grades of 10～20 and 5～10，while areas covering > 20 and < 5 were relatively small. On the whole，the Ca/Mg grades were characterized by interphase distribution in space. In the application grade map of soil magnesium fertilizer obtained from available magnesium content and Ca/Mg ratio，the most suitable application areas were mainly concentrated in the north-central，southeast and northwest regions. Also，the unsuitable grades were mainly distributed in some parts of the southwest and northeast，while the areas of extremely unsuitable grade were very small，and mainly scattered in the southwest. Among all the grades，the areas of suitable and more suitable grades of magnesium fertilizer application accounted for 69.0% and 10.5% respectively. The unsuitable application area accounts for 19.0%，while the proportion of extremely suitable and extremely unsuitable areas account for only 1.3% and 0.2% respectively. 【Conclusion】The results indicate that the Ca/Mg ratio of soil is an important factor to be considered when formulating the application scheme of magnesium fertilizer. If the influence of the Ca/Mg ratio on soil magnesium supply is not considered，the appropriate grade zoning of magnesium fertilizer will have a large deviation，which will have an adverse effect on soil fertilization in tobacco growing areas. It can be seen that comprehensive consideration of soil available magnesium content and Ca/Mg ratio is an important prerequisite for scientifically formulating regional magnesium fertilizer application scheme.

• Composition, Structure and Phosphorus Entrapment Capacity of Periphytic Biofilms of Major Paddy Fields in China

  LU Wenyuan, SUN Pengfei, XU Ying, LIU Junzhuo, WU Yonghong

  2023,60(6):1751-1765, DOI: 10.11766/trxb202203220002

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  【Objective】The periphytic biofilms widely distributed between the water-soil interface are key hot areas and necessary places for material migration and energy exchange in the paddy ecosystem. However, few studies have paid attention to the community characteristics and regulatory functions of the paddy periphytic biofilm. The purpose of this study is to further understand the function of periphytic biofilm biological phosphorus capture. 【Method】This study selects the periphytic biofilms in the main rice areas in China, covering three rice planting areas in the South China, the middle and lower reaches of the Yangtze River, and the Northeast China. The composition and structure of periphytic biofilms communities are analyzed using high-throughput sequencing technology, combined with PLS-PM and regression analysis to reveal factors affecting the capture of phosphorus by periphytic biofilms around the paddy field.【Result】There are significant differences in soil physical and chemical properties in different paddy regions (P<0.05). The phosphorus capture capacity of the periphytic biofilms in main rice regions in China showed an increasing trend from north to south and west to east. There are significant differences in the composition of the periphytic biofilms community of paddy fields in different regions (P<0.05). At the genus level, the periphytic biofilms in South China are dominated by prokaryotic microorganisms such as Acinetobacter and Proteiniclasticum and eukaryotic microorganisms such as Gregarina and Adriamonas. The periphytic biofilms in the middle and lower reaches of the Yangtze River are mainly prokaryotic microorganisms such as Bacillus and Cloacibacterium and eukaryotic microorganisms such as Gregarina and Vermamoeba. In the Northeast, periphytic biofilms are composed of prokaryotic microorganisms dominated by Flavisolibacter and Anaerolinea and eukaryotic microorganisms dominated by Adriamonas and Vermamoeba. It was found that the physical and chemical properties of soil (especially soil organic carbon and pH of floodwater) correlated with the diversity of the periphytic biofilms community. The microalgae in the periphytic biofilms in South China play a certain role in promoting the capture of phosphorus, while the phosphorus accumulating bacteria in the periphytic biofilms in the northeast have a positive effect on the capture of phosphorus.【Conclusion】This study provides deep insight into the understanding of the composition and structure of the periphytic biofilms and their regulation in the phosphorus cycle in paddy fields through analysis of the phosphorus capture capacity of periphytic biofilms in paddy fields in different regions of China. Also, this study provides a theoretical basis for the future development of biotechnology to recycle surplus phosphorous in paddy fields.

• Distribution Patterns of Nitrifiers within Soil Aggregates under Different Cropping Systems

  XIA Weiwei, Li Yikun, ZHANG Meng, SUN Xiangxin, WANG Yufang, JIA Zhongjun

  2023,60(6):1766-1777, DOI: 10.11766/trxb202203220126

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  【Objective】Nitrifiers play an important role in the process of farmland soil nitrogen transformation. A study on the distribution of nitrifying microorganisms in aggregates will help to reveal the interaction mechanism between soil structure, microorganisms and soil nutrient cycling.【Method】The changes in soil aggregate properties and nitrification potential (N_P) in maize monoculture (M-M) and maize peanut rotation (M-P) were compared, and the abundance and community composition of different nitrifying functional genes in soil aggregates were evaluated by quantitative PCR and high-throughput sequencing.【Result】Compared with M-M, M-P significantly increased pH, NH₄⁺ and total carbon (TC) in soil aggregates. M-P also significantly enhanced N_P, but the aggregate size had no significant effect on N_P. The abundance of the AOB amoA gene was higher in M-P and also more abundant in smaller aggregates. The distribution pattern of AOA and comammox amoA genes was opposite to that of AOB, indicating that AOB can better adapt to the micro-environment of smaller aggregates, while AOA and comammox tended to dominate in larger aggregates. In addition, compared with M-M, the difference in AOA/AOB and comammox/AOB ratio between M-P aggregates decreased, indicating that rotation promoted an even distribution of soil nitrifiers among different aggregate sizes. By further analysis of the nitrifying community based on the 16S rRNA gene sequencing, the results showed M-P increased the proportion of Nitrolancea-like NOB and Candidatus Nitrosocosmicus-like AOA, decreased the proportion of Nitrospira-like NOB, and had no significant effect on AOB compositions. The aggregate size only had a significant effect on the proportion of Nitrosospira-like AOB. NH₄⁺ content and pH were the main factors affecting soil N_P and the nitrifying microbial community structure among soil aggregates. N_P was positively correlated with AOB amoA gene abundance and negatively correlated with AOA amoA gene abundance. However, in terms of community composition, Nitrosospira-like AOB, Candidatus Nitrosocosmicus-like AOA and Nitrospira-like NOB all showed positive correlations with N_P.【Conclusion】Soil aggregate size and cropping system can greatly affect the distribution of nitrifying microorganisms in soil aggregates. However, nitrifying microorganisms have different adaptation mechanisms among aggregates. This study provides a theoretical support for improving the ecological adaptation mechanism of soil nitrifying microorganisms in the micro-environments under Gramineae-Legume rotation.

• Response of Nitrite-dependent Anaerobic Methane Oxidation in Paddy Fields to Slow Increase of Atmospheric CO₂ Concentration

  JIN Jinghao, HUANG Hechen, SHEN Lidong, TIAN Maohui, LIU Xin, YANG Wangting, YANG Yuling, LIU Jiaqi, REN Bingjie, XU Jiangbing, HU Zhenghua

  2023,60(6):1778-1789, DOI: 10.11766/trxb202111250641

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  【Objective】The process of nitrite-dependent anaerobic methane oxidation (n-damo) catalyzed by Candidatus Methylomirabilis oxyfera (M. oxyfera) -like bacteria links both the carbon and nitrogen cycles, and has attracted great attention in recent years because of its potential role acting as a microbial methane sink. This process has been reported to be a novel pathway for controlling methane emissions from paddy ecosystems. Elevated atmospheric CO₂ concentration can indirectly affect the structure and function of soil microbial communities. However, the response of n-damo to e[CO₂] is poorly known. This study aims to explore the response of n-damo activity, and the community composition and abundance of M. oxyfera-like bacteria to e[CO₂] in a paddy ecosystem.【Method】Here, ambient CO₂ treatment (CK) and a slow increase of atmospheric CO₂ treatment (EC: an increase of 40 μL·L^-1 per year above CK until 160 μL·L^-1) were set up based on the CO₂ automatic control platform with open-top chambers. The stable isotope tracer experiment, quantitative PCR and high-throughput sequencing were employed to investigate the n-damo activity, abundance, diversity and community composition of M. oxyfera-like bacteria in paddy soils across three key rice growth stages (tillering, jointing and flowering stages) under different CO₂ treatments.【Result】The results showed the occurrence of n-damo activity and the presence of M. oxyfera-like bacteria in the studied paddy soils. It was found that the n-damo activity ranged from 0.31 to 5.09 nmol CO₂ g^-1·d^-1, and the abundance of M. oxyfera-like bacteria varied between 7.51×10⁶ and 5.49×10⁷copies g^-1. Furthermore, EC treatment stimulated the n-damo activity and abundance of M. oxyfera-like bacteria, particularly at the jointing stage, in which the activity and abundance were increased by 137.9% and 96.0%, respectively. In addition, EC treatment significantly changed the community composition and diversity of M. oxyfera-like bacteria, and the diversity was increased under EC treatment. Correlation analyses showed that the soil dissolved organic carbon content, ammonium content, nitrate content and water content all had significant impacts on the community structure of M. oxyfera-like bacteria. The variations in soil dissolved organic carbon content and inorganic nitrogen content under EC treatment could probably cause the change of n-damo activity and the abundance of M. oxyfera-like bacteria.【Conclusion】Elevated atmospheric CO₂ promoted the n-damo activity and M. oxyfera-like bacterial abundance and significantly changed the community structure of M. oxyfera-like bacteria in a paddy ecosystem. In addition, the changes of soil dissolved organic carbon content, inorganic nitrogen content and water content greatly affected the n-damo activity and community structure of M. oxyfera-like bacteria. Taken together, our results showed a positive response of n-damo to the slow increase of atmospheric CO₂ concentration.

• Effects of a New Rice-Shrimp Farming Model on Soil Fertility and Microbial Community Structure in Paddy Field

  LAI Zheng, XIAO Liting, LAI Sheng, YANG Huilin, NI Caiying, YANG Wenjing, JIAN Minfei

  2023,60(6):1790-1800, DOI: 10.11766/trxb202205150255

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  【Objective】This study was designed to explore the impact of a new rice-shrimp farming model (NRS) on soil fertility and microbial community composition in paddy field. 【Method】Three different farming treatments: new rice-shrimp farming model (NRS), traditional rice-shrimp farming model (TRS) and rice monoculture (CK) were set up, with CK as control. The paddy field physicochemical indexes and microbial diversity and community structure were determined by using the soil agrochemical analysis method and 16S rDNA amplicon high-throughput sequencing technology. 【Result】Compared with CK and TRS, NRS significantly improved the contents of soil organic matter, available K, available P and pH. NRS significantly increased the microbial diversity and species richness. A total of 32 phyla, 80 classes, 202 orders, 347 families and 491 genera of bacterial groups were detected in the paddy field of three models. The dominant bacterial phyla were Proteobacteria, Acidobacteriota, Chloroflexi, Verrucomicrobiota and Desulfobacterota. Compared with CK, NRS changed the composition of the soil microbial community. Among the bacterial dominant phyla, the relative abundances of Acidobacteria, Chloroflexi and Verrucomicrobiota were increased by 30.89%, 36.38% and 2.16%, while the relative abundance of Proteobacteria and Desulfobacteria decreased by 17.96% and 58.59%, respectively. Compared with TRS, NRS also changed the composition of the soil microbial community. Among the bacterial dominant phyla, the relative abundances of Desulfobacteria increased by 14.93%, while the relative abundance of Chloroflexi, Verrucomicrobiota, Proteobacteria and Acidobacteria decreased by 39.29%, 37.42%, 16.27% and 6.81%, respectively. Correlation analysis showed that soil organic matter, available potassium, available phosphorus, available nitrogen and pH were the main physicochemical factors affecting the structure of soil microbial community in paddy field. 【Conclusion】The new rice-shrimp farming model is conducive to improving soil fertility, significantly improving soil microbial diversity and altering microbial community structure. The results of this study have certain guiding significance and reference for the demonstration and promotion of the new rice-shrimp farming model.

• Effects of Long-term Different Tillage Practices on Chitin Degrading Microbial Communities and Chitinase Activity in Farmland Black Soil

  SUI Pengxiang, LUO Yang, LI Ruiping, ZHENG Hongbing, YUAN Ye, ZHENG Jinyu, WANG Hao, LIU Wuren

  2023,60(6):1801-1811, DOI: 10.11766/trxb202203180120

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  Abstract:

  【Objective】This study aimed to illustrate the impacts of different tillage practices on chitin degrading microbial communities and chitinase activity in farmland black soil, and to explore the main environmental factors in driving a change in chitin degrading microbial communities and chitinase activity.【Method】Based on the long-term positioning platform of different tillage practices in black soil and the combination of fluorescence quantification and high throughput sequencing technology, this research intends to study the effects of long-term different tillage practices (Conventional tillage, No-tillage, Sub-soiling tillage, Moldboard plowing tillage) on chitin degrading bacteria harboring chiA gene abundance, microbial communities and chitinase activity in 0 - 40 cm soil layers.【Result】Results showed that no-tillage increased chiA gene abundance in the 0 - 20 cm soil layer. Lower chiA gene abundance, alpha diversity and proteobacteria relative abundance, and higher actinobacteria relative abundance in the 20 - 40 cm soil layer of no-tillage than other tillage practices. The abundance of chiA gene and microbial community structure was significantly affected by soil pH, mean weight diameter and nutrients. Compared with conventional tillage, the chitinase activity increased in 0 - 20 cm soil layer under no-tillage, and the chitinase activity was enhanced in 0 - 40 cm soil layer under sub-soiling tillage and moldboard plowing tillage. The simulation result of the structural equation modeling showed that chitinase activity was directly affected by the tillage practice, soil depth, mean weight diameter, organic carbon, total nitrogen, total phosphorus, chiA gene abundance, and actinobacteria relative abundance.【Conclusion】These results provide a theoretical basis for understanding the effect of different tillage practices on soil chitin degradation in black soil areas.

• Effects of Shrub Encroachment on Soil Organic Carbon Components in Qinghai-Tibetan Alpine Grassland

  ZHANG Dong, LIU Jinqiu, MA Wenming, WANG Changting, DENGZENG Zhuoma, ZHANG Ting

  2023,60(6):1812-1823, DOI: 10.11766/trxb202203220004

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  【Objective】Changes in the dominant vegetation community will inevitably affect soil organic carbon (SOC) by altering the quantity of litter and root exudates during shrub encroachment. Thus, this study aimed to explore the response of different active organic carbon fractions in alpine grassland soils to invasion by different shrub species.【Method】Physicochemical fractionation method was used to divide soil organic carbon into non-protected carbon, physically-protected carbon, chemically-protected carbon and biochemically-protected carbon. It was analysed the contents of various organic carbon fractions and factors influencing their contents among four typical shrub-grassland and unshrub-encroached grassland on the east edge of Qinghai-Tibetan Plateau.【Result】The results showed that (1) Shrub encroachment has no significant effect on the SOC content of the surface soil(0-10 cm)in alpine grassland (P>0.05), but the content of organic carbon components was different. After Spiraea alpina and Sibiraea angustata shrubs encroached the grassland, the non-protected organic carbon and biochemically-protected organic carbon contents were significantly decreased (P<0.05) while the non-protected organic carbon content significantly decreased when Potentilla fruticose encroached the grassland. Also, the contents of physically-protected and chemically-protected organic carbon decreased significantly in Caragana microphylla encroached grassland (P<0.05), while the biochemically-protected organic carbon increased significantly (P<0.05). (2) SOC in both grassland and shrub patches soil were dominated by non-protected carbon pool, followed by resistant carbon pool (chemically-protected organic carbon and biochemically-protected organic carbon), while physically-protected organic carbon pool accounted for the least. (3) The contents of soil clay and total nitrogen were the main factors affecting the organic carbon fractions in alpine shrub-encroached grassland, with an explanation degree of 51.2%. 【Conclusion】The invasion of different shrub species had inconsistent effects on the content of different reactive organic carbon fractions. The soils of both unshrub grassland and shrub sample sites on the Tibetan Plateau were dominated by non-protected carbon. Thus, in the presence of external disturbances, the organic carbon pool in the area may become a source of carbon.

• Effect of Long-term Organic and Inorganic Nitrogen Fertilization on Carbon Content and Molecular Structure of Functional Groups in Soil Aggregates in Maize-cowpea Cropping Systems

  WU Mengqin, CAO Cougui, LIU Tianqi, LI Chengfang

  2023,60(6):1824-1833, DOI: 10.11766/trxb202203200122

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  Abstract:

  【Objective】Although many studies have reported the effects of long-term fertilizer application on soil organic carbon composition, molecular structure and functional group, few studies revealed the relationships between soil organic carbon, organic carbon composition and organic carbon functional groups under long-term fertilization conditions. Therefore, a field experiment with a maize-cowpea cropping rotation was conducted. The experiment included three treatments, i.e., organic nitrogen (N)fertilizer (OM), inorganic N fertilizer (IF), and the combination of organic and inorganic N fertilizers (IF+OM). The effect of long-term (9 years) N fertilizer applications on organic carbon composition and molecular structure of soil aggregates were studied to reveal the accumulative mechanism of soil organic carbon. 【Method】The soil was divided into 4 components by dry sieving method: >2 mm, 2-0.25 mm, 0.25-0.053 mm, and <0.053 mm, and then the mean weight diameter (MWD) and geometric mean diameter (GMD) were analyzed. The physical isolation method was used to measure free light particulate organic carbon (fPOC), intra-microaggregate particulate organic carbon (iPOC), silt-clay sized fraction organic carbon within microaggregates (iSOC) and free silt-clay sized fraction organic carbon (fSOC), and nuclear magnetic resonance spectroscopy was used to determine the functional group structure of soil organic carbon. 【Result】The results showed that compared with IF treatment and OM treatment, IF+OM treatment significantly enhanced maize and cowpea yields after 9 years of continuous N fertilization. Moreover, compared with IF treatment, OM and IF+OM treatments significantly increased MWD and GMD, and the effect was more obvious under IF+OM treatment. This study shows that fPOC was the main component of the soil organic carbon fraction, ranging from 21.0 to 29.8 g·kg^-1. The combination of organic and inorganic N fertilizers significantly enhanced the contents of soil organic carbon, fPOC and iPOC by 30.0%, 41.9% and 23.5% relative to IF treatment, respectively, but had no significant effect on the contents of iSOC and iSOC. The type of N fertilizer significantly influenced the ratio of alkyl, alkoxyl and aromatic carbon, which in turn significantly influenced alkyl/alkoxyl carbon and aromaticity in the soil. Compared with IF treatment, the combination of organic and inorganic fertilizer N fertilizers significantly increased alkyl carbon contents, but decreased aromatic carbon. Multi-path analysis showed that the alkyl carbon/alkoxy carbon ratio, hydrophobicity, aromaticity, fPOC and iPOC carbon content were closely related to organic carbon content. 【Conclusion】In conclusion, long-term combined application of organic and inorganic N fertilizers results in increases in crop yields, promotes the transformation of soil fine aggregates to large aggregates, increases fPOC and iPOC contents, optimizes the structure of aggregates, enhances soil stability, and thus promotes soil carbon sequestration, increased organic carbon storage, and thus promotes soil carbon sequestration. These results reveal the improvement mechanism of long-term combined application of organic and inorganic N fertilizers on soil organic carbon content, which would provide a theoretical basis for improving cropland soil fertility and structure.

Research Notes

• Effects of the Deposition of Atmospheric Particulate Matter on the Properties of Urban Soils: Evidence from Magnetic Susceptibility of Road Dusts

  WANG Xindong, HU Xuefeng, ZHANG Yanshuo, CUI Lei, LIU Rui, LAN Wenchong, LI Mei, WANG Jiayuan

  2023,60(6):1834-1842, DOI: 10.11766/trxb202206060235

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  Abstract:

  To study the effects of deposition of atmospheric particulate matter (APM) on the properties of urban soils, the values of magnetic susceptibility (χ_lf) and heavy metals in the topsoils and road dust in the industrial, traffic, residential and agricultural areas of Baoshan District, Shanghai, were analyzed. The topsoils in the different functional areas of Baoshan District, Shanghai, commonly have significantly enhanced magnetic strength (χ_lf = 130.7×10^-8m³·kg^-1 on average) of about 86.2% higher than the local magnetic background. χ_lf of the road dusts nearby the topsoils in the different functional areas was even more significantly enhanced, which was 903.3×10^-8m³·kg^-1 on average. Likewise, heavy metal contents in the road dust were significantly higher than those in the nearby topsoils in the different functional areas. The contents of Cu, Zn, Pb, Cd, Ni, Cr, Co, Mn and Fe in the road dust were 3.4, 2.4, 4.7, 22, 1.5, 2.8, 1.2, 1.4 and 1.6 times of those in the topsoils on average, respectively. Moreover, χ_lfof the topsoils in the Baoshan District was extremely significantly correlated with the contents of Cu, Zn, Cd, Ni, Cr and Mn (P < 0.01), and also significantly correlated with Pb and Fe (P < 0.05). Likewise, χ_lfof the road dust was also significantly correlated with the content of Zn, Ni, Cr, Co, Mn and Fe (P < 0.01), and with Cu (P < 0.05). Nevertheless, such correlations in the different functional areas of the district are highly different. Those in the agricultural topsoils are not significant. The distinctive characteristics of the road dust in the studied areas suggested that the APM under the urban environment contain a certain amount of anthropogenic magnetic particles enriched in heavy metals. The long-term and continuous deposition of such magnetic pollutants has led to the enhancement of magnetic signals and heavy metal contents in urban topsoils synchronously, and also adversely impacted the properties of urban soils significantly.

• Leaching Characteristics of Residual Fertilizer Nitrogen in the Dryland of Loess Plateau During the Summer Fallow Period

  XIA Mengjie, WANG Huimin, LEI Shuang, ZHAO Mengzhen, FENG Hao, ZHOU Jianbin

  DOI: 10.11766/trxb202308250340

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  Abstract:

  【Objective】Summer fallow after winter wheat harvest in dryland is a common practice on the Loess Plateau. However, due to bare land and intensive rainfall during summer fallow, the leaching characteristics of residual fertilizer nitrogen (N) after crop harvest deserve attention. This study aimed to reveal that the destination of applied N fertilizer after wheat season and the leaching characteristics of residual N fertilizer during summer fallow in dryland of the Loess Plateau. 【Method】This study was carried out in large lysimeters (3 m×2.2 m×3 m) by the 15N labeled method. 15N labeled urea was applied at the beginning as basal fertilizer with the rate of 150 kg•hm-2. Firstly, the absorption of 15N labeled fertilizer by wheat and the residual N in the soil after wheat harvest were investigated, and subsequently the 15N abundance and content changes of residual 15N labeled fertilizer in the soil profile were measured during the summer fallow of three years (2015—2017). 【Result】The results showed that the average absorption of nitrogen fertilizer by wheat was 53.9% while the amount of 15N fertilizer distributed in the soil (0-100 cm) after wheat harvest was 36.3% of the N application rate, with an average of 40.1% being in nitrate form. In the first year, the residual 15N fertilizer which accumulated in the 0-40 cm soil layer moved downward and accumulated in the 60-80 cm soil layer during the following summer fallow. The 15NO3--N mainly accumulated in the above 80 cm soil layer before summer fallow, but the accumulation peak of 15NO3--N was in the 80-100 cm soil layer at the end of fallow. In the second and third years, the residual 15N fertilizer and 15NO3--N moved downward about 20 cm, respectively, during summer fallow. After the summer fallow, the amount of residual 15N fertilizer in the 0-100 cm soil layer decreased, but the amount of residual 15N fertilizer and 15NO3--N in the 100-200 cm soil layer both increased. Specifically, the amount of residual N in the 100-200 cm soil layer increased by 1.9 and 7.0 kg•hm-2 during the summer fallow of the second and third years, respectively. Also, the amount of 15NO3--N in the 100-200 cm soil layer increased by 2.7 and 7.0 kg•hm-2 during the summer fallow of the second and third years, respectively. 【Conclusion】During the summer fallow, residual N fertilizer leached significantly. Under normal precipitation conditions, the average downward migration rate of residual N fertilizer during a summer fallow was 20 cm. As the age increased, the residual N fertilizer in the 0-100 cm soil decreased; while it increased in the 100-200 cm soil layer, with nitrate as the main leached form. However, the cumulative total loss of residual N fertilizer in the 0-200 cm soil profile during summer fallow was small, indicating that the redistribution of residual N fertilizer nitrogen in the soil profile was the main mechanism.

• Meta-analysis: Effects of Grazing on Composition and Function of Soil Fungal Community in Northern Grasslands of China

  LIN Xizhao, LI Xinglu, JIANG Xiaoyu, HE Peng, WANG Xuewei, LING Ning

  DOI: 10.11766/trxb202304150149

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  Abstract:

  【Objective】This study aimed to clarify the general rules of the impact of grazing on the composition and function of soil fungal communities in northern grasslands of China, and to provide the theoretical foundation for ecological conservation efforts in these grasslands. 【Method】This study collected 119 raw data of soil fungi from different studies in grazed grasslands, used unified bioinformatics processing methods and meta-analysis to demonstrate the changes in α-diversity, community composition and functional groups of soil fungi within grazed grasslands, and used weighted mixed-effects models for environmental factor analysis. 【Result】The results indicated that grazing reduced the soil fungal α-diversity and significantly decreased the relative abundance of pathotrophic fungi, wood saprotrophic fungi, soil saprotrophic fungi, and endophytic fungi. The change in grazing soil fungal α-diversity and functional fungal relative abundance depended on altered environmental factors in different regions. The negative effect of grazing on soil fungal α-diversity was mitigated to some extent in the regions with lower organic carbon content, lower carbon-to-nitrogen ratio, and higher annual precipitation. Initial soil organic carbon content and grazing exclusion duration influenced the variations in functional fungal abundance, with long-term grazing exclusion promoting the recovery of soil saprotrophic and symbiotrophic fungi communities. As the initial carbon-to-nitrogen ratio increased, the degree of reduction in the relative abundance of pathotrophic fungi under grazing decreased. In contrast, the degree of reduction in the relative abundance of saprotrophic fungi increased. Importantly, in regions with lower precipitation, grazing had a more significant impact on reducing the relative abundance of saprotrophic and symbiotrophic fungi. 【Conclusion】Overall, grazing negatively affected the α-diversity and functional traits of soil fungal communities in the northern grasslands of China. However, the degree and direction of this effect depended on the local environmental conditions.

• Distribution Characteristics and Influencing Factors of Glomalin in Soil Aggregates: A Meta-Analysis

  WANG Guoxi, WANG Ping, LIU Yalong, WANG Jingkuan

  DOI: 10.11766/trxb202301170024

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  Abstract:

  【Objective】This study aimed to understand the role of glomalin in maintaining soil organic carbon (SOC) balance and soil aggregate stability, and construct management strategies for improving soil structure and soil quality. 【Method】 To fully understand glomalin, we collected published data in recent years (332 sets of data from 19 literature), quantitatively analyzed the distribution characteristics of glomalin in soil aggregates, and systematically analyzed its influencing factors. Moreover, the distribution of glomalin in soil aggregates under different land uses was compared. 【Result】The results showed that the weight percentages of the > 2 000 μm and 2 000-250 μm aggregates (about 40%, respectively) were significantly higher than that of the 250-53 μm aggregates ( about 20%). The proportion of easily extractable glomalin in total glomalin was 20% in <53 μm aggregates, which was lower than other particle sizes (> 30%). There was no significant difference in the glomalin-C in SOC in different aggregates. The proportion of easily extractable glomalin-C in aggregates of different particle sizes was about 2%, while the proportion of total glomalin-C was about 8%.【Conclusion】In the >250 μm aggregates, GRSP (glomalin related soil protein) increased with the increase of temperature and precipitation, but decreased with the increase of pH. Although these correlations were not found in <250 μm aggregates, there was a significant positive correlation between glomalin and SOC. By comparing different land use patterns, we found that the glomalin in the aggregates of forest soil was more than those in farmland and grassland, which indicated that forest soil was more conducive to the accumulation of glomalin than farmland and grassland.

• Analysis of Soil Detachment of Typical Grassland on Loess Plateau Based on Mechanical Parameters

  MA Jianye, MA Bo, WANG Chenguang, SHANG Yongze, SHE Fangtao, LI Zhanbin

  DOI: 10.11766/trxb202302060048

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  Abstract:

  【Objective】This study aimed to understand the erosion mechanism of typical grassland in the Loess Plateau by analyzing the mechanical mechanism of soil detachment. 【Method】The representative grassland with tap roots and fibrous roots was selected as the research object in this study. Undisturbed soil samples were collected and subjected to flow scouring, and the relative soil detachment capacity (RSD) was calculated. The soil shear strength and root tensile force were determined, and the root cohesion was estimated based on Wu""s model. 【Result】 The RSD of grassland with fibrous roots was 77.27% significantly lower than that of grassland with tap roots, while the soil cohesion (Cr) was 14.84% higher than that of grassland with tap roots. The expression effect of Cr on RSD in the grassland with tap roots was better than that of root length density, and this effect was not obvious in the grassland with fibrous roots. The correlation between the RSD and soil shear strength under normal stress of 200 KPa (τ200) was better than the shear strength under other normal stresses. In the root-soil composite, the effect of Cr on soil detachment was stronger than that of τ200. Additionally, the soil detachment capacity of the root-soil composite in the grassland with tap roots, could be effectively predicted by the mechanical parameters, but the prediction of soil detachment capacity in the grassland with fibrous roots need to be further explored. 【Conclusion】Thus, this study presents an effective way to analyze the soil detachment mechanism by mechanical properties of root-soil composites. The results could provide a reference for the study of the erosion reduction mechanism of roots in the Loess Plateau.

• Response of Water Stability of Lateritic Aggregates with Different Land Use Types Under Different Antecedent Moisture Content

  WANG Jie, REN Shaocong, WEI Yujie, HUANG Yijing, YANG Bangge, CAI Chongfa

  DOI: 10.11766/trxb202301060007

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  Abstract:

  【Objective】 Antecedent moisture content is a critical factor affecting soil aggregate stability. However, its influence on the aggregate stability of lateritic soils developed from basalt has not been systematically investigated. To unravel the intricate interplay between soil properties, antecedent moisture content, and the water stability of lateritic soils developed from basalt, a meticulous investigation was undertaken. This study delved into the diverse land use types, aiming to shed light on the intricate relationship between these factors and aggregate water stability. 【Method】 In the latosol region of Hainan, a comprehensive study was conducted to examine the influence of three prevalent land use types, forest, cropland, and wasteland, on the soil properties and aggregate size distribution. Through a preliminary investigation, the tested soils were meticulously analyzed. The LB method, specifically the Fast Wetting variant, was employed to determine the aggregate size distribution within the 3-5 mm range across the various land use types. This assessment was performed under five distinct antecedent moisture contents of 3%, 5%, 10%, 15%, and 20%. Subsequently, water stability indices, including Water Stability Index ( WSA), Mean Weight Diameter (MWD ), and Geometric Mean Diameter (GMD ), were meticulously calculated to provide valuable insights into aggregate water stability. 【Result】Distinctive variations in soil properties, encompassing pH, organic carbon, cation exchange capacity, and some exchangeable base cations, were prominently observed across different land use types. The distribution of water-stable aggregates in the lateritic soil exhibited either an unimodal or bimodal pattern, with peaks predominantly observed at 2-1 mm and 0.5-0.25 mm size fractions. Notably, forest soils displayed the highest aggregate stability among surface soils, while cultivated soils exhibited relatively weaker aggregate stability. Furthermore, subsurface soils demonstrated significantly lower aggregate stability (P<0.05) compared to surface soils. When considering air-dry conditions, characterized by moisture content during air-drying, the water stability of surface soil aggregates consistently exhibited high values (WSA > 90%, MWD > 1.5, GMD > 1.2). As the antecedent moisture content increased, the proportion of macro aggregates (> 2 mm) following aggregate fragmentation displayed varying degrees of change, ultimately resulting in an overall increase in the content of macro aggregates (> 2 mm). It is noteworthy that the influence of land use type on aggregate water stability outweighed that of antecedent moisture content (F >56, P<0.01). Soil organic carbon (SOC) emerged as the primary factor explaining the variation in aggregate stability (R²=80.6%, P<0.01), displaying a positive correlation. Non-capillary porosity followed suit, exhibiting a significant positive correlation (R² = 66.0%, P<0.01), while capillary porosity demonstrated a noteworthy negative correlation. Among the soil sesquioxides, aluminum oxides (Ald, Alo) exerted a considerably larger impact on aggregate stability compared to other sesquioxides. In contrast, the influence of antecedent moisture content on aggregate stability was relatively modest, displaying a significant negative correlation (R² = 24.0%, P< 0.01). 【Conclusion】The water stability of lateritic soil aggregates, which developed from basalt, exhibited pronounced sensitivity to land use, with forested areas surpassing wastelands and croplands surpassing cultivated land in terms of water stability. Additionally, the water stability of these lateritic soil aggregates showed an initial increase followed by a subsequent decrease as the antecedent moisture content increased. Notably, when compared to red soil, lateritic soil aggregates displayed a lower sensitivity to dissipative effects. The primary determinant influencing the stability of lateritic soil aggregates is the concentration of SOC. Variations in the stability of these aggregates across different land uses can be attributed to fluctuations in SOC levels.

• Research Progress and Prospects of Human Health Risk Assessment of Heavy Metal Pollution in Farmland Soils of China

  LONG Xinxian, LIU Wenjing, QIU Rongliang

  DOI: 10.11766/trxb202306130229

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  Abstract:

  Heavy metal contamination of agricultural soils poses a great threat to food safety and human health. Heavy metals enter the human body mainly through exposure pathways such as direct ingestion of soil, inhalation of soil particles, dermal exposure and food chain ingestion, with direct ingestion of heavy metal-contaminated soil and eating agricultural products being the main exposure route. Human health risk assessment plays an important role in the classification of agricultural soil quality categories and environmental risk management. Therefore, this paper reviews the development of human health risk assessment of heavy metal contamination in agricultural soils in China, introduces the basic process and assessment techniques of human health risk assessment, and discusses the main factors affecting the accuracy of human health risk assessment and the optimization measures. The research indicates that in the health risk assessment of heavy metals in farmland soil, the coupled pollution source identification technology should be strengthened while the exposure route of food consumption needs more attention. Also, the exposure parameters of different sensitive receptors should be accurately identified, and the exposure parameters of localized sensitive receptors, and the bioavailability of heavy metals should be included to improve the accuracy of health risk assessment of heavy metals in farmland soil. In the future, the health risk assessment of heavy metals in farmland soil can be deepened from many aspects, such as strengthening technical methods to deal with the uncertainty of the health risk assessment process and considering the exposure pathways of various diets. This will help with establishing localized heavy metal toxicity standard data to promote the development of the theory and technology of human health risk assessment of heavy metals in agricultural soils of China.

• Prediction of Spatial Distribution of Soil Organic Carbon in Cultivated Land Based on Phenology and Extreme Climate Information

  ZHOU Qiqing, ZHAO Xiaomin, GUO Xi, ZHOU Yang

  DOI: 10.11766/trxb202211020602

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  Abstract:

  【Objective】As the largest Carbon pool in the terrestrial ecosystem, Soil Organic Carbon (SOC) plays an important role in Soil quality and crop yield. Accurate prediction of the spatial distribution of SOC on cropland is essential for the development of agricultural management measures. In the framework of Digital Soil Mapping (DSM), an important method to improve the precision of SOC spatial prediction is to select an effective environmental covariate. In previous studies, the mean values of remote sensing indices and climate variables for a certain period or point in time were usually used as input variables, while temporal characteristics and events were rarely used for SOC prediction. Therefore, in order to reduce the impact of the lack of part of physical information and climate characteristics, phenological variables and extreme climate variables were added in this study. The response characteristics to the spatial variability of SOC of cultivated land and the feasibility of predicting the spatial distribution of SOC were discussed. 【Method】The research area of this paper is Shanggao County, Jiangxi province. A random forest model was used, in which remote sensing data, DEM-derived variables, phenological parameters and climatic characteristics were selected as environmental covariates, and the model results were corrected for residuals using Ordinary Kriging (OK). The prediction effect and prediction accuracy of the model under different types of variable combinations were compared. 【Result】The results show that chronological variables, phenological variables, and extreme climate variables can improve the prediction performance of the model, and the residual error as an error item can further improve the accuracy of the model. The combination of chronological variables, phenological variables, extreme climate variables, topographic variables, and residuals had the highest prediction accuracy, improving R^2 , MAE, and RMSE by 90.00%, 58.95%, and 57.14% compared to the combination of topographic variables, remote sensing variables, and climate variables. The analysis of variable contribution rates shows that SU, a3 and TXx were important variables affecting the distribution of cultivated land SOC in the study area. 【Conclusion】Phenological variables and extreme climate variables have good application prospects. In the future, it is necessary to verify the validity of extreme climate variables as environmental variables in predicting soil properties under different land use and large-scale study areas.

• Boundary Identification of Purple Soil Horizon Based on K-means Clustering and Image Segmentation

  YANG Kai, CI E, LIU B, CHEN Yangyang, XIE Yu

  DOI: 10.11766/trxb202302070050

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  Abstract:

  【Objective】Pedology begins with the observation of soil profile and its morphological characteristics. The division of the soil profile horizon and description of the characteristics of the horizon boundary are the basis of soil investigation. The division of soil horizon in the field requires rich practical experience in pedology and is more subjective, which makes it difficult to form a set of unified division standards. 【Method】In this paper, the purple soil profile image was taken as the research object, and using K-means clustering and image segmentation technology, combined with the color (CIE Lab color space) and texture characteristics (Entropy) of the image, we identified the horizon boundary of the purple soil profile, by comparing with the results of field division. 【Result】The results show that (1) the a and b channels of CIE Lab color space and Entropy texture characteristics can delineate the master horizon (A , B , and C) and bedrock (R) of the profile; the a channel values range from 7 - 22, the b channel values range from 7 -19, and the Entropy values were 4 or 5; the Munsell colors converted by the CEL XYZ system had a certain deviation from the colors visually discerned in the field using colorimetric cards, with a hue range of 10R- 2.5Y, a value range of 4 - 8, and a chroma range of 3 - 8. (2) The number of soil horizon and the depth of soil horizon identified by clustering were consistent with the results of field identification; the difference between the lower boundary depth of soil horizon identified by clustering identification and those identified in the field was within 3 cm, except for C in profile Z2 and the Ap in profile Z6, where the difference was larger (13 cm and 8 cm, respectively). (3) The topography of the soil horizon identified by clustering was more irregular and the distinctness was more blurred. The clustering algorithm can identify more subtle differences in the soil profile image and reflect the local variation of soil properties in more detail. 【Conclusion】K-means clustering and image segmentation techniques achieved the identification of the horizon boundary of purple soil, and this study provides a scientific reference for the development of an intelligent identification system for soil profiles.

• Spatial Variation of Black Soil Thickness on Slope Measured by Using Ground Penetrating Radar in Northeast China

  LIU Chang, LIU Qin, ZHANG Qiong, DAN Chenxi, LIU Gang

  DOI: 10.11766/trxb202212120687

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  Abstract:

  【Objective】The black soil region of Northeast China is an important commodity grain production base in China. However, long-term high-intensity reclamation and unprotected utilization have led to serious soil erosion and continuous reduction of black soil thickness. In some areas, the low-nutrient loess parent material was exposed, resulting in decreased land productivity, and food production was seriously threatened. However, determination of the distribution of soil thickness on the slope is challenging. The traditional soil thickness measurement methods, including the soil profile method, soil probes, and the drilling method, are inefficient and cannot ensure continuity along the slope. Therefore, this study aims to apply a new method, ground penetrating radar (GPR), to measure the continuous variation of black soil thickness on slopes. 【Method】In this study, the GPR was used to continuously measure the black soil thickness on three slopes (straight, convex, and concave) in northeast China. Firstly, two types of soil, black soil and loess parent material were probed in a wood box to investigate the effect of soil moisture and bulk density on the soil permittivity and to prove the feasibility of GPR determination for black soil thickness. Then, the accuracy of the GPR in measuring black soil thickness was verified in conjunction with field trial excavation profiles and pre-buried iron pipes. 【Result】(1) The soil permittivity increased and decreased with the increasing bulk density and soil moisture, respectively. The relationships among soil moisture, bulk density, and soil permittivity for both black soil and loess parent material can be represented by logarithmic equations with an accuracy of 95.26%~99.66%. (2) Compared with the actual thickness of the soil profile, the accuracy of GPR measurements for black soil thickness was 87.05%~95.58%. (3) The spatial distribution of black soil thickness differed among the three slopes. However, the overall wave-like variation was observed. Deposition occurred at the slope foot and the black soil thickness was thick, while the black soil thickness at the shoulder and back of the slope was thin where soil erosion was more serious. 【Conclusion】Soil moisture content and bulk density had a significant effect on soil permittivity and the soil permittivity decreased with the increasing clay content. Also, there were differences in the permittivity of black soil and loess parent material. It was observed that electromagnetic waves could be reflected at their interfaces, which means that GPR can be applied to detect the black soil thickness on loess parent material. Our analysis revealed that topographic factors significantly affected the spatial variation of black soil thickness among the three slope types studied. Based on these results, this study could provide an efficient and accurate method to investigate soil thickness for further evaluation and conservation of black soil resources.

• Effect of Vegetation Type on Rhizosphere Microorganisms of Reclaimed Soils in Coal Mining Areas

  lihouchun, li junjian, zhanghong, zhangxiujuan, ningyuewei, liuyong

  DOI: 10.11766/trxb202303140100

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  Abstract:

  【Objective】Long-term mining activities have caused serious damage to the ecological environment in the mining area. Soils near mining areas have reduced quality, decreased vegetation cover, and changed microbial habitats. Stripped soil and coal gangue are mixed to form hillocks and the exposed surface of the hillocks is highly susceptible to wind and water erosion, which has resulted in increasingly severe damage to the ecosystems, including changes in plant species composition and community structure, reduced biodiversity and productivity, deterioration of soil and microenvironment, and changes in the relationships between organisms. Hence, the ecological restoration of the coal mines is an urgent task. Interestingly, vegetation types may affect the composition and diversity of microbial communities in rhizosphere soil owing to the growth conditions, vegetation cover, root turnover rates, and the chemical composition of root exudates. Therefore, it is important to explore the response of microbial community composition and diversity under different vegetation types in mining ecological restoration areas.【Method】The rhizosphere soils of five vegetation types (Platycladus orientalis, Picea asperata, Pinus sylvestris, Pinus tabuliformis, and Sabina chinensis) were collected in this study to detect the soil physicochemical properties, enzyme activities, and bacterial community structure. Also, we identified key environmental factors affecting rhizosphere bacterial communities using redundancy analysis and conducted a mantel-test analysis between dominant bacterial phyla and environmental factors. Structural equation models were established to explore the interactions between plants, soil, and microbes. Furthermore, the soil-integrated fertility index was calculated to analyze the ecological restoration effectiveness of different vegetation types.【Result】Vegetation types had significant effects on soil physicochemical properties, enzyme activities, bacterial community composition, and diversity. The P. sylvestris field had significantly higher total carbon content, total nitrogen contents, bacterial abundance, and diversity, while soil alkaline phosphatase and soil urease activities were significantly higher in the P. asperata field. The Proteobacteria, Acidobacteria, Actinobacteria, and Bacteroidetes were the dominant phyla of soil bacterial communities. Also, the dominant genera were RB41, Streptomyces, MND1, Ferruginibacter, and Variovorax. Total sulfur, soil bulk density, and soil alkaline protease were the key factors affecting the structure of rhizosphere soil bacterial communities. Our analysis revealed that vegetation types can directly affect soil physicochemical properties, soil enzyme activities, and bacterial community structure, as well as indirectly affect rhizosphere soil bacterial community structure through soil physicochemical properties and soil enzyme activities. Soil integrated fertility index indicated that P. sylvestris and P. asperata were superior to other vegetation in the ecological restoration of mining areas.【Conclusion】Vegetation types have significant effects on soil physicochemical properties, soil enzyme activity, and bacterial community in the rhizosphere. P. sylvestris and P. asperata can improve the rhizosphere soil bacterial diversity and soil fertility, which is beneficial to the ecological restoration of the coal mine reclamation area. This study provides a scientific basis for vegetation selection for ecological restoration of coal mine reclamation areas in semiarid regions.

• Effects of Foliar Spraying of Sorbitol Chelated Potassium on Peanut Yield and Rhizosphere Soil Microbial Community

  SUN Wei, ZHANG Huanyang, WEI Qianqian, ZENG Fanhe, LI Tengsheng, ZHAO Li, HAN Chuanhao, ZHANG Jing, ZHANG Ziqi, SHI Xiang, YAN Dongyun

  DOI: 10.11766/trxb202301030003

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  Abstract:

  【Objective】China depends heavily on agricultural potassium fertilizer imported from abroad. Thus, it is important to improve potassium utilization efficiency by changing the existing forms of potassium.【Method】In this paper, a two-year field trial (in 2020 and 2021) was set up using Virginia-type peanut Huayu 22 to investigate the effects of inorganic potassium (free ionic state) and sorbitol chelated potassium on peanut yield, dry matter accumulation, potassium accumulation, and bacterial community structure in peanut rhizosphere soil by a completely randomized block design. Under the premise of conventional fertilization, peanut spraying experiments were carried out at different growth stages and with five treatments: CK, water control; IK, inorganic potassium; MK, sorbitol mixed inorganic potassium; SK, sorbitol chelated potassium ( self-made); and LK, commercially available chelated potassium (Canada).【Result】The results showed that foliar topdressing potassium fertilizer on leaves could significantly increase the peanut yield. Compared with the treatment of IK or LK treatments, the two-year average yield of SK treatments increased by 18.9% and 14.97%, respectively. The yield components of 100-seed weight, 100-pod weight, and full fruit rate were all significantly improved. Also, the dry matter accumulation and potassium accumulation of peanut plants treated with sorbitol-chelated potassium were significantly increased. Compared with CK, IK, and LK treatments, the total dry matter of peanut plants treated with SK increased by 19.5%, 19.1%, and 15.7% in the stage of the full pod, and increased by 22.8%, 27.4%, and 11.7% at the mature stage, respectively. Potassium accumulation in peanut kernels increased by 30.6%, 49.8% and, 44.8% in the stage of full pod, and increased by 30.8%, 59.1%, and 10.8% at the mature stage, respectively. The above results showed that self-made sorbitol-chelated potassium could promote the absorption and distribution of potassium nutrients in plants. Furthermore, the microbial diversity and richness of peanut rhizosphere soil increased under SK treatment compared with the other treatments. Compared with CK, MK, and LK treatments, the Sobs index of microbial communities in SK treatment increased by 10.7%, 12.5%, and 10.7%, respectively. The species significantly enriched in SK treatment were p-Verrucomicrobiota_g-Roseimicrobium and p-Planctomycetota_c-vadinHA49. The correlation analysis showed that the increase in production was significantly related to the absorption and distribution of potassium and the changes in rhizosphere microorganisms.【Conclusion】In summary, compared with inorganic potassium form, sorbitol-chelated potassium could promote the absorption and accumulation of potassium in peanuts at the same potassium application level, which is comprehensively reflected in production. The research results could provide theoretical and practical references for improving potassium efficiency.

• Distribution Characteristics of Fe (Al)-C in Zonal Soils of the Three-River Source Region

  ZHOU Shaolong, LI Yuemei, ZHANG Zhichun, ZHEN Guoyun, SUN Fenghao, OU Jianfang

  DOI: 10.11766/trxb202212130690

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  Abstract:

  【Objective】 This study aimed to understand the soil stable organic carbon (SSOC) storage of natural grassland in the hinterland of the Qinghai-Tibet Plateau, and clarify its carbon fixation capacity and potential for increasing sinks. 【Method】The soil in the Three-River Source Region was divided according to regional space and three typical grassland types and the active layer soil was taken as the object. The soil total organic carbon (TOC) and Iron (aluminum)-bounded carbon [Fe(Al)-C] were analyzed, the relationship model was established with the geographical and climatic data, and the temporal and spatial variation law in recent 60 years (1961-2020) was retrieved. 【Result】The results show that: 1) The average content of Fe(Al)-C is 6.07 g·kg-1 and the average content of [Fe(Al)-C]/TOC is 16.87% in the Three-River Source Region, with obvious zonal characteristics. Also, the content in the central and eastern regions was significantly higher than that in the western region (P < 0.05); 2) The contents of Fe(Al)-C and [Fe(Al)-C]/TOC in the three types of grassland were 2.35 ~ 8.81 g·kg-1and 11.99%~20.52%, respectively, and the alpine shrub meadow and alpine meadow were significantly higher than those in alpine steppe (P < 0.05). Fe(Al)-C was positively correlated with TOC in the three typical natural grassland types (P < 0.01). 3) The results of analog- digital mapping showed that the distribution area change of Fe(Al)-C in the Three-River Source Region has changed in the recent 20 years (2001-2020). Compared with the past two periods; 1961-1980 and 1981-2000, the distribution area with its content >5.75 g·kg-1 and increased by 1.64% on average. 【Conclusion】From our analysis, it was deduced that whole area is in a state of carbon sink, and the C fixation potential of Fe(Al)-C in soils in the Three-River Source Region can not be overlooked.

• Effects of Long-term Tillage on Hydraulic Properties of Typical Black Soils

  HUANG Yiting, CHEN Junxi, GAO Yuhao, LI Xinyue, ZOU Ziqiang, CHEN Jiazhou

  DOI: 10.11766/trxb202212010665

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  Abstract:

  【Objective】 Undisturbed woodland and cultivated land soils from vertical and horizontal directions were collected across different latitudes in typical black soil regions in Northeast China for this research. The objective was to investigate the effects of long-term tillage in cultivated land on the black soil hydrological degradation. 【Method】 Nine typical cultivated land units were selected across three latitudes, including Jiusan Farm Management Area in Nenjiang (48°46′N), Hailun (47°30′N), and Bayan County in Harbin (46°23′N). Intact soil cores were collected from 0-15 and 15-30 cm depths in vertical and horizontal directions to determine soil penetration resistance (SPR), and hydraulic properties (water retention and saturated hydraulic conductivity (Ks). 【Result】 Results showed that soil SPR significantly increased in cultivated land compared to woodland, and the SPR in tillage pan layer (15-30 cm) (897.04 kPa) was 1.89 times higher than that in woodland. Soil hydraulic properties also significantly decreased in cultivated land, whose soil available water decreased to 0.15 (0.10-0.21) cm3·cm-3 compared to 0.19 (0.14-0.23) cm3·cm-3 in woodland. Using soil physical quality index S to assess the over black soil quality showed that S value decreased from excellent 0.061 (0.041-0.094) in woodland to poor 0.025 (0.009-0.040) in cultivated land. The degradation of cultivated land quality was attributed to the significant reduction in soil organic matter content and significant increase in soil bulk density (1.31 g·cm-3 in cultivated land vs. 1.03 g·cm-3 in woodland). Long-term ridge tillage resulted in a 10 times reduction in Ks in tillage pan layer (6.61 cm·d-1), and this can be attributed to the disruption of balance between tillage and tillage pan layer and enlargement of magnitude difference for Ks and bulk density between two layers. Tillage resulted in a lower Ks in the vertical direction (64.67 cm·d-1) than in the horizontal direction (82.84 cm·d-1) in the tillage layer. The Ks decreased in a larger degree in the vertical direction and less degree in the horizontal direction. Thus, this heterogeneity of Ks in directions interfered the original water movement direction in tillage layer. The low hydraulic conductivity of the plough pan tends to accumulate precipitation and produce lateral interflow. 【Conclusion】 Generally, long-term tillage has severely degraded the physical and hydraulic properties of the soil. The huge difference of soil compactness and Ks between the tillage layer and plough pan produced an artificially stratified soil in cultivated land. The limitation of water infiltration is a dominant reason for the "furrow effect" in cultivated land.

• A Comprehensive Evaluation of the Effect of Desulfurized Gypsum for Improving Saline-alkali Soil

  JIANG Zhanbo, NING Songrui, WANG Quanjiu

  DOI: 10.11766/trxb202209020488

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  Abstract:

  【Objective】In order to comprehensively study the effect of desulfurized gypsum in improving saline-alkali soils, this paper statistically analyzed the change characteristics of soil pH value, exchangeable sodium percentage (ESP), soil electrical conductivity (EC), and crop yield after applying 0~60 t·hm−2 desulfurized gypsum in the northwest, north, northeast, and coastal areas of China through literature search. To achieve this, a comprehensive improvement evaluation model of saline-alkali soil was used in which the desulfurized gypsum amount was designed as an independent variable based on the grey relational analysis and entropy weight method. 【Method】Soil pH value and ESP are often used to evaluate the alkalization property of saline-alkali soil while EC is used to evaluate the salinization property of saline-alkali soil. This paper used the data of literature to explore the relative change rates of soil pH, ESP, and EC in 0~20 cm soil layer with and without desulfurized gypsum within 1 year after the crop harvest in order to quantitatively reveal its improvement effect. Grey relational analysis and entropy weight method were used to synthesize three soil indexes to evaluate the improvement effect of desulfurized gypsum on saline-alkali soil. Due to the few literature data on light saline-alkali soil and moderate saline-alkali soil, the application of desulphurized gypsum in severe saline-alkali soil was mostly studied. This paper combined light saline-alkali soil and moderate saline-alkali soil into light and moderate saline-alkali soil for analysis. 【Result】Application of desulfurized gypsum reduced soil pH and ESP and increased crop yield, but increased EC. As the application rate of desulfurized gypsum increased, the decrease rate of pH and ESP and the increase rate of crop yield increased first and then decreased whereas the increase rate of EC showed an increasing trend. When the amount of desulfurized gypsum applied to moderate saline-alkali soil and severe saline-alkali soil exceeded 30 t·hm−2, the increase rate of crop yield (Oil sunflower, alfalfa, corn, rice, wheat, Lycium barbarum, and sweet sorghum) showed a decreasing trend. To further analyze the effect of desulfurized gypsum on the improved saline-alkali soil, an entropy weight grey correlation evaluation model was established, and the application of desulfurized gypsum was optimized. 【Conclusion】Through the study on the improvement effect of desulfurized gypsum applied in the range of 0~60 t·hm−2 in saline-alkali soil, using statistical analysis and mathematical modeling, it was concluded that the amount of 18∼22 t·hm−2 desulfurized gypsum in light and moderate saline-alkali soil; the amount of 23∼29 t·hm−2 desulfurized gypsum in severe saline-alkali soil could achieve good soil improvement effect and increase crop yield. The research results provide a reference for improving saline-alkali soil with desulfurized gypsum.

• Research on Digital Soil Mapping Based on Feature Selection Algorithm

  ZHANG Xiaoting, HUANG Wei, FU Peihong, MENG Ke, WANG Sufang

  DOI: 10.11766/trxb202208090441

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  Abstract:

  【Objective】Traditional digital soil mapping methods are unable to produce detailed soil maps within a reasonable cost and time. Digital soil mapping is a powerful technique, which is popular and widely used by scholars coupled with environmental covariates to map soil types or properties. The selection of environmental covariates is the key to ensuring the accuracy of mapping. Previous studies have proven that remote-sensing images can be used as auxiliary factors for reasoning mapping. Remote sensing data can provide rich soil landscape information, which is consistent with the core idea of using grids to express spatial changes of soil features in digital soil mapping. Moreover, remote sensing technology can obtain real-time information quickly. However, there are few relevant studies on how principal components and texture information of remote sensing factors contribute to the reasoning process. Thus, determining the weight of remote sensing factors in the reasoning process is the key content of this study, which is tested by the reliability of testing mapping results.【Method】Chengmagang Town, Macheng City, Hubei Province was selected as the study area. Using Chinese soil classification and soil type map with a spacing of 10 meters, which were extracted from the contour data and remote sensing image using a variety of feature selection algorithms to effective screening of variables, this study conducted the soil digital mapping by reasoning machine learning algorithms. Specifically, the recursive feature elimination screening algorithm, ReliefF algorithm and tree-based feature screening algorithm were used to rank all environmental factors in the whole area, plain and hilly areas of the study area, respectively. Then, it screened the effective environmental variables of environmental factors and analyzed the weight of remote sensing factors in the reasoning process. The factors involved in plant-hill region mapping were explored and their importance was determined. According to the selected relatively stable indicators, the gradient boosting decision tree model after parameter tuning of the Bayesian optimization algorithm based on TPE was used for modeling. Also, the mapping accuracy results after different feature screening algorithms were compared between the whole region and the terrain region to further explore ways to improve the accuracy of soil type mapping.【Result】The soil type inference map was verified by 141 independent field sampling sites. The results showed that the importance of remote sensing factors in the plain area was higher than that in the hilly area and the NDVI and Mean values of the remote sensing factors were relatively stable. The highest accuracy of topographical inference mapping based on the recursive feature algorithm was 75.89%, which was higher than the 13.48% and 4.97% of the ReliefF algorithm and tree-based feature screening algorithm, respectively. In addition, among the mapping results of the three feature screening algorithms, the accuracy of the mapping based on terrain factors was higher than that of the overall region mapping. It suggests that remote sensing factors as an auxiliary means to participate in the reasoning process can effectively improve mapping accuracy. 【Conclusion】This study uses a feature selection algorithm to select features with a strong correlation with soil types as auxiliary variables in the machine learning model. The method is efficient and cost-effective for soil type prediction. Compared to other methods, the soil type mapping method based on machine learning is advantageous and the feature mining and machine learning algorithms have theoretical significance and practical value.

• The adaptative mechanisms of methane-oxidizing bacteria for elevated atmospheric CO2 in paddy soil

  Cao weiwei, Yan Chen, Zhong Wenhui, Zhu Chunwu, Zhu Jianguo, Jia Zhongjun

  DOI: 10.11766/trxb202302160061

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  Abstract:

  【Objective】CH4 is the second most potent greenhouse gas only next to CO2. Continued CH4 and CO2 emissions by human activities pose a major challenge to the mitigation of global climate change. Rice paddy, a main form of artificial wetland, accounts for ~8% of anthropogenic sources of CH4. The elevated atmospheric CO2 (eCO2) affect the cycling of nutrients and elements in paddy fields mainly through the changes in plant-soil-microbe interactions, which also influence net CH4 flux associated with both the methanogenic and methanotrophic processes. However, how eCO2 affects aerobic methane oxidation in paddy soils has rarely been examined, and the adaptative mechanisms of active methane-oxidizing bacteria (MOB) for eCO2 remain unclear. This study aimed to explore the changes in methane-oxidizing rates and identify the active MOB phylotypes in paddy soil under the eCO2 treatment. 【Method】We collected paddy soil samples from China’s FACE (Free Air CO2 Enrichment) experiment station, with FACE treatment and ambient CO2 concentration treatment (aCO2). The CH4-feeding microcosm incubation was applied to learn the methane-oxidizing rates in the two soils. DNA-based stable isotope probing (DNA-SIP) combined with quantitative polymerase chain reaction (qPCR) of methane-oxidizing functional gene pmoA was used to identify the 13C-labeled DNA. High-throughput sequencing and phylogenetic analysis for the 16S rRNA gene amplicons of the 13C-DNA were used to identify the active microbiomes during methane oxidation. 【Result】The results showed that eCO2 significantly stimulated aerobic methane-oxidizing rate when compared to the ambient CO2 treatment, with 301.8 and 243.3 nmol CH4 g-1 d.w.s hour-1, respectively. The abundance of MOB increased by 1.1~1.2- folds under eCO2. A group of MOB assimilated 13CH4 and synthesized 13C-DNA, which were separated into heavy fractions during DNA-SIP. The result of high-throughput sequencing for 13C-DNA showed that Methylobacter and Methylosarcina predominated the active MOB phylotypes. The relative abundance of Methylobacter increased by 16.2~17.0% while the relative abundance of Methylosarcina decreased under eCO2. eCO2 also stimulated the activity of non-methanotrophic bacteria, such as Acidovorax and Pseudomonas, which implies a methanotrophy-induced microbial community response to eCO2. 【Conclusion】This study reveals positive effects of elevated atmospheric CO2 on aerobic methane oxidation in paddy soil, with the predominant and active MOB of Methylobacter playing crucial roles, indicating an improved potential of methane oxidation under the scenarios of global climate change.

• Effects of Combined Application of Straw and Organic-inorganic Fertilizers on Key Microorganisms and Wheat Yield in Fluvo-aquic Soil

  GUO Wei, ZHOU Yunpeng, CHEN Meiqi, LI Dandan, WANG Qingxia, ZHOU Tantan, ZHAO Bingzi

  DOI: 10.11766/trxb202303010086

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  Abstract:

  【Objective】The combined application of crop straw with chemical fertilizers and chicken manure can change soil microbial community structure and the interaction between microorganisms. However, whether there is a correlation between these changes and wheat yield remains unclear. 【Method】A 7-year field experiment was used as the research platform, and this included five management strategies: (1) N0S0: no fertilizer or crop straw returning, (2) N0S: crop straw returning, (3) NS0: traditional chemical fertilization, (4) NS: crop straw returning with chemical fertilizer, and (5) NSM: crop straw returning with chemical fertilizer and the nitrogen was substituted 20% by chicken manure. The effects of different management strategies on microbial community composition in bacterial-fungal co-occurrence networks and the correlation between key microorganisms and wheat yield were studied. 【Result】The results showed that compared with N0S0 treatment, the grain yield of wheat under NS0, NS and NSM treatments increased by 539.20%, 611.56% and 676.56%, respectively, while there was no significant change under N0S treatment. The bacterial and fungal community compositions were divided into three significantly different groups: N0S0 and N0S, NS0, and NS and NSM, respectively, indicating that the microbial community composition was significantly different with or without chemical fertilizer application. Under both chemical fertilizer applications, there was a significant difference in whether organic materials were applied. Ranked from high to low importance, we found that available phosphorus, electrical conductivity, microbial biomass nitrogen, soil organic carbon, readily oxidizable organic carbon, and particulate organic carbon were the main soil physicochemical properties that caused the changes in bacterial community composition under different treatments. Also, electrical conductivity, microbial biomass nitrogen, readily oxidizable organic carbon, particulate organic carbon, available phosphorus, and soil organic carbon were the main soil physicochemical properties that caused the changes in fungal community composition under different treatments. In the bacterial-fungal co-occurrence network, two key modules (module 1 and module 4) were significantly correlated with wheat yield changes. NS+NSM treatments increased the relative abundance of beneficial microorganisms in module 4, including Nocardioides, Cellulomonas, Pir4_lineage, Chrysosporium, Acaulium, and Schizothecium, which were positively correlated with wheat yield. These beneficial microorganisms could degrade cellulose and lignin, promote nutrient conversion and recycling, or inhibit the growth of the potential pathogen. NS+NSM treatments also significantly reduced the relative abundance of plant pathogenic fungi in module 1, including Stachybotrys, Achroiostachys, and Fusicolla, which were negatively correlated with wheat yield and were detrimental to soil health and crop growth. 【Conclusion】Therefore, crop straw returning with chemical fertilizer and crop straw returning with chemical fertilizer and chicken manure were beneficial to the increase of key beneficial microorganisms and the decrease of pathogenic fungi. The function and the relative abundance of key microorganisms had effects on wheat yield.

• Effects of Biochar and Organic Fertilizers Combined Application on Spectral Characteristics of Soil Dissolved Organic Matter in Paddy Soil

  LIANG Dong, ZHOU Qiaolin, ZHANG Hui, MA Hongbo, Ning Yunwang, ZHANG Yongchun, XU Cong, JIAO Jiaguo, WANG Jidong

  DOI: 10.11766/trxb202302020039

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  Abstract:

  【Objective】This study aimed to investigate the long-term and synergistic effects of Biochar and organic fertilizer on dissolved organic matter (DOM) in paddy soil. 【Method】Several fertilization treatments were tested over five years, including a control (CK), biochar (BC), fertilizer (N), biochar+fertilizer (N+BC), manure+fertilizer (MF, 25% nitrogen replacement), and manure+fertilizer+biochar (MF+BC, 25% nitrogen substitution). The effects of these treatments on soil pH, total nitrogen, available phosphorus, accessible potassium, soil organic carbon (SOC), readily oxidizable organic carbon (ROC), and dissolved organic carbon were examined. The spectral properties and fluorescence components of DOM were characterized using the ultraviolet-visible spectrum (UV-Vis), fluorescence spectrum, and parallel factor analysis. Also, the specific UV absorbance, UV absorption slope rate, fluorescence index, biological index, humification index, and relative amounts of fulvic acid, tryptophan, and humic acid of the DOM were examined. 【Result】The results showed that by utilizing biochar and organic fertilizer, soil acidity could be decreased and rice productivity effectively increased. The MF+BC treatment had the highest rice productivity and soil available phosphorus of all the treatments. Significantly (P＜0.05) favorable correlations between rice yield and DOM""s bioavailability, aromatization, humification, tryptophan concentration, and hydrophilicity were found. The order of the degree of humification and bioavailability increase in DOM was manure > biochar. Furthermore, biochar significantly increased DOM, fulvic acid, and tryptophan components and promoted the conversion of ROC to dysoxidizable-organic carbon, whereas organic fertilizer increased ROC, fulvic acid, tryptophan, and humic acid components. The application of Biochar and organic fertilizer had an interaction effect on the increase of rice production, ROC, DOM, fulvic acid, tryptophan, aromatization, humification, and DOM bioavailability. 【Conclusion】Thus, the combined application of biochar and organic fertilizers increased rice yield while also enhancing the functional diversity of organic carbon and DOM components in paddy soil.

• Dry-wet Alternation Regulate Soil Active Bacterial Communities and Potential Functions in Paddy Fields

  DING Chenxiao, LIU Yaowei, LIU Haiyang, YE Xinzhe, CHEN Yawen, YE Jing, DI Hongjie, XU Jianming, LI Yong

  DOI: 10.11766/trxb202302180065

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  Abstract:

  【Objective】A large number of studies have found that changing from dry to wet significantly affects soil microbial communities and greenhouse gas emissions. However, the transient dynamic of active microorganisms and greenhouse gas emissions of soils under dry to wet fluctuations are still unclear. 【Method】In this study, the dynamic of bacterial communities and greenhouse gas emissions under dry, wet, and dry-wet changes conditions in paddy soil were investigated. The diversity, assembly, and potential functions of active bacterial communities under dry-wet change conditions were further revealed by combining 18O-based DNA stable isotope probing technology (DNA-SIP) and high-throughput sequencing. 【Result】Dry-wet change treatment significantly promoted emissions of carbon dioxide and contained significantly higher relative abundances of Actinobacteria and planctomycetes compared with those in the dry and/or wet treatments. The relative abundances of Proteobacteria, Actinobacteria, and planctomycetes increased significantly along with the incubation. DNA-SIP experiment showed that the alpha diversity of active bacteria in the dry-wet change treatment decreased significantly along with the incubation. Proteobacteria and Actinobacteria dominated the active bacterial communities, and the relative abundance of Myxococcales in Proteobacteria increased significantly along with the incubation. The assembly of active bacteria was dominated by determinism, and the contribution of determinism was increased along with the incubation. Functional prediction of active bacteria further found that carbohydrate metabolic potential decreased significantly during the incubation. 【Conclusion】In conclusion, the dry-wet change treatment significantly changed the soil bacterial community and promoted carbon dioxide emission in paddy soil. The active bacteria in the dry-wet change treatment were dominated by Proteobacteria and Actinobacteria, and their assembly was dominated by a deterministic process.

• Creation and Evaluation Method of Plough Layer Reconstruction Materials for “Non-Grain Production of Cultivated Land”

  HAO Dian, ZHOU Runhui, GAO Wenzhe, LUO Jipeng, WANG Yuanfan, LI Tingqiang

  DOI: 10.11766/trxb202307140272

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  Abstract:

  【Objective】Economical crops like seedlings and flowers are frequently sold with soil transplantation practices, which directly leads to the soil plough layer becoming shallow or even stripped and eventually disappearing. This type of "non-grain production of cultivated land" with stripped plough layer can cause soil structure damage, nutrient imbalance, and fertility degradation, thus, it is a serious threat to the foundation of national food security and the healthy development of agriculture. The main problem with the stripped "non-grain production of cultivated land" is the lack of a high-quality plough layer. Therefore, a solution promoting the reconstruction of the high-quality plough layer to meet the fundamental needs of crops is key to replanting these soils. However, there is currently no systematic research aimed at solving this problem. 【Method】A novel plough layer reconstruction material was developed using long-lasting organic materials such as herbal peat, moss peat, rice husk biochar, sawdust biochar, active organic material vegetable corn husk, and microbial inoculants. We employed cluster and principal component analyses to identify the minimum data set of quality evaluation indicators for plough layer reconstruction materials, which was then combined with the quality index model to create a comprehensive quality evaluation system. 【Result】The result showed that the plough layer reconstruction materials with moss peat and rice husk biochar as main raw materials had higher quality and could effectively improve the fertility and compact structure of plough layer damaged soils. This material was characterized by a loose texture, bulk density of 0.1347~0.1466g·cm-3, high capillary porosity (64.83%~67.82%), strong water-holding capacity, high organic matter content (658.85~704.92g·kg-1), and high SOC recalcitrance index of 75.27%~84.71%., with a high potential for sequestration and sink enhancement. The minimum data set constructed with SOC, Labile C, HS, TN, TK, capillary porosity, and pH can be used as a quality evaluation system for plough layer reconstruction materials. Based on the above system, the optimal formulation of the plough layer reconstruction material was screened as follows: when moss peat (M) is mixed and configured with rice husk biochar (R) at mass ratios of 1:1, 2:1, 3:1, and then 10:1 with vegetable corn husk (C); ((M+R)10C1, (2M+R)10C1, and (3M+R)10C1), a high-quality ploughing layer reconstruction material can be formed. On "non-grain production of cultivated land," the application of selected plough layer reconstruction materials can dramatically lower soil bulk density and raise soil organic matter content by 177.35% to 204.31% compared to the control. Additionally, the treatment also increased the soil""s effective nutrient content and soil carbon sequestration potential. The plant height, weight, and number of spikes of wheat were higher than those in the control after the application of the plough layer reconstruction material. This resulted in the yield of wheat being 5.6 times higher than that of the control, which demonstrates the benefit of this type of material for crop growth. 【Conclusion】The indicator evaluation system established by this research can comprehensively and objectively evaluate the overall quality of plough layer reconstruction materials, and the materials created with moss peat and rice husk biochar as raw materials showed high application value in improving soil quality, increasing soil carbon sequestration capacity, and restoring crop production.

• Quick Acquisition of Black Soil pH Values from Northeast China by Portable Soil Multi-parameter Rapid Detection Instrument

  Feng Zhang, Wenyou Hu, Liangliang Wang, Decheng Li, Chao Zhang, Enzhe Xie, Guojing Yan, Jun Jiang, Renkou Xu

  DOI: 10.11766/trxb202304200157

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  【Objective】Soil pH is a crucial indicator of arable land quality. Therefore, precise and rapid measurement of soil pH is essential for the implementation of digital agriculture. 【Method】In the present study, pH levels of the black soil in the Liaohe and Songnen plains were determined in situ using a self-developed portable soil multi-parameter rapid detection instrument (SHMI2000). The results were compared to those obtained in the laboratory using the potentiometry method (HJ 962–2018). 【Result】(1) The laboratory observations showed that surface and subsurface soil pH values ranged from 4.04 to 10.09, and 4.01 to 10.06, respectively. The mean values were 6.13 and 6.47, and the variation coefficient values were moderate at 19.64% and 18.37%, respectively. Also, the study also revealed that the soils in the southwest black soil area were predominantly alkaline, whereas the soils in the east (Sanjiang Plain), north (Songnen Plain), and south (particularly in the Southern Heilongjiang, Jilin, and Liaoning Provinces) were acidic in nature. (2) The Pearson correlation analysis showed a strong relationship (correlation coefficient of 0.81, P=9.11×10-52) between pH values obtained in situ and the laboratory. (3) The correlation coefficient increased to 0.93 after the moving average process, using 0.2 pH units as step size.【Conclusion】Therefore, the SHMI2000 instrument can accurately and reliably acquire black soil pH values in situ.

• Effects of Long-term Straw Burying and Nitrogen Fertilizer Application on Soil Bacterial Community Characteristics

  liumingfeng, zhouguixiang, zhangjiabao, zhangcongzhi, Xue Zaiqi, Zhao Zhanhui

  DOI: 10.11766/trxb202303090096

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  Abstract:

  【Objective】In order to reveal the response mechanism of microbial community and ecological network to straw returning process in typical fluvo-aquic soil, we experimented with different straw-returning treatments under long-term wheat-maize rotation. 【Method】The high-throughput sequencing and ecological network methods were utilized to analyze the soil bacterial community composition, bacterial network co-occurrence and their relationships with soil nutrient concentrations. 【Result】The results indicated that compared to straw removal and no nitrogen fertilizer treatment, straw returning with conventional fertilization treatments significantly reduced soil pH, while increasing the content of TN, SOC, AP, AK, NO3- -N (P < 0.05). The treatments of straw burying with nitrogen fertilizers were beneficial for increasing soil nutrient content. Moreover, no significant difference in bacterial alpha diversity was observed between different straw-returning methods and different amounts of nitrogen fertilizers, but a significant difference was observed in bacterial community structure. Factors such as pH, SOC, and TN drove variations in bacterial community structure.Also, Acidobacteriota, Proteobacteria, Bacteroidota and Chloroflexi were the dominant phyla in the fluvo-aquic soil. Furthermore, co-occurrence network analysis revealed four main ecological clusters that were significantly correlated with soil nutrients. The abundances of taxa in module 1 were found to be inversely correlated with SOC, TN, TP, NO3- -N, AP and AK (P < 0.001), and positively correlated with pH (P < 0.001). Conversely, the abundances of taxa in module 2 and module 3 were significantly positively correlated with most nutrient content, and negatively related to pH. 【Conclusion】Therefore, it can be concluded that straw burying combined with nitrogen fertilizers can improve soil nutrient by regulating microbial interactions. The findings of this study can provide a scientific basis for the efficient utilization of straw and the efficient management of soil fertilization.

• Input and Output Balance of Heavy Metals (Cd, Cu, Pb) in Arable Soils in Atmospheric Deposition Area of Typical Smelter

  MI Yazhu, LIANG Jiani, ZHOU Jun, LIU Mengli, KOU Leyong, XIA Ruizhi, TIAN Ruiyun, SHI Ying, SHU Tiancai, SHU Wuxing, ZHOU Jing

  DOI: 10.11766/trxb202302180064

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  Abstract:

  【Objective】This study aimed to investigate the input and output characteristics of cadmium (Cd), copper (Cu), and lead (Pb) in different atmospheric deposition areas.【Method】The arable soils (0-20 cm) of Guixi Smelter with main wind direction at 34 km (background site), 6 km (moderate deposition site) and 1 km (high deposition site) were selected as the research objects. The main input (atmospheric deposition, irrigation water, pesticides, and fertilizers) and output pathways (surface runoff, leaching water, and grain harvest) were monitored and quantitatively analyzed for three years by using the chemical mass balance (CMB) method.【Result】The results showed that the average annual input fluxes of Cd in the background, moderate, and high deposition sites by atmospheric deposition were 0.84, 2.26, 9.01 mg•m-2•a-1, accounting for 43.18%, 38.33%, and 100%, while the average annual input fluxes of Cu were 17.62, 99.68, 747.6 mg•m-2•a-1, accounting for 80.76%, 86.24%, 100%, respectively. Also, the average annual input fluxes of Pb were 13.93, 27.43, 73.17 mg•m-2•a-1, accounting for 97.75%, 92.36%, and 100%, respectively. Specifically, the average annual input fluxes of Cd in the background and moderate deposition sites due to irrigation water were 1.05 and 3.60 mg•m-2•a-1 and accounted for 54.62% and 60.82%, respectively, whereas the annual heavy metal input fluxes by pesticides and fertilizers accounted for less than 5%, which could be ignored. The main output pathways of arable soil in different atmospheric deposition areas were surface runoff and leaching water, with the output ratio ranging from 86.66% to 100%, and the output ratio of the grain harvest ranging from 2.88% to 13.34%. From 2019 to 2021, the average annual net input fluxes of Cd, Cu, and Pb were all greater than 0 in the background site, moderate deposition site, and high deposition site. For example, the average annual net input fluxes of Cd were 1.54, 1.96, and 4.38 mg•m-2•a-1, for Cu were 12.72, 28.02, and 184.0 mg•m-2•a-1, and for Pb were 13.03, 21.31, 55.04 mg•m-2•a-1 in the background site, moderate deposition site, and high deposition site, respectively. 【Conclusion】In general, it is advisable to strengthen the long-term supervision of atmospheric pollution sources and irrigation water quality in the study area and avoid the direct return of straw to the field. This study provided theoretical support for the remediation of heavy metal pollution and the protection of environmental quality in regional arable soils.

• A Meta-Analysis of Soil Microbial Necromass Accumulation in Response to Climate Warming

  LU Mengya, DING Xueli

  DOI: 10.11766/trxb202303200109

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  Abstract:

  【Objective】The effect of warming on the accumulation dynamics of microbial necromass is of great significance to the balance of soil carbon (C) pool. However, the impact of climate warming on microbial necromass is poorly understood. Thus, the objective of this study was to evaluate the responses of microbial necromass to climate warming and the main factors controlling this feedback.【Method】In this study, a meta-analysis was conducted to reveal general patterns of climate warming on amino sugars (microbial necromass biomarkers) in soils under grasslands, forests, and croplands. Here, 12 published publications from international and domestic journals were collected and extracted independent observations that met our criteria (29 for total amino sugars, 35 for glucosamine, 39 for muramic acid, and 25 for galactosamine).【Result】The results showed that the overall effects of warming could promote the accumulation of microbial necromass. However, warming effect sizes on microbial necromass were not consistent across different ecosystems, with the most sensitive responses occurring in cropland. The response of fungal and bacterial necromass differed under climate warming. Specifically, warming significantly increased the content of galactosamine and muramic acid, with an increase of 10.3% and 5.0%, respectively. Together with the significant decline in the ratio of glucosamine to muramic acid, the results suggested that warming benefited the accumulation of bacterial necromass compared to fungi. Also warming significantly increased the proportion of bacterial necromass to soil organic carbon (SOC), while the contribution of fungal and total necromass to SOC did not change significantly, suggesting that the contribution of fungal-derived C to SOC was weakened under warming scenarios. Warming magnitude was a key factor affecting the accumulation of microbial necromass. For instance, the accumulation of microbial necromass increased by 2.7%-14.6%, when the warming magnitude was less than or equal to 2 ℃ relative to unwarmed control. However, when the warming amplitude was greater than 2 ℃, the accumulation of microbial necromass was decreased by 8.0%-14.3%. Interestingly, the duration of warming was an important factor affecting the accumulation of microbial necromass.【Conclusion】The results demonstrate that warming has significant effects on the accumulation dynamics of microbial necromass and their contribution SOC pool. The intensity and direction of the warming impact are largely dependent upon ecosystem type and soil depth, in which warming amplitude, warming duration, and mean annual precipitation are important factors controlling the sequestration of the microbial-derived C under global climate warming.

• Effects of Green Manure, Rice Straw Return and Lime Combination on Soil Acidity and Rice Yield

  LIU Fangxi, FANG Changyu, YU Zhenyu, GAO Yajie, ZHANG Jianglin, LU Yanhong, LIAO Yulin, CAO Weidong, NIE Jun, TU Naimei

  DOI: 10.11766/trxb202304040125

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  Abstract:

  【Objective】 Long-term tillage and fertilization accelerate soil acidification of red loam rice. Thus, this study was designed to study the effects of green manure, straw return, and lime combination on the soil acidity characteristics of rice soil and rice yield. 【Method】This study is based on the long-term positioning micro-area experiment started in 2016 to explore the effects of no fertilization (CK), chemical fertilizer (F), chemical fertilizer + milk vetch + rice straw return (GRF), chemical fertilizer + milk vetch + straw return (GRFL) treatment on rice yield and different forms of acid in red soil. The effects of soil salt-based ions and soil acid-base buffer capacity was resolved, and the correlation between soil acid-base buffer capacity, exchangeable acid, organic matter, and exchangeable salt-based ions was investigated. 【Result】 The results for seven consecutive years showed that compared with F treatment, the yield of early and late rice treated by GRF increased by 19.9% and 5.1%, respectively, and the average yield increase rate in 7 years was 12.8% and 5.9%, respectively. The yield of early and late rice treated by GRFL increased by 23.4% and 14.2%, respectively, and the average yield increase rate in 7 years was 11.1% and 8.9%, respectively. During this time, the soil pH of early and late rice treated with CK, F and GRF showed a decreasing trend year by year, while the soil pH value of GRFL treatment showed a trend of first increasing and then decreasing. Compared with F treatment, GRF and GRFL treatment significantly improved the exchangeable K, the total amount of exchangeable salt-based ions and the acid-base buffer capacity of early and late rice soil, and there was no significant difference between GRF and GRFL treatments, but all indexes of GRFL treatment showed an improvement trend. Correlation analysis showed that pH was negatively correlated with exchangeable acidity and exchangeable H+ (P < 0.01) and positively correlated with acid-base buffer capacity, exchangeable Na+, exchangeable Mg2+, and the total amount of exchangeable salt group ions (P < 0.01). Also, the soil acid-base buffer capacity was mainly related to the exchangeable acidity, exchangeable H+, exchangeable Na+ and exchangeable Mg2+. In addition, rice yield was related to soil acidity properties and nutrient effects, and the soil acidity properties had the greatest impact. 【Conclusion】 The results showed that rolling green manure and straw returning to the field could effectively alleviate the acidification of paddy soil and improve rice yield, and the addition of lime could enhance its effect, and the exchangeable acidity, exchangeable H+, acid-base buffer capacity, exchangeable Na+, exchangeable Mg2+, and total exchangeable salt-based ions were the main factors affecting soil pH.

• Source-Route-Receptor-Based Spatial Zoning Study on Soil Heavy Metals Pollution Risk

  YI Shiyi, LI Xiaonuo, CHEN Weiping, CHEN Xinyue

  DOI: 10.11766/trxb202303220112

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  Abstract:

  【Objective】The establishment of a spatial zoning system of soil pollution risk management indicates the concrete implementation of “classification, division and phased soil environmental management” claimed in Soil Pollution Prevention and Control Law. The high-resolution risk spatial mapping can undoubtedly provide scientific and effective decision-making guidance not only for delineating prior areas for soil pollution risk management but also for facilitating the overall deployment of soil pollution prevention and control works at a large scale.【Method】This study first adopted positive matrix factorization (PMF) model to identify emission sources and the corresponding contribution rate of Cr, Cu, As, Cd, Pb, Ni, Sb and Hg in an industrial agglomeration area in Ningbo City, Zhejiang Province. Then, a spatial zoning technical system for risk management on soil heavy metals pollution was developed based on the source-route-receptor relationship and mass balance theory.【Result】The results showed that: (1) the spatial distribution of soil heavy metals presented a significant heterogeneity and five factors were primarily determined as the emission sources of soil heavy metals including coal-fired power generation source (17.08%), other industrial sources (17.94%), natural source (28.61%), agricultural source (26.07%), and traffic source (10.31%); (2) five risk levels were clustered using the established spatial zoning technical system, including extremely high-, high-, medium-, low- and extremely low-risk accounting for 8.64%, 17.28%, 18.27%, 22.92%, and 32.89% of the total area, respectively. 【Conclusion】The quantification of the regional risk stress levels can effectively map high-risk hotspots to apply prior measures for precise soil pollution management.

• Improvement Cultivated Land Quality by Diversified Cropping System: Advances and Prospects

  TIAN Shenzhong, GUAN Xilin, NING Tangyuansup> †, SUN Tao, ZHANG Yufeng, BIAN Wenfan, DONG Liang, GAO Xinhao

  DOI: 10.11766/trxb202209160509

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  Abstract:

  Diversified cropping system is an important strategy of ecological intensive agriculture. It makes significant improvements to soil quality, ecosystem stability and land productivity. Under the background of a global shortage of food supply and cultivated land, diversified cropping system play an increasingly important role in ensuring food security and improving the quality of cultivated land in China. Currently, diversified cropping system has become a research hotspot in soil, ecology, crop, and tillage sciences. Nevertheless, the research about diversified cropping system in the recent period is more focused on improving its biodiversity and ecological functions but with limited understanding of how these diversified systems impact soil quality and productivity due to the changes of soil physical, chemical, and biological properties. In this paper, we analyzed the connotation of diversified cropping system and its significance on promoting soil health and improving ecological service function, and systematically summarized the advances in the effect of diversified cropping system on some soil properties including: (1) Physical properties: We focused on the improvements of soil porosity, aggregates, water binding capacity, etc., by different crop root morphology (biological tillage) and straw inputs under diversified cropping system. (2) Chemical properties: We analyzed diversified cropping system optimized light, water, and heat resources to increase the utilization efficiencies of nitrogen and phosphorus, promote soil organic carbon sequestration, balance soil nutrients and regulate root exudates, mitigate using differences in spatial and temporal niche and nutrient niche between aboveground and underground parts. (3) Biological properties: We reviewed the biological effect and advantageous changes of soil biodiversity under diversified cropping system including soil microbial diversity, arbuscular mycorrhizal fungi, soil enzyme activity, and soil animals. However, there are still some challenges limiting the development of diversified cropping systems including the lack of theoretical systems, production technology and machinery equipment, technological polarization, and policy support. Furthermore, we proposed four areas where future research should focus on improving cultivated land quality by diversified cropping system: (a) Develop multi-functional diversified cropping system including soil amendment, bioremediation, and low-carbon cropping system; (b) Supplement the theoretical system of cultivated land quality improvement under diversified cropping system including crop-soil interaction mechanism and nutrient regulation, ecological versatility and environmental response mechanisms at different scales; (c) Establish appropriate technology system for diversified cropping system including suitable special varieties or their combinations, optimization production technology and machinery equipment; and (d) Applicability and popularization strategies of diversified cropping system including planning and design, policy guidance and financial support to establish typical diversified cropping system in different regions. On the whole, this review provides a reference for the diversified cropping system to play a greater role in the strategy of improving cultivated land quality.

• Spatial Distribution Characteristics and Influencing Factors of Magnetic Susceptibility of Topsoil on the Qinghai-Tibet Plateau

  CHEN Yamin, SONG Xiaodong, LIU Feng, YE Mingliang, ZHANG Chu, GU Jun, ZHANG Ganlin

  DOI: 10.11766/trxb202206180326

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  Abstract:

  【Objective】Soil magnetic susceptibility is a commonly used proxy index for paleoenvironment reconstruction. The study on the relationship between topsoil magnetic susceptibility and the modern environment is helpful to understand the reasons for the difference in magnetic susceptibility. Researchers around the world had conducted numerous studies on the correlation between soil magnetic susceptibility of sediments and modern soils in different regions and environmental factors. However, previous studies mainly focused on the correlation between soil magnetic susceptibility and climate. This correlation between soil magnetic susceptibility and climate was inconsistently recognized by different researchers because climate is only one of the influencing factors for the variation of soil magnetization rate. The main controlling factors of soil development and soil magnetic susceptibility may vary from region to region, and the magnetic susceptibility reflects the combined effect of multiple environmental factors. At present, the lack of understanding of the causes of soil magnetic susceptibility changes at the regional scale limits the accurate application of magnetic susceptibility as an important proxy index for paleoenvironmental reconstruction. Thus, we hypothesized that (1) the spatial distribution patterns of soil magnetic susceptibility in different regions can respond to environmental variables besides climate and (2) the Normalized Difference Vegetation Index (NDVI), which is the result of the combined effect of climate, topography and soil, can better respond to magnetization rates. 【Method】The Qinghai-Tibet Plateau is the youngest natural geographic unit in the world with closely integrated horizontal and vertical zonation, influencing regional and global energy and water cycles. It is one of the areas where global changes have had the most significant impact on the land surface because it had undergone six major geological tectonic events and has a variety of parent rock types. The natural environment of the Qinghai-Tibet Plateau is harsh and large-scale soil sampling is very difficult, so regional magnetic studies are limited. In this study, 254 soil samples from the surface layer (layer a of the occurrence layer) of the Qinghai-Tibet Plateau were systematically investigated to determine the soil magnetic susceptibility and other soil properties. Combined with the data of parent material, climate, topography and vegetation, the spatial variation characteristics of soil magnetic susceptibility in the Qinghai-Tibet plateau were clarified and its main influencing factors were analyzed. 【Result】 The results showed that: (a) There was no significant difference in low-frequency magnetic susceptibility χlf of topsoil between different parent materials and the difference of percentage frequency magnetic susceptibility χfd% was significant. Specifically, the weathering of loess and sand shale > weathering of aeolian sand, moraine and crystalline salt, and there was no significant difference between other parent material types. Among different land uses, there was no significant difference in topsoil, but a significant difference in topsoil χfd%: forest and upland > grassland > wasteland. (b) The influence of each principal component on soil magnetic susceptibility was of the order vegetation component > soil physical property component > terrain component > parent material component. (c) Spatially, the variation law of soil magnetic susceptibility was most consistent with that of vegetation normalization index, χlf and χfd% in the Southeast both showed higher values. Also, the spatial distribution of χlf decreased from Southeast to Northwest, the high-value area was located on the southeast edge while the low-value area was located in the middle. Similarly, the spatial distribution of χfd% showed a high value in the southeast area and a low value in the western area. 【Conclusion】 Our study shows that magnetic susceptibility can better reflect the spatial distribution characteristics of the vegetation index.

• Phytoextraction of the Soils from the East of Yunnan Province with a High Cadmium Geological Background and Its Effect on Rice Cadmium Uptake

  WU Tuozheng, ZHOU Jiawen, ZHOU Tong, LI Zhu, HU Pengjie, HUANG Huagang, LI Tingxuan, ZHANG Xizhou, LUO Yongming, ZHAN Juan

  DOI: 10.11766/trxb202303060092

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  Abstract:

  【Objective】Yunnan Province is one of the typical high geological background regions in China. However, a few studies have focused on the phytoextraction of high geological soils for safe agricultural production. 【Method】This research was conducted to investigate cadmium (Cd) phytoextraction efficiency of the high geological background soils from Shilin, Fuyuan, and Luoping in Yunnan Province by the Cd/zinc (Zn) hyperaccumulator Sedum plumbizincicola and its effect on plant growth and Cd uptake by rice (Oryza sativa) through pot experiments. 【Result】After triple-cropping of S. plumbizincicola, the total Cd and available Cd concentrations in soils showed a substantial decrease, with the total Cd decreasing to 24.8%, 30.9%, and 58.8% of the original values for soils from Shilin, Fuyuan, and Luoping, respectively. S. plumbizincicola showed better growth when grown in soils from Fuyuan developed from basalt with more soil nutrients but presented a greater Cd phytoextraction efficiency when grown in soils from Shilin developed from limestone with higher soil pH, thereby greater Cd mobilization capacity. These significant differences indicated that plant growth and heavy metal accumulation of hyperaccumulators were affected by the comprehensive effects of soil parent materials, soil nutrients, and heavy metal availability in soils. After a triple-cropping of S. plumbizincicola, Cd concentration in brown rice and rice straw was significantly decreased under flooding conditions through the whole growth period, resulting in a Cd-safe production. However, the rice grain possessed a high Cd pollution risk without phytoextraction when grown under a dry cultivation system. 【Conclusion】The phytoextraction of high geological background soils by S. plumbizincicola combing with water management measures benefits greatly the safe production of rice crops, thereby providing a theoretical basis and technical support for the safe production of the high geological background soils.

• Particle Size Distribution Characteristics of the Rare Earth Elements in Sediment from Different Shapes of River Valleys

  SHANG Yueting, ZHANG Jiaqiong, BAI Ruru

  DOI: 10.11766/trxb202207070375

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  Abstract:

  【Objective】Rare earth elements (REE) are one of the most important tracers in soil erosion study. Understanding the content variation of REEs alongside particle size ranges is significant to accurately quantify soil erosion rates. 【Method】Based on the REE contents in different particle size ranges (< 1, 1-10, 10-50, 50-250 and 250-1000 μm) of soil/sediment samples measured by Samonova et al. (2020), this study analyzed the effects of valley morphology, landforms, erosional and depositional areas on the contents and enrichment coefficient of REE in soil/sediment at the left bank of the Protva River in Russia. Landform types including hillslope, gully slope/wall, valley bottom and alluvial fan, were separately selected from a “U” and a “V” shape valley, respectively. These four landforms were further classified into erosional (i.e., hillslope and gully slope/wall) and depositional areas (i.e., valley bottom and alluvial fan). 【Result】The results showed that: (1) The contents of light rare earth elements (LREE), heavy rare earth elements (HREE) and total rare earth elements (ΣREE) were all decreased with the increase of particle size ranges under the four landform types of “U” and “V” shape valleys. Under the condition of the same landform types, the contents of LREE, HREE and ΣREE in fine particles (< 50 μm) of the “U” shaped valley were 14.6%-24.7%, 10.0%-33.5% and 14.2%-21.1% lower than those of the “V” shaped valley, respectively. (2) Both LREE and HREE were enriched in fine particles at all landform types for both “U” and “V” shape valleys. Particularly for the “V” shape valley, LREE and HREE were significantly enriched in < 10 μm particles. (3) Comparing the erosional and depositional areas, the enrichment degree of LREE and HREE in the fine particles of the depositional areas in both “U” and “V” shape valleys was significantly (P < 0.05) higher than that of the erosional area. 【Conclusion】Accordingly, REE were enriched in fine particles regardless of river valley shapes, landforms, and erosional or depositional areas. However, both valley shape and erosion-deposition processes had important impacts on the REE content variation in different particle size ranges.

• Isolation and Application of Rhizosphere Core Strains to Improve Salt Tolerance of Rice

  MA Aiyuan, REN Yi, WANG Jiao, YAN He, SHI Chenyu, SHEN Qirong, ZHANG Ruifu, XUN Weibing

  DOI: 10.11766/trxb202302190069

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  Abstract:

  【Objective】Rhizosphere beneficial microorganisms can enhance plant salt stress tolerance through multiple pathways, including re-establishing ion and osmotic homeostasis, preventing damage to plant cells, and resuming plant growth in saline soil. This study aimed to obtain plant growth-promoting rhizobacteria that can improve salt tolerance of rice and to explore its application effects.【Method】Two rice cultivars were used in this study, of which one is salt-tolerant cultivar Hunanxian and the other is salt-sensitive cultivar Nanjing 46. The physiological characteristics of rice seedlings were compared after planting in sterile and non-sterile saline soils. Then, the key rhizobacterial groups associated with salt tolerance, which were enriched in the rhizosphere of salt-tolerant rice cultivars, were identified by compositional differences and co-occurrence network analyses based on the 16S rRNA gene amplicon sequencing. Subsequently, the culturable strains of the key rhizobacterial groups were isolated through the high-throughput cultivation and identification method of rhizobacteria. Finally, pot experiments were conducted to evaluate the beneficial effects of the strains on enhancing the salt tolerance of salt-sensitive rice cultivar.【Result】The height of shoot and root length of salt-tolerant rice were significantly higher while the content of proline was significantly lower when cultivated in non-sterile soil than in sterile soil under salt stress. This indicates that the rhizosphere microbial community of salt-tolerant rice cultivars may play a crucial role in enhancing the salt tolerance of the host plant. Amplicon sequencing results demonstrated that the composition of the rhizosphere microbial communities of salt-tolerant and salt-sensitive rice cultivars was significantly different. The bacterial families of Flavobacteriaceae and Pseudomonadaceae were the key rhizobacterial groups that were both enriched in the rhizosphere of the salt-tolerant rice. Several bacterial strains affiliated with Flavobacteriaceae and Pseudomonadaceae were isolated, in which two strains of Pseudomonas punonensis P34 from Pseudomonadaceae and Chryseobacterium taeanense C18 from Flavobacteriaceae were screened to be the most efficient strains in improving the salt tolerance of rice by germination and hydroponics tests using salt-sensitive rice under salt stress. Finally, the efficient strains of C18 and P34 were applied as direct inoculants and seed-coating agents in pot experiments, and the results demonstrated that they were able to promote the growth of salt-sensitive rice under salt stress. 【Conclusion】Two rhizobacterial strains of C18 and P34 showed great capacity to enhance the salt tolerance of rice and they could be developed as bacteriological agents for seed coating or microbial fertilizer for application in saline lands.

• Inversion of Water Infiltration Processes in the Profile of Red Soil Based on ERT Technology

  TIAN Yuan, ZHONG Xuemei, PENG Xinhua, WANG Yaji, GAO Lei

  DOI: 10.11766/trxb202209220525

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  Abstract:

  【Objective】 Soil moisture movement is the main driving force of the material and energy transport in soil. However, the paths of soil moisture in soils are complex and difficult to comprehend. This is especially true in the red soil region with abundant rainfall and diverse land use types.【Method】With the help of an electrical resistivity tomography (ERT), soil moisture infiltration processes in the vadose zone were captured for the forest land and farmland of the red soil from Quaternary red clay.【Result】 The results showed that in the red soil region, ERT could realize the visualization of the soil moisture infiltration process in the soil profile of the red soil. There was a highly significant correlation (P < 0.01) between the resistivity measured by ERT and the soil moisture measured by the oven drying method. The linear coefficients of determination between them were 0.72 for forest land and 0.53 for farmland. Land use types affected the mode and depth of soil moisture infiltration. With a 2-cm water head height and 100-L water injection volume, the infiltration depth of forest land was more than 80 cm, much deeper than that of farmland (50 cm). With the continued injection of water for 200 min, the infiltration depth of the two land uses exceeded 150 cm and a preferential flow phenomenon was observed during the infiltration process. However, the preferential flow of forest land was more developed than that of farmland. The preferential flow of forest land moves down rapidly through macropores formed by plant roots and soil animal activities while the preferential flow observed in farmland moved to the deep layer intermittently mostly in the way of the finger flow. In addition, the forest land was dominated by vertical infiltration with weak horizontal flow while the horizontal movement in farmland was stronger.【Conclusion】Under the influences of disadvantageous factors such as complex soil layers, high background water content and high soil clay content, ERT technology still could successfully capture the occurrence and development processes of preferential flow in red soil area.

• Organic Matter Compensation Scheme and Preliminary Mechanism for Remediation of Soil Productivity Decline in Continuous Cropping Garlic

  HONG Huayang, WEI Tianqi, ZHOU Hongmei, REN Yanyun, MA Longchuan, SU Yanhua, ZHANG Huanchao

  DOI: 10.11766/trxb202303140101

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  Abstract:

  【Objective】This study aimed to use different proportions of organic fertilizer instead of chemical fertilizer as organic matter compensation schemes to study their effects on garlic yield attenuation in long-term continuous cropping garlic fields in the main garlic-producing area of Jinxiang County, Shandong Province. 【Method】The representative fields with more than 25 years of continuous cropping history were selected in this experiment. The wheat field without garlic planting was used as the non-continuous cropping field control. Four treatments were set up : conventional chemical fertilizer fertilization ( CF ) and organic fertilizer to replace chemical fertilizer with 25% ( M25 ), 50% ( M50 ) and 100% ( M100 ) based on nitrogen ( N ).【Result】The results showed that in the long-term garlic continuous cropping soil, organic fertilizer instead of chemical fertilizer treatment had a significant effect on the increase (20%) of garlic yield in the current season. Also, the content of N in continuous cropping soil and the proportion of soil > 2 mm aggregates were increased, and the N nutrient supply status and soil aggregate structure in the soil were improved. Among the treatments, 25% organic fertilizer instead of chemical fertilizer treatment ( N ) had the best yield and economic benefit of garlic, and also had a better repair effect on the decline of soil productivity of continuously cropping garlic. However, in non-continuous cropping soil without organic matter deficit, organic substitution treatment did not have a direct effect on increasing production. 【Conclusion】This study clarified that the application of organic fertilizer (partial organic fertilizer instead of chemical fertilizer treatment) based on chemical fertilizer application can only promote the formation of large-grained soil aggregates and enhance the holding capacity of soil available nutrients during the whole growth period in the continuous cropping garlic soil with obvious deficiency of soil organic matter. It also has a significant restoration effect on the degradation of continuously cropping garlic soil productivity. This study provides a useful reference for alleviating similar soil degradation problems and maintaining the sustainability of soil productivity in continuous cropping systems.

• Effects of Seed Soaking in Fe3O4 Nanoparticle on Tomato Seed Germination and Seedling Protective Enzyme System under Saline Stress

  CHEN Siyuan, LU Yao, WU Sifan, QI Yongbing, ZHENG Qingsong, ZHANG Xinyue, ZHAO Wenjia†, CHEN Jun

  DOI: 10.11766/trxb202302090055

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  Abstract:

  【Objective】This study examined the effect and mechanism by which nano-sized iron oxide regulates crop tolerance to salt. 【Method】Nanoparticle Fe3O4 (Fe3O4NPs) with a particle size of about 10 nm was synthesized by the coprecipitation method and characterized by X-ray diffractometry and electron microscopy. Selected tomato seeds were soaked in 0, 1, 10, 50, 100, 200, 300, and 400 mg?L–1 of Fe3O4NPs solution and the effects on seed germination, seedling growth and antioxidant system under NaCl stress were evaluated. 【Result】 Fe3O4NPs with a particle size of 10 nm were synthesized and successfully passed the characterization analysis and identification. It was found that under salt stress, soaking tomato seeds in 1 mg?L–1 Fe3O4NPs reduced seed germination. However, seed germination was improved as the concentration of Fe3O4NPs was increased. Under 100 mmol?L–1 NaCl stress, the seed germination potential and hypocotyl length after soaking in 200 mg?L–1 Fe3O4NPs reached the peak, which was significantly higher than those treated with salt stress only. Salt stress of 100 mmol?L–1 NaCl significantly reduced the seedling rate, fresh biomass and water content of tomato seedlings, and this negative trend was intensified after soaking the seeds in 1 mg?L–1 Fe3O4NPs. With an increase in the concentration of Fe3O4NPs, the negative impact of salt stress was alleviated and the fresh biomass and water content of seedlings soaked with 200 mg?L–1 Fe3O4NPs reached the peak, which was significantly higher than those treated only with salt. Under salt stress, the activities of superoxide dismutase (SOD) and peroxidase (POD) in tomato seedlings soaked in 1 mg?L–1 Fe3O4NPs increased significantly, while the activity of catalase (CAT) decreased significantly. With an increase in the concentration of Fe3O4NPs, the activities of SOD and POD gradually decreased and then gradually increased while that of CAT gradually increased and then decreased. Specifically, the activities of SOD and POD in seedlings treated with 100-200 mg?L–1 Fe3O4NPs were the lowest, while the activity of CAT was the highest. Also, the contents of malondialdehyde (MDA), proline (Pro), superoxide anion (O2?－) and hydrogen peroxide (H2O2) in seedlings treated with 200 mg?L–1 Fe3O4NPs were the lowest of all treatments. The correlation analysis showed that the fresh biomass and seedling rate of seedlings were significantly negatively correlated with the activities of SOD and POD, as well as the contents of MDA and reactive oxygen species. 【Conclusion】 Fe3O4NPs with a particle size of 10 nm were prepared by the coprecipitation method. It was found for the first time that the germination and emergence of tomato seedlings under salt stress could be mitigated by Fe3O4NPs and the effect was proportional to the concentrations of Fe3O4NPs. For example, treating seeds with 1 mg?L–1 Fe3O4NPs inhibited germination due to increased oxidative stress whereas 200 mg?L–1 Fe3O4NPs showed significant promotion of germination, seedling formation and seedling strength. This study provides scientific basis and technical support for the application of nanomaterials to improve agriculture in saline soil.

• Structure and Function of Microbial Nanowires: Controversy and Progress

  YE Yin, ZHOU Shungui, LIU Xing

  DOI: 10.11766/trxb202303140103

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  Abstract:

  Soil extracellular respiration is the engine driving the global biogeochemical cycle, in which microbial nanowires serve as an important pathway for microbes to realize it. Microbial nanowires are electrically conductive fibrous structures that can be tens of microns long and grow on the surface of microorganisms. It directly works on the electron transfer between microorganisms and soil minerals, biomethanation and methanogens, etc, thus affecting the migration and transformation of soil minerals and the emission reduction of greenhouse gases. Microbial nanowires were originally discovered on the surface of Geobacter sulfurreducens when the strain was reducing ferrihydrite. G. sulfurreducens is widely distributed in paddy fields, wetlands, reducing soil, and surface sediments. Due to the abundant extracellular nanowires, G. sulfurreducens occupies a key niche in the food chain of anaerobic microorganisms and participates in the global biogeochemical cycling of some key elements, such as C, N, S and Fe. Because of the accessibility to complete genomic information and genetic maneuverability, G. sulfurreducens has become the model microorganism for studying microbial nanowires. For a long time, experimental evidence based on molecular biology has shown that G. sulfurreducens nanowires are conductive type IV PilA-N pili composed of PilA monomeric subunits and multiple conceived models of electron transfer in PilA-N pili have been developed. However, the recent nanowire structure analysis based on cryo-electron microscopy (cryo-EM) found that G. sulfurreducens expressed various c-type cytochrome nanowires, including but may not be limited to OmcS nanowire, OmcZ nanowire and OmcE nanowire, which were anatomically different conductive cytochrome nanowires with their specific electron transfer roles in G. sulfurreducens. Furthermore, the cryo-EM also showed the expression of PilA-N-C pili, which was located in periplasm, hardly had electronic conductivity, and mainly functioned at assisting the secretion of cytochrome nanowires. The lack of either conductivity or typical type IV nanowire functions indicated that the biological role of PilA-N–C pili is completely different from the previously described PilA-N pili of G. sulfurreducens but is pseudo-pili-like. All these findings constantly questioned and challenged the theory of PilA-N pili. Since then, the issue of "the nature of nanowires" has become the focus of academic debate. As the saying goes, "the more the truth is debated, the clearer it will be." Here, the timeline of G. sulfurreducens nanowires"" theoretic studies is taken to summarize the understanding of the structure and function of nanowires. Also, the evidence based on the "nature of nanowires" dispute is systematically analyzed, which will promote the early settlement of the dispute, as well as help mature the theory of soil extracellular respiration and the application of microbial nanowires.

• Recent Advances in Hydrogen Metabolism and Its Environmental Bioremediation Function

  XU Yongfeng, LUO Yongming

  DOI: 10.11766/trxb202301180025

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  Abstract:

  Molecular hydrogen is a key intermediary in the metabolic interactions of a wide variety of microorganisms. The activities of hydrogen-producing and hydrogen-consuming microorganisms in the environment determine the global hydrogen cycle, which has a potential driving effect on the biogeochemical cycle of other important elements. Environmental functional microorganisms play an important role in maintaining the balance of ecosystems and eliminating secondary pollution. Therefore, understanding the impact of hydrogen metabolizing (production and consumption of hydrogen) microorganisms on the ecological environment and its role and function in environmental bioremediation has vital significance and practical value for understanding the ecological and environmental effects of hydrogen and its application to bioremediation. This paper systematically analyzed the hydrogen metabolism process and the classification and function of hydrogenase, summarized the various ways of hydrogen production and consumption by microorganisms and their effects on soil ecological environment and bioremediation. The scientific and technical challenges existing in current hydrogen metabolism processes and the application of hydrogenase in environmental bioremediation were summarized. Besides, it was also proposed research ideas and key directions in this field to promote hydrogen as a bioenergy since it has become a promising strategy for environmental pollution remediation.

• Research Progress of Photochemical Reactive Intermediates Processes and Abiotic Transformation of Pollutants in Paddy Water

  ZENG Yu, ZHANG Mingyang, LI Mabo, CHEN Ning, FANG Guodong†, GAO Juan, WANG Yujun, ZHOU Dongmei

  DOI: 10.11766/trxb202302010037

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  Abstract:

  Rice is the staple food for about half the world""s population and one of the most widely grown crops. Because long periods of flooding are needed during rice planting, paddy water is becoming an important sink of contaminants such as herbicides, pesticides and heavy metal(loid)s (e.g., arsenic). Compared with surface water, the concentrations of nitrite/nitrate and dissolved organic matter (DOM) in paddy water are usually higher, due to the extensive application of nitrogen fertilizers and release of DOM from microbial degradation of soil organic matter. Owing to long-term flooding during rice cultivation, desorption of soil humic substances, reductive dissolution of mineral–OM complexes, and root exudation release a large amount of DOM into paddy water, which can generate reactive intermediates (RIs) such as triple excited organic matter (3CDOM*), singlet oxygen (1O2) and hydroxyl radicals (?OH) under sunlight. These RIs usually exhibit high reactivity and play an important role in pollutant transformation and element cycling in paddy fields. In this paper, the generation process and mechanism of RIs in paddy water were reviewed and the type and concentration of RIs in different growth stages of rice were emphasized. Compared with the typical surface water, quantum yields of 3CDOM* and ?OH were comparable, while quantum yields of 1O2 were about 2.4-6.7 times higher than those of surface water. DOM in paddy water with lower molecular weight and humification extent generated more RIs, and nitrite contributed to 23.9%–100% of ?OH generation. DOM with more saturated and less aromatic formulas could produce more 3CDOM* under irradiation, while the polyphenolic components of DOM inhibited the formation of RIs. The effects of different environmental factors on the production of RIs were discussed. The application of straw and lime increased the RI concentrations by up to 16.8 and 11.1 times, respectively, while biochar addition had limited effects on RI generation from paddy water. Furthermore, the solar radiation directly affected the quantum yields of RIs in paddy water, and the radiation intensity showed a linear positive correlation with the concentration of free radicals. The mechanism of abiotic transformation of arsenic and different organic pollutants in paddy water was described and the degradation of contaminants, including As(III), 2,4-dichlorophenol (2,4-DCP), polycyclic aromatic hydrocarbons (PAHs), chlorotoluron, diuron, dimethomorph, and propanil, was significantly accelerated by photoinduced RIs generated in paddy water. Most of previous studies were conducted with stimulation experiments in the laboratory and the underlying mechanisms of RIs generation in paddy water have not been fully elucidated. Future studies should pay more attention to the generation of RIs in the paddy field and link global scale factors such as photoactive material flux, different soil properties and improvement measures, as well as the transformation of pollutants and material circulation to form a systematic understanding. In addition, future studies should not only focus on the degradation of these pollutants themselves, but also on the toxicity and ecological risks of the degradation products of these pollutants. More attention should be paid to the transformation of emerging pollutants, such as new pesticides, antibiotics and microplastics, in the paddy system.

• Study on the Mechanism of Increased Iron Availability by Rhizosphere Iron-Solubilizing Bacteria in Combination with AM Fungi in Calcareous Soil

  PENG Haiying, SHAO Yadong, LI Han, LI Peigen, DING Bailing, YANG Tianjie, XU Yangchun, SHEN Qirong, DONG Caixia

  DOI: 10.11766/trxb202212080680

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  Abstract:

  【Objective】The low availability of iron in calcareous soil leads to serious iron-deficiency chlorosis in plants. Thus, it is important to screen highly efficient iron-solubilizing bacteria and explore their collaboration with mycorrhizal fungi (AM) to increase the available iron content and improve plant iron nutrition. 【Method】Pot experiments were conducted with calcareous soil and tomato (Lycopersicon esculentum) as test materials. They were inoculated with Advenella kashmirensis (B1), Arthrobacter cupressi (B2), Klebsiella variicola (B3), Variovorax guangxiensis (B4) and Enterobacter ludwigii (B5), and treatment with no bacteria inoculation as the control group (CK). Efficient iron-solubilizing bacterial strains B1, B2 and B3 were screened and combined with AMF (Rhizoshagu irregularis, Ri) as B1+Ri, B2+Ri, B3+Ri and B1+B2+B3+Ri treatments. Also, AM fungi were inoculated alone (Ri) to explore the mechanism of synergistic effect between different iron-solubilizing bacteria and AMF to mobilize insoluble iron in calcareous soil and promote iron absorption in plants. 【Result】The results showed that compared with the control treatment, inoculation with B1, B2 and B3 strains could significantly increase the tomato biomass and the total iron accumulation in root and shoot increased by 6.48 and 2.61, 4.11 and 2.03, 4.37 and 2.25 times, respectively. The active iron content in new leaves increased by 74.21%, 133.66% and 175.84%. Compared with inoculation with AMF alone, different co-inoculation combinations significantly increased the tomato biomass, and the average total iron accumulation in different parts of the plant increased by 58.32%-119.43%. Under B3+Ri and B1+B2+B3+Ri treatments, the active iron content in tomato roots increased by 41.47% and 44.30%, and new leaves increased by 12.61% and 12.77%, respectively. Different co-inoculation combinations could effectively improve the root architecture of the plant, and the mycorrhizal infection rates of AM fungi under different co-inoculation treatments were 13.35%-30.99% higher than those under inoculation alone. The root iron reductase activity was significantly increased by 9.86%-22.07% compared with the inoculation with AM fungi alone, and the relative expressions level of LeFIT1, LeFRO2 and LeMYB72 in tomato roots was significantly up-regulated. Compared with exclusive AMF inoculation, B3+Ri and B1+B2+B3+Ri treatments reduced the rhizosphere soil pH value by 0.21 and 0.09, respectively, but increased the soil available Fe content by 15.78% and 55.23%. 【Conclusion】It was concluded that the synergistic effect of AM fungi and three high-efficiency iron-solubilizing bacteria could significantly improve iron availability in calcareous soil and enhance plant iron nutrition. However, the synergistic mechanism between different types of iron-solubilizing bacteria and AMF was different and provided a microbial approach to solve the problem of low iron availability in calcareous soil.

• Effects of Freeze-thaw Cycles on Soil Aggregates Turnover in Mollisols Using Rare Earth Oxides as Tracers

  LIU Yajun, LIU Shuai, GAN Lei, ZHANG Zhongbin, PENG Xinhua

  DOI: 10.11766/trxb202212060674

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  Abstract:

  【Objective】In order to elucidate the effects of freeze-thaw cycles and initial water content on soil aggregates structure, rare earth oxides (REOs) were used as tracers to separate soil aggregates formation and breakdown processes. 【Method】REOs-labelled soil was reformed and investigated herein. Two initial water contents (50 % field water holding capacity (T50) vs. 100 % field water holding capacity (T100)) and five freeze-thaw cycles (0, 3, 6, 12 and 20 cycles) were involved in the simulation experiments. Soil aggregates distribution, mean weight diameter (MWD), the aggregate turnover process were measured accordingly. 【Result】The results showed that freeze-thaw cycles significantly reduced MWD, the contents of > 0.25 mm aggregates and <0.053 mm aggregates but increased the contents of 0.25~0.053 mm aggregates under the same initial water content. After 6 freeze-thaw cycles, MWD was significantly higher under T50 compared with that under T100(P < 0.05), there was no significant difference between the aggregate content of 5~2 mm and <0.25 mm. Except for 5~2 mm aggregates, the intensive transformations between neighboring size aggregates were observed during the whole simulation experiments. For the same freeze-thaw cycles, the fragmentation amount of 5~2 mm aggregate to 0.25~0.053 mm aggregate was significantly higher at T100 compared with T50 treatment(P < 0.05).The freeze-thaw cycles promoted the breakdown of >0.25 mm aggregates and the formation of 0.25～0.053 mm aggregates both under T50 and T100 treatments. MWD was significantly positively correlated with the relative formation of soil aggregates and negatively related with the relative breakdown of soil aggregates(P < 0.05). The turnover time of soil aggregate significantly increased with freeze-thaw cycles(P < 0.05). The aggregate turnover time of > 0.25 mm aggregates was higher than that for <0.25 mm aggregates. The aggregate turnover time was significantly higher under T100 than that under T50 with the same freeze-thaw cycle(P < 0.05). 【Conclusion】In conclusion, the number of freeze-thaw cycles and the initial water content of the soil significantly affect the aggregate turnover, which changes the stability of the soil structure by affecting the aggregate formation and fragmentation process. The results can provide a theoretical basis for further exploration of the structural changes of black soil under the freeze-thaw cycle.

• Effects of Free-air CO₂ Enrichment and Temperature Increase on Related Proteins and Defense Enzymes in Plants Infected with Rice Sheath Blight

  shenmin, Cai Chuang, Song Lian, Zhang Jishuang, Tao Ye, Wang Dongming, Yang Xiong, Wei Wei, Zhu Chunwu

  DOI: 10.11766/trxb202302220074

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  【Objective】Sheath blight (ShB) is a soil-borne disease, whose occurrence and development seriously threatens rice (Oryza sativa L.) production. However, it is still unclear how elevated CO2 concentration ([CO2]) and temperature affect pathogenesis-related proteins (PR proteins) and defense enzymes in plants infected with Rhizoctonia solani.【Method】In this study, temperature by free-air CO2 enrichment (T-FACE) system was used with four treatments: ambient condition; elevated [CO2] ([CO2] up to 590 μmol·mol-1); elevated temperature (temperature increased 2 ℃); the combination of elevated [CO2] and elevated temperature. Two cultivars (a susceptible variety, Lemont and a resistant variety, YSBR1) were planted to explore the response of PR proteins and defense enzymes activities in leaves and stems for two cultivars by artificial inoculation of R. solani, as well as basic physical and chemical properties of soil.【Result】Results indicated that there was no significant difference in the growth rate of R. solani on soil extract medium, which was made by bulk soil under elevated [CO2] and temperature. After inoculation with R. solani, the development rate of the ShB lesion was not related to the basic physical and chemical properties of soil. The combination of elevated [CO2] and elevated temperature induced different effects on PR proteins and defense enzymes activities in the leaves of two cultivars. For the PR proteins and defense enzymes in stems, the combination of elevated [CO2] and elevated temperature obviously increased the catalase (CAT), phenylalanine ammonia-lyase (PAL), β-1, 3-glucanase (GLU) or superoxide dismutase (SOD) activities for both Lemont and YSBR1. For different cultivars, after being infected with R. solani, the activities of PR proteins and defense enzymes in the leaves and SOD and CAT in the stems for YSBR1 were significantly higher than those for Lemont under different treatments, and the development rate of ShB lesion for YSBR1 was significantly lower than that for Lemont. During the whole disease infection, elevated [CO2] and the combination of elevated [CO2] and elevated temperature both significantly increased the development rate of rice ShB for Lemont by 21%-45%, but not for YSBR1. The correlation analysis showed that under different [CO2] and temperature treatments, the development rate of ShB was significantly positively correlated with GLU activity in stems for Lemont and YSBR1.【Conclusion】After inoculated R.solani, the defense reaction formed by PR proteins and defense enzymes in resistant cultivar can effectively reduce the effect of elevated [CO2] and temperature on the development rate of ShB in the future. This study can provide applications for breeding ShB-resistant cultivars to ensure global rice production under future climate change.

• Effects of Sediment Abrasion on Microplastic Fragmentation

  HAO Yongli, HU Yaxian, GUO Shengli

  DOI: 10.11766/trxb202208250469

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  Abstract:

  【Objective】As one of the typical forces in the process of erosion and migration, sediment abrasion can accelerate the fragmentation of microplastics, thereby affecting microplastic migration and redistribution within the watershed. However, how sediment abrasion affects the fragmentation behavior of microplastics is still unclear. Therefore, the objective of this study was to investigate the effect of sediment abrasion on the fragmentation of microplastics. 【Method】In this study, topsoil was collected from a mulched cornfield in the Wangdonggou small watershed of the Loess Plateau and the abundance, type, and morphology of microplastics were analyzed using a laser infrared imaging system after different treatments. The different treatments include air-dried original soil, sediment standstill, and sediment abrasion with three concentrations of 560 kg·m-3, 800 kg·m-3 and 930 kg·m-3. 【Result】The results showed that: (1) PU, Polytetrafluoroethylene (PTFE), and Rubber (RB) were the main microplastics in the study area, mostly in the form of fragments with a diameter of 10~50 μm. (2) The average area of microplastic was largest in the air-dried soil treatment (5,234 μm2) and the smallest (2,067 n·kg-1) was in the sediment standstill treatment. The microplastics after sediment abrasion treatments had the greatest average abundance (14,400 n·kg-1) and the smallest average area (2,868 μm2). (3) The average abundance and area of microplastic under the three sediment abrasion treatments were significantly different. The average abundance of microplastic followed the pattern: moderate sediment concentration (18,300 n·kg-1) > low sediment concentration (13,730 n·kg-1) > high sediment concentration (8,667 n·kg-1), whilst the average area of microplastic showed: low sediment concentration (3,932 μm2) > moderate sediment concentration (2,472 μm2) > high sediment concentration (2,099 μm2). 【Conclusion】Overall, this study demonstrates that sediment abrasion significantly increased the microplastic abundance and reduced their areas, but the average abundance of microplastic reached the maximum at the moderate sediment concentration abrasion intensity. The sensitivity of different microplastic types to sediment abrasion was different, providing guiding information for the risk assessment of soil microplastic fragmentation and migration in eroding settings.

• Response of Dissolved Nutrient Transport to “Source” and “Sink” Landscape Pattern in Typical Agricultural Small Watersheds in the Three Gorges Reservoir Area

  NI Ke, WANG Xiaoyan, YANG Lan, CUI Can, LI Jiaming, LONG Yi

  DOI: 10.11766/trxb202205190263

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  Abstract:

  【Objective】 The “source” and “sink” landscape pattern reflects the land use allocation and spatial element distribution. It equally controls the energy flow and water sediment process of the watershed, which is an important factor affecting nutrient loss in small watersheds. The purpose of this research was to investigate the effect of landscape patterns on the transport of dissolved nutrients in agricultural small watersheds under different rainfall types. 【Method】 The traditional agricultural catchments and agroforestry catchments in the Shipanqiu watershed of the Three Gorges Reservoir Area were selected as the research objects. The concentrations of dissolved nitrogen and phosphorus in the runoff at the outlet section of the catchments were monitored during different intensities of erosive rainfall events. Also, aerial survey data combined with the minimum cumulative resistance model were used to identify the “source” and “sink” landscape spatial pattern. The location-weighted landscape index (LWLI) was used to analyze the impact of the “source” and “sink” landscape pattern on dissolved nutrient transport in the small watershed. On this basis, the response mechanism of dissolved nutrient transport in the small watershed to the “source” and “sink” landscape pattern was further clarified. 【Result】 The results showed that: ① In the traditional agricultural catchment area, the landscape area ratio of “source” and “sink” was 1.8:1, which was dominated by “source” landscape, and the vertical differentiation of landscape was obvious. In the agroforestry composite catchments, the landscape ratio of “source” and “sink” was about 1:1, which was evenly distributed, but the high and steep slope area accounted for a high proportion and the average slope was large. ② In the two catchments, the loss load of dissolved nitrogen and phosphorus was rainstorm > moderate rain > heavy rain. In different rainfall events, the nutrient output load and its coefficient of variation in the traditional agricultural catchments were higher than those in agroforestry catchments. The nutrient transport had strong volatility and was more vulnerable to the change in rainfall intensity. ③ Agricultural land was the main source of nutrient loss in both catchments, but due to the limitation of a slope, other woodlands may be important nutrient migration areas in the agroforestry composite catchments. The LWLI of the traditional agricultural catchment was as high as 0.75, which indicated the risk of high nitrogen and phosphorus loss in this catchment. Also, the LWLI of the agroforestry catchment area was 0.28 and with a low nutrient output. This was attributed to the joint action of reasonable landscape spatial patterns and the agroforestry management model. 【Conclusion】 The “source” and “sink” landscape patterns had a significant impact on nutrient loss in small watersheds. The risk of nutrient loss in small watersheds can be judged by the “source” and “sink” location-weighted landscape contrast index. Accordingly, it can provide a basis for the optimization of “source” and “sink” landscape pattern and the prevention and control of non-point source pollution in small watersheds.

• Research on Water and Sand Prediction Model of Purple Soil Slope Based on Machine Learning

  CHEN Qitao, WANG Tian, LI Zhanbin, ZHANG Jiao, LI Peng, LI Binbin

  DOI: 10.11766/trxb202207020361

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  Abstract:

  Purple soil is one of the unique soils in China. Because of its low degree of soil development and poor soil erosion resistance, soil erosion in the purple soil area is very serious, which seriously hinders local agriculture and economic development. 【Objective】 To accurately predict soil erosion changes, we need to scientifically and rationally prevent the occurrence of soil erosion, provide a reference for the prevention and control of soil erosion on purple soil slopes, and promote research on soil and water conservation in purple soil areas. 【Method】Based on the rainfall data of 43 typical purple soil run-off communities, rainfall, duration and I30 are used as characteristic indicators, and the K-means clustering algorithm was used to classify rainfall; the Random forest (RF) algorithm was used to evaluate the importance of each influencing factor on the depth of run-off (H) and soil loss (S), and the important factor screening was carried out in combination with the path analysis method. The key factors obtained from the screening were used as the input variables of the model, with H and S as the outputs. Also, a predictive model was constructed using BP neural network. 【Result】The results showed that: (1) The erosive rainfall in the purple mound area in the southwest can be divided into three categories. Among them, the A rain type had a long duration, medium rain intensity, heavy rain volume, the lowest frequency of occurrence, and the greatest erosion, which was an important rain type that caused slope erosion in the area; the B rain type had a short duration, heavy rain, and light rain volume, and the most frequent occurrence, which was the main rain type that caused slope erosion in the area; and the C rain type, which had a medium duration, medium rain intensity, and medium rainfall, which occurred more frequently and also made a greater contribution to slope erosion in the area. (2) The importance of characteristic factors to H and S under each rain type was significantly different. For rain type A, the rain duration (T) was the most important to S (31%), and the importance of each factor to H was relatively uniform. Under rain type B, the influence of each factor on S was small, and the rainfall erosion force (F) was the most important to H (29%). Also, the degree of importance was the highest (29%). Under the rain type C, rainfall (Pr) was the most important to H and S (33%, 36%). (3) The H and S under the three rain types were significantly affected by Pr and the H and S under the B and C rain types were most significantly affected by F, vegetation cover (Vs), and average plant height (Ph) at the same time. (4) The prediction accuracy of H and S using the BP neural network was high, the efficiency coefficient of Nash-Suttclife is higher than 0.95, and the accuracy of the prediction model for H was higher than that of the prediction model for S. 【Conclusion】Research on the purple soil mound area in the southwest needs to focus on preventing soil erosion caused by high-frequency heavy rainfall. In this study, the two models that used rainfall and other factors to calculate H and S had high forecasting capabilities, which provide technical support for soil erosion prediction to achieve accurate forecasting of soil erosion.

• Multidimensional Spatial Characteristics and Risk Assessment of Soil Salinization in the Old Yellow River Basin

  SONG Ying, XU Zexin, WANG Jiafan, GAO Mingxiu

  DOI: 10.11766/trxb202205160256

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  Abstract:

  【Objective】This study aimed to grasp the multidimensional spatial distribution characteristics of soil salinization, analyze the factors influencing salinization risk, implement risk area zoning control and improve the efficiency of saline land use. 【Method】 In this study, the Yellow River old riverway in Hekou District, Dongying City, Shandong Province, was selected as the study area. Descriptive statistics on soil salinization status were conducted using classical statistical methods, the two-dimensional spatial distribution pattern of salinization in the study area was analyzed based on GIS interpolation, the three-dimensional spatial distribution of salinity and its change trends were visualized using GMS three-dimensional inverse distance weight interpolation, and a soil salinization risk evaluation model was constructed to quantitatively analyze the risk. 【Result】 The results show that the average salinity of the soil in the study area was 5.84 g·kg-1, representing severe salinization; and the average pH value was 7.82, indicating weakly alkaline. In two–dimensional space, the areas with high salinity (≥6 g·kg-1) were mainly located in the north of the study area, and the overall trend was decreasing from the coast to the inland. In three–dimensional space, the distribution characteristics of the soil salinity profile were mainly homogeneous, with local surface aggregation and clustering at both ends, showing a complex coexistence of three types: surface aggregation, homogeneous, and clustering at both ends. The risk degree of salinization was divided into four levels and the extremely high-risk areas were mainly distributed in the north-central and northeast of the study area. Also, high-risk areas were mainly distributed in the middle and northeast, moderate-risk areas in the west and southeast, and low-risk areas in the southwest of the study area. 【Conclusion】We recommend that the following measures should be employed to minimize the risk of salinization and improve the efficiency of resource utilization: preventive measures in extremely high-risk areas, control measures in high-risk areas, and improvement measures in moderate and low-risk areas.

• Multiple fertilization models regulate arbuscular mycorrhizal fungi to promote maize phosphorus uptake

  HE Gang Hui, SHEN Yi, WANG Zi Xuan, LU Ju Meng, SUN Bo, CHEN Yan

  DOI: 10.11766/trxb202209070494

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  Abstract:

  【Objective】The use of arbuscular mycorrhizal fungi (AMF) to obtain nutrients from agricultural ecosystems is an effective way for red soil crops to absorb soil phosphorus (P). Given the problems of biological function degradation, low phosphorus bioavailability, and low crop yield in red soils of Southern China, regulating the AMF community in the rhizosphere of crops and optimising the mutualistic symbiotic relationship with the host is the key to breaking the bottleneck of crop phosphorus uptake in the red soil region.【Methods】In this study, four diversified fertilization measures were combined with ecological intercropping in red soil dryland with organic (straw, pig manure, bio-fertilizer) and inorganic fertilizers, and the optimal fertilization mode was screened based on crop yield and phosphorus activation level in red soil. Further, we used amplicon high-throughput sequencing and microscopic observation techniques to analyze how the optimal fertilization measures in red soil dryland regulate the composition of the AMF community and the mechanism through which the optimized AMF community stimulates phosphorus uptake by the host maize. 【Results】 The results showed that the organic-inorganic application of peanut/corn intercropping combined with straw/biofertilizer (In+NPKSB) increased total phosphorus (TP) and available phosphorus (AP) by 29.07% and 1.35 times in red soil dryland compared with other fertilization methods, respectively. Moreover, the relationship between AMF family levels in maize roots was enhanced and the AMF colonization rate of this measure was 2.24 times higher than that of the traditional fertilization measures. Also, the activities of acid/alkaline phosphatase (ACP/ALP) in the maize rhizosphere were increased by 32.18% and 41.66% while the maize biomass and yield increased by 34.98% and 67.27%, respectively. 【Conclusion】Our study confirmed that the fertilization measures of peanut/maize ecological intercropping in red soil dryland combined with the organic and inorganic application of straw/bio-fertilizer can optimize the AMF community composition in maize roots, promote soil phosphorus activation, and improve the phosphorus transport efficiency of host roots, which is beneficial for red soils. These results provide a theoretical basis for promoting the integrated application of sustainable agricultural development in red soil dryland according to local conditions.

• Research Progress on the Mechanism by which Soil Microorganisms Affect Soil Health

  KONG Yali, QIN Hua, ZHU Chunquan, TIAN Wenhao, ZHU Xiaofang, YU Yijun, ZHANG Junhua

  DOI: 10.11766/trxb202301200448

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  Abstract:

  Soil health is the central theme of sustainable agricultural development. Soil microorganisms cooperatively drive the soil life system by regulating soil ecological functions, environmental functions and immunologic functions, which are the keys to maintaining soil health. Understanding the mechanisms of soil microorganisms mediated soil health is essential to effectively utilize these core microorganisms to maintain and improve soil health. Thus, soil functions, such as soil carbon cycling, nutrient cycling, soil structure regulation, plant disease and insect inhibition and contamination control mediated by soil microorganisms are reviewed to summarize their roles in maintaining or enhancing soil health. Furthermore, as a sensitive indicator of soil health, the roles of soil microorganisms in soil health indication and warning were also studied. Research about mining, construction and application of the core microbiome information database that drives the specific function of soil health and multiple biological processes should be strengthened in the future. This will help to provide a scientific basis for improving the function of agricultural soil ecosystems using soil microorganisms, maintaining soil health and soil sustainable development.

• Cadmium Remediation Strategies in Alkaline Arable Soils in Northern China: Current Status and Challenges

  ZHANG Lihao, BAI Jiaojie, TIAN Ruiyun, WANG Guochang, YOU Laiyong, LIANG Jiani, CI Kaidong, LIU Mengli, KOU Leyong, ZHOU Lingli, WU Dafu

  DOI: 10.11766/trxb202209110503

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  Abstract:

  Cadmium (Cd) pollution is dispersed over a wide area in farmland soils and seriously threatens the safety of agricultural produce and sustainable development of agriculture due to rapid industrialization and inadequate environmental protection in China. Compared to other toxic elements, Cd is highly carcinogenic and readily accumulates in edible portions of plants to levels that are toxic to humans. Traditional technologies of chemical remediation, physical remediation and phytoremediation have been widely applied to remediate Cd-polluted arable soil, especially in acid soil in some areas of southern China. However, little is known about the remediation technologies of Cd for alkaline arable soils. Alkaline soils are mainly distributed in North China. This area is an important hub for both the crop growing and animal breeding industries, and is suffering from severe Cd pollution as well. To ensure food safety, it is necessary to establish the technology and theory of Cd purification in alkaline soils. This paper reviews the domestic and foreign research trends of Cd remediation strategies, hot technologies, Cd geochemical cycle, and Cd transport and accumulation mechanisms in wheat grains, and analyzes the scientific and technological issues of Cd management and control in alkaline soils. The Web of Science core collection database (WOS) were employed to conduct a bibliometric analysis of the literature on remediation technologies of Cd in alkaline arable soils from 2000-2021 via VOSviewer software. The immobilization technology is popular to remediate Cd contamination in alkaline soils and the top three countries in the number of publications are China, the United States and Australia because of their abundant agricultural resources. Besides, soil acidification is the main reason for the increasing grain concentrations of Cd in alkaline arable soils. Meanwhile, lower soil Eh can increase Cd bioavailability by flooding in alkaline soils, suggesting that irrigation and drainage projects should be built in dry-land soil in North China. However, compared with acidic soil, the research on Cd remediation technology in alkaline arable soils is relatively weak. Currently, alkaline amendments such as clay minerals, biochar and lime are usually applied to lower Cd bioavailability in alkaline soils. However, it is difficult to inhibit the accumulation of Cd in crop grains by improving soil pH due to the large amount of carbonate in alkaline soils. Moreover, the excessive addition of alkaline amendments can destroy the soil structure, leading to soil hardening. Also, in phytoremediation, the high pH of alkaline soil will reduce the uptake of Cd by plant roots, resulting in low remediation efficiency and high cost. The accumulation of Cd in wheat grains is affected by both biotic and abiotic factors, and the complex molecular mechanism of its uptake and transport also limits the development of low-accumulation varieties. Thus, local governments should monitor the Cd concentration and it is imperative to explore and develop new technologies for inhibiting the transfer of Cd to food crops in alkaline soils.

• Promoting Effect of Natural Humic Material on the Release of Water-soluble Phosphorus from Low-grade Phosphate Rock Powder

  YANG Qiang, ZHANG Congzhi†, ZHANG Jiabao, PAN Hui, CHEN Zhuo, LI Jianpeng, ZHANG Can, TAN Jun

  DOI: 10.11766/trxb202212130689

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  Abstract:

  【Objective】The objective of this study was to disclose the structural characteristics and the relationship with phosphorus validity in the promoted phosphate rocks (PPR), which were made by mixing low-grade phosphate rock powder and natural humic material materials.【Method】Continuous water extraction, X-ray diffraction (XRD), fourier transform infrared spectrometry (FTIR), and pot experiment were carried out to explore the phosphorus validity mechanism of PPR from dynamic release, structural characteristics and fertilizer effects. 【Result】The results showed that the release of water-soluble phosphorus showed an increasing trend with the increase of activator addition. After five leachings, the total water-soluble phosphorus released was 1.54 and 1.72 times higher than that of the control treatment when the mass ratio of natural humic material or HNO3-treated natural humic material mixed with low-grade phosphate rock powder was 20:80. X-ray diffraction analysis showed that the characteristic diffraction peaks corresponding to P2O5 and Ca(PO3)2 showed a significant decrease after five leaching of natural humic material or HNO3-treated natural humic material mixed with low-grade phosphate rock powder. The results of FTIR spectral analysis showed that the disappearance of the PO43- symmetric stretching vibration v1 at 966 cm-1 was evident after five leaching cycles of natural humic material or HNO3-treated natural humic material mixed with low-grade phosphate rock powder, while the intensity of the PO43- asymmetric stretching vibration v3, H2PO4- associated absorption peaks, and HPO42- associated absorption peaks at 1 127, 673 and 612 cm-1 were significantly decreased. The pot experiment further showed that natural humic material or HNO3-treated natural humic material as a high-quality organic material applied at 6 g?kg-1 or 9 g?kg-1 while mixed with low-grade phosphate powder at a 20:80 mass ratio could significantly increase the available phosphorus content of the soil, while rapidly increasing the soil organic matter content. When natural humic material was applied at 9 g?kg-1 and mixed with low-grade phosphate powder at a mass ratio of 20:80, soil available phosphorus was increased by 29.86%, 29.47%, and 36.48% while soil organic matter was increased by 34.16%, 8.05%, and 47.40%, respectively, compared to control treatment on days 14, 30, and 60 after sowing. Also, when HNO3-treated natural humic material was applied under similar conditions, soil available phosphorus was increased by 36.97%, 94.44%, and 34.51% while soil organic matter was increased by 27.29%, 14.57%, and 45.41%, respectively, compared with control treatment on days 14, 30, and 60 after sowing.【Conclusion】Natural humic material or HNO3-treated natural humic material with acidic pH, high specific surface area, high humus content and a high number of active functional groups were responsible for enhancing the water-soluble phosphorus content of low-grade phosphate rock powder and soil available phosphorus.

• Research Progress on the Transformation Mechanism of Toxic Organic Pollutants on Soil Mineral Interface Under Water-unsaturated Conditions

  CHENG Pengfei, ZHAO Xuqiang, GAO Yanzheng

  DOI: 10.11766/trxb202212180694

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  Minerals are critical active components of soils, which can drive the chemical transformation of toxic organic pollutants in the soil environment and reduce the risk of environmental contamination. Previous studies of the interface behavior of toxic organic pollutants on soil mineral surfaces mainly focused on the water environment or mineral suspension systems. Natural soils, especially surface soils, are usually under water-unsaturated conditions. In recent years, the transformation mechanism of toxic organic pollutants on water-unsaturated soil mineral surfaces has attracted considerable attention, and a series of fascinating discoveries have been made. The water-unsaturated iron and manganese minerals, clay minerals and metal ion-saturated clay minerals drive the transformation of the hydrophobic toxic organic pollutants such as polycyclic aromatic hydrocarbons and antibiotics. Water molecules at the interface of water-unsaturated minerals have weak competition with toxic organic pollutants for active sites, and the dehydration process of minerals also makes them change to highly active structures. However, an appropriate increase in the moisture of dry soil minerals can enhance the transformation of toxic organic pollutants. A small amount of water molecules can improve mass transfer and promote the transfer of toxic organic pollutants to the active sites of soil minerals. The different moisture state of soil minerals leads to the formation of various products. The water-unsaturated condition is more conducive to the formation and stability of persistent free radicals and halogenated dioxins. Also, the transformation of toxic organic pollutants is influenced by the catalytic activity of soil minerals and the physical and chemical properties of toxic organic pollutants. In previous studies, electron transfer reaction was considered as the transformation mechanism of toxic organic pollutants on soil minerals. However, free radical catalysis and hydrolysis mechanisms have been gradually discovered. Transition metal elements in iron manganese minerals and metal ion-saturated clay minerals can receive or give electrons during the transformation of toxic organic pollutants. The defects of soil minerals tend to induce the generation of active free radicals. While, the active hydroxyl, Br?nsted acid sites, and Lewis acid sites in soil minerals can accelerate the hydrolysis of toxic organic pollutants. The development of detection technology and theoretical calculation has made the relevant mechanisms precise to the mineral crystal type and plane structure. Additionally, Soil, a complex system, is mainly composed of minerals, organic matter, and microorganisms. And organic matter and microorganisms have an important effect on the transformation of toxic organic pollutants at the mineral interface. Most notably, they can promote the reduction of mineral dissolution, and improve the reduction of toxic organic pollutants. Although the transformation and mechanism of toxic organic pollutants at the interface of water-unsaturated minerals have been gradually evident, the breadth and depth of the research need to be further expanded and deepened. It is suggested that future research focus on the following aspects: reveal the transformation of toxic organic pollutants in the natural soil systems, strengthen the research on the reduction and transformation processes, develop the in situ reaction devices and detection methods, and analyze the transformation mechanism of toxic organics at the mineral interface from micro and nanoscale and molecular level.

• Relative Contribution of Ammonia-oxidizing Microorganisms to Nitrous Oxide Emissions in Upland Agricultural Soils

  Yang Yu, Zhao Yongjian, Song Xiaotong, Zhang Limei, Ju Xiaotang

  DOI: 10.11766/trxb202303250115

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  【Objective】The relative contribution of ammonia oxidizing microorganisms determines the ammonia oxidation rate and N2O emission. However, the composition of their relative contribution to N2O emission in different soils and agricultural management has not been systematically studied.【Method】We studied the contributions of AOB, AOA+comammox and heterotrophic nitrifiers to the potential nitrification rate, net nitrification rate and N2O emission in typical upland surface soils (fluvo-aquic soil, black soil, latosol), and in latosols from soil profile under organic fertilizer amendment.【Result】In the surface fluvo-aquic soil, black soil and latosol, pH was 8.0, 6.7 and 5.7, potential nitrification rate was N 32.5, 6.6 and 4.8 mg?kg-1?d-1, net nitrification rates was N 7.1, 3.0 and 0.5 mg?kg-1?d-1, and N2O emission was N 38.0, 35.4 and 8.7 μg?kg-1, respectively. AOB dominated potential nitrification rate in the above surface soils, with contributions of 82%, 58% and 100%, respectively. For net nitrification rate, AOB and AOA+comammox contributed equally (30%-40%) in the fluvo-aquic soil and latosol, while AOB dominated in the black soil (72%). AOB dominated N2O emission from the above surface soils, contributing 72%, 92% and 58%, respectively. In the latosols from soil profile, at the 0-20 cm, 20-40 cm and 40-60 cm layers, pH was 7.0, 5.5 and 4.9, potential nitrification rate was N 6.6, 2.0 and 1.1 mg?kg-1?d-1, net nitrification rate was N 4.1, 0.9 and 0.2 mg?kg-1?d-1, and N2O emission was N 16.3, 6.5 and 2.8 mg?kg-1?d-1, respectively. The increase in potential nitrification rate and net nitrification rate at the 0-20 cm layer was dominated by AOA+comammox (contributing 63% and 54%) and the increase in N2O emissions was dominated by AOB (contributing 54%).【Conclusion】This study provides new evidence for developing reduction measures of N2O emissions that match the soil ammonia oxidation characteristics and soil properties.

• Microbial Mechanisms of Bacillus Resistance to Arsenite in Rice Rhizosphere

  Wang Dongya, Chenguanhong, Fangliping, Lifangbai

  DOI: 10.11766/trxb202211230642

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  【Objective】Microbial arsenic (As) methylation is a vital As resistance mechanism that alters the toxicity and mobility of As, and can be used for the control of As contamination in soils. As-resistant plant growth-promoting bacteria use this mechanism to positively affect the growth of rice in As-contaminated soil. However, the arsenic methylation efficiency of rice rhizosphere bacteria and its effect on rice growth under arsenic stress remain unclear.【Method】In this study, an As-methylating functional Bacillus sp. LH14 was isolated from rice rhizosphere soil contaminated with As. The As methylation efficiency, As resistance and plant growth-promoting traits of the strain were analyzed. Additionally, the effect of strain inoculation on rice growth, rhizosphere As species and microbial interactions in As-contaminated soil were explored.【Result】The results show that strain LH14 promoted As methylation and volatilization and produced dimethylarsenate and trimethylarsenic oxide, which accounted for 54.9% of the initial As(III) in the medium. LH14 inoculation significantly increased the copy numbers of As(III) methyltransferase gene (arsM) and methylated As in rhizosphere soil, indicating that LH14 was involved in soil As transformation. LH14 produced IAA under As stress and significantly increased seed germination rate, root and shoot length and biomass in the presence of high As concentration. Also rice growth in the soil was significantly promoted by LH14 inoculation, and this was associated with the enrichment of beneficial microorganisms (e.g., Burkholderiaceae and Gemmatimonadaceae) in the rhizosphere. 【Conclusion】Inoculation with As-methylating plant growth-promoting bacteria altered As speciation in rice rhizosphere and directly or indirectly promoted rice growth by producing plant hormones, enriching beneficial bacteria, and alleviating As stress. These findings provide theoretical support for the application of As-methylating bacteria in the remediation of As-contaminated soil and alleviation of As stress in plants.

• Effects of Iron and Sulfate Reduction on the Mobilization and Thionation of Diphenylarsinic Acid in Acrisol

  ZHU Meng, HE Yuhuan, WEI Xiaobao, LI Yuan, YANG Ruyi

  DOI: 10.11766/trxb202209080499

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  【Objective】Diphenylarsinic acid (DPAA) is one of the main degradation products of arsenic-containing chemical weapons in the environment. The objective of this study was to investigate the effects of iron and sulfate reduction on the mobilization and thionation of DPAA in soil.【Method】Acrisol from a peanut field and woodland was selected for soil incubation experiment, and both were spiked with DPAA and different concentrations of sodium lactate (C source) and sodium sulfate (S source) under flooded condition. Four treatments were established in the current study, treatment one (S-C-) was created without the addition of S or C sources, treatment two (S+C-) only received 426 μg?g-1 S, treatment three (S+C+) received 426 μg?g-1 S and 1 300 μg?g-1 C, and treatment four (S+C++) received 426 μg?g-1 S and 2 170 μg?g-1 C. Samples of the soil and supernatant were collected for the analysis of DPAA, Fe2+, HCl-extractable Fe2+, SO42-, sulfide, pH, Eh and bacterial community structure.【Result】Results for the peanut field indicated that the mobilization of DPAA was significantly enhanced in the S+C+ and S+C++ treatments due to the addition of carbon, as compared to S-C- and S+C- treatments without carbon. This difference was likely caused by the elevated Fe reduction (> 45%) due to lactate addition, which then promoted DPAA mobilization. In comparison to other treatments, sulfate reduction was most significant in the S+C+ treatment of the peanut field (with the concentration of dissolved sulfide reaching 11.28 mg?L-1 after 13 weeks of incubation), where the removal rate (59.6%) of DPAA was the highest and DPAA was primarily thionated. However, the increased Fe reduction and decreased sulfate reduction in the S+C++ treatment were not conducive to the thionation of DPAA. Unlike peanut land, the mobilization and thionation of DPAA were not observed in woodland regardless of the addition of sodium lactate and sulfate. This difference can be explained by the lower degree of Fe reduction (< 25%) and the absence of sulfate reduction (without the detection of dissolved sulfide) in woodland. The relative abundances of Clostridium, Bacillus and Desulfosporosinus were significantly higher in the peanut field soil than those in woodland. This probably promoted the occurrence of iron and sulfate reduction, respectively, and both processes ultimately had a stronger influence on the mobilization and thionation of DPAA.【Conclusion】Generally, instead of the stimulating effect of Fe reduction on DPAA mobilization, the degree of sulfate reduction and the concentration of sulfide in the liquid phase is a more significant factor in determining DPAA thionaiton in Acrisol under flooded condition. The findings will serve as a theoretical foundation for the in-depth understanding of the environmental behavior of DPAA as well as the development of biostimulation remediation solutions for DPAA-contaminated Acrisol.

• Spatial and Temporal Variation of Soil Carbon and Nitrogen in Typical Counties of North Loess Plateau and Influencing Factors

  GAO Jing, LI Jianhua, ZHANG Qiang, ZHENG Bizhao, WANG Rui, MENG Qiuxia, GAO Chunhua, XU Minggang

  DOI: 10.11766/trxb202210050549

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  【Objective】The ecological environment of Loess Plateau is fragile and once the soil quality of cultivated land changes, it will directly affect the level of soil productivity. A long-term cultivated land in Tianzhen County, a typical county in the north of the Loess Plateau, was selected to study the spatiotemporal evolution of soil organic matter and total nitrogen and their influencing factors.【Method】Based on the cultivated land quality data in 1983, 2008 and 2019, the temporal and spatial evolution characteristics and distribution patterns of organic matter and total nitrogen in cultivated soil of Tianzhen County were analyzed using GIS and geostatistics methods.【Result】(1) In the past 36 years (1983—2019), soil organic matter and total nitrogen content in Tianzhen County showed a significant change characteristic, which increased as a whole and rose rapidly in the later period. The average annual increase of organic matter and total nitrogen content was lower in the early period (1983—2008), showing 0.20 g?kg-1 and 0.01 g?kg-1, respectively, while the number was higher in the late period (2008—2019), showing 0.29 g?kg-1 and 0.03 g?kg-1. In the early stage of the study period, the ratio of carbon to nitrogen showed no significant change, but showed a significant decrease in the late stage, from 9.32 in 1983 to 8.43 in 2019. (2) The semi-analysis of variance (ANOVA) results revealed that over the past 30 years, the block-base ratio of soil organic matter increased from <25% to 49.8% and the block-base ratio of soil total nitrogen increased from <25% to 38.5%. This indicated that the influence of natural factors such as topography was gradually diminished, while the influence of human factors such as fertilizer application was enhanced. (3) The spatial distribution characteristics of soil organic matter and total nitrogen had similar characteristics and showed a pattern of low in the west and high in the east. From 1983 to 2008, the content of soil organic matter showed an overall increasing trend, with a significant increase in the northwest and a slow increase in other regions; total nitrogen increased significantly in the northwest and decreased in the east. Also, from 2008 to 2019, soil organic matter decreased slightly in the south while it increased in other regions; total nitrogen increased significantly in the north but more slowly in other regions. 【Conclusion】Over the past 36 years (1983—2019), the soil organic matter and total nitrogen content in Tianzhen County showed an overall upward trend, and factors such as fertilization and straw returning to the field were the main factors leading to the changes in organic matter and total nitrogen content. Combined with the local conditions to increase the application of organic fertilizer, straw returning and rational application of nitrogen fertilizer can quickly improve the soil fertility of cultivated land. Therefore, this study can provide a theoretical basis for improving the quality of cultivated land on the Loess Plateau and protecting the agricultural ecological environment.

• Soil Methane Production and Oxidation Potential and Its Response to Temperature Under Rice-aquaculture Co-culture Systems

  ZHAO Jianting, FANG Xiantao, ZOU Jianwen, LIU Shuwei

  DOI: 10.11766/trxb202207070376

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  Abstract:

  【Objective】Paddy fields are important anthropogenic sources of atmospheric methane. This study is to investigate the methane production and oxidation potentials and their responses to temperature under different rice-based land use types. 【Method】Soil samples from four typical land use types in Jurong City, Jiangsu Province, including conventional rice area (CR), rice-crayfish rice area (R-CR), rice-crayfish crayfish area (R-CC) and conventional crayfish area (CC) were collected. Laboratory culture experiments were conducted at 5 ℃, 15 ℃, 25 ℃ and 35 ℃ for 30 days. 【Result】The results showed that land use transformation had significant effects on methane production potential and methane oxidation potential. The methane production potential was 1.14 μg?g-1?d-1 in the R-CC area, 0.33 μg?g-1?d-1 in the CC area, 0.25 μg?g-1?d-1 in the R-CR area and 0.17 μg?g-1?d-1 in CR area. Also, the values of methane oxidation potential were 1.38 μg?g-1?d-1 in the CR area, 1.01 μg?g-1?d-1 in the CC area, 1.00 μg?g-1?d-1 in the R-CR area and 0.71 μg?g-1?d-1 R-CC area. The methane production potential increased exponentially with the increase in temperature. The average values of methane production potential at 5 ℃, 15 ℃, 25 ℃ and 35 ℃ were 0.13, 0.26, 0.55 and 0.95 μg?g-1?d-1, respectively. However, the methane oxidation potential was sensitive only at low temperatures. Specifically, the methane oxidation potential at 15 ℃, 25 ℃ and 35 ℃ were significantly different from the methane oxidation potential at 5 ℃, while there was no significant difference between the three culture temperatures. The average values of methane oxidation potential at 5 ℃, 15 ℃, 25 ℃ and 35 ℃ are 0.71, 1.14, 1.14 and 1.11 μg?g-1?d-1, respectively.【Conclusion】 Due to differences in water management, feed and nitrogen fertilizer input, substrate and environmental factors led to differences in the activities of methanogenic bacteria and methane-oxidizing bacteria. Therefore, soils with different land use types presented different characteristics of methane production and oxidation potentials. Generally, the methane production potential was more sensitive to temperature than the methane oxidation potential. The soil methane production potential and oxidation potential were significantly affected by temperature or land use type (P < 0.01), but the interaction between the two factors only had a significant impact on soil methane production potential but not on methane oxidation potential.

• Effects of Pear Pruning Branches Mulching on Soil Nutrition and Microbial Community Structures

  YANG Tianjie, WANG Xiaofang, HU Hongju, YANG Jian, OU Jiwang, WANG Xiaoxiang, HAO Baofeng, WANG Zhonghua†, DONG Caixia†, XU Yangchun

  DOI: 10.11766/trxb202208050430

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  【Objective】As a by-product of fruit tree shaping and pruning, pear branches are important biomass resources. The use of crushed branches for soil mulch under trees is one of the effective ways to utilize waste resources, which is conducive to increasing soil organic matter and improving soil fertility in pear orchards. 【Method】In order to assess the effects of short-term pear branch mulching on soil properties and structure of microbial community, soil samples were collected from five pear orchards in different latitudes (Bijie City of Guizhou Province, Changli City of Hebei Province, Harbin City of Heilongjiang Province, Zhijiang City of Hubei Province and Xuchang City of Henan Province) after 1-2 years of mulching. Soil basic physiochemical characteristics of the soil and the bacterial, fungal and protist communities were detected. 【Result】Results showed that the soil organic matter and available phosphorus content were significantly increased in pear branches mulching treatment in general, and the soil bacterial, fungal and protists community structure also changed significantly. Specifically, the mulching of pear branches significantly enriched the relative abundance of taxa such as Proteobacteria and Acidobacteria in bacteria, Basidiomycota in fungi, and Rhizaria and Alveolata in protists. The model prediction accuracy was as high as 94.44%, and the key species were mainly bacteria, including Acidibacter, Xanthobacteraceae, Nitrosomonadacee and other microorganisms related to the degradation of organic residues. Soil-available phosphorus content was found to be the main driver of variations in soil microbial community structure. 【Conclusion】The study preliminarily assessed the effect of pear tree branch mulching on soil nutrients and microbiome and excavated potential key microorganisms. The findings can serve as a reference for managing the health and fertility of orchard soils.

• Acidification and Phosphorus Enrichment Affect Silicon Availability in Two Farmland Soils

  ZHANG Gengjin, WEI Zongqiang, WU Jianfu

  DOI: 10.11766/trxb202208300482

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  【Objective】Soils and their functions are under threat from acidification. Phosphorus (P) and silicon (Si) mobility and their interactions in soils are sensitive to soil pH. Although Si fertilizer application has been reported to efficiently increase P availability in soils, the responses of Si mobility and availability to soil P enrichment are not well understood, especially in areas of intensive agriculture where soil P accumulation is significant.【Method】This study investigated the effects of P addition and artificial soil acidification on Si sorption and mobility in two typical farmland soils with different available silicon levels (the lower available silicon level, LASi and the higher available silicon level, HASi) using P and Si competitive adsorption experiments and soil incubation experiments.【Result】When Si and P were simultaneously added at equimolar concentrations between pH 3.5 and 8.0, the presence of P decreased Si adsorption by 26%-74% and 31%-84%, respectively, in LASi and HASi soils at the corresponding pH, suggesting that P had a greater affinity to soil solids than did Si. Si sorption by the soil generally decreased with decreasing pH in the pH range of 3.5 to 8.0, and the reduction of Si sorption due to P addition was more significant under higher pH conditions. 【Conclusion】Soil acidification and P addition decreased Si sorption and the soil HOAc-NaOAc-extractable Si content. The responses of soil CaCl2-extractable Si content to soil acidification and P addition were different between the two farmland soils, and further studies are needed to understand the mechanisms.

• Effects of Temperature and Arsenic on Growth and Arsenic Uptake of Different Rice Varieties during Seedlings Stage

  ZHAI Yiran, LI Renying, ZHANG Qi, QI Mengru, LU Binghao, HUANG Lidong, XU Xianghua

  DOI: 10.11766/trxb202302120058

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  Abstract:

  【Objective】Temperature and exogenous arsenic are important factors affecting rice growth. Due to climate warming, rice growth is affected by a combination of temperature and arsenic in rice fields contaminated by arsenic. Clarifying the combination can provide a theoretical basis for rice management and safety production.【Method】Germination and culture experiments were carried out in the artificial climate chamber under the condition of different exogenous arsenic concentrations [0 (As0), 0.5 (As0.5) and 1 (As1) mg?L-1] and different temperature simulations [daytime/nighttime 30 ℃/25 ℃ (T0) and 35 ℃/30 ℃ (T1)] using eight common rice varieties in Jiangsu Province. Seed germination, seedling growth and arsenic uptake of different rice varieties were analysed. 【Result】The results showed that exogenous arsenic inhibited sprout length and vigor index of rice. Compared with T0As0, T0As1 reduced the sprout length and vigor index of different rice varieties by 13.69%-43.34% and 28.14%-52.88%, respectively, and the effect of temperature on rice seed germination was related to rice varieties. Under the condition of T1 treatment, the germination rate, sprout length and vigor index of Yanliangyou 1618 were better than those of other varieties. The interaction of temperature and exogenous arsenic significantly decreased the sprout length (P < 0.05). Compared with T0As0, T1As1 decreased sprout length by 5.66%-43.34%. Also, single temperature or exogenous arsenic had a significant effect on rice root length and root vigor. Compared with T0As0, T0As1 reduced root vigor by 3.01%-58.21%. The interaction of temperature and exogenous arsenic inhibited rice root length and root vigor. Compared with T0As0, T1As1 significantly reduced root vigor of different rice varieties by 53.80%-91.69%. The seedling height and root vigor of different rice varieties had significant differences (P < 0.05) under the same treatment of temperature or exogenous arsenic, among which the seedling height and root vigor of Yanliangyou 888 were at higher levels. The arsenic concentration in rice stems and leaves increased significantly under exogenous arsenic while the arsenic concentration in rice stems and leaves decreased under the increase in temperature. Furthermore, compared with single arsenic treatment, arsenic concentration in rice stems and leaves decreased under the interaction of temperature and exogenous arsenic. 【Conclusion】From the above results, it can be concluded that temperature and exogenous arsenic affected rice growth and arsenic uptake. However, rice growth conditions and arsenic concentration were significantly different among rice varieties. The germination and growth of Yanliangyou 888 and Yanliangyou 1618 were better than other rice varieties under the condition of temperature and exogenous arsenic.

• Study on the Degradation of Fenpropathrin in Soil and Its Toxic Effect on Earthworms

  YANG Furong, RAN Lulu, YANG Mu, LIU Chang, CHEN Min, CAI Yiyun, YANG Cancan, HE Lin

  DOI: 10.11766/trxb202210130560

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  Abstract:

  【Objective】The goal of this study was to evaluate the degradation of fenpropathrin in soil and its effects on earthworms, as well as to establish a foundation for a full environmental risk assessment of fenpropathrin.【Method】High performance liquid chromatography was used to identify the bioaccumulation of fenpropathrin and the major metabolite, 3-phenoxybenzoic acid, then soil exposure tests were used to assess the toxicity of fenpropathrin to earthworms.【Result】(1) Fenpropathrin decomposed four times more quickly in unsterilized soil than in sterilized soil and more quickly in alkaline soil than in acidic soil, suggesting that microorganisms and pH were the main factors affecting the degradation rate of fenpropathrin in soil. Moreover, during the decomposition process, the synthesis of its primary metabolite, 3-phenoxybenzoic acid, was discovered. (2) Fenpropathrin content in earthworms increased, then dropped, with a maximum bioconcentration factor of 0.3. (3) The subacute toxicity data showed that after 14 d exposure to high doses (5 mg?kg-1) of fenpropathrin, the protein content in earthworms was significantly reduced (P<0.05). Also, the cytochrome P450 (CYP450), carboxylesterase (CarE), glutathione-S-transferase (GST), superoxide dismutase (SOD) and catalase (CAT) activities and malondialdehyde (MDA) content were significantly increased (P<0.05) after 14 d of fenpropathrin exposure, and there was a dosage effect.【Conclusion】The rate of fenpropathrin degradation in soil was strongly linked with soil characteristics, and fenpropathrin residues in soil could cause subacute toxic effects in earthworms. These findings help in a thorough evaluation of the ecotoxicity and environmental behavior of fenpropathrin in soil, as well as a more solid foundation for pyrethroid pesticide risk assessment.

• Vertical Variations of Thermal Stability of Soil Organic Matter in Black Soils under Different Pedogenetic Modes

  GONG Keyang, YANG Fei, LONG Hao, GU Jun, ZHANG Ganlin

  DOI: 10.11766/trxb202211180627

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  Abstract:

  【Objective】Soil organic matter (SOM) content and its stability are important indexes to evaluate soil quality. Thermogravimetric analysis has gained attention due to its good performance in reflecting SOM content and SOM stability. The objective of this paper is to explore the vertical variation patterns of SOM thermal stability in black soils under different pedogenetic modes. The causes for these variations are also explored. This study will provide a theoretical reference for the protection of black soil resources and carbon sequestration. 【Method】Black soils of two major pedogenetic modes, i.e., naturally developed mode and depositional mode were selected for comparison. The former one included three typical black soils under stable topographic conditions (flat terrain) and the latter one included two black soils affected by erosional-depositional processes under unstable topographic conditions (with surface erosion and sedimentation) in the typical black soil area of Northeast China. Thermogravimetric analysis was used as a tool to evaluate SOM thermal stability. Two SOM fractions were recognized based on mass loss in responding to different temperature intervals, with Exo1 (mass loss during 200～350 ℃) representing thermally labile SOM and Exo2 (mass loss during 350～550 ℃) representing thermally stable SOM. In addition, derivative thermogravimetry curves and two thermogravimetric parameters including Exo1/Exo2 and TG-50 were adopted to characterize the variations of SOM thermal stability in different soil profiles. Fourier transform infrared spectroscopy was used to assess SOM chemical stability. 【Result】For naturally developed black soils from the stable land surface, the content of thermally labile SOM (Exo1) decreased at a higher rate with depth than that of thermally stable SOM (Exo2). With the increase of depth, Exo1/Exo2 decreased, TG-T50 increased, and aliphatic C/aromatic C decreased, indicating that the SOM of naturally developed black soils tended to be thermally stable with depth. Under unstable geomorphic settings, on the contrary, the thermal stability of SOM did not show a regular decrease trend with depth, and the content of SOM and Exo1/Exo2 in deeper layers could be higher than those in the surface layer. This was mainly due to the different land surface histories that caused variations in sources of soil parent material and SOM. 【Conclusion】This study confirmed the usefulness of thermogravimetric analysis in reflecting SOM stability. Spatial variations in SOM stability in black soils were largely conditioned by a pedogenetic mode which was largely related to geomorphic stability. We found that depositional landscape positions tended to stack a large amount of labile SOM, which was carried by erosional processes. This occurs both at hillslope and watershed scales. These thermally unstable SOMs could be preserved in the deep soil for a long time, due to the blocking effect of burial. Once eroded, however, these blocked labile SOMs are easily decomposed, which may also lead to the release of a large amount of buried ""old carbon"" and become the ""hot spot"" of carbon emissions in the black soil area.

• Green Manuring-induced Changes in Soil Metabolome and Microbiome Alleviate Strawberry Autotoxicity While Improving Fruit Yield and Quality

  GUO Qiao, XIAO Li, LI Jin, SUN Chenyu, FU Huijing, SHU Xiaolong, XUE Quanhong, LAI Hangxian

  DOI: 10.11766/trxb202211050608

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  【Objective】Green manuring is considered to be an effective strategy to achieve sustainable development in agriculture. It plays key roles in ameliorating soil fertility, improving fruit quality, and enhancing resource use efficiency. China is the world’s largest strawberry (Fragaria × ananassa Duch.) producer, with strawberry cultivation taking place mainly in greenhouses. However, many field management practices, such as long-term monoculture and irrational chemical fertilization, reduce the fruit yield and quality of strawberries. Therefore, it is important to investigate the effects and mechanisms of green manuring on strawberry yield and quality in greenhouses. 【Method】 Three gramineous green manures, i.e., maize (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], and sorghum-sudangrass (Sorghum × sudangrass), were selected to carry out a field experiment from 2017 to 2021. There were four treatments: fallow farmland–strawberry (control), maize–strawberry, sorghum–strawberry, and sorghum-sudangrass–strawberry. Samples were collected in the full fruit stage of strawberries to determine plant growth and physiological parameters, in addition to fruit yield and quality attributes. Rhizosphere soil chemical properties, bacterial community structure, and metabolome were also analyzed. 【Result】 The different green manure treatments promoted plant growth and yield formation, and improved the fruit quality of subsequent strawberry crops. The most prominent effects were observed for the corn green manure treatment, which increased strawberry plant dry weight, root growth, and leaf chlorophyll content (SPAD value) by 53.4%, 21.0%~94.7%, and 7.8%, respectively, compared with the control treatment. Also, fruit yield per plant was markedly improved by 44.6% in the corn green manure treatment, along with the increase of nutrient contents (total sugar: by 13.9%; vitamin C: by 14.4%; and soluble solids: by 12.8%). Soil pH, cation exchange capacity, organic matter content, and nutrient availability (N, P, and K) were also strongly increased under the corn green manure treatment, while sucrase, phosphatase, and urease activities were enhanced simultaneously. Green manuring mediated an increase in the diversity and abundance of rhizosphere soil bacterial communities, coupled with a distinct enrichment of potentially beneficial bacteria, such as Flavobacterium, Variovorax, and Pedobacter. The increase in the abundance of potentially beneficial bacteria might be related to a considerable increase in the relative abundance of carbohydrate metabolites (e.g., sorbose, mannose, and fructose) associated with green manuring. A remarkable decrease in the relative abundance of lipid metabolites (e.g., palmitic acid, stearic acid, and oleic acid) alleviated the autotoxicity of strawberries. 【Conclusion】 Gramineous green manure-mediated shifts in specific metabolites in the rhizosphere soil improved strawberry yield and quality by recruiting potentially beneficial bacteria and alleviating allelopathic autotoxicity. Maize green manure is a better option compared to sorghum and sorghum-sudangrass green manures for greenhouse strawberry production.

• Carbon Footprint and Economic Benefits Analysis of Rice Planting Patterns in Jiangsu Province

  JiGuojun, JiHongting, Chengkun, LiuManqiang, JiangYu, HuZhengkun, ZhangYuefang, HuNaijuan, HuFeng

  DOI: 10.11766/trxb202212180695

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  【Objective】 Little or no research has been done on the carbon footprint and economic benefits of different rice planting patterns at the provincial level. Thus, a systematic analysis of the carbon footprint and economic benefits of different rice planting patterns is of great significance for carbon emission reduction of rice production and the development of low-carbon agriculture. 【Method】Based on the survey data of rice farming in Jiangsu Province, the carbon footprint and economic benefits of different rice planting patterns in Jiangsu Province were quantitatively analyzed by using the life cycle assessment method. 【Result】The results showed that from 2016 to 2020, the carbon footprint per unit area, the carbon footprint per unit yield, and the carbon footprint per unit value were 11.28-14.39 t?hm-2, 1.30-1.52 kg?kg-1 and 0.49-0.58 kg?yuan-1, respectively. The carbon footprint per unit area, per unit yield and per unit output value of different rice production and planting patterns were in order of broadcasted seeding rice or manual transplanting rice, mechanical transplanting rice, direct seeding rice. The carbon footprint per unit area of mechanical transplanting rice and manual transplanting rice production showed a decreased trend with the increase of years. Also, the carbon footprint per unit yield of mechanical transplanting rice, manual transplanting rice, and direct seeding rice production showed a decreased trend with the increase of years. Methane emissions from rice fields accounted for the largest proportion, followed by carbon footprints caused by nitrogen fertilization, nitrous oxide emissions from rice fields and carbon footprints caused by irrigation electricity. Nitrogen fertilizer and irrigation electricity were the main driving factors affecting the regional differences in the carbon footprint of different rice planting patterns. The total income of different rice planting patterns was between 2.51?103-2.75?103 yuan?hm-2, the resource input cost was 1.88?103-1.99?103 yuan?hm-2, the carbon emission cost was 0.20?103-0.25?103 yuan?hm-2, and the net income (NI-CO2) considering carbon emissions was 0.39?103-0.64?103 yuan?hm-2. The NI-CO2 of mechanical transplanting rice was lower than that of manual transplanting rice, broadcasted seeding rice and direct seeding rice. This was mainly caused by the higher total income and the lower resource input cost and carbon emission cost of mechanical transplanting rice. 【Conclusion】In conclusion, direct seeding rice was the lowest carbon emission rice planting pattern. Considering the carbon emission and economic benefits, machinal transplanting rice was superior to manual transplanting rice, direct seeding rice and broadcasted seeding rice.

• Dissolution of Chromium and Oxidation of Exogenous Trivalent Chromium in Latosol

  Yang-xiao-xiao Shi, Jiang, Ke-wei Li, Ren-kou Xu

  DOI: 10.11766/trxb202301290034

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  Abstract:

  【Objective】The contents of background chromium (Cr) and manganese (Mn) oxides in latosols are high. The dissolution of Cr and subsequent oxidation of Cr(III) in the soils may occur to produce Cr(VI) with high toxicity, thus, posing a threat to the surrounding environment and humans. Therefore, this study aimed to study the dissolution of Cr and the oxidation of Cr(III) in latosols collected from Yunnan, Hainan, and Guangdong Provinces to understand the ecological and environmental risks associated with chromium in latosols.【Method】The dissolution of Cr was investigated using batch experiment , while both batch and incubation experiments were used to investigate the oxidation of Cr(III) in the soils. The concentration of Cr in extractants was determined by an atomic absorption spectrometer. Also, sodium hydrosulfite-sodium citrate-sodium bicarbonate (DCB) extraction and electron probe scanning were used to examine the forms of Cr in the soils.【Result】The results of DCB extraction and electron probe scanning showed that Cr in latosols was mainly combined with iron oxides and silicates. Acidification by hydrochloric acid and complexation by citric acid promoted the dissolution of Cr from the soils. However, even in 1 mol?L-1 hydrochloric acid, only 3.68% and 3.54% of total Cr was dissolved from the latosols of Hainan 3 and Guangdong 9, respectively, suggesting that Cr in latosols is stable and presents a low environmental risk. The oxidation of Cr(III) was observed in the soils during a 42-day incubation experiment. Based on the net production of Mn(II), Cr(VI) content, and organic matter content, it is probable that the Cr(VI) generated in the soils might be reduced to Cr(III) again by soil organic matter. The results of the batch experiment showed that the exogenous Cr(III) was oxidized to Cr(VI) in the latosols with organic matters removed, and the amount of Cr(III) oxidized was determined by the content of easily reducible Mn(III/IV) oxides in the soils. With the increase of suspension pH, the oxidized amount of Cr(III) increased firstly, reached the largest amount at pH 4.5 and then decreased. At this pH, only 1.48% of Cr(III) added was oxidized to Cr(VI). Although exogenous Cr(III) can be oxidized to Cr(VI) by soil Mn(III/IV) oxides in the latosols, the percentage of Cr(III) oxidized to Cr(VI) in the latosols was small, indicating that the risk of exogenous Cr(III) oxidization in the soils was very low.【Conclusion】Despite the high contents of background Cr and easily reducible Mn(III/IV) oxides in the latosols, the dissolution of Cr and oxidation of Cr(III) were difficult. This shows that under the experimental conditions, it was not easy to convert Cr(III) to Cr(VI) through oxidation reactions, therefore, the risk of background Cr in latosols is low.

• Modelling Soil thickness Evolution: Advancements and Challenges

  LIU Jintao, ZHAO Wei, LIU Yu

  DOI: 10.11766/trxb202207070374

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  【Objective】Global soil thickness is only about 1 m. Its spatial distribution is nevertheless crucial in many hydrological and ecological processes, and it also determines hillslope stability and channel initiation in geomorphological fields. Due to its significant spatial heterogeneity, it is difficult to obtain the soil thickness distribution on a catchment scale based on existing soil survey databases, geophysical investigations, or empirical models. Therefore, it is urgent to develop a process-based model for soil thickness prediction. 【Method】In this study, methodologies and theories were comprehensively reviewed, and the applicability of different soil production and soil transport models were evaluated. 【Result】This study pointed out that the mechanism of soil production by chemical weathering is still unclear and is a theoretical bottleneck restricting the development of soil thickness evolution models. Moreover, the methodology of the model still needs to be further developed, and it is urgent to develop and improve the parameter estimation methods and the adoption of equation forms for describing soil production and soil transport in such models upon applications. From our analysis, we inferred that a hybrid model combining stochastic and process-based models as well as mathematical physically-based methods for determining parameters may help solve many difficulties faced in model applications. 【Conclusion】Finally, we discussed the possible integration of soil thickness evolution models and soil pedogenesis models based on the theoretical frame of catchment coevolution for predicting soil thickness, texture, layering and organic carbon content variation in the landscape.

• Effects of Top Soil Structure on Runoff and Sediment Yield of Red Soil Slope Cropland

  ZHANG Ziwei, ZHAO Wenjun, LI Qi, MA Yichun, TIAN Liang, YANG Guangyong, LI Zhongwu, LIU Yaojun

  DOI: 10.11766/trxb202205280284

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  【Objective】Based on the current situation and severity of soil and water loss, it is vital to investigate the nature and extent of surface structure degradation of slope farmland and long-duration rainfall characteristics in the red soil region of southern China.【Method】The method of long-term rainfall simulation were adopted to test the effects of topsoil structure and rainfall intensity on rainfall redistribution, runoff and sediment yield. In this paper, three rainfall intensities, 30 mm·h-1, 60 mm·h-1 and 90 mm·h-1, respectively, and three cultivation depths, 10 cm, 20 cm and 30 cm, respectively, were set to study the effects of tillage lager depth and rainfall intensity on surface flow, subsurface flow, soil loss rate and erosion pattern.【Result】The results showed that: (1) The topsoil structure significantly changed the redistribution process of runoff. Higher tillage layer depth can mitigate the effects of rainfall intensity, reduce the surface flow coefficient, and increase subsurface flow. Under the condition of 60 mm·h-1 and 90 mm·h-1 rainfall intensity, the average surface flow coefficient decreased in the sequence of 70.5％ (TLD10 cm), 62.9% (TLD20 cm), and 56.8% (TLD30 cm), and the average subsurface flow ratio increased in the sequence of 7.1% (TLD10 cm), 12.3％ (TLD20 cm), and 18.1% (TLD30 cm). (2) The soil loss rate was enhanced with the increase in rainfall intensity but decreased with the depth of the tillage layer. Under 60 mm·h-1 rainfall intensity, the peak soil loss rate of 10 cm, 20 cm and 30 cm tillage depth were 35.1, 25.6 and 20.5 g·m-2 min-1, respectively. For 90 mm·h-1 rainfall intensity, these values were 68.7, 55.8 and 48.4 g·m-2 min-1, respectively. (3) Rainfall intensity and topsoil structure significantly affect the final slope erosion forms. With the increase of tillage layer depth, the erosion degree decreased significantly. Under the condition of 30 mm·h-1 rainfall intensity, the surface of the soil was relatively intact, and the soil erosion type was splash erosion. Also, under the condition of 60 mm·h-1 rainfall intensity, the soil erosion was all sheet flow erosion, under 10 cm and 20 cm tillage depth, spot erosion appeared in the lower part of the slope, and the soil erosion degree was lower for sheet flow erosion at 30 cm tillage depth. For the 90 mm·h-1 rainfall intensity, rill erosion appeared on the slope while at 10 cm tillage depth, rill erosion was well developed. In addition, at 20 cm tillage layer depth, rill erosion development was significant while at 30 cm tillage depth, slope erosion was mainly sheet flow erosion.【Conclusion】The top soil structure can significantly change the relationship between rainfall and runoff. Higher tillage layer depth can reduce surface erosion, promote the deep infiltration of soil moisture, and increase the soil""s deep-water holding capacity. Also, this research can serve as a reference for the rational layout of topsoil structure, improvement of rainfall utilization rate and enhancement of soil erosion resistance in the southern red soil area.

• Effect of Soil Moisture and Phosphorus Level on Degradation Kinetics of Glyphosate Pesticides

  DING Lingling, XUE Sha, YANG Xiaomei

  DOI: 10.11766/trxb202205110244

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  Abstract:

  In recent years, more attention has been paid to the persistence of glyphosate and its degradation product, ammethylphosphoric acid (AMPA), in soil, as well as their environmental risks. However, with a similar structure as phosphate and with a positive charge, glyphosate may compete with phosphate for adsorption sites on the surface of soil particles, thereby affecting its environmental behavior and the bioavailability of phosphorus in soil.【Objective】Our aim was to investigate the degradation kinetics of glyphosate pesticide, soil available phosphorus and soil enzyme activity in Loess soil.【Method】Laboratory experiments were carried out under different phosphate application levels (0, 50, and 100 mg.kg-1) and water conditions (20% field water capacity (20FC) and 60% field water capacity (60FC)).【Result】The results showed that: 1) The degradation rate of glyphosate was fast at the initial stage of spraying and gradually slowed down at the later stage under different levels of phosphate application and soil moisture. Different phosphate levels had no significant effect on glyphosate degradation while different soil moisture did. Also, the content of AMPA increased with the degradation of glyphosate, and there was no significant difference in the content of AMPA under different phosphate levels. However, the peak and variation characteristics of AMPA under different soil moisture significantly differed. The peak was reached on day 14 after spraying for 20FC and on day 7 for 60FC. In addition, the quantitative characteristics of glyphosate residues fitted the first-order kinetic degradation model, with a half-life time of 69.3~77.0 d (20FC) and 10.5~12.8 d (60FC). 2) After spraying glyphosate, the content of available phosphorus decreased first and then increased with the degradation of glyphosate, which was significantly affected by soil moisture. In addition, phosphatase activity was significantly inhibited after glyphosate application, while the activities of N-acetylamino-β-glucosidase, β-glucosidase and leucine aminopeptidase changed dynamically. Phosphate levels showed no significant effects on soil enzymes’ activities while soil moisture did.【Conclusion】The findings indicate that phosphorus level in Loess soil had no significant effect on the degradation characteristics of glyphosate, but soil moisture significantly affected the degradation rate of glyphosate and the residual level of its metabolite. Meanwhile, glyphosate application had a significant effect on the activities of available phosphorus and phosphatase, which may affect soil phosphorus cycling and plant utilization. Therefore, the feed-effects of glyphosate and soil phosphorus components as well as the related enzyme activities should be considered in follow-up studies, especially the relationship between the persistence of glyphosate and its metabolite and soil health indicators under drought conditions. This will provide scientific-based information to guide glyphosate use in Loess soil regions.

• A Review and Discussion on the Earth’s Critical Zone Research: Status Quo and Prospect

  YANG Shunhua, SONG Xiaodong, WU Huayong, WU Kening, ZHANG Ganlin

  DOI: 10.11766/trxb202211230640

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  Abstract:

  In the past twenty years, the emerging and rising of the "Earth""s Critical Zone" study has provided a new perspective for re-examining the functions of water, soil, air, life, rock and their intrinsic interactions in earth""s surface system. By collecting relevant researches on Earth""s Critical Zone from 2001~2021 at home and abroad, we conducted a bibliometric analysis using CiteSpace. We introduced the history and current status of Earth""s Critical Zone research, in order to provide a theoretical and decision-making support for the comprehensive management of natural resources and ecological restoration of territorial space. The results show that: (i) Earth""s Critical Zone have received widespread academic attention from developed countries in Europe, the United States and China; (ii) The research priorities are obviously different among the three stages (i.e. germination, early and rapid development stage); (iii) Soil is the link and core connecting surface and underground processes; (iv) Geophysical technology has become an important tool for understanding the structure and processes of Earth""s Critical Zone; (v) Networked observations and model simulations are important directions in the next stage; (vi) The quantification, trade-off, and improvement of functions and services in Earth""s Critical Zone are expected to become important decision-support tools. In the future, there is still a need to strengthen research aimed at (i) Boosting infrastructure construction and building a more collaborative network of Earth""s Critical Zone observatory; (ii) Construction of interdisciplinary research and talent teams and training new generations of critical zone scientists; (iii) Serving the social needs of sustainable development, apply and develop the Earth""s Critical Zone science in practice; (iv) Developing new technologies and methods, and improve theories, models and methodological systems; (v) Revealing the coupling mechanisms of the Earth""s Critical Zone processes and their environmental effects, and strengthen the research on the impacts of human activities on water and soil processes, material cycles and energy exchange.

• Effects Of Rice Phenological Characteristics on Soil Organic Carbon Mapping in Paddy Fields in Zhangzhou City, Fujian Province

  WU Qihang, YAO Yuan, LI Yifan, CAO Wenqi, CAI Xinyao, WU Ting, ZHANG Liming, XING Shihe

  DOI: 10.11766/trxb202205150253

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  Abstract:

  【Objective】 High-precision soil organic carbon mapping is the basis for studying the spatiotemporal pattern of cultivated soil organic carbon and its influencing mechanism. Results of the relevant research can provide decision support for the designation of farmland management regarding "carbon sequestration and emission reduction". Agricultural management activities are an important influencing factor of soil organic carbon changes in farmland, but soil organic carbon mapping based on agricultural management activities is relatively rare. The phenological parameters extracted from remote sensing images are a direct reflection of agricultural management activities and have great application potential in studying the impact of agricultural management activities on farmland soil organic carbon. 【Method】 This study selected the paddy fields in Zhangzhou City, Fujian Province as the research object. We used the random forest algorithm, based on five different variable combinations (Group A: only natural environment variables; Group B: natural environment variables + early rice phenological parameters: Group C: natural environment variables + late rice phenological parameters; Group D: natural environment variables + early rice phenological parameters + late rice phenological parameters; Group E: early rice phenological parameters + late rice phenological parameters), to build soil organic carbon content prediction models. By comparing the prediction accuracy of the five groups of models, the spatial distribution characteristics of predicted values, the importance of related influencing factors, and the influence of phenological parameters on the accuracy of soil organic carbon mapping were analyzed. Also, the main influencing factors of soil organic carbon mapping in paddy fields in Zhangzhou City were excavated. Agricultural management activities that have an important impact on soil organic carbon in paddy fields in Zhangzhou City were also identified. 【Result】The results showed that the differences in the spatial distribution of soil organic carbon in paddy fields in Zhangzhou resulted from the combined effect of natural environmental factors and agricultural management measures. Phenological parameters can effectively improve the mapping accuracy of soil organic carbon in paddy fields in Zhangzhou City. Compared with the prediction model based only on natural factors, the addition of phenological parameters can reduce the error of the prediction model and improve the ability of the model to explain variance. The phenological parameters that had the greatest impact on soil organic carbon in paddy fields in Zhangzhou City were the rate of increase at the beginning of the early rice growing season (h1), the time for the start of the early rice growing season (a1), and the rate of decrease at the end of the early rice growing season (i1). These three most important phenological parameters were positively, negatively, and negatively correlated with soil organic carbon content, respectively. 【Conclusion】The adoption of water and fertilizer management measures that can promote early growth and rapid germination of the early rice, accelerate the tillering rate of the early rice, and slow down the senescence rate of the early rice will increase the soil organic carbon content in the cultivated land. Building a prediction model based on phenological parameters can effectively improve the accuracy of farmland soil organic carbon mapping. The research on farmland soil organic carbon mapping based on phenological parameters can provide decision support for farmland management. The results of this study can provide a theoretical basis for related research.

• Effects of Long-term Different N Application Rates on Aggregate Distribution and Fungal Community Composition in Fluvo-aquic Soil

  GUO Wei, ZHOU Yunpeng, CHEN Meiqi, LI Dandan, WANG Qingxia, MA Donghao, ZHAO Bingzi

  DOI: 10.11766/trxb202210090556

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  Abstract:

  【Objective】The aggregate distribution, the composition of the fungal community, and the production of biological binding agents can be significantly changed by different nitrogen (N) application rates. However, whether there is a correlation between these properties remains unclear. 【Method】A 16-year field experiment located in Fengqiu Agro-ecological National Experimental Station was used as the research platform, and this included five levels of N application rates, i.e. (1) F0: 0, (2) F1: 150 kg?hm-2, (3) F2: 190 kg?hm-2, (4) F3: 230 kg?hm-2, and (5) F4: 270 kg?hm-2. The effects of different N application rates on water-stable aggregate distribution (>2 000 μm, 2 000-250 μm, 250-53 μm and <53 μm) were explored, and the correlation between aggregate distribution and the major biological binding agents (glomalin-related soil proteins（GRSP）and microbial biomass carbon（MBC)) and soil fungal community was studied. 【Result】The soil aggregate distribution and fungal community composition were divided into three significantly different groups: F0, F1 and F2, F3 and F4, respectively. The results showed that: (1) F1 and F2 treatments had the highest mean weight diameter of soil aggregates and significantly increased the proportion of >2 000 μm aggregates and this was mainly related to the enrichment of Pyrenochaetopsis; (2) F1 and F2, F3 and F4 treatments all increased the proportion of 2 000-250 μm aggregates, while they significantly decreased the proportion of <53 μm aggregates. The increase of the proportion of 2 000-250 μm aggregates was significantly positively correlated with the ratio of easily extractable glomalin-related soil proteins to total glomalin-related soil proteins (EE-GRSP/T-GRSP) and easily extractable glomalin-related soil proteins (EE-GRSP). However, it was significantly negatively correlated with the relative abundance of Didymella and Mortierella. The decrease of the proportion of <53 μm aggregates was significantly positively correlated with the relative abundance of Mortierella, Phlebia, Melanospora, Fusicolla, Podospora and Didymella, but significantly negatively correlated with EE-GRSP and/or the relative abundance of Acremonium, Scytalidium and Exophiala, EE-GRSP/T-GRSP and MBC. 【Conclusion】The variation of soil aggregate stability was affected by the level of N application. Also, the stability of soil aggregates under N application rates of 150 kg?hm-2 and 190 kg?hm-2 was higher than that under N application rates of 230 kg?hm-2 and 270 kg?hm-2, which was significantly correlated with the changes in fungal community composition and biological binding agents under different N application rates.

• The distribution and potential functions of prokaryotic communities in saline soils of Hetao Irrigation District

  ZHANG Lu, YANG Jingsong, YAO Rongjiang, WANG Xiangping, XIE Wenping

  DOI: 10.11766/trxb202209010393

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  Abstract:

  【Objective】 Soil salinization affects the quality of arable land and threatens the sustainable development of agriculture. As an important indicator of soil environment, soil microbes play important roles in driving soil nutrient cycling and maintaining ecosystem productivity. Therefore, deciphering the response of microbial communities and their potential functions to the degrees of soil salinization and land use type is of great significance for understanding the elemental cycling processes and interactions with plants in a saline-affected agroecosystem. 【Method】 In this study, we explored the composition and potential functions of prokaryotic communities and their environmental drivers in saline soils from farmlands and wastelands with different salinization degrees, by combining prokaryotic high-throughput sequencing and soil physicochemical analysis methods in a typical saline area of Hetao Irrigation District of China. 【Result】 Compared with wastelands, the farmlands exhibited a lower soil salinity but a higher content of soil organic matter (SOM) (P < 0.05). In farmlands with different salinity levels, mild saline soil had a significantly higher yield of sunflower than the moderate and severe saline soils. Meanwhile, the saline soils in farmland exhibited a higher prokaryotic α diversity than that in the salinized wasteland, with a large number of unique ASVs (Amplicon sequence variants). The prokaryotic α diversity indexes were positively associated with SOM contents but negatively correlated with soil pH, EC, moisture and bulk density. Non-metric multidimensional scaling (NMDS) analysis based on the β diversity of prokaryotes further indicated that the prokaryotic community was mainly differentiated between farmland and wasteland, followed by the soil salinity level in each land use type. Specifically, the prokaryotic community was dominantly driven by environmental factors including EC, pH and SOM, as suggested by canonical correlation analysis (CCA) and Mantel test. Moreover, the phylum including Acidobacteriota, Chloroflexi, Planctomycetota, Crenarchaeota, and Myxococcota in farmlands showed significantly higher abundance than wastelands, whereas Halobacterota and Bacteroidota showed an opposite trend, with Halobacterota only detectable in wastelands and relative abundance ranging from 10.13% to 39.41%. Through predicting the potential functions of the prokaryotic community, we found that there were high abundances of nitrogen cycling-related microbes like Nitrososphaeraceae and Nitrososmonadaceae, and potential plant growth-promoting bacteria including Nocardioidaceae and Sphingomonadaceae in salinized farmlands. By contrast, the salinized wasteland enriched prokaryotic groups with potential hydrocarbon decomposition function. 【Conclusion】 Our study indicates strong selection effects of different land use types on prokaryotic communities in salinized soil of Hetao Irrigation District, which has important implications for clarifying the feedback between prokaryotic community and physicochemical properties of saline soils, as well as revealing the synergy effect among soil-plant-microorganism for soil nutrient turnover and agricultural sustainability.

• The Response of Soil Fungal Communities and Potential Functions to the Application of Exogenous Bt Toxins

  Li Yujie, Ge Lei, Hu Cong, Wang Luyao, Guo Guanqing, Wu Guogan, Wang Cui, Song Lili, Sun Yu, Wang Jinbin, Zeng Haijuan, Xu Qinqing, Quan Zhexue, Li Peng

  DOI: 10.11766/trxb202209070496

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  Abstract:

  【Objective】Bt toxins released from Bt plants and BT biopesticides are potential exogenous pollutants in the environment with biocidal activity. The environmental behavior and ecological effects of Bt toxins are the focus of safety risk assessment of transgenic plants and transgenic microorganisms. Fungus is an important component of soil microbes and plays a key role in maintaining soil ecosystem stability, but the dynamic response of soil fungal communities and potential functions to exogenous Bt toxins remains unclear. 【Method】In this study, the retention dynamics of Bt toxins in soils incorporated with different concentrations of Bt toxins were analyzed, and high-throughput sequencing technology of fungal 18S rRNA gene was used to analyze the effects of Bt toxins application on the soil fungal community and functional diversity. 【Result】The results showed that the concentration of water-dissolved Bt toxins in soil decreased significantly with the prolongation of soil incubation time, and the amounts of water-dissolved Bt toxins in soil with initial Bt toxins concentrations of 50, 100 and 500 ng·g-1 decreased to those of control soil on the 100th day. Both the application of Bt toxins and incubation time could significantly affect the composition of the soil fungal community, and with an increase of initial Bt toxins concentration and prolongation of soil incubation time, the difference in soil fungal community gradually widened. The application of Bt toxins increased the Shannon index of the soil fungal community, the negative correlation and modules of the association network, and thus it did not adversely affect the diversity and stability of the soil fungal community. 【Conclusion】The results indicate that the initial concentration of Bt toxins and its long-term effects should be of concern when assessing the environmental behavior and micro-ecological effects of Bt toxins. With the increase of Bt toxins concentration, the relative abundances of Phymatotrichopsis, Homalogastra, Geosmithia and Apiotrichum increased significantly, as well as functional genes encoding enzymes involved in protein degradation, carbon metabolism and phosphorus metabolism. It is speculated that the above-mentioned fungal taxa and potential functions were involved in the degradation and transformation process of Bt toxins in the soil. This study provides a scientific reference and theoretical basis for the ecological safety risk assessment of Bt plants, Bt recombinant biopesticides and Bt toxins.

• Soil Environmental Criteria of Polycyclic Aromatic Hydrocarbons for Ecological Security Based on Literature Data

  DENG Jibao, XIANG Dazhou, LIN Bozheng, HU Xiaojie, WANG Hefei, GAO Yanzheng

  DOI: 10.11766/trxb202211040517

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  Abstract:

  【Objective】 Polycyclic aromatic hydrocarbons (PAHs) have carcinogenic, teratogenic, and mutagenic effects, and soil PAH pollution has become a world-wide problem. However, ecological soil screening and controlling levels (Eco-SSCLs) for PAHs in China have not yet been established. Thus, soil ecological security risk assessment is still unsubstantiated. 【Method】 Here, we systematically investigated the research outcomes in related fields at home and aboard, and screened out 248 toxicity data (Effect concentration10, EC10 and No observed effect concentration, NOEC) of 16 pri-control PAHs listed in US EPA. The species sensitivity distributions were developed by a series of cumulative distribution functions, and were successfully used to derive soil environmental criteria of each PAH (PAH-SEC) for ecological security under different land use types. 【Result】 The PAH-SEC values under different land use types were 1.00~10.60 mg·kg-1 (natural reserve and agricultural land), 1.03~25.44 mg·kg-1 (parkland), 1.12~51.00 mg·kg-1 (residential land), 1.20~68.41 mg·kg-1 (commercial service and industrial land). 【Conclusion】 The results can provide data support for the formulation of soil environmental quality standards for ecological security, and offer bases for ecological risk assessment of PAHs polluted soil.

• Research Progress and Hotspots Analysis of Soil Antibiotic Resistance Genes

  Zhang Youai, Wang Tingting, Hu Xiaojie, Qin Chao, Gao Yanzheng

  DOI: 10.11766/trxb202210200578

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  Abstract:

  【Objective】The increasing emergence and spread of antibiotic resistance genes (ARGs) poses a great threat to global public health. Soil as an important repository and medium for ARGs has attracted extensive attention from many scholars. 【Method】In order to have a comprehensive understanding of the research progress and hotspots in the field of soil ARGs, the VOSviewer and CiteSpace software were used to perform a bibliometric analysis of the papers related to soil ARGs published from 2013 to 2022 in “Web of Science” database. More specifically, density visualization analysis, keyword emergence analysis, and contribution network analysis were performed to deeply discuss the types of publications, annual frequency of citations, country/region and institution of publications, keywords, research directions, and the hotspots and trends of research. 【Result】Our results demonstrated that the number and citation frequency of the publications related to soil ARGs increased year by year. The number of publications increased slowly in the first five years (2013–2017), while it rapidly increased in the last five years (2018–2022). Besides, the maximum citation frequency was 22123 times. China published the most papers in the field of soil ARGs, accounting for 61.40% of the total number of publications, and China cooperated closely with 27 countries, including Australia and the United States. Tetracycline and sulfadiazine were the two main types of antibiotics in the soil ARGs field, and Escherichia coli as model bacterium was a microbial type of great interest in this field. The results of citation burst and co-occurrence analysis indicated that research hotspots of soil ARGs differed significantly in different periods. At first, scholars focused on the understanding and quantification of ARGs. Subsequently, more attention was paid to the source analysis of ARGs and their intrinsic connection with microorganisms. The study of the spread and fate of ARGs has become a hot topic of interest and research for scientists today. 【Conclusion】In conclusion, this study conducted a comprehensive bibliometric analysis of the relevant literature in the field of soil ARGs. On the whole, the research on the propagation deterrence and reduction techniques of soil ARGs is still insufficient. Future research may focus on the development and improvement of monitoring system as well as mathematical model establishment to assess the environmental risks of soil ARGs and their effects on human health. Besides, prevention-oriented source control of soil ARGs should be expanded. In addition, the diffusion mechanisms and influencing factors should be explored further to lay a solid foundation for ARGs reduction technology.

• Effects of Pore-scale Structure of Saturated Soil with Different Cementation Degrees on Groundwater Seepage Characteristic

  HOU Yusong, HU Xiaonong, SU Jingfang, WU Jichun, XING Liting

  DOI: 10.11766/trxb202208180459

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  Abstract:

  【Objective】The study of the groundwater seepage process in saturated soil media is of great importance in many fields, and the differences in the pore-scale structure of soil media have a significant effect on the properties of groundwater seepage. Soil grains cementation degree is one of the basic properties of soil media, but there are few studies on the effect of pore-scale structure differences of soil media with different cementation degrees on the properties of the groundwater seepage process. 【Method】In this paper, related research is carried out based on pore-scale simulation. Soil media with different cementation degrees are constructed based on the global rearrangement algorithm, and the finite element software package is adopted to simulate the flow fields. 【Result】The results showed that as the percentage of cemented soil particles Pc increased from 0 to 60.20%, the variation function of the flow field increased by 70.15% (from 1.233 to 2.098). Namely, the spatial heterogeneity of the flow velocity was significantly increased with increasing cementation degree. In addition, the probability density distribution of the flow velocity along the main groundwater flow direction and perpendicular to the main flow direction were increasingly divergent. The area where the flow velocity was close to the mean velocity decreased, and the stagnant regions and the preferential flow areas extend significantly at the same time. When Pc increased from 0 to 60.20%, the proportion of stagnant regions in the groundwater rose 23 times (from 2.06% to 48.31%), while the proportion of dominant flow areas increased nearly 9 times (from 0.27% to 2.41%). Also, when the average velocity of fluid was different, the above change trends of the seepage characteristics with rising cementation degrees remained the same. 【Conclusion】These findings indicate that the cementation degree of soil particles has a significant effect on the characteristics of the groundwater flow field in saturated soil media. Besides, this paper found that the pore-scale structure differences of soil media with different cementation degrees are the internal reason for the above changes in groundwater seepage process characteristics. The dead-end pore structure formed by cementation, the irregular boundary of the cementation group, and the areas with poor connectivity upstream but connected to the flow area downstream often lead to the appearance of stagnant flow regions. With the increase of the stagnant regions, the fluid flows into the well-connected pores and flows rapidly along these pores. As a result, the dominant flow areas also increased with the rising cementation degree and even formed continuous dominant seepage channels. Under the influence of the simultaneous increase of stagnant regions and the dominant flow areas, the spatial heterogeneity of velocity was significantly enhanced.

• The Traits of Microbial Sulfur Cycling Metabolic Pathways in two red paddy soils developed from different Parent Materials

  lizhitong, kangzongjing, wangzhihui, zhaoyongpeng, yuzijie, jiangxianjun

  DOI: 10.11766/trxb202210090382

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  Abstract:【Objective】The frequent redox alternations in paddy soils make the biochemical reactions of different forms of sulfur active, which has a significant influence on rice production.【 Method】This study aimed to explore the characteristics of sulfur cycling pathways in red paddy soils with different parent materials. Also, the influence of parent materials on the characteristics of sulfur cycling pathways, sulfur metabolizing microorganisms, and the main functional microbial communities responsible for each sulfur cycling pathway; including the organic sulfur transformation pathway, other (transfer) pathway, assimilate sulfate reduction pathway, sulfur oxidation pathway, alienation sulfate sulfur reduction approach and disproportionation.【Result】The two kinds of parent material developed red paddy soils had the same characteristics of the sulfur cycle pathway. The frequency of microbial functional gene abundance in the organic sulfur transformation pathway was the highest, with an average of 16,000 organic sulfur transformation functional genes detected per million annotated bacterial sequences. Also, the frequency of the abundance of sulfur disambiguation pathway functional genes was the lowest, and only 116 genes were detected per million annotated bacterial sequences. At the level of phylum classification, there was no significant difference in the composition of microorganisms leading the sulfur cycle in the two parent soils. Proteobacteria, Acidobacteria and Chloroflexi were the dominant groups, accounting for 55.19%, 10.61% and 7.18%, respectively. There were significant differences in species classification, and the relative abundance of sulfur-cycling microorganisms in paddy soils developed from granitic parent material was higher. The dominant bacteria in all the channels were the Deltaproteobacteria bacterium, Acidobacteria bacterium, and Betaproteobacteria bacterium, and this abundance accounted for more than 40% of the sulfur-circulating microorganisms in granitic parent paddy soil. However, dominant functional microorganisms involved in each pathway of the sulfur cycle were more abundant in paddy soil developed from Quaternary red clay parent material, for example, Gemmatirosa kalamazoonesis had the highest abundance in organic sulfur transformation pathway while Azoarcus sp. was found in other (transport) pathways. The microorganisms with the highest abundance in the assimilation sulfate reduction pathway are Anaeromyxobacter sp.【Conclusion】The same sulfur cycling pathway was observed in paddy soils derived from red earth with two different parent materials. There was no significant difference in the dominant sulfur-cycling microorganisms in paddy soils derived from red earth with two parent materials at the phylum level. However, there were significant differences in species-level classification, indicating that there is unique dominant sulfur transformation functional flora in soils of different parent materials.

• Characteristics of Soil Nitrogen Transformation in Different Clonal Chinese Fir Plantations

  WANG Jing, FU Ruibiao, HAO Zhaodong, ZHENG Renhua, YE Daiquan, ZHENG Xueyan, CHEN Jinhui†, CHENG Yi

  DOI: 10.11766/trxb202210150568

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  Abstract:

  【Objective】This study aimed to reveal the characteristics of soil nitrogen (N) transformation in different clonal Chinese fir plantations in Yangkou National Forest Farm of Fujian. This study provided theoretical basis for artificial nitrogen management and improved seed breeding of different clones of Chinese fir plantations.【Method】An incubation experiment was carried out with 7 different kinds of 15-year old third-generation excellent culture materials and seedlings (Y003, Y008, Y020, Y061, Y062, Ysec and Ymix) as the research objects, and the basic physical and chemical properties, net N mineralization and nitrification rate of soil of different clones were evaluated.【Result】The results showed that the net rates of N mineralization and nitrification were significantly affected by different clonal Chinese fir plantations. Specifically, the net mineralization rate and net nitrification rate were -0.09-0.118 mg?kg-1?d-1 and -0.021-0.051 mg?kg-1?d-1, respectively. During the whole incubation period, the average net soil N mineralization rate of Y061 was 0.117 mg kg-1 d-1, which was significantly higher than that of other clones and followed by Ymix (0.046 mg?kg-1?d-1) and Y062 (0.033 mg?kg-1?d-1). In contrast, the average net N mineralization rates of the other four clones were negative, indicating the occurrence of net N immobilization. The average net soil nitrification rate of the Y008 clone was the highest, which was 0.051 mg kg-1 d-1, followed by Ymix (0.003 mg?kg-1?d-1) and Y020 clone (0.007 mg?kg-1?d-1). There were no significant differences in soil pH, ammonium nitrogen, C/N and the composition of silt and sand, but there were significant differences in soil nitrate nitrogen, organic matter, total nitrogen and clay composition. The results showed that ammonium nitrogen, nitrate nitrogen, pH and total nitrogen in soil were the main factors affecting the net nitrification rate and were all positively correlated, In contrast, the average net nitrification rate of the other four clones was negative, indicating the occurrence of net immobilization of nitrate. There were no significant differences in soil pH and carbon (C)/N among different clones, but significant differences in soil particle size composition, organic matter and total N content. Soil pH and total N were positively correlated with net mineralization and net nitrification rate, while soil C/N was negatively correlated with sand content.【Conclusion】The results showed that the soil N supply capacity and N retention capacity of Y061 and Y062 clones were significantly higher than those of other clones, and the risk of N loss such as leaching in Y008 clones was higher than that of other clones. Therefore, the clone species should be rationally selected to ensure the soil fertility supply in actual planting. This study provides a theoretical basis for artificial nitrogen management and improved seed breeding of different clones of Chinese fir plantations.

• Comparative Study on Prediction of Soil Nutrients by Visible-Near Infrared and Mid-infrared Spectroscopy

  LI Xuelan, LI Decheng, ZHENG Guanghui, ZENG Rong†, CAI Kai, GAO Weichang, PAN Wenjie, JIANG Chaoying, ZENG Yuntao

  DOI: 10.11766/trxb202210040548

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  Abstract:

  【Objective】Predicting soil nutrients by visible-near infrared (vis-NIR) and mid-infrared (MIR) spectroscopy has the advantages of being fast, cost-effective and environmental friendly. Soil spectra contain abundant information of soil properties, and can be combined with machine learning methods to effectively and accurately predict soil nutrients, which can provide support and guidance for timely fertilization management. The objective of this study was to compare the predictive ability of vis-NIR (350-2500 nm) and MIR spectroscopy (4000-650 cm-1) for predicting both the total and available contents of soil nitrogen (N), phosphorus (P) and potassium (K), in order to construct an optimal model for estimation of different nutrient contents. 【Method】In this study, 500 samples were collected from the surface layers (0-20 cm) of the dryland in Guizhou Province for determination of soil N, P and K contents and spectral analysis. The vis-NIR spectra were measured by Cary 5000 and the MIR spectra by Thermo Scientifit Nicolet iS50. Soil spectra were pre-processed by Savitzky-Golay (SG) smoothing for denoising and standard normal variate (SNV) transformation for baseline correction. Partial least squares regression (PLSR) and support vector machine (SVM) were used to predict the contents of total nitrogen (TN), total phosphorus (TP), total potassium (TK), alkali-hydrolyzable nitrogen (AN), available phosphorus (AP) and available potassium (AK). 【Result】The results showed that: (1) Whether using the vis-NIR spectroscopy or the MIR spectroscopy, the prediction accuracy of PLSR model was better than that of SVM model. (2) The accuracy of MIR spectroscopy for prediction of TN, TK and AN was significantly higher than that of vis-NIR spectroscopy. Vis-NIR and MIR spectroscopy could reliably predict TN and TK (ratio of performance to interquartile distance (RPIQ) > 2.10), while MIR spectroscopy could predict AN with moderate accuracy (RPIQ = 1.87). However, both types of spectra had poor ability to predict TP, AP and AK (RPIQ < 1.34). (3) When the variable in the projection (VIP) score was > 1.5, there were more important bands selected by PLSR models in the MIR region than the vis-NIR region. The important bands selected for estimation of TN were mainly concentrated near 1910 and 2207 nm in the vis-NIR region, and centered around 1 120, 1 000, 960, 910, 770, and 668 cm-1 in the MIR region. The important bands of TK were mainly distributed around 540, 2 176, 2 225, and 2 268 nm in the vis-NIR region, and around 1 040, 960, 910, 776, 720, and 668 cm-1 in the MIR region. 【Conclusion】Therefore, MIR spectroscopy combined with PLSR model proved to be promising for accurate prediction of soil nutrients, especially for the estimation of TN and TK, and can provide technical support for guiding timely fertilization.

• Comparative Study on Colloidal Aggregation Kinetics of Brown Earth under Long-term Fertilization

  renkailu, zuoyan, kouqi, zhangguangcai, zhangyun, wangjingkuan, gaoxiaodan

  DOI: 10.11766/trxb202208300347

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  Abstract:

  【Objective】The aggregation of soil colloids is closely related to the formation of soil aggregates. Fertilization can change the environment of soil solution, and affect the formation of soil aggregates, soil structure and soil mineral composition. It is necessary to explore the relationship between the long-term effects of different fertilization on the microscopic properties and interactions of soil colloids and thus the macroscopic phenomena of soils. 【Method】Based on a 35-year long-term fertilization monitoring experiment in the experimental station of brown earth, soils treated with no fertilization (CK), nitrogen fertilizer (N), organic fertilizer (M) and the combination of nitrogen fertilizer and organic fertilizer (N+M) were selected as the research objects in this study. Dynamic light scattering technology was used to monitor the dynamic aggregation process of soil colloids with different fertilization treatments. The effects of fertilization treatments on colloid aggregation were comparatively analyzed through the organic matter content, soil mineral composition and surface chemical properties. 【Result】The soil colloids of the four treatments showed the characteristics of slow aggregation (RLCA) at low electrolyte concentration and fast aggregation (DLCA) at high electrolyte concentration. The order of critical coagulation concentration of four different fertilization treatments was M > N+M > CK > N. Also the long-term application of organic fertilizer increased soil organic matter, thereby increasing the electric field strength near the surface of colloidal particles and the electrostatic repulsion between colloidal particles. Furthermore, the steric hindrance effects of humus weakened the phenomenon of colloid aggregation; On the other hand, long-term fertilization did not change the soil clay mineral composition type, but had an impact on its relative content. The application of organic fertilizer increased the relative content of 2:1 type illite and decreased the relative content of 1:1 type kaolinite. The application of nitrogen fertilizer reduced the relative content of illite and increased the relative content of kaolinite. 【Conclusion】 Different fertilization treatments for a long time changed the basic physicochemical properties and mineral composition ratio of brown earth colloids, which in turn affected the aggregation kinetics of brown earth colloids.

• Bamboo Invades Surrounding Forest Increased Soil pH, Changed Soil Chemical Nutrient and Microbial Community： A Meta-Analysis

  SHI Yusen, WANG Shanshan, FANG Wei, ZHENG Mengqi, JIANG Binghong, SHAO Shuai, MA Xiaomin, XU Qiufang

  DOI: 10.11766/trxb202208210462

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  Abstract:

  【Objective】In the past decades, the surface area of land covered by bamboo (Phyllostachys edulis) in China has rapidly increased. Many studies on bamboo forests have highlighted that bamboo invasion is associated with an increase in the soil pH. The objective of this study was to verify the mechanism by which bamboo invasion increased soil pH as well as to explore the accompanying soil nutrients and microbial properties change trend.【Method】A meta-analysis was conducted to test whether the invasions of bamboo into the adjacent forests lead to an increase in soil pH. The changes in soil nutrients and microbial community after the bamboo invasion were also analyzed. In this meta-analysis, 101 sets of data from 42 studies were collected. Besides data from references, 18 sets of data from 12 plots of bamboo invasion zones from experimental plots were also used to analyze soil pH and nutrient change.【Result】Overall, the results showed that in all the data sets, 84.9% of the soil pH increased by different amplitude after the bamboo invasion. The magnitude of soil pH increased with invasion time but decreased with soil depth. Also, the increase of soil pH in a coniferous forest (CF) was higher than that in a broadleaf forest (BL). The invasive pure bamboo forest (BB) decreased soil total nitrogen (-15.9%, P<0.05), nitrate nitrogen (-21.7%, P<0.05), total organic carbon (-2.0%, P<0.05), but increased soil available phosphorus (+54.9%, P<0.05), ammonia nitrogen (+14.7%, P<0.05) and alkali-hydrolyzable nitrogen (+8.2%, P<0.05) compared with the original forest. In addition, the bamboo invasion also changed soil microbial community structure and the relative abundance of Actinomycetes was increased (+25.86%, P<0.05), while that of Acidobacteria (-15.49%, P<0.05), planctomycetes (-26.66%, P<0.05) and Bacteroidetes (-22.58%, P<0.05) was decreased. Based on the meta-analysis results, the ammonia nitrogen was increased while nitrate nitrogen decreased after the bamboo invasion. It could be inferred that the process of ammonification (NH3+H+→NH4+) was improved while nitrification (NH4++2O2→NO3-+H2O+2H+) was suppressed. Therefore, the possible mechanism of soil pH increase was attributed to the reduction of the accumulation of soil protons released during nitirifcation.【Conclusion】Bamboo invasion into adjacent forests increased soil pH, altered soil chemical properties and microbial community. The effect of bamboo invasion on soil pH is a common phenomenon and the possible mechanism for increasing pH may be related to changes in soil ammonia nitrogen and nitrate nitrogen concentrations.

• The Fate of Fertilizer Nitrogen under Different Straw Returning Methods in Maize Field of Black Soil

  WU Mengna, WANG Shaojie, LAN Chang, YAN Xu, FENG Guozhong, GAO Qiang

  DOI: 10.11766/trxb202207120379

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  Abstract:

  【Objective】Investigating the fate of fertilizer nitrogen in a two-season crop system under different straw returning methods can provide an important basis for nitrogen management under black soil protection.【Method】This study conducted a 15N micro-plot experiment in 2020-2021 at Lishu County of Jilin Province using the 15N tracer technique. Three straw-returning methods were set up: no straw returning (CK), straw deep tillage returning (DTS) and straw mulching with no tillage (NTS). Under each method, two nitrogen levels were set: 180 kg?hm-2 (N1) and 270 kg?hm-2 (N2). 【Result】At maturity stage, 38.0%-46.8% and 12.9%-18.6% of plant nitrogen in the current season and the second season were derived from 15N labeled nitrogen fertilizer, respectively, and fertilizer nitrogen was mainly distributed in grains (59.8%-68.5% in the current season and 59.3%-79.6% in the second season). The utilization, residual and loss rates of fertilizer nitrogen in the current season were 32.4%-43.9%, 32.8%-51.4% and 13.2%-32.7%, respectively. The NTS combined with an appropriate amount of nitrogen fertilizer (180 kg?hm-2) significantly increased the utilization rate of fertilizer nitrogen by 29.5%, while DTS significantly increased the residual rate of fertilizer nitrogen in soil by 18.2%. Also, the utilization and loss rates of fertilizer nitrogen in the second season were 8.5%-14.9% and 5.1%-14.6%, respectively. The cumulative utilization, residual and loss rates were 40.9%-58.8%, 10.4%-26.4% and 18.4%-47.3%, respectively. Compared with CK, NTS treatment significantly increased fertilizer nitrogen utilization efficiency by 18.3% (N1) and 45.9% (N2) in the second season, while the DTS treatment significantly increased fertilizer nitrogen utilization efficiency in the second season by 42.3% under N2. For the total fate of fertilizer nitrogen in two crops, compared with CK, NTS treatment significantly increased the cumulative utilization efficiency of fertilizer nitrogen by 26.4% (N1) and 21.8% (N2), while DTS treatment significantly increased the total residual rate of fertilizer nitrogen by 64.0% (N1) and 72.9% (N2). In addition, the NTS and DTS treatments significantly reduced the total losses of fertilizer nitrogen. Compared with N2, the N1 treatment significantly increased the utilization and residual rates of fertilizer nitrogen and reduced the loss rate of fertilizer nitrogen in two seasons. 【Conclusion】Straw mulching combined with an appropriate amount of nitrogen fertilizer is beneficial to improve fertilizer use efficiency while straw deep plowing is more conducive for the maintenance of fertilizer nitrogen in the soil, especially under high nitrogen application rate, and increases the use efficiency by next crop. Both straw mulching and straw deep plowing could significantly reduce nitrogen loss.

• Progress of soil temperature prediction equation

  Zhang Jianbin, Gao Zhi Qiu, Tong Bing, Wang Linlin

  DOI: 10.11766/trxb202210220581

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  Abstract:

  Soil temperature (especially surface temperature) is a key physical quantity in the interaction between land and atmosphere, and plays a very important role in the earth system. Soil temperature prediction technology has always been the core scientific problem in land surface model, numerical weather prediction and climate prediction. This paper systematically reviews the research progress of soil temperature prediction equation, from the classical heat conduction equation to the heat conduction convection equation that takes into account the physical process of vertical movement of soil moisture, from the single sine wave approximation to the Fourier series approximation of the daily change of surface temperature, from the assumption that the diurnal change of convection parameters is constant to the consideration of its diurnal change, and emphatically summarizes the creation, improvement and solution of the soil heat conduction convection equation. Finally, this paper reviews the application of heat conduction convection equation in the study of surface energy balance, vertical movement of soil moisture, water flux, earthquake and frozen soil heat transfer. At the same time, it is pointed out that the influences of soil water phases and plant roots on the heat conduction-convection equation is warranted for the future research of soil temperature prediction equation.

• Application and Prospect of Biofilm Techniques Based on Quorum Sensing in Soil Pollution Remediation

  Sheng Hongjie, Wang Fang, Feng Fayun, Cheng Jinjin, Zhang Yinping, Ge Jing, Zhang Leigang, Jiang Xin, Yu Xiangyang

  DOI: 10.11766/trxb202208210463

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  Abstract:

  Due to its high efficiency, safety and cost-effectiveness, biofilm remediation technology has been widely used in the removal of refractory pollutants in the environment. Biofilm technology refers to the adhesion, enrichment and reproduction of plankton microorganisms, eventually forming biofilm structure on the surface of the abiotic carrier, which leads to an increase in total biomass density and highly efficient metabolism of hydrophobic and toxic compounds. Compared with planktonic cells, a biofilm matrix can provide microorganisms with stronger resistance to high pressure of survival competition, harsh environmental conditions or harmful toxins. Changes in the local concentration of nutrients in the biofilm matrix and differences in the division of labor among microorganisms can induce differential gene expressions, leading to biofilm cells differing (phenotypically and metabolically) from the planktonic cells. It is beneficial for microorganisms to degrade pollutants through multiple metabolic pathways. Meanwhile, bacteria chemotaxis and flagellar movement can help the microorganism get access to pollutants, thereby improving their biodegradation efficiency. The formation and dispersal of biofilm are regulated by quorum sensing. The generation of extracellular polymeric substances is regulated by signal molecules by quorum sensing (QS), thereby changing the biofilm characteristics and enhancing the bioremediation of pollutants. Quorum sensing is a form of cell-cell communication among microorganisms. Through the diffusion of autoinducers among cellular matrix, bacteria can perceive cell density and species complexity and regulate their gene expressions when the concentration of signal molecules reaches a threshold level. So far, many different structural QS signals have been identified. Although many of them are specific among species, some QS signals can be produced and recognized by many species, thereby allowing inter-species communication. N-acyl homoserine lactones (AHLs) are often employed as QS signal molecules for many Gram-negative bacteria regulated by members of Luxl/R family genes, while Gram-positive bacteria use processed oligo-peptides to communicate. Biofilm formation and dispersal are genetic processes, therefore, they can be manipulated with synthetic biology tools like other genetic systems. Thus, biofilms and the biodegradation of pollutants may be controlled by manipulating signals. Successful application of a bioremediation process relies upon an understanding of interactions among microorganisms, contaminants and carrier materials. At present, more and more researches focus on pollution remediation using engineering biofilm technology, including in-situ and ex-situ bioremediation technology. During this process, quorum sensing or quorum quenching acts a crucial role. Quorum sensing plays a major role in various microbial physiological functions, such as biofilm formation and biofilm repair in polluted environments. Biofilms provide an optimal environment for cell-to-cell interactions, cell-to-cell exchange of genetic material and signals, and dispersal of metabolites. Biofilm quorum sensing technology exhibits an ideal application prospect in the remediation of contaminated soils. For the biofilm QS system, it is very important to clarify the generation rules of signal molecules among microorganisms, as well as the signal conduction path and its mechanism, which is conducive to the engineering design and application of functional bacteria. However, most of the well-studied QS systems are from Gram-negative bacteria. More research is needed to uncover and study the details of QS in a variety of microbial species, including Gram-positive bacteria and fungi. The role of QS in microbial populations, including QS crosstalk and signal specificity, is another important area of research that will impact strategies to regulate biofilm formation and pollutant elimination. Furthermore, QS signals regulation under defined conditions could contribute to the stability of the microbial community and the repair ability of functional microorganisms. Therefore, synthetic biologists should also focus on engineering mixed flora based on biofilm QS systems.

• Bibliometric Analysis of Research on Soil Colloids Affecting the Behavior of Heavy Metals Based on Web of Science

  HU Pengjie, DU Yanpei, XIA Bing, QIU Hao, WU Longhua†, LUO Yongming

  DOI: 10.11766/trxb202207270413

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  Abstract:

  【Objective】With the rapid development of industrialization and urbanization, heavy metal pollution in soil has attracted worldwide attention. Natural soil colloids, as well as engineered nanoparticles introduced into soil by direct or indirect pathways, play an important role in the migration and bioavailability of heavy metals. However, there is a lack of research on the current status and frontier trends of soil colloids"" effect on the behavior of heavy metals. 【Method】Based on the Web of Science (WoS) core collection database, a bibliometric study on the effect of soil colloids on the behavior of heavy metals during 1990—2021 was carried out using analysis tools self-provided by WoS, HisCite citation analysis software, VOSviewer and Citespace visual analysis software. 【Result】Results indicated that the number of publications increased steadily year by year worldwide, with an average increase of two publications per year. The research in this field started late in China but it showed a momentum of rapid development in recent years which may be due to a series of important measures for soil pollution control implemented in China. The countries and research institutions with the most publications in this field were the United States and the Chinese Academy of Sciences, respectively. Environmental Science & Technology was the most published journal. The major subjects involved in this field were the intersection of environmental sciences and ecology. The results of keywords cluster analysis indicated that “particle size fractionation and heavy metal speciation distribution of soil colloids”, “release, deposition of soil colloids and adsorption of heavy metals” and “migration mechanism and migration model of soil colloids” were the dominating research topics. Also, the first dominating research topic tended to describe the state of distribution and morphology of heavy metals in soil with different particle sizes. Furthermore, the second and third dominating research topics tended to focus on the dynamic process of release, migration and deposition of soil colloids, the binding effect of soil colloids on heavy metals and their cooperative transport behavior. The current research hotspot involves the study of the behavior, migration, transformation and bioavailability of engineered nanoparticles in soil using advanced characterization techniques such as field flow-fractionation technology. 【Conclusion】These results provide important insights into the research direction, growing trend and research hotspots in the field of soil colloids affecting the behavior of heavy metals. In the future, it should be prioritized that the application of field-flow fractionation technology combined with single particle inductively coupled plasma mass spectrometry or other technologies to further study the complex interaction between soil colloids and engineering nanoparticles. Also, the influence on the migration and environmental fate of engineered nanoparticles is expected to be a future research direction.

• Exogenous Phosphorus Addition Can Increase Phosphorus Bioavailability in Paddy Soil of Different Cultivated Years

  CAO Hua, LI Huan, FAN Huilin, NIU Ben, WANG Yanling

  DOI: 10.11766/trxb202205230266

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  Abstract:

  【Objective】Phosphorus is an essential nutrient element that affects crop growth, yield enhancement and quality improvement. Due to the application of a large amount of phosphate fertilizer and the lack of scientific management, the utilization rate of phosphate fertilizer is low and the environmental risk increases. Thus, it is important to know the effects of different amounts of exogenous phosphorus (P) addition on P bioavailability components in paddy soil under flooding conditions.【Method】Three soil samples were collected from the new paddy field (NP, 2-3 years), medium-term paddy field (MP, 20-30 years) and old paddy field (OP, 400-500 years) in Sunjia small watershed of Yingtan, Jiangxi Province. Based on the flooding culture experiment (0-80 days) with different concentrations of exogenous P addition [0 (CK), 125 (P1), 250 (P2), 500 (P3), 625 (P4), 750 (P5) mg?kg-1], the test for simulating the bioactivation process of biologically based P (BBP method) was adopted. The dynamic changes in the increment (?) of soluble P (Ca-P), easily activated and released P (Ci-P), easily mineralizable acid phosphatase (En-P), and the potential inorganic P (HC-P) were analyzed, and the correlation between all P components and influencing factors were evaluated.【Result】The results showed that under flooding conditions, exogenous P addition could significantly increase the available P (Bray-P) and BBP components such as Ca-P, En-P, Ci-P and HC-P in paddy soil, and the increment of P contents of each component increased significantly with an extension of P addition. The increment of BBP components was changed by the order: ?Ca-P < ?En-P < ?Ci-P < ?HC-P. On day 15 of incubation, the ?Ca-P and ?Ci-P in the new paddy field reached a maximum value while on day 60, the ?Ca-P, ?En-P, ?HC-P and ?Bray-P in the medium-term paddy field reached their maximum value. However, the P content of each component did not change significantly in the old paddy field. The ratio of ΔBray-P to ΔTP (ΔBray-P/ΔTP) in paddy soil after exogenous P addition showed the same trend as that of ΔBray-P, but there was no significant difference among different P additions. Path analysis showed that exogenous P addition had a significant direct positive effect on ?Bray-P in new and old paddy soil; ?Ci-P had a significant direct positive effect on ?Bray-P in new paddy field; ?HC-P and ?Ca-P had a significant direct positive effect on ?Bray-P in medium-term paddy field, and ?En-P had a significant direct positive effect on ?Bray-P in old paddy field.【Conclusion】Although exogenous P addition can significantly increase the components of the bioavailability of P in paddy soil, the emergence stage of the maximum increment bioavailability of P in paddy soil is different. Therefore, it is of great significance to timely and appropriately apply P fertilizers for the improvement of P fertility and the risk control of P loss in paddy fields.

• Study on the Characteristics of Soil Nitrate Nitrogen Accumulation of Rare Earth Tailing in Southern Jiangxi

  XU Zhe, YANG Jinling, ZHAO Yue, ZHANG Ganlin

  DOI: 10.11766/trxb202207280415

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  Abstract:

  【Objective】Rare earth mining excessively increased the content of leaching agents (e.g. ammonium sulfate) in the soil. The high concentration of ammonium nitrogen (NH4+-N) may be converted into nitrate nitrogen (NO3--N) under active biochemical action, resulting in potential environmental risks, especially nitrate pollution of water bodies around tailings. Therefore, it is necessary to evaluate the content of soil NO3--N, explore the influencing factors and understand the nitrate pollution degree of the rare earth tailings. 【Method】We chose an ionic rare earth tailing after in-situ mining in southern Jiangxi province, which used ammonium sulfate as a leaching agent. Up to sampling, this mine had been closed for 4 years. We set three sampling points regularly from the top to bottom of this mine and collected soil profile samples in different layers from the topsoil to the bedrock. Soil samples were divided into two parts. One part was stored at a low temperature to analyze soil nitrate nitrogen and ammonium nitrogen. The other one was used for analyzing relevant physical and chemical properties after air drying. 【Result】The results showed that the variation range of soil NO3--N content in the tailing area was large (2.80 to 193.99 mg·kg-1), with a mean of 46.30±55.16 mg·kg-1. The average content of topsoil NO3--N was 5.16 mg·kg-1, which was similar to that of natural soil. Also, the average content of soil NO3--N in ore-bearing layers was 48.64 mg·kg-1, which was nearly 10 times that in the natural soil. The soil NO3--N of the ore-bearing layer in the deep profile was higher than that of the top layer. Moreover, the distribution of NO3--N with depth was different from that of the natural soil and was mainly caused by a large number of leaching agents remaining in the ore body. NH4+-N content dominated the generation of NO3--N and determined the upper limit of soil NO3--N accumulation. The accumulation degree of NO3--N in different soil layers and different parts of mountains was controlled by rainfall leaching and the NO3--N migration process. However, the soil""s physical and chemical properties, including water content, cation exchange capacity and particle composition, had no significant correlation with NO3--N content, and were not the determining factors of NO3--N content. 【Conclusion】The soil NO3--N in the tailing mainly originated from nitrification. Four years after mining, a large amount of NH4+-N remained in the tailing, and the NO3--N generated by nitrification was continuously released into the environment. In the long term, the soil NH4+-N enriched in tailing will be transformed into NO3--N and the NO3--N will migrate with water, threatening the ecological environment and human health. This study can provide a theoretical basis and scientific reference for the assessment and treatment of soil and downstream water pollution in rare earth in-situ leaching sites.

• Influencing Mechanisms of Humic Acid and pH on the Migration Behavior of Typical Tire Wear Particles

  LI Kun, KONG Deyue, CHEN Xingyue, PENG Yonghong, XIU Xiaojia, SU Han, PAN Minyu

  DOI: 10.11766/trxb202206200329

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  Abstract:

  【Objective】Tire wear particles (TWPs), as one of the important types of microplastics (MPs), have received a lot of attention from ecologists for their ecological risk in recent times. Usually, the environmental behavioral processes of particulate pollutants are important influencing factors of their ecological risk. However, the migration process and influencing mechanisms of TWPs in porous media such as soil have not been reported so far. 【Method】In this paper, C-TWPs prepared by freezing crushing and R-TWPs (rolling friction) and S-TWPs (sliding friction) produced by road wear were selected as typical research objects, and quartz sand columns were used to simulate and study the migration behavior of TWPs in environmental porous media such as soil, and to investigate the effects of natural organic matter humic acid (HA) and different pH (4, 7 and 10) environments on the migration behavior of the above three types of TWPs.【Result】The results showed that HA (50 mg?L-1) significantly enhanced the mobility of the three types of TWPs, and the migration behavior of TWPs was differently affected by different pH (4, 7 and 10) environmental conditions in the presence of HA (50 mg?L-1), with the medium-alkaline environment (pH = 7/10) being more favorable for the migration of TWPs. This was mainly due to an increase in the negative zeta potentials of the surfaces of TWPs and quartz sand particles in the presence of HA and/or the medium alkaline environment (simultaneously). Also, the dispersion of TWPs was improved for smaller particle size distribution while the electrostatic repulsion between TWPs and quartz sand particles was increased, which contributed to the migration of TWPs. It is worth noting that the migration of C-TWPs prepared by low-temperature crushing was stronger than that of R-TWPs and S-TWPs in the presence of HA and under different environmental pH conditions. This was mainly attributed to the fact that C-TWPs carried a larger negative charge, smaller isoelectric point and stronger hydrophobicity, and these properties also contributed to the adsorption of more HA, thus enhancing their electronegativity. Nevertheless, R-TWPs and S-TWPs had less electronegativity on the surface due to the adhesion of road minerals, metal salts or dust that reduced the magnitude of the mentioned properties.【Conclusion】These results reveal the variability of the geochemical transport behavior of different types of TWPs in nature and suggest the necessity of studying the source properties (discharge mode) to determine the inherent differences in environmental behaviors and ecological risks of microplastics of the same material.

• Effect of Manure with Biomass Carbon on Forms of Nutrients and Nitrogen in Rhizosphere / Non-Rhizosphere Soils

  LI Yue, WANG Ying, XIONG Zi-yi, XIE Jun, WANG Zi-fang, GAO Ming

  DOI: 10.11766/trxb202206200331

  Abstract(132) HTML(0) PDF(1.34 M)( 448) Collect

  Abstract:

  【Objective】To clarify the effects of fertilizer and organic fertilizer combined with biochar on the forms of nutrients and nitrogen in rhizosphere / non rhizosphere soil, which is helpful for the efficient utilization and scientific management of farmland nitrogen .【Methods】Taking the pot experiment of lemon as the research object, this paper set up six treatments: no fertilizer (CK), chemical fertilizer (CF), manure (M), chemical fertilizer with biochar (CFB), manure with biochar (MB) and fresh manure with biochar (FMB). By measuring the changes of nutrient content in rhizosphere and non rhizosphere soil and the transformation of soil nitrogen storage forms, the effects of organic fertilizer combined with biochar on the forms of soil nutrients and nitrogen in rhizosphere and non rhizosphere were studied. 【Result】The results showed that compared with CK treatment, MB treatment increased non rhizosphere and Rhizosphere Soil pH by 0.32 and 0.28 units, and FMB treatment increased rhizosphere soil pH by 0.63 units; MB and FMB treatments increased the content of organic matter in rhizosphere soil by 25.37% and 84.88% respectively, and significantly increase the total nitrogen content of Rhizosphere Soil by 25.42% and 50.93%. Combined application of biochar (CFB, MB and FMB) could promote the transformation of soil non convertible nitrogen (NTF-N) to two more active nitrogen forms, iron manganese oxide bound nitrogen (IMOF-N) and organic sulfide bound nitrogen (OSF-N). IMOF-N and OSF-N accounted for 35.85%~61.72% and 26.65%~46.56% of convertible nitrogen, respectively, and were the main components of rhizosphere and non rhizosphere soil convertible nitrogen (TF-N). Therefore, manure combined with biochar is the most effective way to improve nutrients and regulate nitrogen transformation in rhizosphere and non rhizosphere soil.