Insights and Perspectives

• Re-thinking the Establishment of the Farmland Soil Health Assessment System

  ZHANG Jiangzhou, WANG Guangzhou, LI Yizan, ZHANG Wenju, ZHANG Junling, ZHANG Fusuo

  2024,61(4):879-891, DOI: 10.11766/trxb202310020406

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  Abstract:

  Healthy soil is the foundation for food security, farmland productivity, and high-quality agricultural development. Currently, soil health assessment has globally become the focus and hotspot of the soil science discipline. The selection of soil health assessment methods and indicators has been systematically summarized. However, there is still a lack of practical suggestions for specific evaluation processes. This paper focuses on analyzing the characteristics of soil health and multifunctionality, the general principles of soil health evaluation, the n+X model for selecting indicators, and the selection and implementation of evaluation methods. We propose the soil health gap and benchmark, the selection of basic and restrictive indicators, as well as the adaptability of indicator selection. In addition, the establishment of a soil health indicator system needs to take into account factors such as soil texture, crop type, land use, and climate conditions. The implementation of soil health technology and paradigm needs to be integrated with relevant policies. In the future, it is necessary to further research the driving mechanisms of soil health and the cultivation of healthy soils. Based on long-term experiments and monitoring networks for farmland quality, the soil health indicator system, threshold, database, and decision support system were established depending on soil texture, crop type, land use, management objectives, and evaluation scales. Combined with relevant policies and regional environmental constraints, a consensus, convention, and action across regions and countries should be formed to promote the implementation of global soil health action and sustainable agricultural development.

Reviews and Comments

• Research Progress on Soil Pollution Characteristics in China and Bioaccessibilities of the Priority-controlled Polycyclic Aromatic Hydrocarbons at Home and Abroad

  CHEN Mengfang, ZHOU Yuan, HAN Lu, LI Yilian, CHEN Xueyan, HOU Shaolin, LI Jing

  2024,61(4):892-915, DOI: 10.11766/trxb202304170151

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  Abstract:

  Polycyclic aromatic hydrocarbons (PAHs) are a class of persistent organic pollutants, which readily accumulate in the soil with significant toxicity. However, PAHs could be strongly adsorbed by the solid phase of soil, the exposure based on the total pollution mass will lead to the overestimation of human health risks. Based on 123 papers published from 2000 to 2020, this study summarized the distribution and composition characteristics of soil concentrations of 16 priority-controlled PAHs (Σ₁₆PAHs) in China, introduced 11 commonly used testing methods and main influencing factors for modelling bioaccessibilities, and summarized the ranges of bioaccessibility coefficients of PAHs. The results showed that the maximum and average concentrations of Σ₁₆PAHs in soil were 23 250 and 1 314.7 μ·kg^-1 respectively. In recent years, mainly based on the physiologically-based extraction tests (PBET), the bioaccessibility test methods of PAHs are continuously improved and modified in enriched simulation of digestion processes and adsorbents, while the digestion conditions and soil properties etc. have a great impact on the bioaccessibility results. The average bioaccessibilities of 16 PAHs ranged from 13.2% to 72.4%, among which higher values were identified for chrysene and benzo (b) fluoranthene, contributing significantly to the total Σ₁₆PAHs exposure. This study therefore provided an important theoretical ground for undertaking detailed risk assessment of PAHs.

• Recent Advances in Hydrogen Metabolism and Its Environmental Bioremediation Function

  XU Yongfeng, TENG Ying, LUO Yongming

  2024,61(4):916-928, 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

  2024,61(4):929-938, 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.

Research Articles

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

  YANG Kai, CI En, LIU Bin, CHEN Yangyang, XIE Yu

  2024,61(4):939-951, 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

  2024,61(4):952-963, 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.

• 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

  2024,61(4):964-977, DOI: 10.11766/trxb202212060674

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  Abstract:

  【Objective】To elucidate the effects of freeze-thaw cycles and initial water content on soil 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), and the aggregate turnover process were measured accordingly. 【Result】The results showed that freeze-thaw cycles significantly reduced MWD, > 0.25 mm aggregates and < 0.053 mm aggregates proportions, 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 (P< 0.05) higher under T50 compared with that under T100, but there were no significant differences between the contents of 5～2 mm and < 0.25 mm aggregates. Except for 5～2 mm aggregates, the intensive transformation between neighboring size aggregates was observed during the whole simulation experiments. In the same freeze-thaw cycles, the transformation proportions from 5～2 mm to 0.25～0.053 mm aggregate were significantly (P < 0.05) higher under T100 compared with T50 treatment. 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. Also, 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 remarkably increased with the freeze-thaw cycles (P < 0.05) and the aggregate turnover time of > 0.25 mm aggregates was higher than that of < 0.25 mm aggregates. Comparatively, the aggregate turnover time was significantly higher under T100 than that under T50 with the same freeze-thaw cycle (P < 0.05). 【Conclusion】The freeze-thaw cycles and soil initial water content significantly affect the aggregate turnover. Both parameters change the stability of soil structure by affecting the aggregate formation and fragmentation processes. The results provide a theoretical basis for further exploration of the structural changes of black soil under freeze-thaw cycles.

• 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

  2024,61(4):978-988, DOI: 10.11766/trxb202301060007

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  【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%,PR² = 66.0%, P<0.01), while capillary porosity demonstrated a noteworthy negative correlation. Among the soil sesquioxides, aluminum oxides (Al_d, Al_o) 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.

• Error Analysis of Soil Hydrothermal Parameters Synchronization Measurement Using Active Heated Fiber Optic

  HU You, SI Bingcheng, LI Min, HE Hailong, HE Dong, REN Hengye, LIU Lügang

  2024,61(4):989-997, DOI: 10.11766/trxb202301160020

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  Abstract:

  【Objective】Soil hydrothermal parameters are fundamental physical parameters for studying soil thermal and hydraulic transport. Currently, the heat pulse probe HPP) method can synchronously measure soil hydrothermal parameters. However, but this method is limited to point-scale measurements, while the active heated fiber optic (AHFO) method holds the potential to extend the measurement scale to field-scale kilometers. 【Method】To investigate the errors of AHFO, we conducted comparative experiments between the AHFO and the HPP methods for measuring soil hydrothermal parameters. 【Result】 The results showed that, using the HPP method as a reference, the root mean square error (RMSE) of thermal conductivity measured by the AHFO method was 0.13 W·m^–1.·℃^–1. The thermal conductivity measured by the AHFO was significantly higher than that by the HPP method. This difference was attributed to the significant increase in temperature during the measurement by fiber optic which led to a temperature effect on the soil thermal conductivity around the fiber optic.【Conclusion】The measurement of error order of soil hydrothermal parameters using the AHFO method mainly originates from the contact thermal resistance between multiple interfaces (fiber optic core-air layer-metal layer-sheath-soil), the temperature sensitivity of the fiber optic, noise interference, and moisture migration under temperature gradients. This study can provide a theoretical reference for improving the accuracy of soil hydrothermal parameter determination by the AHFO method.

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

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

  2024,61(4):998-1008, DOI: 10.11766/trxb202212010665

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  【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 (K_s). 【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·^–3 compared to 0.19(0.14-0.23) cm³·^–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 K_s in the vertical direction (64.67 cm·d^–1)than in the horizontal direction (82.84 cm·d^–1) in the tillage layer. The K_s decreased in a larger degree in the vertical direction and less degree in the horizontal direction. Thus, this heterogeneity of K_s 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 K_s 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.

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

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

  2024,61(4):1009-1020, 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 (C_r) was 14.84% higher than that of grassland with tap roots. The expression effect of C_ron 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 C_ron 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.

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

  SHI Yangxiaoxiao, JIANG Jun, LI Kewei, XU Renkou

  2024,61(4):1021-1030, 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, dithionite-citrate-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.

• 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

  2024,61(4):1031-1041, 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^–1and 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.

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

  JI Guojun, JI Hongting, CHENG Kun, LIU Manqiang, JIANG Yu, HU Zhengkun, ZHANG Yuefang, HU Naijuan, HU Feng

  2024,61(4):1042-1054, DOI: 10.11766/trxb202212180695

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  Abstract:

  【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.

• 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

  2024,61(4):1055-1065, 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 302 and 243 nmol CH₄·g^–1 d.w.s·h^–1, respectively. The abundance of MOB increased by 1.1 folds -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 Free-air CO₂ Enrichment and Temperature Increase on Related Proteins and Defense Enzymes in Plants Infected with Rice Sheath Blight

  SHEN Min, CAI Chuang, SONG Lian, ZHANG Jishuang, TAO Ye, WANG Dongming, YANG Xiong, WEI Wei, ZHU Chunwu

  2024,61(4):1066-1076, DOI: 10.11766/trxb202302220074

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  Abstract:

  【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 Phosphogypsum on Coastal Saline-sodic Soil and the Growth of Winter Wheat

  WU Hongsheng, CHEN Xiaoqing, MA Wenzhou, WANG Xiaoyun, CHENG Cheng, DING Jun, LI Yanhui, LIU Zheng, DUAN Yajun, DI Mingchun, LI Zhenwei, FENG Yingcheng, SHI Youhua

  2024,61(4):1077-1087, DOI: 10.11766/trxb202302010038

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  【Objective】There are about 0.66 million hectares of coastal saline-sodic soil in Jiangsu that have not been developed and used as arable land for agriculture. This is because the saline-sodic soil has a higher concentration of salt that requires urgent ameliorating. 【Method】This study used waste phosphogypsum (PG), a kind of by-product from the phosphate industry, to conduct an amelioration experiment of saline-sodic soil in the field. Eight treatments were employed in the field experiment: no fertilizer and PG, fertilizer but no PG, and compound fertilizer + different amounts of PG. 【Result】Results showed that pH was decreased by 0.07～0.40 pH units in the depth of 0～20 cm topsoil treated with PG compared to the control. Soil bicarbonate and sodium ions decreased by 15.81%～43.53% and 17.25%～89.83%, respectively. The concentration of potassium ion, calcium ion, and organic matter in the amended soil treated with PG was increased by 8.17%～384.90%, 59.51%～1977.72%, and 4.51%～19.50%, respectively. Also, the amounts of total N and P in the wheat leaves in the PG treatment were increased by 7.85%～26.21% and 5.02%～35.97%, respectively, and the wheat grain yield increased by 11.41%～45.26%. Overall, PG can be used to ameliorate costal saline-sodic soil with better effectiveness. Mechanistically, the increase in calcium ions occurred as PG exchanged with sodium ions adsorbed in soil, and the sodium ions were leached underground during irrigation and rain to decrease the soil pH. Also, some acid-containing groups in PG were able to neutralize the bicarbonate ions to decrease the soil pH. PG increased the N uptake in wheat leaves and the yield of wheat grain due to the increased P from PG which induced a proportionate uptake of nutrients by the plant. Comprehensively, the best performance was the treatments of 30% compound fertilizer (1050 kg`hm<sup>-2</sup>)＋ PG (1125 kg`hm^-2) and 30% compound fertilizer (1050 kg`hm<sup>-2</sup>)＋ PG (2250 kg`hm^-2).【Conclusion】The positive effect of PG should not be considered proportional to the amount applied, because trace hazardous elements in PG could accumulate in the soil which will result in environmental risks and grain safety issues. Thus, proper care should be taken when using high doses of PG for soil amendment.

• 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

  2024,61(4):1088-1098, DOI: 10.11766/trxb202212130689

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  【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 PO₄^3- 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 PO₄^3- asymmetric stretching vibration v₃, H₂PO₄^- associated absorption peaks, and HPO₄^2- 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<sup>-1</sup> 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.

• 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

  2024,61(4):1099-1110, 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.

• 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

  2024,61(4):1111-1122, 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%, 1.33 times and 1.75 times. 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 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

  2024,61(4):1123-1133, 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.

• 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

  2024,61(4):1134-1146, 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.

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

  WANG Guoxi, WANG Ping, LIU Yalong, WANG Jingkuan

  2024,61(4):1147-1155, 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, published data in recent years (332 sets of data from 19 literature) were collected, the distribution characteristics of glomalin in soil aggregates were quantitatively analyzed, and its influencing factors were systematically analyzed. Moreover, the distribution of glomalin in soil aggregates under different land uses was compared. 【Result】The results showed that the mass 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, it was 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 farmlands and grasslands.

• 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

  2024,61(4):1156-1165, DOI: 10.11766/trxb202302120058

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  Abstract:

  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%-89.01%. 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.

• 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

  2024,61(4):1166-1178, 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^-1of 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^-1Fe₃O₄NPs reduced seed germination. However, seed germination was improved as the concentration of Fe₃O₄NPs was increased. Under 100 mmol·L^-1NaCl stress, the seed germination potential and hypocotyl length after soaking in 200 mg·L^-1Fe₃O₄NPs reached the peak, which was significantly higher than those treated with salt stress only. Salt stress of 100 mmol·L^-1NaCl 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^-1Fe₃O₄NPs. 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^-1Fe₃O₄NPs 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^-1Fe₃O₄NPs 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^-1Fe₃O₄NPs 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.

• Isolation, Identification, and Characteristics of Autotrophic Nitrogen-fixing Bacteria in Vegetation Concrete Under Freeze-thaw Conditions

  LIU Daxiang, XU Zhihai, GAO Xian, XU Boyang, ZHENG Wei, XIA Dong, XU Wennian, YANG Yueshu

  DOI: 10.11766/trxb202312110525

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  【Objective】This study aimed to isolate and identify autotrophic nitrogen-fixing bacteria in vegetation concrete under freeze-thaw conditions and to investigate their effects on the physical and chemical properties of vegetation concrete and the growth of ryegrass. 【Method】Autotrophic nitrogen-fixing bacteria GDJ-1 and GDJ-2 were isolated from vegetation concrete that had experienced multiple freeze-thaw cycles by selective nitrogen fixation medium. The strains were identified by morphological, physiological, and biochemical characteristics, 16S rDNA, and phylogenetic analysis. The effects of target strains on physicochemical indexes of vegetation concrete and the growth of ryegrass were explored. 【Result】Strain GDJ-1 was identified as Microbacterium proteolyticum, a Gram-positive bacterium with a round yellow colony. The strain GDJ-1 did not produce oxidase but was capable of producing catalase and it could not degrade gelatin or hydrolyze starch. This bacterium exhibited favorable growth under pH levels that ranged from 7 to 9 and in the presence of sodium chloride (NaCl) concentrations between 0.5% and 2%. After treatment with GDJ-1, the aboveground fresh biomass, aboveground dry biomass, belowground fresh biomass, and belowground dry biomass of ryegrass increased by 29.09%, 5.05%, 13.40%, and 16.40%, respectively, compared with the control group. The contents of organic matter, total nitrogen, alkali-hydrolyzed nitrogen, and available phosphorus in vegetation concrete were increased, and the increase of alkali-hydrolyzed nitrogen was 62.95%. Furthermore, strain GDJ-2 was Ralstonia pickettii, a Gram-negative bacterium with a round beige colony. The strain GDJ-2 produced oxidase but did not produce catalase, and was capable of hydrolyzing gelatin and starch. It exhibited favorable growth under conditions with a pH range of 7 to 9 and a sodium chloride (NaCl) concentration of 0.5% to 2%. After treatment with GDJ-2, the aboveground fresh biomass, aboveground dry biomass, belowground fresh biomass, and belowground dry biomass increased by 35.71%, 4.93%, 46.38%, and 13.79%, respectively, compared with the control group. The contents of organic matter, total nitrogen, alkali-hydrolyzed nitrogen, and available phosphorus in vegetation concrete were increased, and the increase of available phosphorus reached 35.73%.【Conclusion】There were great differences in morphology and enzyme metabolism between the two strains, but both were capable of enhancing the nutrient condition of vegetation concrete and promoting the growth of ryegrass. In the ecological restoration of vegetation concrete, autotrophic nitrogen-fixing bacteria GDJ-1 and GDJ-2 displayed application potential. GDJ-1 possessed a robust nitrogen fixation ability, effectively converting nutrients in the soil, which was more suitable for regions where the soil was poor or lacking nutrients. However, GDJ-2 demonstrated superior environmental adaptability, especially exhibiting heightened tolerance to alkaline environments, making it more fitting for regions with stringent conditions such as saline-alkaline soils. Considering the necessity for nutrient balance in actual engineering projects, further research can be conducted on freeze-thaw tolerant indigenous phosphate-solubilizing, potassium-releasing, and cellulose-decomposing bacteria, to develop a composite bio-agent tailored for vegetation concrete ecological restoration in freeze-thaw areas.

• Effects of Bacterial Residue Organic Fertilizer on Tomato Growth and Soil Antibiotic Resistance Genes Accumulation

  CUI Gege, ZHANG Yaozhong, YANG Tianjie†, WANG Shimei, HUANG Yishuo, XU Yangchun, SHEN Qirong

  DOI: 10.11766/trxb202402180072

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  【Objective】Bacterial residue is a solid waste produced during the fermentation process of antibiotic synthesis intermediate (6-aminopenicillanic acid). Improper treatment will endanger environmental safety and increase the risk of the spread of antibiotic resistance genes (ARGs). At present, composting is the main method for treating residues due to its harmless and resourceful characteristics. Thus this study was designed to investigate the effects of composted bacterial residue organic fertilizer on tomato growth and soil ARGs accumulation and to assess the ecological risks of residue organic fertilizer. 【Method】In a field experiment, the tomato plant was used as the research object and the effects of organic fertilizer fermented from bacterial residue of penicillin synthesis intermediates on tomato growth, soil physicochemical properties, bacterial community structure, and the diversity and abundance of antibiotic resistance genes were analyzed【Result】The results showed that the application of residue organic fertilizer can increase the aboveground dry biomass of tomatoes in the field, and continuous application for two seasons can increase the vitamin C content of tomato fruits and soil nitrate nitrogen content. After being treated with organic fertilizer, there was no significant change in the diversity of bacterial communities in the rhizosphere soil. However, compared with conventional fertilization, the abundance of Proteobacteria significantly increased, while the abundance of Chloroflexi significantly decreased. There was no significant change in the diversity of ARGs in tomato soil after the application of residue organic fertilizer, but the amino glycoside resistance gene aada1 and sulfonamide resistance gene sul (II) were significantly higher than those in conventional compound fertilizer treatment. Also Luteimonas sp. was positively correlated with tetracycline, aminoglycoside, and sulfonamide resistance genes. 【Conclusion】After applying microbial residue organic fertilizer in tomato rhizosphere soil, there was no enrichment of β-lactam ARGs. However the risk of accumulation of tetracycline, aminoglycoside, and sulfonamide ARGs in rhizosphere microorganisms needs further evaluation.

• Mechanisms of Mn-modified Biochar to Mediate Inorganic Arsenic Speciation in the Soil-Solution System

  HUANG Qin, TONG Fei, WANG Bo, DU Xiaofei, FAN Guangping, LIU Lizhu, ZHANG Mingchao, QIU Yige, GAO Yan

  DOI: 10.11766/trxb202401030007

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  【Objective】The reductive release of arsenic (As) from paddy soils can be enhanced under waterlogged conditions. This study aimed to investigate the mechanisms of Mn-modified biochar (MBC), with high oxidation and adsorption capacity, on inhibiting As release in the waterlogged paddy soil microcosms and to reveal the potential pathways of mediating As transformation and speciation in soil solution and soil. 【Method】This study determined changes in the basic properties of soil solution, soil, and biochar through mixed or separate incubation of biochar and flooded soil. 【Result】The results showed that, compared with the control and unmodified biochar, MBC significantly promoted the oxidation of As(III) to As(V) in the soil solution, keeping a low concentration of As(III) (0.02-0.88 mg?L-1) throughout the incubation period. The Mn released from MBC into the soil solution was readily precipitated with As(V). Also, the MBC containing rich pore structure and oxygen-containing functional groups would promote its adsorption for more inorganic arsenic (iAs). MBC showed greater affinity for Fe (3.12 mg?g-1 of Fe was adsorbed on MBC after 28 d), leading to a significant decrease of Fe concentrations in the soil solution (P < 0.05) and enhanced the adsorption of iAs on the solid-phase. The reduction of Mn-oxides on MBC increased the pH (0.08-0.22 pH units) of the soil solution, which further promoted the precipitation of Fe on the solid phase thereby strengthening its adsorption for iAs. As a result, the concentration of iAs extracted from the MBC was 12 times higher than that of the unmodified biochar after incubation of 28 d. The high oxidative properties of MBC inhibited the reductive dissolution of Fe minerals, thereby significantly reducing the soil-available Fe and As concentrations (P < 0.05). This led to the transformation of soil available As to iron-manganese bound and residual fraction As. As a result, the soil available As was stabilized under a lower range of concentrations. 【Conclusion】Generally, the addition of MBC to waterlogged paddy soil can inhibit the release of iAs from the solid phase and promote the transformation of mobile iAs into more stable forms in the soil, resulting in a significant reduction in arsenic mobility and toxicity in waterlogged paddy soil.

• Effect and Mechanism of Food Waste Compost on the Stability of Paddy Soil Aggregates

  AO Hui, CHEN Chong, ZHOU Hu

  DOI: 10.11766/trxb202402240077

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  【Objective】 Food waste composting is one of the potential directions of food waste resource utilization. Food waste compost is rich in organic matter and salt, and its impact on soil aggregates is still unclear. Exploring the influence of food waste compost application on the stability of paddy soil aggregates and its mechanism can provide references for agricultural utilization of food waste compost. 【Method】 Six treatments were set up in this study: No fertilizer (CK), Chemical fertilizer (F), Food waste fresh compost (FC), Food waste aged compost (AC), Chicken manure organic fertilizer (CM), Pig manure organic fertilizer (PM), The effects of these treatments and the influence of food waste compost on the stability of soil aggregates and soil surface electrochemical parameters were investigated. Correlation analysis and redundancy analysis (RDA) were used to investigate the main factors affecting the stability of aggregates. 【Result】 The results showed that: (1) Food waste compost enhanced the water stability of paddy soil aggregates, and reduced the slaking and differential swelling effects. Also, the MWDYoder, MWDLB-fast, and MWDLB-slow of AC were 21.4%, 107.8%, and 49.3% higher than CK, respectively. (2) The electrochemical properties of the soil surface were the main factors affecting the stability of aggregates and the surface charge density of the four organic fertilizers increased by 29.0%-45.2%. (3) Organic matter has a significant correlation with surface charge density, specific surface area, and surface charge number, and the correlation coefficients are 0.67, 0.53, and -0.63, respectively. Furthermore, exchangeable calcium showed a significant positive correlation with organic matter and the correlation coefficient was 0.90. 【Conclusion】 Food waste compost can enhance the surface charge density of soil by increasing soil organic matter, thus increasing the cementation between exchangeable calcium and soil particles and enhancing the stability of soil aggregates.

• Research on Soil Type Inference Based on Combinatorial Cartography Method

  LI Kun, HUANG Wei, FU Peihong, CHEN Yuhao, WANG Ziying

  DOI: 10.11766/trxb202402030056

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  【Objective】For the rational use of land resources, it is important to obtain accurate spatial distribution of soil types using digital soil mapping technologies.【Method】In this study, environmental factors were screened according to the soil parent material type based on field sampling points, and then three different mapping methods, random forest, SoLIM, and KNN, were used to map the zones according to the selected environmental factors, respectively. Each method was used individually to generate zoning maps, providing different reasoning for the spatial distribution of soil types. The zoning mapping results were obtained and combined to form a universal spatial distribution map of soil types, and then, we used the FP-Growth algorithm to effectively mine the internal correlation between environmental factors. By combining these associations with different mapping results obtained previously, the spatial distribution of soil types in the study area was deduced and used to obtain higher quality and precision inference results. 【Result】The mapping results revealed several key findings: (1)The independent mapping of soil type based on the parent material type of soil by three different mapping methods is more effective and accurate than the joint mapping of all parent materials, and the inference of spatial distribution of soil types is also more reasonable. (2) Among the three mapping methods adopted in this study, the method combining random forest and frequent itemset mapping had the highest accuracy of 70.73%. Moreover, the results obtained by this combined method are similar to the spatial distribution of soil types inferred by the other two combined methods. Through comparative analysis, we were able to determine the approximate spatial distribution of soil species in the study area. (3) After the three mapping methods were combined with frequent itemsets, we observed that all methods had different degrees of improvement in accuracy verification and Kappa coefficient. Among them, the KNN method had the most significant improvement effect, the total mapping accuracy increased by 9.76%, and the Kappa coefficient increased by 11.70%. On the contrary, the random forest method had the smallest improvement, wherein, the total mapping accuracy and the Kappa coefficient increased by 4.88%, and 5.85%, respectively. These results validate the effectiveness of the combination method designed in this study. 【Conclusion】The first, aspect of this study aimed to investigate the influence of soil parent material type on environmental factor screening. This aspect had relatively important reference significance for selecting appropriate environmental factors in the process of digital soil mapping. On the other hand, by combining frequent itemsets with the three different mapping methods used, this study not only provides a new method and idea for the exploration and application of digital soil mapping, but also provides a useful reference for the information application of frequent itemsets association.

• The Influence of Ion Interface Reaction on the Permeability Pressure Characteristics of Typical Granite Benggang Sandy Loam Red Soil Layer in Anxi Country

  WU Yunbo, ZHANG Zhi, LI Xiaofei, MAO Xiaohua, ZHANG Yue, JIANG Fangshi, HUANG Yanhe, LIN Jinshi

  DOI: 10.11766/trxb202401040012

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  【Objective】Rainfall can alter the movement of water in the soil of landslide-prone slopes, affecting the types and concentrations of ions in various soil layers, thereby influencing ion-interface reactions on soil particle surfaces. Additionally, moisture accumulation can exert high permeability pressure on the underlying soil layers, making them prone to deformation and instability. Soil with weaker resistance to permeability pressure, when closer to the surface, is more susceptible to soil erosion. Previous research has mainly focused on the influence of soil water stability and mechanical stability on landslide erosion, however, the impact of ion-interface reactions based on ion characteristics on the permeability characteristics of landslides is not well understood. 【Method】This study focused on the red soil layer of a typical landslide in Anxi County and used ion solutions with different valences and concentrations to manipulate ion-interface reactions on the soil particle surfaces and analyzed their effects on the permeability characteristics of the landslide""s red soil layer. 【Result】K+ reduced soil porosity and decreased the soil""s permeability and conductivity, while Mg2+ increased soil porosity and enhanced the soil""s permeability and conductivity. There was a good single exponential increasing relationship between the permeability coefficient and the electrolyte concentration, with the fitting equations for various consolidation pressures expressed as k = ae-x/t + b, R2 > 0.845, P < 0.1. Also, K+ increased the electrostatic repulsion between soil particles, resulting in net repulsion forces between them, while Mg2+ reduced the electrostatic repulsion, leading to net attraction forces between soil particles. Higher electrolyte concentrations have a more significant impact on altering the internal forces within the soil. 【Conclusion】Ion-interface reactions based on differences in ion characteristics can influence the internal forces of the soil, causing some degree of structural changes in landslide-prone soil.

• Effects of Iron Oxides on the Priming Effect of Topsoil and Subsoil Carbon Decomposition in A Subtropical Forest

  ZHANG Yuting, XU Wenhao, WANG Qingkui, TIAN Peng

  DOI: 10.11766/trxb202401030009

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  【Objective】The relationship between soil organic carbon and iron oxides is crucial to the regulation of soil carbon stability. In terrestrial ecosystems, subsoil is an important organic carbon reservoir, which has been paid increasing attention due to its dynamic processes. However, little is known about how carbon inputs affect the interactions between soil minerals and organic carbon, especially in the subsoil.【Method】To address the knowledge gap, this study investigated the effects of two different crystalline forms of iron oxides, goethite and ferrihydrite, on the priming effect of topsoil (0~10 cm) and subsoil (20~40 cm) in subtropical forests. We incubated the soils by adding 13C-labeled glucose to quantify the intensity of the priming effects in a laboratory experiment.【Result】The results show that the priming effects of topsoil and subsoil were 1.63 mg·g−1and 0.61 mg·g−1, respectively, indicating that the priming effects decreased with soil depth. An interactive effect was observed between the type of iron oxides and soil depth on the priming effect of SOC. In topsoil, the addition of goethite significantly decreased the intensity of the priming effect (P < 0.05), while ferrihydrite showed no significant influence on it. In the subsoil, the addition of ferrihydrite significantly increased the intensity of the priming effect (P < 0.05), but the addition of goethite had no significant effect on the priming. In topsoil, after goethite was added, the co-precipitation produced iron-bound organic carbon, which inhibited the mineralization of organic carbon, influenced microbial carbon limitation, and further decreased the intensity of the priming effect. In the subsoil, the intensity of the priming effect was influenced by the limitation of microbial carbon and phosphorus. Glucose acted as an electron shuttle, increasing iron reduction and CO2 production. The reduction and dissolution of ferrihydrite reduced the protective effect of iron oxide on SOC, which in turn enhanced the mineralization of SOC. Iron oxides can increase SOC accumulation and stability through mineral protection and lead to SOC mineralization through redox reaction.【Conclusion】Overall, the priming effects of topsoil and subsoil have different responses to iron oxides, and the influence of iron oxides on organic carbon accumulation is affected by their properties and soil conditions.

• Dynamic Characteristics of Cynodon Dactylon Root Growth and Its Influence on Soil Pore Evolution

  ZHANG Jing, RAN Yiguo, MA Donghao, CHEN Lin, WU Yingbo, HUANG Ping

  DOI: 10.11766/trxb202310310446

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  【 Objective 】 Cynodon dactylon is a commonly used herbaceous plant for ecological greening, soil consolidation and slope protection, vegetation restoration, and soil and water conservation. Its developed root system network and unique growth characteristics have a significant impact on the formation and spatial reorganization of soil pores. Current research has mostly focused on the role of the plant’s roots in soil aggregate formation and stability, however, the dynamic impact of root growth on soil pores remains unclear. 【 Method 】 This study employed a pot experiment, selecting Cynodon dactylon as the model plant and typical purple soil and yellow soil from the mountainous and hilly regions of southwestern China as the culture substrates. Four different treatments were established: purple soil with Cynodon dactylon (G), purple soil control (CK), yellow soil with Cynodon dactylon (YG), and yellow soil control (YCK). The soil profile images under different treatments were continuously collected using the minirhizotron technique. The root traits of Cynodon dactylon and soil pore structure parameters at different stages were quantified through optimized root extraction algorithms and image processing techniques. Combined with statistical analysis, the study explored the dynamic growth of Cynodon dactylon roots and their impacts on the evolution of soil pore structure. 【 Result 】 The results showed that: (1) Cynodon dactylon grew well in both purple and yellow soils, and the root growth rate was higher in purple soil than in yellow soil. The root length, root surface area, and root volume of Cynodon dactylon in purple soil were nearly three times higher than those under yellow soil cultivation conditions; (2) Compared with the unplanted CK and YCK, the growth of Cynodon dactylon significantly reduced the number of pores, porosity, and fractal dimension of purple and yellow soils, and the reduction effect of roots on soil pores continuously increased with root growth; (3) Redundancy analysis indicated that roots explained 40.60% of the variation in soil pore structure, and root length, root surface area, and root volume were the key root traits that reduced soil pore structure parameters. 【 Conclusion 】 In summary, through the optimized minirhizotron technique, continuous observation of plant roots and soil pores was achieved on site. It was found that Cynodon dactylon significantly reduced pore number and other parameters during its growth period, providing methodological support for in-situ, non-destructive, and dynamic studies on root-pore interactions, as well as theoretical support for vegetation restoration and soil and water conservation in ecologically fragile areas.

• Research Progress on Soil Organic Phosphorus Mineralization and Its Regulation

  Zhang Wannian, Yang Zi, Yan Yupeng, Wang Xiaoming, Yin Hui, Xu renkou, Tan Wenfeng, Feng Xionghan

  DOI: 10.11766/trxb202404140154

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  Soil organic phosphorus (P) is an important component of the soil P pool and its mineralization plays an important role in global P cycling. Understanding the mineralization of soil organic P is beneficial for the efficient utilization and management of P in terrestrial ecosystems. In recent years, the application of advanced techniques such as modern spectroscopy, chromatography, and mass spectrometry has provided crucial avenues for a more comprehensive characterization of the composition and structure of organic P. This review summarizes the applications of these technologies in quantifying changes in soil organic P content. Organic P, following mineralization, is converted into inorganic P(Pi), making it available for direct uptake and utilization by plants and microorganisms. Soil organic P mineralization is orchestrated by two primary pathways: enzymatic and mineral-mediated processes. Delving into the mechanisms of biological catalysis and abiological mineral-mediated catalysis is crucial for elucidating the control pathways of organic P. The mechanisms of soil organic P mineralization can be divided into biological mineralization driven by the oxidation of organic matter by microorganisms (phoA, phoD, and phoX) in response to energy demand, and biochemical mineralization driven by the release of Pi nutrients from plants in response to the demand for P nutrients mediated by phosphatases. Recent investigations have underscored the significance of minerals as an abiological mineralization pathway, shedding light on the mechanisms and actions of mineral-mediated catalysis. The surfaces of minerals (such as iron (hydro)oxides, manganese (hydro)oxides, and aluminum (hydro)oxides) provide an enzyme-like environment, facilitating the cleavage of phosphate ester (P-O-C) and terminal phosphoanhydride (P-O-P) bonds, resulting in the hydrolysis of organic P to Pi. In soil ecosystems, the biogenic elements carbon (C) and nitrogen (N) are intimately linked with soil organic P mineralization. From a nutrient factor perspective, elucidating the driving patterns of organic P mineralization can inform strategies to regulate soil P pools. Specifically, C effectively drives microbial mineralization of organic P, whereas N influences enzymatic metabolism, with the interplay between the two elements profoundly influencing the soil organic P mineralization process. The multiple forms of organic P present in soils are susceptible to influences from various external factors, which modulate phosphatase activity and alter organic P content, thereby further affecting the mineralization process. Various factors, including agricultural practices (such as fertilizer application, tillage practices, and biochar application), soil physical and chemical properties (such as pH, temperature, soil water content, and soil aeration status), microbial biomass, soil CO2 concentration, vegetation, and pollutants all impact soil organic P mineralization, resulting in corresponding environmental ecological effects. Therefore, regulating organic P mineralization is crucial for enhancing soil fertility and protecting the environment. Future strategies can focus on enhancing phosphatase activity, altering organic P composition, and increasing the abundance of phosphorus-solubilizing microorganisms to improve soil organic P mineralization. This review summarizes the advances in soil organic P mineralization research, synthesizing the soil processes, influencing factors, and control pathways, and highlighting the existing challenges and prospects.

• The Influence of Root Zone Fertilization in Combination with Azolla and soil pH on Ammonia Volatilization

  ZhuTong, LiHong, zhouyanping, zhengjicheng, YinBin, YaoYuanLin

  DOI: 10.11766/trxb202301180026

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  【Objective】Azolla has a highly biological nitrogen fixation ability, however, the growth of Azolla is sensitive to ammonium nitrogen in water and is easily affected by water pH. Research suggests that root zone fertilization of fertilizers can effectively reduce the concentration of ammonium nitrogen in floodwater. However, it is unknown whether culturing Azolla under root zone fertilization of fertilizers can stably inhibit ammonia volatilization and increase yield for paddy soils with different pH values. This study aimed to determine the effect of root zone fertilization of fertilizers in combination with Azolla on ammonia volatilization and rice yield in paddy soils with different pH values.【Method】A pot experiment was conducted with three types of paddy soil (acid, neutral, alkaline), two methods of fertilization (broadcasting and root zone fertilization of fertilizers), and two modes of rice cultivation (with or without Azolla). The ammonia volatilization potential and grain yields of rice were determined for these 15 treatments. 【Result】The results showed that: (1) Under the same nitrogen application rate, root zone fertilization of fertilizers treatments only volatilized NH3-N 1.0-1.8 kg·hm-2(calculated by nitrogen), which were 96% lower than surface application of nitrogen fertilizer for the three types of paddy soil, and Azolla-rice co-culture treatments lowered the ammonia volatilization by 17%-50% when compared with those of rice mono-culture treatments; (2) Compared with rice mono-culture treatments, Azolla-rice co-culture treatments produced higher rice yield. Moreover, root zone fertilization of fertilizers combined with Azolla reached the highest rice yield in black soil, increased by 41% compared with the grain yield of black soil surface application without Azolla. 【Conclusion】 In conclusion, root zone fertilization of fertilizers can significantly reduce ammonia volatilization for paddy soils with different initial pHs while root zone fertilization of fertilizers combined with Azolla has greater potential for increasing rice yield.

• Variation of the Increased CH4 Emissions in Paddy Fields with Straw Incorporation across 11 Consecutive Years

  YANG Zhengyu, LI Zongming, LI Yanyan, SHEN Jianlin, WU Jinshui

  DOI: 10.11766/trxb202402230076

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  【Objective】 This study aimed to explore the variations of the increased methane (CH4) emissions and its mechanisms in paddy fields with straw incorporation across 11 consecutive years, so as to provide a scientific basis for the accurate assessment of CH4 emissions under long-term straw incorporation.【Method】A typical double-cropping rice field in the subtropical region was selected as the research subject, and the fertilizer only treatment (CON), low amount of straw incorporation treatment (3.0 t?hm-2, LS) and high amount of straw incorporation treatment (6.0 t?hm-2, HS) were set up. The field experiment was conducted for 11 years (2012—2022) with CH4 fluxes and related soil and environmental factors measured in the early and late rice seasons across the 11 years.【Result】The results showed that in the 11th year of straw incorporation, CH4 emissions in both the LS and HS treatments were substantially higher than those in the CON treatment, with the highest emissions recorded in the HS treatment, followed by the LS and then the CON treatment (HS > LS > CON). However, it was noted that the increment in CH4 emissions due to straw incorporation in the 11th year had diminished by 75.1% and 83.5% when compared to the increment in the first year (P < 0.05). In the 11th year, the contents of soil organic carbon (SOC), ammonium nitrogen (NH4+-N), and dissolved organic carbon (DOC) in the LS and HS treatments showed significant increases by 7.90% and 20.8% (LS and HS treatments, the same as below), and 15.0% and 25.7%, 19.5%, and 31.3%, respectively, compared to the CON treatment (P < 0.05). However, the redox potential (Eh) and soil bulk density (BD) exhibited significant reductions of 14.1% and 21.7%, and 10.3% and 7.76%, respectively (P < 0.05). Furthermore, the abundance of the mcrA and pmoA genes, which are instrumental in methanogenesis and methane oxidation processes, respectively, as well as the mcrA/pmoA gene ratio, were significantly enhanced in the LS and HS treatments compared to the CON, which increased by 96.0% and 152%, 12.7% and 34.8%, and 73.9% and 85.8%, respectively (P < 0.05). Through redundancy analysis, it was determined that in the 11th year of straw incorporation, CH4 emissions in the paddy field displayed a significant positive correlation with the abundance of mcrA and the mcrA/pmoA ratio in the soil (P < 0.05). The decrease in BD and the rise in Eh, induced by the increase in SOC content, likely fostered the augmentation in pmoA gene abundance, which might be the principal reason for the undermined increase in CH4 emissions for the straw treatments observed in the later stages of the experiment.【Conclusion】 In the subtropical regions, relative to CON, the increases in CH4 emissions under long-term straw incorporation was reduced by approximately 80% (P < 0.05) compared to the increase under short-term straw incorporation due to the changes in SOC, BD, and Eh. Therefore, the assessment of CH4 emissions from paddy fields with straw incorporation needs to be dynamically adjusted according to the year of duration of straw incorporation.

• The Decomposition Characteristic of Crop Straws and Their Released Dissolved Organic Matter Properties

  YIN Yingjie, SHANG Jianying

  DOI: 10.11766/trxb202311130472

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  Abstract:

  【Objective】It is an essential prerequisite to understanding the environmental behavior of straw carbon in farmland soil to understand the decomposition characteristics of crop straw and the properties of dissolved organic matter (DOM) released. However, the information on straw decomposition characteristics obtained from relevant studies needs to be more comprehensive and requires further investigation. 【Method】In this study, the straws of corn, wheat, bean, and rape were laboratory incubated for 69 days. The two-dimensional correlation-Fourier Transform infrared spectroscopy (2D-COS-FTIR), ultraviolet-visible spectroscopy (UV-Vis), three-dimensional Excitation-Emission-Matrix Spectra (3D-EEM), and parallel factor analysis (PARAFAC) were employed to monitor the changes in the components of straw during decomposition (0–69 days), as well as the humification characteristics of their released DOM. 【Result】The results showed a double increase in corn, wheat, and corn straws during their decomposition period, and all four straws reached maturity at 65–69 d. At the end of decomposition, the mass loss rates of the four straws were 56.8 % (rape), 51.1 % (corn), 48.5 % (soybean), and 44.0 % (wheat), respectively. Although the decomposition order of different substances differed in the four straws, the decomposing intensity of functional groups on the surface of the corn, wheat, and rape straw exhibited the same order (C=O > O-H > -CH2 > -COO-) but the bean straw showed a different order. The dissolved organic carbon (DOC) content released by the corn, wheat, bean, and rape straws gradually decreased and was stable at 69 days of decomposition, of which the DOC content was 23.6, 12.2, 17.2, and 10.7 mg·g-1 biomass, respectively. During the decomposition, the SUVA254 value and aromaticity of DOM released from decomposed corn and soybean straws gradually increased, and the E2/E3 value gradually decreased. In contrast, those in wheat and rape straws showed a fluctuating trend. At the end of the decomposition, the aromaticity of DOM released from decomposed corn, wheat, bean, and rape straw was 20.58, 10.55, 17.45, and 8.32, as well as the E2/E3 value being 3.27, 4.29, 3.16, and 5.77. In addition, the aromaticity of maize and soybean straw DOM was higher than that of wheat and rape straw, and the E2/E3 value showed the opposite trend. The 3D-EEM results showed that though the DOM composition in the four crop straws varied, a similar conversion was observed from protein-like substances (I + II) to humic-like and fulvic-like substances (III + V). Four fluorescence components in the straw DOM identified by the parallel factor analysis model showed similar results. Finally, the humic-like substances (C2 and C4) comprised 35.0%–41.9%, and the fulvic-like substances (C1) accounted for 19.9%–42.9%. In contrast, the protein-like substances (C3) only accounted for 10.0%–29.4%. 【Conclusion】Our study revealed that the decomposition of straw and the content of its released DOM were influenced by the type of crop, while the substance degradation strength and transformation pattern remained consistent.

• Effects of Organic Fertilization on the Phosphorus Solubilizing Bacteria Community and Maize Productivity in Dryland Red Soil

  YANG Yeyuping, ZHENG Jie, JIN Lele, PENG Ziyi, WANG Xiaoyue, XU Qinsong, JIANG Yuji

  DOI: 10.11766/trxb202311170480

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  Abstract:

  【Objective】Phosphorus solubilizing bacteria (PSB) is an important functional group of the soil microbial community. The changes in the abundance, composition, and diversity of the PSB community in the rhizosphere can affect soil alkaline phosphomonoesterase (ALP) activity and phosphorus (P) cycle dynamics. Here, we explored the mechanism of the abundance, composition, and diversity of the PSB community in regulating maize productivity under different organic fertilization treatments.【Method】In this study, we conducted a long-term field experiment with different organic fertilization treatments at the Yingtan National Agroecosystem Field Experiment Station of the Chinese Academy of Sciences in Jiangxi. The field experiment included four treatments: no manure (M0), low manure (M1), high manure (M2), and high manure with lime addition (M3). Illumina sequencing was used to investigate the abundance, composition, and diversity of the PSB community in the rhizosphere.【Result】Different organic fertilization treatments (M1, M2, and M3) significantly increased pH, soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), available phosphorus (AP), abundance of PSB, ALP activity, and maize productivity compared to M0 treatment, with the highest values observed under M3 treatment. Organic fertilizer treatments affected the PSB community composition and diversity in the rhizosphere. Bradyrhizobium, Mesorhizobium, and Pseudomonas were the dominant genera in the PSB community under M2 and M3 treatments. Compared with the M0 treatment, the PSB community diversity was significantly increased under the M1 treatment. The abundance and dominant genera of the rhizosphere PSB community were mainly affected by AP. Correlation analysis and structural equation modeling revealed that AP and TP indirectly affected maize productivity by increasing the abundance and changing the relative abundance of dominant genera of PSB.【Conclusion】Taken together, this study elucidates the promotion mechanisms of the rhizosphere PSB community on the mineralization of soil organic phosphorus and maize productivity. Our findings provide a scientific basis for establishing better organic fertilization practices and enhancing the fertility and health of red soils.

• Hot Moments and Hot Spots and the Associated Influencing Factors of Denitrification along Farmland Soil Profiles in Southern China

  Zhou Han, Wang Xiaomin, Wei Zhijun, Ma Xiaofang, Zhang Yumeng, Shan Jun, Yan Xiaoyuan

  DOI: 10.11766/trxb202401020003

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  【Objective】Denitrification is the primary pathway for removing NO3?-N in agricultural soil profiles, converting NO3?-N into N2, and reducing the risk of NO3?-N accumulation. However, due to methodological limitations, previous studies have mainly focused on the accumulation patterns in soil profiles or the transformation of NO3?-N in the surface soil, with less attention to its removal throughout the entire soil profile. Thus, the rate of denitrification and absolute amount of nitrate removal capacity along the soil profile remain unclear. Furthermore, the existence of “hot moments” and “hot spots” for denitrification in soil profiles is still unknown. 【Method】To evaluate the NO3?-N removal capacity of typical farmland profiles in southern China and to explore the hot moments and hot spots of denitrification, paddy fields (rice-wheat rotation), vegetable fields, and vineyard in the Taihu Lake region were selected for this study. Near in-situ incubation of flooded and non-flooded layers of the soil profile (0-300 cm) of these fields was performed using the Membrane Inlet Mass Spectrometer (MIMS) and Robotized continuous flow incubation system (RoFlow) over a year.【Result】Our results showed that the soil denitrification rate exhibited distinct hot moments and hot spots across the three planting patterns. Denitrification hot moments in rice fields were primarily observed in October during the rice season, with a rate of 17.6±1.0 nmol N g?1 h?1. The denitrification hot moments of vegetable fields and orchards mainly occurred in March, with rates of 44.2±2.5 nmol N g?1 h?1 and 45.3±7.5 nmol N g?1 h?1, respectively. The hot spots of denitrification in the paddy field occurred in the topsoil (0-20 cm) with an average rate of 3.4±0.4 nmol N g?1 h?1. The denitrification hot spots of the vegetable field and orchard mainly occurred at 20-100 cm, with average rates of 11.7±1.3 nmol N g?1 h?1 and 9.4±2.3 nmol N g?1 h?1, respectively. Also, the removal rate of NO3?-N in these denitrification hot spots exceeded 90%, and almost all NO3?-N in the soil profile was removed under the three planting patterns. Correlation analysis results indicated that the soil NO3?-N content was the primary limiting factor for denitrification. 【Conclusion】Our study reveals that the farmland soil profiles under the three planting patterns in the Taihu Lake area exhibit high denitrification rates with distinct denitrification hot moments and hot spots, effectively removing NO3?-N from the soil profile. These findings deepen our understanding of the NO3?-N removal process in farmland soil profiles, holding significant implications for accurately assessing the cumulative risk and removal capacity of NO3?-N in high N input areas of southern China.

• Environmental Behavior and Terrestrial Ecological Risks of Typical Rubber Antioxidants and Their Derivatives

  JiangJinlin, WuHuiyi, WangLei, DongShunan, CaoShaohua

  DOI: 10.11766/trxb202308310345

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  Soil is the main natural resource for human survival and development. In recent years, the aquatic risks of tire rubber antioxidant N-(1, 3-dimethylbutyl-N""-phenyl-p-phenylenediamine (6PPD) and its ozonated product N-(1, 3-dimethylbutyl-N"" -phenyl-p-benzoquinone (6PPD-Q) have attracted global attention, but little is known about their soil environmental behavior and soil biota effects. Research has shown that soil is an important "aggregation" of tire wear particles, and the TWPs entering the environment release various of additives, such as rubber antioxidants, silica, metals, etc. Among them, p-Phenylenediamines(PPDs) are the most widely added rubber antioxidants due to their excellent performance, which can be released as TWPs entered environmental media and produced derivatives such as PPD-Qs. Therefore, studying the fate and ecological environmental risks of 6PPDs and their derivatives in soil is of great significance. This article focuses on soil environmental safety and ecological health, stating the behavioral characteristics of the occurrence, migration, and transformation of 6PPD and 6PPD-Q in the soil environment. For providing a theoretical basis of the ecological risk assessment and prevention and control of 6PPD and 6PPD-Q pollution, this paper introduces the accumulation, transportation, and metabolic mechanisms of 6PPD and 6PPD-Q in soil organisms, and elaborates on their toxic effects and mechanisms on soil organisms.

• Soil Iron Speciation Transformation and in-Situ Monitoring of Element Bioavailability During the Flooding-drainage in Polluted Paddy Soils

  ZHAO Wantong, WANG Yufeng, LIU Zhe, HUANG Qiaoyun, YI Ceng, FENG Xionghan, WANG Xiaoming

  DOI: 10.11766/trxb202310210430

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  【Objective】Paddy soils are extensively polluted by heavy metals (HMs) in China and present significant challenges for safe agricultural use. Thus, this study seeks to address the heavy metal pollution in China""s paddy soils, focusing on polluted soils from the Dabaoshan mining areas in Shaoguan, Guangdong Province.【Method】A flooding-drainage incubation experiment was conducted and combined with chemical extraction, diffusive gradients in thin films (DGT) technology, and correlation analyses. Also, the impact of phosphorus (P) and humic acid (HA) addition on soil Fe speciation and the bioavailability of related elements was evaluated. The selection of P and HA concentrations was based on common agricultural practices to ensure the environmental relevance of this study.【Results】The results revealed that soil pH gradually became neutralized while redox potential (Eh) decreased during the flooding period. The concentrations of acid-soluble Fe2+, amorphous Fe, and Fe activation degrees increased from 1.5 g?kg-1 to 4.8 g?kg-1, 6.6 g?kg-1 to 10.1 g?kg-1, and 21% to 29%, respectively, with a decrease in amorphous Fe content observed in treatments with added P and HA from 2 to 42 days of flooding. After soil drainage, both amorphous Fe (Feox) and Fe activation degree rapidly decreased to 7.4 g?kg-1 and 21.6%. Regarding CaCl2-extractable heavy metals, the lowest values were observed after 14 days of flooding, whereas levels of As, Cd, Cu, and Zn rapidly increased to 0.1, 0.4, 0.3, and 7.0 mg?kg-1, respectively, after drainage. The addition of P and HA in the early flooding stage increased the As content by 80% and 35% compared to the control, respectively, but decreased the contents of Cu, Zn, and Cd, with HA addition, the reduction rates of CaCl2-extractable Cu, Zn and Cd were over 67%. During flooding, DGT-extracted P and Fe content initially increased then decreased, while Zn content gradually reduced. The addition of P and HA significantly reduced the bioavailable Zn content in the early stages of flooding while the bioavailable content of P and As was primarily controlled by bioavailable Fe.【Conclusion】During the soil flooding-drainage incubation, significant changes occurred in soil physicochemical parameters including pH, Eh, and speciation of Fe. The addition of P and HA could regulate the bioavailability of elements such as Fe, P, and HMs. These findings offer valuable insights for the remediation of HMs-polluted soils, highlighting the potential for using P and HA in improving soil quality and ensuring safe agricultural production.

• Temporal Dynamics and Content of Soil Particulate Organic of Gahai Wetland in Gansu Province During Vegetation Degradation Succession

  MA Weiwei, LIU Qiang, LI Guang, CHANG Wenhua

  DOI: 10.11766/trxb202309040355

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  【Objective】Soil particulate organic carbon (POC) is a key player in the transformation and sequestration of soil carbon pools. However, POC content is significantly regulated by changes in soil environment. Therefore, this study was aimed to clarify the change of POC and its influencing factors with vegetation degradation of alpine wetlands, in an attempt to provide certain basic data for further understanding the responses of soil carbon pool dynamics to climate change and human activities in alpine wetland. 【Methods】In this study, the swampy meadow of Gahai wetland in the northeastern edge of the Qinghai-Tibet Plateau (QTP) was taken as the study area. In the typical vegetation growth area around Gahai Lake, the spatial instead of temporal method was used to characterize the degree of degradation. Sample plots were set up by selecting lots with gentle terrain and consistent slope orientation. Different vegetation degradation levels were classified according to the indicators of plant species composition, aboveground biomass, community height and cover. Soil samples were collected from four vegetation degradation levels, including non-degraded (ND), slightly degraded (SD), moderately degraded (MD), and heavily degraded (HD) in swampy meadow at Gahai wetland. The contents of soil POC were investigated in in the growing seasons of 2016-2017 by field sampling and laboratory analysis. Three-factor analysis of variance was used to analyze the effects of vegetation degradation, soil layer, sampling time and their interactions on soil moisture, soil organic carbon (SOC) and POC contents. Redundancy analysis was performed to determine the dominant factors affecting the change of SOC components in each vegetation degradation levels. 【Results】The results showed that vegetation degradation significantly decreased the amount of POC at soil surface layers (0-10 and 10-20 cm), but there was no significant effect on the deep layers (20-40, 40-60, 60-80 and 80-100 cm). As the growing season progresses, the contents of POC at 0-10 and 10-20 cm layers decreased first and then increased in four vegetation degradation levels. However, the contents of POC at the other deep layers did not change significantly. In terms of inter-annual variation, soil POC levels and fluctuations were higher in 2016 than in 2017. Analysis of variance (ANOVA) showed that the sampling time, the vegetation degradation and soil layer had significant effects on the POC content, respectively. Meanwhile, the interaction of sampling time, vegetation degradation and soil layer had a significant effect on soil POC content. To further identify the intrinsic factors affecting changes in POC content. Redundancy analysis was utilized to reveal the differences between the studied factors. The results showed that total nitrogen and below-ground biomass were the main factors driving changes in soil organic carbon fractions. 【Conclusion】In summary, the process of vegetation degradation in alpine wetlands may impair the accumulation of surface soil carbon pools in the wetlands of the QTP. The original POC accumulation is gradually lost with the increasing degree of vegetation degradation. This phenomenon suggests that vegetation degradation may have transformed the QTP wetlands into a new potential carbon source.

• Effects of Chinese Milk Vetch Incorporation on the Gene Abundance of Ammonia-oxidizing Microorganisms in Red Paddy Soil

  SUN Luyuan, LIU Jia, FENG Mengmeng, LIU Han, MA Tingting, CHEN Xiaofen, LIN Yongxin

  DOI: 10.11766/trxb202401110021

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  Abstract:

  【Objective】 Nitrification, an important component of nitrogen cycling, has the potential to influence soil nitrogen availability. As a result, it will lead to ecological and environmental issues such as eutrophication, and greenhouse gas (nitrous oxide) emissions. The objective of this study was to explore the effect of Chinese milk vetch incorporation on the gene abundance of ammonia-oxidizing microorganisms in red paddy soil under a rice-Chinese milk vetch planting system. 【Method】 In a field experiment, five fertilization treatments were applied, including Chinese milk vetch incorporation (G), 100% chemical fertilizer (C), Chinese milk vetch incorporation + 100% chemical fertilizer (GC), and Chinese milk vetch incorporation + 20% chemical fertilizer reduction (GCT20), with a no fertilization treatment serving as the control (CK). Real-time quantitative PCR was used to determine the abundance of ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and comammox Nitrospira Clade A and Clade B in each treatment. 【Result】 The results showed that Chinese milk vetch incorporation increased soil organic carbon and total nitrogen content compared with CK, while the 100% chemical fertilizer treatment showed no significant effect. There was no significant difference in AOA and Clade B abundance among all the treatments, indicating a weak response to nitrogen inputs from both chemical fertilizers and green manure. However, both the sole application of chemical fertilizer and its combination with Chinese milk vetch incorporation significantly increased the abundance of AOB and Clade A. Additionally, Chinese milk vetch incorporation alone had no significant effect on AOB and Clade A, suggesting their sensitivity to chemical fertilizer, but resistance to green manure nitrogen input. Furthermore, gene abundance of all ammonia-oxidizing microorganisms showed a similar trend across growth stages, with higher abundance observed during the mature stage followed by the booting stage and then the tillering stage. This suggests that growth stage and oxygen concentration are key factors influencing the growth of these microorganisms in paddy soils. 【Conclusion】 Growth stage is a key factor affecting the abundance of ammonia-oxidizing microorganisms in paddy soils. Additionally, Chinese milk vetch incorporation had a weaker promotion effect on AOB and Clade A abundance compared to chemical fertilizer, potentially contributing to nitrogen retention and stability in paddy soils.

• Environmental Footprint Assessment of in Situ Chemical Oxidation Remediation for Contaminated Aquifer Based on SiteWiseTM Method

  LIU Peng, SANG Chunhui, ZHANG Hongzhen, XIAO Meng, MENG Hao, LI Xianglan

  DOI: 10.11766/trxb202312090523

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  Abstract:

  【Objective】The environmental footprint assessment of in-situ chemical oxidation remediation technology (ISCO) for polluted sites has important scientific research value and practical significance for promoting green and sustainable remediation. However, its application in chlorinated hydrocarbon-contaminated sites has not received much attention. 【Method】 This study employed the ISCO method to remediate a chlorinated hydrocarbon-contaminated site. The remediation of polluted sites using ISCO is divided into four stages: material consumption, transportation process, remediation process, and sampling testing. SiteWiseTM tool was used to conduct an environmental footprint assessment. 【Result】The results showed that using ISCO technology to remediate 73 800 cubic meters of polluted aquifers resulted in 1 261 tons of greenhouse gas (GHG) emissions, total energy consumption of 16 876 GJ, 4 096 kg of SOx emissions, 2 678 kg of NOx emissions, and 912 kg of particulate matter 10 (PM10) emissions. The environmental footprint mainly came from the use of materials such as sodium persulfate and sodium hydroxide, and the consumption of construction electricity caused higher atmospheric pollutant emissions. The Monte Carlo analysis results indicated that the coefficient of variation of greenhouse gas emissions was less than 10%. Also, the sources of uncertainty in this study mainly included redundant designs from ISCO, as well as significant differences in mechanical efficiency and emission factors between different countries. 【Conclusion】The SiteWiseTM tool has reference value for the environmental footprint assessment of ISCO remediation projects in polluted sites in China and future researchers should update it locally by considering machinery types and efficiencies, emission factors, and units of measurement. These considerations will improve applicability to the environmental footprint assessment of polluted sites in China.

• Effects of Experimental Warming on Soil Microorganisms: A Meta-Analysis

  ZHAO Wenyu, MIAO Run, CHENG Cheng, WANG Qi

  DOI: 10.11766/trxb202402180071

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  【Objective】Microbial community plays an important role in soil ecological activities. It can regulate soil nutrient supply by changing the structure and function of the soil ecosystem. At present, the response of soil microbial community to warming and the main influencing factors are not well understood.【Method】This study collected 1 020 sets of data from 206 published domestic and foreign research literature and synthesized them to evaluate the effects of experimental warming on soil microbial community (microbial biomass, community diversity, and soil enzyme activity) using meta-analysis. The different responses of soil microbial communities to different magnitudes, durations and methods of warming, as well as planting habits and ecosystem types were evaluated and discussed. Also, the relationship between the response of soil microbial communities to warming treatment and environmental factors (annual mean precipitation, annual mean temperature, and mean altitude) was explored.【Result】It was found that experimental warming decreased the soil microbial community diversity by 6.7%, increased the activities of soil antioxidant enzymes, enzymes related to carbon (C), and nitrogen (N) conversion by 7.5%, 10.8%, and 19.7%, respectively. A high magnitude of warming (≥4℃) significantly reduced soil microbial biomass and increased the activities of soil antioxidant enzymes and enzymes related to C conversion. Low- temperature increase (≤2℃) had more significant effects on soil microbial community diversity and soil enzymes related to N and phosphorus (P) conversion. Also, long-term warming (>2 years) had significant effects on soil microbial biomass, community diversity, antioxidant enzymes and enzymes related to C conversion. The responses of enzymes related to N and P conversion to medium-term warming (0.5 to 2 years) were more significant and the response of soil microorganisms to experimental warming was different among different ecosystems. Further analysis revealed that the response of enzyme activities related to P conversion to warming was positively correlated with annual mean temperature and annual precipitation. The response of soil microbial community diversity was negatively correlated with mean annual temperature, annual precipitation and mean altitude.【Conclusion】In summary, the experimental warming significantly reduced the diversity of soil microbial communities while increasing soil enzyme activity. The warming amplitude, warming duration, and ecosystem type all affect the effects of experimental warming on soil microbes.

• Assessing the Impacts of Extreme High Temperatures and Long-Term Warming on Paddy Soil Organic Carbon based on the DNDC Model-A Case Study in Zhangzhou of Fujian Province

  ZHANG Liming, LI Jing, CHEN Weiming, SUN Jiarui, XIE Xilin, ZHANG Hua, SHEN Jinquan, LIAO Wenqiang, XING Shihe

  DOI: 10.11766/trxb202402070064

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  Abstract:

  【Objective】 Soil organic carbon (SOC) is an essential indicator of soil health. It not only provides a carbon source for plant growth and maintains the physical structure of soil, but also releases carbon into the atmosphere in the form of greenhouse gases, such as carbon dioxide. Therefore, it plays a critical role in the global carbon balance. Currently, the world is experiencing climate change characterized predominantly by warming and increasing frequency and intensity of extreme weather events. However, the impacts of the changing climate, including long-term warming and extreme weather events on SOC are not entirely the same. Distinguishing and quantifying the effects of extremely high temperatures (EH) and global warming (GW) on SOC is the key to formulating adaptive strategies.【Method】 In this study, we focused on paddy soils in Zhangzhou of Fujian Province, a typical subtropical region of China. Based on a 1:50,000 detailed soil database, we employed the biogeochemical process model (DeNitrification-DeComposition, DNDC) to simulate SOC dynamics under four climate scenarios: de-trended climate base state (CTRL), extreme high temperatures (EXP_EH), long-term warming (EXP_GW), and measured temperatures (EXP_obs).【Result】 The results revealed that the total amount of carbon sequestered by paddy fields in Zhangzhou from 1980 to 2016 under the four different climate scenarios (CTRL, EXP_EH, EXP_GW, and EXP_obs) was 1,032.17, 952.15, 1,045.98 and 966.03 Gg, with the corresponding average annual sequestration rates of 93.98, 86.70, 95.24, and 87.96 kg·hm-2, respectively. The long-term warming led to a net increase of 13.81 Gg of SOC in paddy fields across Zhangzhou, while extremely high temperatures resulted in a net decrease of 80.02 Gg. The combined effect of these two factors was -66.14 Gg in SOC, indicating that long-term warming promoted the sequestration of organic carbon in paddy soils, while extremely high temperatures reduced the soil carbon sink capacity, with extremely high temperatures exerting a dominant negative effect. Also, the variations in annual carbon sequestration rates between different climate scenarios indicated that extremely high temperatures throughout the years from 1980 to 2016 had a negative effect on carbon sequestration in the paddy soils of Zhangzhou, but the long-term warming effect on SOC turned from positive to negative around the year of 2000. This may be related to the diminishing effect of warming on plant growth over time. The results of grey relational analysis-structural equation modeling also indicated that the clay content, bulk density, and organic fertilizer application rate were most closely associated with the carbon sequestration rate in rice fields of Zhangzhou, followed by the annual average temperature, precipitation, and pH levels. At the county level, climate change had the greatest impact on the carbon sequestration of Nanjing County. Additionally, the extremely high temperatures and long-term warming caused -26.23% and 7.27% impacts on its carbon sequestration rate, respectively. Among subclasses of rice soils, acid sulfate paddy soils were most affected, with -23.05% and 8.10% changes in carbon sequestration rate caused by warming and extremely high temperatures, respectively. Furthermore, among different terrain and topographical areas, the carbon sequestration rate of hilly and mountainous areas was significantly affected by extremely high temperatures and long-term warming, with -8.84% and 1.98% changes, respectively. 【Conclusion】 In conclusion, while the paddy soils in Zhangzhou still maintain a strong carbon sequestration capacity in the context of climate change, the increasing extreme high-temperature events in the future may potentially contribute to greater carbon losses to some extent.

• Characteristics of Natural Humus Modified Materials and Their Growth-promoting Effects on Maize Under Drip Irrigation

  CHEN Zhuo, ZHANG Congzhi, ZHANG Jiabao, ZHAO Bingzi, PAN Hui

  DOI: 10.11766/trxb202312170531

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  Abstract:

  【Objective】This study aims to analyze the physicochemical properties of two natural humus-modified materials (M1 and M2) produced by different processing methods, compare the differences between the two materials, and investigate their effects at different concentrations on the growth of maize under drip irrigation conditions. The goal is to explore the most suitable application concentration and amount of humus under drip irrigation and provide new perspectives and practical bases for agricultural production. 【Method】The content of humus and its components in M1 (natural humus sand grinding fluid) and M2 (fully water-soluble potassium nitrohumate) was determined and the physical and chemical properties of the materials were analyzed through elemental analysis, scanning electron microscopy, and Fourier transform infrared spectroscopy (FTIR). Then, field experiments were designed to evaluate the effects of applying different concentrations (0.2, 0.4, 0.6, 0.8, 1.0, 1.5, 2.0 g?L-1) and amounts (650, 1 300, 1 950 L?hm-2) of M1 and M2 on the height, biomass, and yield of maize. 【Result】The results showed that: 1) There were significant differences in chemical composition between M1 and M2. M1 had a higher content of humus, larger molecular weight, more complex structure, and stronger stability in soil. On the other hand, M2 had a lower total content of humus, a high content of fulvic acid (FA), a smaller molecular weight, and a lower degree of humification. 2) The microstructure of M1 and M2 differed. M1 had a rough and complex particle surface with uneven particle size while M2 exhibited a smoother and looser sponge-like appearance with no chaotic structure on the particle surface. FTIR analysis showed that M1 may contain more aromatic structures or carboxylate salts and silicate impurities while M2 may contain more carboxyl groups. 3) Although the application of M1 and M2 had little effect on plant height, it significantly increased the biomass and yield of maize. Especially for M2, when its concentration was 1.0 g?L-1 and the amount was 1 300 or 1 950 L?hm-2, the biomass of maize plants increased significantly by 40.11% and 40.74% and the yield increased significantly by 25.75% and 27.45%, respectively.【Conclusion】The application of different concentrations and amounts of M1 and M2 effectively promoted the growth of maize, with M2 exhibiting greater growth potential under the same conditions. This may be attributed to the role of humus in improving soil structure, increasing and retaining soil moisture and nutrient content, activating specific biochemical pathways, and enhancing soil microbial activity, thereby improving the nutrient absorption efficiency and photosynthetic capacity of maize plants. Considering factors such as cost, it is recommended to apply M2 at a concentration of 1.0 g?L-1 and an amount of 1 300 L?hm-2 in the field to fully exploit its effects in promoting maize growth potential and increasing yield. This provides new perspectives and practical bases for the efficient utilization of humus in agriculture.

• Kinetic Study of Montmorillonite-humus Condensation Induced by Mixed Electrolyte

  HE Aizhou, YU Linqiao, LI Hang†

  DOI: 10.11766/trxb202311080466

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  【Objective】Natural soil typically consists of a variety of colloids and multiple electrolytes coexisting simultaneously. However, existing studies on soil colloid coagulation have mostly been conducted under conditions involving a single electrolyte and a single colloid. In this study, the coagulation dynamics of a mixed colloid system comprising montmorillonite and humic acid under mixed electrolyte conditions were systematically investigated attempting to explain the coagulation effect and mechanism of mixed electrolyte on the mineral-organic mixture.【Method】Using dynamic laser scattering (DLS) technique, the coagulation kinetics of montmorillonite colloids and montmorillonite-humic acid mixed colloids under the influence of mixed electrolytes were studied by considering key parameters such as the average coagulation rate, critical coagulation concentration (CCC), and coagulation activation energy.【Result】The results revealed the following key findings: (1) Under mixed electrolyte conditions, whether involving a single colloid or a mixed colloids, there was only one CCC. This indicates that under mixed electrolyte conditions, both the two cations in the mixed electrolyte system play a cooperative role in the coagulation of the colloid. Although both cations collaboratively influenced colloid coagulation, the analysis of colloid coagulation rate, CCC, and coagulation activation energy revealed that the cation with stronger competitive adsorption ability played a decisive role. For example, in the 99% Mont(Montmorillonite) + 1% HA(Humic acid) mixed colloids system, the CCC (97.41 mmol?L-1) of the Na+ + K+ mixed system closely resembled the CCC (94.91 mmol?L-1) of K+ alone system, indicating that the role of Na+ in the coagulation of this mixed colloid was almost negligible. This implies that in the Na+ + K+ mixed system, K+ plays a decisive role in colloid coagulation. (2) Increasing the content of humic acid significantly enhanced the stability of the mixed colloid, resulting in the requirement of a higher electrolyte concentration to induce colloid coagulation. This effect can be attributed to the fact that the addition of humic acid increased the surface charge density of the organic/inorganic composite colloidal particles, thereby strengthening the electrostatic repulsion between particles.【Conclusion】The scientific findings of this study not only provide guiding significance for further unraveling the formation mechanism of soil organic-inorganic complexes, but also shed light on the cooperative role of cations in colloidal coagulation under mixed electrolyte conditions. The results underscore the decisive role of the cation with stronger competitive adsorption ability in colloid coagulation. Furthermore, the study reveals that increasing the content of humic acid significantly enhanced the stability of the mixed colloid, necessitating a higher electrolyte concentration to induce colloid coagulation. These insights contribute to the understanding of the complex interplay between organic and inorganic components in soil, paving the way for future research in this field.

• Effect of Basal Application of Magnesium Sulfate and Magnesium Chloride on Seed Yield and Quality of Rapeseed

  GENG Guotao, YE Xiaolei, YU Xiaohong, CONG Rihuan, LI Xiaokun, ZHANG Yangyang, LU Zhifeng†, LU Jianwei

  DOI: 10.11766/trxb202311180483

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  Abstract:

  【Objective】Rapeseed (Brassica napus L.), one of the most important oilseed crops in China, is sensitive to magnesium (Mg) deficiency. The Yangtze River Basin is the main planting area for winter oilseed rape in China, and the climatic characteristics of the region with simultaneous rain and heat, high-intensity planting patterns and long-term unbalanced fertilization have led to serious depletion of soil magnesium. It provides a theoretical basis for the rational application of Mg fertilizers in rapeseed cultivation to investigate the impact of different Mg fertilizers on seed yield and quality of rapeseed in China’s main winter oilseed rape production areas. 【Method】Between 2019 and 2020, 56 field trials were conducted in the main rapeseed-growing regions in China. The trials followed a one-way experimental design, with three distinct Mg fertilizer treatments: no Mg fertilizer (CK), magnesium sulfate at the rate of 45 kg?hm-2 (Calculated as MgO, the same as below) (MgSO4?H2O, referred to as MgSO4), and magnesium chloride, also at the rate of 45 kg?hm-2 (MgCl2, referred to as MgCl2). The response of rapeseed to the two Mg fertilizers was evaluated by analyzing the rapeseed yield, yield components, oil, protein, sulfide content and fatty acid fractions. 【Result】The results revealed that the application of both MgSO4 and MgCl2 significantly increased rapeseed yield by 14.1% and 11.8%, respectively. The increase was primarily attributed to an increase in pod number per plant and seeds per pod. MgSO4 and MgCl2 increased the pod number per plant by 10.2% and 8.2%, and the seeds per pod by 3.9% and 2.4%, respectively. Analyzing the relationship between soil Mg content, sulfur content and yield increase resulting from Mg application indicated that the increase in seed yield was mainly associated with soil Mg content but not soil sulfur. The addition of MgSO4 and MgCl2 resulted in an 11.8% and 8.7% increase in seed Mg content (relative to no Mg application treatment), respectively. However, Mg accumulation was similar in both Mg application treatments. Additionally, the application of Mg fertilizer significantly improved rapeseed quality by increasing oil, oleic acid, and linoleic acid content by 5.5% and 4.8%, 8.3% and 7.7%, 7.8% and 11.4% for MgSO4 and MgCl2, respectively. Meanwhile, stearic acid, palmitic acid, and erucic acid contents were decreased by 4.60% and 26.1%, 7.5% and 13.9%, and 33.2% and 24.1% for MgSO4 and MgCl2, respectively. Although the application of MgSO4 resulted in a significant increase in sulfide, it remained below the national limits for edible rape oil and feed cake meal for double-low oilseed rape. 【Conclusion】In the main winter oilseed rape production areas in China, the application of MgSO4 and MgCl2 can significantly increase rapeseed yield, with MgSO4 having a slightly greater effect compared to MgCl2. Magnesium application also increases the Mg content and improves the oil quality of rapeseed by increasing the content of oleic acid and linoleic acid while reducing stearic acid and palmitic acid contents. These synergistic improvements contribute to both yield and quality enhancement.

• Evaluation of Improvement Effect and Analysis of Influencing Factors of Different Amendments on Saline-sodic Soils Based on a Meta-analysis

  HUANG Guangzhi, HUANG Lihua, LIU Baishun, JIANG Xiaotong, YANG Can, LIANG Yanping, Cai Jinghui

  DOI: 10.11766/trxb202309060360

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  【Objective】 Saline-sodic soils are widely distributed in the western part of the Songnen Plain. A variety of materials or measures have been used to improve soils in the process of long-term saline-sodic land management, and get great improvement effect. However, the improvement effect of these amendments on saline-sodic soils is mostly an assessment of individual factors, thus, the quantitative assessments for the impacts on multiple soil functions of different amendments are still lacking. 【Method】Based on this, Our study used a meta-analysis to obtain 854 sets of relevant data from 589 papers on the improvement of saline-sodic soils in the past 30 years. The improvement effects of gypsum type amendment, biochar, and mixed amendments(combined application of 2 or more amendments) on saline-sodic soil and the factors influencing the improvement effect were quantitatively evaluated and analyzed with a meta-analysis and the Random Forest method.【Result】The results showed that the effects in saline sodic paddy fields of the three amendments on decreasing alkalinity were -29.1%, -38.6%, and -41.1%, respectively, and the effect of improvement was significant, however, the difference in improvement effectiveness between amendments was not significant; Furthermore, biochar (47.7%) had the best effects on improving soil nutrient content, while gypsum-type amendments (26.3%) were relatively the lowest. The three amendments were mostly used for soil amendment at the top soil layer (0~20 cm) of moderate and heavy saline-sodic soils, and there were differences in the application amount and application duration on the effect of soil improvement. Amendment application amount was a significant factor affecting the effectiveness in reducing soil salt/alkali of gypsum type amendments.【Conclusion】The main working principle of gypsum-type amendments is to reduce soil alkali, indirectly enhance soil nutrients and promote crop growth, whereas biochar and mixed amendments have the combined effect of reducing soil alkali and directly promoting soil nutrients. The selection of soil amendments should take into account not only the amount, but also the crop types, the cost of the amendments, the durability of the effect, and environmental safety issues.

• Effects of High CO₂ Concentration on Soil Organic Carbon Mineralization

  WANG Ruoyao, LI Yuanyuan, XIA Bin, GAO Zihui, ZHAO Yunge, XU Mingxiang

  DOI: 10.11766/trxb202312010505

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  【Objective】Soil CO2 concentration is often higher than that of the atmosphere. Current studies on soil organic carbon mineralization are mostly conducted under conditions of increasing atmospheric or simulated atmospheric CO2 concentration. This may lead to deviation of the results from the actual organic carbon mineralization process in the soil profile or impose some bias on indoor mineralization incubation experiments towards the "mineralization potential" rather than the actual mineralization rate. How and to what extent soil organic carbon mineralization is affected by high CO2 concentrations in the soil profile? The lack of a clear answer to this question limits the comprehensive understanding of soil organic carbon stability. 【Method】In this paper, an indoor mineralization incubation test was conducted with six CO2 concentration gradients of CK (400 μmol·mol-1, atmospheric level), 800, 2 000, 4 000, 6 000, and 8 000 μmol·mol-1, and three replicates were set for each treatment. The effects of different concentrations of CO2 on the rate of soil organic carbon mineralization, cumulative mineralization, and active organic carbon fractions were investigated, and the extent to which CO2 concentration and other influencing factors explained the cumulative mineralization was analyzed.【Result】The results showed that: 1) High concentration of CO2 (2 000-8 000 μmol·mol-1) in soil significantly inhibited the mineralization of soil organic carbon, with the mineralization rate decreasing by 6.27%-45.61%, and the cumulative amount of mineralization decreased by 1.72%-40.82%; 2) Lower concentration of CO2 (800 μmol·mol-1) in soil significantly promoted the mineralization of soil organic carbon, the mineralization rate increased by 4.38%-12.65%, and the cumulative mineralized amount increased by 17.37%-48.43%; 3) The CO2 concentration in the soil effected the content of active organic carbon fractions. At a range of CO2 concentrations, soil microbial biomass carbon (MBC) content increased significantly and dissolved organic carbon (DOC) content decreased significantly compared to CK. However, the content of easily oxidizable organic carbon (EOC) was not significantly changed; 4) The mineralization characteristics of organic carbon showed a significant negative correlation with CO2 concentration, a significant positive correlation with DOC, a negative correlation with EOC, and no significant correlation with MBC; 5) Under the appropriate conditions of temperature and humidity, the contribution of CO2 concentration to the cumulative mineralization of soil organic carbon reached 22.93%. 【Conclusion】High CO2 concentration significantly inhibited soil organic carbon mineralization by affecting the soil organic carbon readily available carbon source, which may be one of the important factors to maintain soil organic carbon stability.

• Effects of Facility Cultivation Pattern on Soil Bacterial Community in Ningxia Region

  SUN Yinqinqin, YAN Yuanyuan, QU Jisong, ZHANG Lijuan, ZHU Qiannan, ZHAO Jun, ZHANG Jinbo, CAI Zucong, HUANG Xinqi

  DOI: 10.11766/trxb202312070519

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  【Objective】Soil bacterial community characteristics are important indicators of soil quality, however, little is known about the effects of facility cultivation on soil microbiological properties. Thus, clarifying the responses of soil bacterial community and functions to facility cultivation is of significance for the sustainable utilization of facility soil.【Method】To reveal the change of soil bacterial community under intensive cultivation and its main influencing factors, this study collected and analyzed 67 facility-open field paired soil samples in Ningxia region. Based on amplicon sequencing technology, the effects of facility cultivation on soil bacterial community diversity, composition, interspecific interaction, and assembly process were investigated.【Result】The results showed that compared with the open field soil, the number of bacteria, Shannon, ACE, and Pielou indices of the bacterial community increased by 63.3%, 3.20%, 11.4%, and 1.69%, respectively. The facility cultivation significantly changed the soil bacterial community structure. Redundancy analysis (RDA) showed that the content of available phosphorus, pH, and electrical conductivity were the main environmental factors determining bacterial community structure. Physicochemical parameters such as pH and soil available nutrient contents significantly affected the bacterial community composition of the facility soil, and the climatic factors including annual average precipitation and annual average temperature significantly affected the bacterial community composition of the open field soil. At the phylum level, the relative abundances of Planctomycetes and Firmicutes increased significantly, while the relative abundances of Gemmatimonadetes and Myxobacteria decreased significantly in the facility soil. At the genus level, the dominant genera such as Bacillus and Pseudomonas were enriched in the facility soil. Co-occurrence network analysis showed that the edge, average degree, clustering coefficient, and modularization degree of the bacterial network in the open field soil increased by 10.8 times, 11.0 times, 36.8%, and 1.78 times compared to those in the facility soil, respectively. Also, facility cultivation significantly reduced the complexity and modularization degree of the soil bacterial network. Functional prediction using the Functional Annotation of Prokaryotic Taxa (FAPROTAX) database showed that facility cultivation significantly increased the relative abundance of carbon, nitrogen, and other element cycles and bacterial functional groups related to pathogenic bacteria. The distance decay relationship of the bacterial community in the facility soil was weaker than that in the open field soil. The community assembly was greatly affected by the deterministic process and the diffusion limitation was higher in the facility soil compared to that in the open field soil.【Conclusion】Collectively, facility cultivation in Ningxia region significantly changed multiple properties of the soil bacterial community. These results can provide theoretical guidance for the sustainable utilization of local facility soil.

• Short-term Low Nitrogen Addition Alters the Molecular Composition and Stability of Soil Dissolved Organic Matter in a Pinus taiwanensis Forest

  YUAN Xiaochun, ZHANG Xiaoqing, ZHOU Qian, WU Lianzuan, CHEN Junming, ZENG Quanxin, BAI Xinyu, LI Wenzhou, CHEN Yuemin

  DOI: 10.11766/trxb202311160476

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  【Objective】Dissolved organic matter (DOM) is highly sensitive to environmental changes, and its dynamic changes are crucial for understanding regional/global carbon cycling under global change scenarios. However, it is not yet clear how the characteristics of soil DOM molecules change under nitrogen deposition. This study aimed to investigate the response of DOM molecular composition and stability to nitrogen addition. 【Method】In this study, three nitrogen addition levels (0, 40, and 80 kg?hm-2?a-1) were conducted in a Pinus taiwanensis forest by using urea addition to simulate nitrogen deposition in the field. The effect of short-term (three years) nitrogen addition on the molecular composition of DOM and its stability was investigated using high-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). 【Result】The results of FT-ICR MS analysis revealed that DOM molecules were mainly concentrated in 250-400 Da, and CHO compounds accounted for more than 50% of all compounds. Of the eight types of DOM molecules, lignin-like molecules dominated all soil DOM molecules, followed by tannins and condensed aromatics, with the relative abundance of readily decomposable small molecules (including lipids, proteins, and carbohydrates) being low. There was no statistically significant change in the content and optical properties of DOM under nitrogen addition, but significant changes occurred in the properties and composition of DOM molecules. Compared to high nitrogen treatment, low nitrogen treatment significantly reduced the relative abundance of carbohydrate molecules in DOM by 73.33%. This may be largely attributed to the increase in microbial biomass and hydrolytic enzyme activities. Nitrogen addition did not change the nitrogen-containing compounds in DOM molecules, but reduced the sulfur-containing compounds. Furthermore, the average molecular weight and ratio of double bond equivalent to carbon atom number (DBE/C), modified aromaticity index (AImod), and aromaticity equivalent (Xc) of DOM molecule did not show significant changes under nitrogen addition. However, a significant increase in DBE values was observed under low nitrogen addition, indicating an improvement in the molecular stability of DOM. The improvement of DOM molecular stability may have a potential impact on soil carbon pool stability. Pearson""s correlation analysis revealed that DBE values were significantly negatively correlated with small molecule compounds such as carbohydrates and proteins/amino sugars, while the correlation with large molecules such as lignin and condensed aromatics was not significant. Besides, nitrogen addition did not significantly change the difficult-to-decompose molecules such as lignin and condensed aromatic compounds in DOM. This suggests that the molecular stability of DOM under short-term nitrogen addition may depend on the removal of readily decomposable small molecules, such as carbohydrates, rather than the increment of refractory molecules.【Conclusion】Collectively, this study provides a new perspective at the molecular level for understanding the behavior of soil DOM under nitrogen deposition, and a reference for understanding the potential relationship between DOM molecules and soil carbon stability.

• A Review of Soil 3D Prediction and Modelling Techniques

  XIE Xianli, XIA Chengye, YIN Biao, LI Anbo, LI Kaili, PAN Xianzhang

  DOI: 10.11766/trxb202311140473

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  Abstract:

  Soil is a complex with high heterogeneity. The early research on digital soil mapping mainly focused on the lateral variation of soil, with less consideration of the vertical variation and three-dimensional (3D) digital soil mapping. In recent years, the rapid developments of 3D geographic information technology and earth observation and detection technology have greatly promoted research on soil 3D data acquisition, 3D prediction, 3D data modeling, 3D model and visualization. In this paper, we reviewed the existing research on soil prediction and soil model construction in 3D space, to provide suggestions for the application and development of 3D digital soil mapping. We searched the Web of Science database by using 3D soil mapping, 3D GIS, 3D data model, 3D geological modeling, 3D visualization, soil spatial variability, spatial prediction, Kriging interpolation, soil-landscape analysis, depth function, machine learning, geostatistics, random simulation as keywords, and selected the key literatures for analysis based on correlation, citation rate and literature sources. We summarized the popular methodologies for soil spatial variability, 3D spatial soil prediction, soil 3D data model, and 3D model construction, and evaluated the advantages, disadvantages and application scenarios of each method. This review presents the common problems of 3D soil mapping, such as sparse soil profile data, low accuracy of 3D soil prediction, and insufficient information to create the data source for 3D soil modelling, and put forward some feasible research prospects.

• In situ Dissolution Kinetics of Ammonium Nitrogen Interacting with Precipitated Calcium Phosphate Determined by Atomic Force Microscopy

  GE Xinfei, ZHANG Wenjun

  DOI: 10.11766/trxb202309210395

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  【Objective】The increase in global food demand and the consumption of phosphorus (P) fertilizer in modern agriculture have caused P accumulation in extensively managed croplands. Most of the accumulated P deposits exist in sparingly soluble or insoluble species, leading to their low availability, which is almost impossible to use directly by plants or microorganisms. Therefore, improving the utilization of soil accumulated P is not only one of the effective ways to enhance the utilization efficiency of P fertilizers but also relieves the increasing tension of P resources. At present, a large number of macroscopic field experiments have revealed the synergistic promoting effect of nitrogen (N) on P activation and uptake. However, in the N and P interaction, in-situ observation of dissolved N interacting with precipitated P has been lacking. 【Method】Herein, Ca-P precipitates with different solubilities, namely sparingly soluble (DCPD) and insoluble (HAP), were selected as test materials. Taking aqueous solution as control, five NH4Cl concentrations (0.5, 5, 50, 500, 1,000 mmol?L-1) were set as N sources. The in-situ dissolution kinetics of DCPD and HAP at different N levels were directly observed by atomic force microscopy (AFM). AFM-based dynamic force spectroscopy (DFS) technique was employed to characterize the interaction between ammonium cations and DCPD/HAP surfaces at the molecular scale. 【Result】The result showed that the surface dissolved immediately, accompanied by the formation of triangular etch pits, following the addition of NH4Cl. When increasing the NH4Cl concentration, the surface dissolution rate of DCPD was significantly promoted. The quantitative results further exhibited the dissolved P mass was significantly increased from 27.00 mg?kg-1 to 145.0 mg?kg-1 with the increase of NH4Cl concentration from 0.5 mmol?L-1 to 1 000 mmol?L-1. By contrast, the surface morphology of HAP almost remained constant without obvious dissolution even if the NH4Cl concentration was up to 1 000 mmol?L-1. The dissolved P mass was 5.00 mg?kg-1, which was not significant compared with the dissolved P mass of 3.00 mg?kg-1 in aqueous solution. AFM-based DFS results showed that the interaction force between ammonium cations and DCPD (230.6 pN) was significantly greater than that between ammonium cations and HAP (154.0 pN). Due to the difference in binding strength of ammonium cations on Ca-P surfaces at the molecular level, the hydration layer of mineral surfaces is destroyed at different degrees. As a result, the surface dissolution kinetics of DCPD and HAP were significantly different when regulated by ammonium cations. 【Conclusion】This research provides method guidance for in-situ observation of nanoscale dissolution kinetics of different Ca-P minerals. It also illustrates the enhanced interface dissolution on negatively charged DCPD induced by ammonium cation to release available P, thus improving the continuous P supply capacity in soils.

• Characteristics of Spatial Distribution of Soil Organic Carbon in Anhui Province Based on Soil Profile Occurrence Layer and Environmental Variables

  GAO Wenjing, XIA Bing, LU Yuanyuan, YING Rongrong, HU Pengjie, LI Yixu, CHEN Hongfeng, QIAN Jiazhong

  DOI: 10.11766/trxb202402040063

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  Abstract:

  【Objective】Soil organic carbon (SOC) plays an important role in the global carbon cycle, and extremely small changes in SOC could cause dramatic changes in atmospheric CO2 concentration. Accurately grasping the spatial distribution characteristics of SOC and its main controlling factors is an important requirement for improving soil carbon sequestration potential and coping with climate change. Therefore, this study aimed to analyze the spatial distribution of SOC in the topsoil layer (A genetic horizon), subsoil layer (B genetic horizon), and parent material layer (Parent material) in Anhui Province from the perspective of the soil profile occurrence layer and explore the factors controlling the changes of SOC in different profile occurrence layers.【Method】 In this study, a total of 451 sites were distributed in the study area using the systematic distribution method combined with the judgmental distribution method. The basic soil parameters, such as SOC content, pH, soil texture, and bulk density, were obtained from 451 sites through wild sampling and indoor experiments. Meanwhile, the related environmental variables, such as climatic factors, topographic factors, and normalized difference vegetation index, were also collected. Also, we used geostatistical methods to obtain the best half-variance function model and spatial distribution characteristics of SOC content at different soil profile levels, as well as correlation analysis and random forest regression analysis to explore the influencing factors of spatial differences in SOC content.【Result】The results showed that the average organic carbon content of the soil profile in Anhui Province was 8.47 g?kg-1 and there was a phenomenon of surface aggregation of SOC, whose occurrence in the layer was as follows: A genetic horizon: 15.86 g?kg-1 ＞ B genetic horizon: 5.80 g?kg-1 ＞ Parent material: 3.74 g?kg-1 and all of them had moderate spatial variability. The spatial distribution map of SOC showed that the spatial distribution of organic carbon content in each occurrence layer was generally increasing from north to south. We also found that there were some differences in the driving factors of SOC content in different profiles of the occurrence layer. In the A genetic horizon, soil texture, and bulk density were the most important factors affecting SOC content; as the depth of the soil layer increased, the influence of topographic factors and soil texture gradually strengthened on the accumulation of SOC content in the B genetic horizon. For the Parent material, the influence of soil texture, topographic factors, and bulk density were all more influential on the SOC content.【Conclusion】Soil texture is the main factor driving the spatial distribution characteristics of SOC in Anhui Province, but the effects of topographic factors and bulk density should also be fully considered in the subsequent development of SOC control measures, to provide theoretical support for improving soil quality and coping with climate change.

• The Microbial Diversity of Reclaimed Soil Drives Its Multifunctional Variation in the Eastern Plain Mining Area

  MA Jing, HUA Ziyi, YOU Yunnan, ZHU Yanfeng, ZHNAG Qi, CHEN Fu

  DOI: 10.11766/trxb202401010001

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  Abstract:

  【Objective】Land reclamation is a significantly important way to restore soil productivity in high groundwater mining areas. However, most of the reclaimed soil always shows poor functions, such as lower fertility and biodiversity, while the in-depth understanding of microbiological mechanisms underlying the formation and restoration of multifunctional reclaimed soil is still deficient. 【Method】Four reclamation plots including 9 years, 12 years, 15 years, and 18 years of reclamation, and 1 control plot from the Dongtan mining area in Zoucheng City, Shandong Province, were selected as the research objects. A total of 75 surface soil samples were collected, and 18 soil physical, chemical, and biological indicators such as organic carbon were measured to explore the interaction between soil microbial communities and soil multifunctionality, as well as the microbiological mecha-nisms of multifunctionality variation. Moreover, based on the molecular ecological network methods, supplemented by statistical analysis methods, several microbial networks were constructed to investigate the interaction between microbial community di-versity, network structure, and soil multifunctionality. 【Result】 The results showed that: (1) Land reclamation activities and the normal vegetation rotation of the cultivated land have significantly improved soil multifunctionality, with soil multifunctionality almost reaching the undisturbed control level after 18 years of reclamation. Moreover, among the soil properties, soil organic carbon, pH, available phosphorous, and most enzyme activities were important influencing factors for multifunctionality. (2) With the increasing reclamation years, soil microbial diversity significantly increased, while the richness performance of bacteria and fungi was different. The increasing trend of bacteria was not significant after 12 years of reclamation whereas fungi in-creased significantly until 18 years of reclamation. However, the abundance of bacteria and fungi reached normal farmland lev-els after 15 years and 18 years of reclamation, respectively. (3) The analysis results of the microbial co-occurrence network showed that the nodes, edges, average degree, average path length, network density, clustering coefficient, and betweenness centrality in the bacterial community co-occurrence network significantly increased with the increase of reclamation time. More-over, the topological properties of bacterial and fungal subnetworks such as edge, degree, and network density were signifi-cantly positively correlated with soil multifunctional properties. The diversity of microbial communities showed a positive im-pact on the network complexity, enhancing the association between species and thereby enhancing their versatility. Both the complexities of bacterial and fungal community networks presented significant correlations with soil multifunctionality. The impact of bacterial network complexity on soil multifunctionality was not affected by other indicators, whereas the correlation between fungal network complexity and soil multifunctionality was influenced by bacterial richness, soil microbial diversity, and fungal richness. The structural equation model results indicated that microbial diversity can directly and positively regulate soil multifunctionality, or indirectly manipulate soil multifunctionality by positively influencing the network complexity of bacteria and fungi.【Conclusion】 This study has revealed the driving mechanism of multifunctional restoration of reclaimed soil in the eastern plain mining area, which would provide important guidance for the deeper understanding of the development and func-tional succession of reclaimed soil microbiota, as well as soil quality management and protection.

• Effects of Biochar on Red Soil Nematode Community Characteristics under Chemical Fertilizer Reduction

  CHENG Liuzhu, ZHU Baijing, CHENG Yanhong, WAN Bingbing, LIU Ting, TAO Yiheng, CHEN Xiaoyun, HU Feng, LIU Manqiang

  DOI: 10.11766/trxb202311120469

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  Abstract:

  [Objective] The approach of reducing chemical fertilizer usage while increasing the application of organic materials is a common strategy for maintaining optimal crop yields and preserving soil ecological functions. Biochar, as a carbon-rich, alkaline, and porous byproduct produced from biomass pyrolysis, has great potential in soil biodiversity restoration and soil health improvement in acidic red soil areas. [Method] This study conducted a 2×3 full factorial interactive design experiment in red soil cultivated with sweet potato-rapeseed in subtropical arid areas. The experiment involved the application of organic materials (control without organic material application, straw, and biochar) and two fertilizer application rates (full dose of NPK fertilizer and reduced dose of 60% NPK fertilizer), totaling six treatments. The aim was to investigate the impact of biochar application on nematode communities in upland red soils and to understand the underlying mechanisms after five years of application. [Result] The results indicated that under full chemical fertilizer application, the use of biochar significantly increased the abundance of bacterivores and the ratio of microbivores to herbivores, reduced the root-to-shoot ratio of sweet potatoes and soil soluble organic carbon, and increased soil mineral nitrogen. Under reduced chemical fertilizer application, compared to the control and straw application, biochar significantly increased the abundance of total nematode, bacterivorous, herbivorous, and omnivorous predators. Simultaneously, it increased the sweet potato root biomass, root-to-shoot ratio, and soil pH but significantly decreased soil mineral nitrogen. By analyzing the relationship between soil nematode communities and plant growth as well as soil properties, it was evident that the application of biochar in combination with reduced chemical fertilizer led to a reduction in soil nutrient availability, thus nutrient limitation prompted plants to allocate more photosynthetic products below ground, resulting in increased crop root biomass and the abundance of herbivores. [Conclusion] This study suggests that under the background of reducing chemical fertilizer and increasing the application of organic materials in China, soil fertilization practices combining biochar application with reduced chemical fertilizer should take into comprehensive consideration the potential adverse effects of nutrient deficiency on crop growth.

• Effect and Mechanism of Polystyrene on the Co-transport of Copper and Soil Colloids in Saturated Porous Media

  GONG Jiaqi, DONG Yanan, XU Shaohui, LIN Qing

  DOI: 10.11766/trxb202401150028

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  Abstract:

  【Objective】The ubiquitous colloidal substances in the environment profoundly affect the transport and transformation of pollutants in soil and groundwater. The impact of microplastics, as an emerging pollutant, on the transport of colloids and colloid-associated pollutants is still unclear. 【Method】Therefore, column experiments were conducted in saturated quartz sand, with polystyrene (PS) microplastics as the research object. By combining with sedimentation experiments, Fourier infrared spectroscopy (FTIR), and other methods, the influencing mechanisms of microplastics on soil colloid, copper (Cu2+), and their co-transport were investigated. 【Result】The results showed that PS facilitated the transport of soil colloids through mechanisms involving heterogeneous aggregation with soil colloids, competition for surface sites on quartz sand, and steric hindrance. This promotional effect was more pronounced in the presence of Cu2+. In comparison to soil colloid, the effect of PS on Cu2+ migration was not obvious due to its low concentration as well as low adsorption capacity. In the presence of PS, 83.47% of Cu2+ was transported in dissolved form, while 35.25% of Cu2+ was transported in colloidal form under the effluence of soil colloid. PS enhanced the mobility of soil colloids, but it concurrently reduced the adsorption of Cu2+ and facilitated the transport of dissolved Cu2+ compared to the scenario with only soil colloids. However, PS did not have a significant impact on the effluent concentration of total Cu. Furthermore, the mobility of PS was also influenced by soil colloids and Cu2+. 【Conclusion】 In general, microplastics in the soil environment not only directly interact with Cu2+, but also alter the properties of soil colloids. Changes in colloidal properties may be the primary reason for the impact of microplastics on the environmental behavior of Cu.

• Methods of Filling in Bulk Density Gaps of Cropland Topsoil in The Sichuan Basin

  LI Aiwen, LI Wendan, SONG Liangying, RAN Min, CHEN Dan, CHEN Jinli, QI Haoran, GUO Conghui, LI Qiquan

  DOI: 10.11766/trxb202311270498

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  Abstract:

  【Objective】This study aimed to construct a high precision prediction method for soil bulk density to accurately complete the regional soil attribute database.【Method】Based on the data of 2,883 typical cropland samples in the Sichuan Basin (including Sichuan Province and Chongqing Municipality) obtained during the second national soil census, this study used correlation analysis, variance analysis, and regression analysis to reveal the statistical characteristics and main controlling factors of the cropland topsoil bulk density in the Sichuan Basin. The traditional pedotransfer functions (PTFs), multiple linear regression (MLR) models, radial basis function neural network (RBFNN) model, and random forest (RF) models were used to establish a soil bulk density prediction model through three modeling methods: whole region, by river basin and by soil type, to fill the missing value of soil bulk density.【Result】The results show that the cropland topsoil bulk density in the study area ranged from 0.60 to 1.71 g·cm-3, with a mean value of 1.29 g·cm-3. Soil organic matter, soil subgroup, and rainfall in summer were the most important factors influencing bulk density. The RBFNN model constructed by the river basin can better capture the nonlinear relationship between soil bulk density and the influencing factors and the spatial non-stationarity of this relationship. The coefficient of determination (R2) and root mean square error (RMSE) of the 432 independent validation samples were 0.519 and 0.095 g·cm-3, respectively, which were significantly better than those of other methods.【Conclusion】Therefore, the RBFNN prediction model constructed in sub-basin is helpful to improve the imputation accuracy of the missing values of topsoil bulk density in the Sichuan Basin, and also provides a method reference for the imputation of missing values of soil properties in other regions.

• Screening of Indigenous Microbial Helpers for the Chlorpyrifos-degrading Bacterium Shingopyxis granuli CP-2

  LI Mei, WANG Zhongyang, JING Lili, HOU Yugang, MA Liya, SHENG Hongjie, YU Xiangyang†

  DOI: 10.11766/trxb202311200486

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  Abstract:

  【Objective】Chlorpyrifos residue poses a significant challenge to food safety. Microbial degradation which is called bioaugmentation is an effective approach for the elimination of such residues. Bioaugmentation often involves an invasion process requiring the establishment and activity of a foreign microbe in the resident community of the target environment. Interactions with resident micro-organisms, either antagonistic or cooperative, are believed to impact invasion. However, few studies have examined how the interactions between the invaded degrading bacteria and resident microorganisms in the target environment can influence microbial degradation. In this study, chlorpyrifos-degrading bacteria Shingopyxis granuli CP-2 was used as material, from the perspective of microbe-microbe interactions, to select resident bacterial helper of CP-2. 【Method】Soils from the field were first collected, a batch of bacteria from the soil was isolated by continuous dilution method, and identified by full-length sequencing of the 16S rRNA gene. The 16S rRNA gene sequences of all isolates were aligned using MUSCLE. Sequences in the alignment were trimmed at both ends to obtain maximum overlap using the MEGA X software, which was also used to construct taxonomic cladograms. A maximum-likelihood (ML) tree was constructed, using a general time reversible (GTR) + G + I model, which yielded the best fit to our data set. Bootstrapping was carried out with 100 replicates retaining gaps. A taxonomic cladogram was created using the EVOLVIEW web tool (https://evolgenius.info//evolview-v2/). The taxonomic status (phylum) of each rhizobacterial strain was also added as heatmap rings to the outer circle of the tree. The resident bacterial helper which could promote the growth of CP-2 was then screened by supernatant assay from the isolates isolated from soils, and the bioinformatics results of these helpers were analyzed. At last, a bacterial isolate which well promoted the growth of CP-2 was chosen, and its effect on CP-2""s ability to degrade chlorpyrifos was investigated in vitro. 【Result】109 strains of indigenous bacteria were isolated and were classified into four main phyla: Proteobacteria (54.1%), Actinobacteria (14.8%), Firmicutes (15.6%), and Bacteroidetes (15.6%). Among them, 41.3% significantly inhibited the growth of CP-2, 17.4% had no significant effect on CP-2, and 41.3% (45 bacterial strains) significantly enhanced CP-2""s growth and were identified as indigenous bacterial helpers of CP-2. The 45 bacterial strains in the helper bank mainly belong to 3 phyla, 4 classes, 7 orders, 13 families and 20 genera. One strain (B72), which exhibited a strong growth-promoting effect on CP-2 was selected to assess its impact on chlorpyrifos degradation by CP-2. The results demonstrated that both the bacterial strain B72 and its supernatant significantly promoted the chlorpyrifos degrading ability of CP-2. 【Conclusion】Together, the strains identified in this study provide valuable resources for future research and applications involving microbial degradation of soil toxicants such as chlorpyrifos or other pollutants. Furthermore, the indigenous bacterial helper of chlorpyrifos degrading bacterium CP-2 significantly promoted its ability to degrade chlorpyrifos, which offers theoretical guidance and technical support for potential co-inoculation strategies involving both chlorpyrifos-degrading bacteria and indigenous bacterial helpers aimed at pollution remediation.

• Progress of Survey, Monitoring, and Control Technology of Benggang Erosion in Red Soil Hilly Area

  DENG Yusong, CAI Chongfa

  DOI: 10.11766/trxb202312120526

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  Benggang is aunique type of soil erosion in the south of China, which refers to the erosion phenomenon of collapse and scouring of the hillside damaged by the combined action of hydraulic force and gravity. Bengngang erosion is an advanced stage of gully development and is a permanent gully that cannot be filled in by farming practices. Benggang mainly occurs in the southern granite hill region which is mostly agricultural production, and its harmful effects are serious, destroying land resources, affecting agricultural production, and seriously impeding the coordinated and sustainable socio-economic development. Due to the complexity of the factors involved in the formation of Benggang, the knowledge of the mechanism and the management measures are still being explored. The objective of this study was to identify the current status of soil erosion in the region by outlining the survey methods of Benggang erosion, to obtain basic information on Benggang erosion, and to provide a scientific and theoretical basis for the development of soil and water conservation measures. Specifically, this study detailed the methodology, content, and purpose of individual Benggang surveys, and through this process grasped the basic characteristics of Benggang erosion. Subsequently, the methodology of investigating the regional influencing factors of the Benggang was introduced, which mainly includes the main influencing factors of the Benggang, such as geological geomorphology, climatic conditions, soil parent material, vegetation, and anthropogenic activities. Based on the investigation, this study also compiles the monitoring techniques of the Benggang used in recent years, combining the traditional manual methods with emerging technologies to truly and efficiently grasp the distribution characteristics, influencing factors and erosion development trend. Then, the research progress on the risk assessment and prediction methods of Benggang was reviewed to objectively assess the losses or impacts caused by Benggang disasters and to explore preventive and control measures. Finally, existing measures and models for the prevention and control of Benggang are discussed based on the survey of basic information on Benggang, field monitoring methods and risk assessment and prediction studies. Our investigation shed light on the current situation of erosion and the prediction of the development trend of Benggang, which is of great significance to the prevention and control of erosion in the Benggang region in China. The contents of the review in this study also assist in providing a basis for methods of investigation in the same erosion types, which can be generalized to the research of soil erosion in regions with similar geomorphology.

• Inhibition Mechanisms of Acidification Induced by Urea Application Using Organic Carbon Sources with Different Availability for Microorganisms in Ultisol

  GUAN Peng, WANG Ruhai, SHI Renyong, Li Jiuyu, XU Renkou

  DOI: 10.11766/trxb202308140323

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  Abstract:

  【Objective】 This study investigated the mechanism of different organic carbon (C) sources to control fertilizer nitrogen (N) transformation and its induced soil acidification. 【Method】 Four types of organic C sources (glucose, sodium benzoate, cellulose, and lignin) with different availability for microorganisms were selected for a 45-day indoor incubation experiment. It was conducted under the condition that the C/N ratio of C source and fertilizer (urea) was 40. The effects were analyzed for the combined application of organic C source and urea on N transformation and soil acidity in Ultisol. 【Result】 The results showed that intensive nitrification occurred when urea was used solely in Ultisol, resulting in a soil pH decrease of 1.17 pH units at the end of the incubation. Compared with the sole application of urea, the combined application of organic C sources and urea significantly enhanced soil respiration, and decreased soil inorganic N by 17.1%-99.4% and soil NO3--N by 46.1%-99.9%. However, these organic treatments increased soil microbial biomass N and solid organic N (non-extractable N) by 3.0%-14.8%, and increased soil pH by 0.67-3.11 pH units. These findings suggest that the combined application of organic C sources and N fertilizer promoted the immobilization of fertilizer N by soil microorganisms and soil N sequestration, thereby significantly reducing nitrification and soil acidification induced by N fertilizer. Specifically, as a labile organic C source, glucose facilitated the rapid immobilization of fertilizer N by microorganisms in the early stage and the mineralization of organic N in the later stage. It indicated that glucose could play a role in temporary storage and slow release of fertilizer N in the soil. Cellulose was less easily utilized by microorganisms and also promoted microbial immobilization of fertilizer N. Although cellulose was not as fast as glucose, it had strong immobilization capacity and high C use efficiency, which was conducive to the long-term immobilization of fertilizer N in the soil. Lignin, a resistant organic C source, weakly promoted microbial immobilization of fertilizer N but directly inhibited nitrification. The mentioned C sources regulated the N transformation process and increased the soil pH by approximately 0.6 pH units. Sodium benzoate, as a labile organic acid salt, reduced nitrification directly by inhibiting nitrification and indirectly by promoting microbial N immobilization, although the microbial immobilization of fertilizer N was significantly lower than that of glucose and cellulose. Decarboxylation of sodium benzoate rapidly consumed a substantial amount of H+ and significantly increased the soil pH by approximately 3.0 pH units. 【Conclusion】 The chemical properties of organic C sources, including the complexity of their chemical structure, microbial availability, microbial C use efficiency, and microbial toxicity, are the main factors affecting the transformation process of soil C and N, and consequent soil acidification. The findings obtained in this study provide significant theoretical support for the effective and sustainable management of soil nutrients and acidity in cropland.

• Effects of Dazomet Fumigation and Reductive Soil Disinfestation on Antibiotic Resistance Genes in Farmland Soil

  YU Wenhao, LI Shu, LIN Yulan, ZHANG Jingqing, XU Chenwei, LIU Liangliang, ZHANG Jinbo, CAI Zucong, ZHAO Jun

  DOI: 10.11766/trxb202309100369

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  [Objective] The prevalence and dissemination of antibiotics resistance genes (ARGs) in farmland soils have become a major threat to food security and human health. However, there is still no effective method to remediate ARGs-contaminated farmland soil. Chemical fumigation and reductive soil disinfestation (RSD) are widely used to kill soil-borne pathogens in agricultural production, but it is still unknown whether they are capable of reducing the abundance of ARGs in ARGs-enriched soil. [Method] In this study, an ARGs-enriched farmland soil due to long-term application of chicken manure was selected, and soil incubation experiment with seven treatments: CK (control without soil treatment), FCK (maximum water holding capacity treatment), DZ (chemical fumigation with 0.02% dazomet), and RSD with 1% ethanol (ET, TOC: 521.7 g·kg-1), alfalfa (AL, TOC: 454.9 g·kg-1, C/N: 21.2), molasses (MO, TOC: 270.1 g·kg-1, C/N: 12.6) and the mixture of alfalfa and molasses (AM, m/m=1:1), were conducted to investigate the shifts in absolute abundance and relative abundance of ARGs and mobile genetic elements (MGEs) via real-time PCR. The effects of different treatments on soil ARGs and MGEs were evaluated by reduction rate. [Result] Results showed that RSD treatment could decrease the relative abundance of aadA21, msrE, tetG, tetM, and ErmF genes, with the reduction of the aadA21 gene in relative abundance being 50.5%~58.3% in AL-, MO-, and AM-treated soils, while the relative abundances of msrE, tetG and tetM genes were significantly lowered by ET treatment, with the reduction rate being as high as 80.9%, 78.3%, and 66.9%, respectively. Meanwhile, RSD treatment could significantly decrease the relative abundance of MGEs (IS6100 and IS26 gene), with the reduction rate being 67.7%~74.3% and 38.1%~42.6%, respectively. In addition, the relative abundances of ARGs and MGEs were slightly increased in DZ treatment, with the increasing rate of ARGs and IS26 gene being 21.9% and 42.6%, respectively. [Conclusion] Collectively, RSD treatment can decrease soil ARGs contamination by reducing the relative abundance of ARGs and MGEs, limiting the horizontal transfer ability of ARGs, and the reduction effect is related to the type of organic materials used. Moreover, RSD treatment is more effective in reducing the relative abundance of ARGs and MGEs than dazomet fumigation and has the potential for rapid remediation of ARGs-contaminated soil.

• Characteristics of Soil Organic Carbon Fraction Accumulation and Stability under Different Rice-rape Rotation Measures

  SHU Yeqin, PENG Fuxi, LEI Wenshuo, JIANG Tongtong, CHEN Yumei, LIU Weimin, ZHANG Zhenhua, XIA Yinhang

  DOI: 10.11766/trxb202311030452

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  Abstract:

  Rape multiple-cropping is an important planting mode to promote grain stabilization and rapeseed increase in South China rice growing area. We explored the influence of soil organic carbon (SOC) accumulation and its stability characteristics under different rice-rape rotation measures with whole-straw returning, which is of great significance for in-depth analysis of soil carbon cycle in paddy fields by making full use of winter fallow fields to plant rape. This study is based on an 8-year yield localization experiment. In contrast with rice-rice-winter fallow, we explored the characteristics of SOC and its fraction accumulation under three rice-rape rotation treatments: rice-rice-rape, rice-rape-tillage, and rice-rape-no tillage. The results indicated that the content of SOC in 0~20 cm soil layer was increased by 5.28%~25.12% under the three rice-rape rotation treatments, especially under the rice-rice-rape treatment. Also, the increasing rate of SOC in 20~40 cm soil layer was 18.48%~43.97%, among which the rice-rape-tillage and the rice-rape-no tillage treatment reached a significant level. Except for rice-rape-tillage treatment in 0~20 cm soil layer, the content of mineral-associated organic carbon (MAOC) from all the rice-rape rotation measures was increased significantly in different soil layers. At the same time, the ratio of particulate organic carbon (POC) to SOC was significantly decreased while the ratio of MAOC to SOC increased in each treatment from both 0~20 cm and 20~40 cm soil layer. The increasing rate of MAOC/SOC were 2.31%~7.49% and 1.56 %~2.66% in the two soil layers, respectively. Possible causes of these results may be that rice-rape rotation increased the activity of organic carbon invertase enzyme (β-glucosidase、β-1,4-glucanase and Laccase) as well as microbial biomass carbon in 0~20 cm soil layer to varying degrees, thereby promoting the conversion of POC to MAOC. In summary, rape multiple-cropping in winter fallow not only promoted the accumulation of SOC in paddy field, but also increased the ratio of MAOC/SOC, ultimately enhancing the stability of soil carbon pool.

• Effect of Soil Acid Reduction and Fertilizer Cultivation Under Conditioner Application: Meta-analysis Based on Acid Soil Improvement Studies in China

  MING Runting, WAN Fang, NA Liping, WU Haicheng, WANG Wei, TAN Wenfeng, WU Yupeng†

  DOI: 10.11766/trxb202311050456

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  Abstract:

  【Objective】This study aimed to accurately evaluate the effect of soil conditioner application on acid reduction and fertilizer cultivation of acidic soils in China. 【Method】This study conducted a meta-analysis of 127 published literature, and identified the effects of acid soil conditioner application on soil acidity, soil fertility, and crop yield. 【Result】The results showed that the acid reduction effect of the conditioner in extremely acidic soil (pH≤4.5) was the best. After application, the soil pH increased by 14.39%, and the reduction rates of exchangeable Al and exchangeable acidity reached 68.61% and 69.90%. The pH and basicity of the conditioner itself were the main factors affecting the acid-lowering effect of the conditioner, among which the lime conditioner had the best effect. It was observed that the soil pH increased by 18% and the exchangeable acidity decreased by 75.81% after application. The nutrient content of the conditioner itself and the amount of the conditioner were the main factors affecting the soil fertility after the conditioner application and the application of organic fertilizer had the best effect on the improvement of soil available nitrogen and available phosphorus (60.16%, 135.30% respectively). Also, biochar amendments had the best effect on the improvement of soil-available potassium and organic matter (75.52% and 76.02%). The application of amendments can reduce soil acidity and increase soil fertility to increase production, and biochar amendments had the best effects of increasing production, reaching 78.23%.【Conclusion】For managing acidic soils, it is recommended to apply high pH and high alkalinity amendments such as lime and biochar. For acidic soils with low organic matter content, it is recommended to apply high-alkalinity organic fertilizer, biochar and other amendments while biochar and mineral amendments are recommended for acidic soils with high organic matter content. For weakly acidic soil, it is recommended to apply common organic fertilizer. Nevertheless, it is necessary to further strengthen research on the combined application of inorganic and organic amendments to obtain a better effect on acid soil improvement.

• Research of Paddy Soil Dissolved Organic Matter Composition and its Binding Process with Cd2+

  LIANG Yihao, NI Caiying†, LI Yanliang, XIAO Luochang, JIAN Minfei

  DOI: 10.11766/trxb202310180426

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  Abstract:

  【Objective】Cadmium (Cd) is the heavy metal pollutant with the highest over-limit rate in paddy soil in China. The bioavailability and mobility of Cd are affected by dissolved organic matter (DOM) in the soil. Paddy fields are important food production areas in China. As an important ecological agriculture mode in the rice industry, integrated planting and breeding of rice fields is of great significance to rural revitalization. The modification of paddy field environments and fishing can change DOM, but the complexation process between soil DOM and Cd2+ in paddy soil and during integrated planting and breeding of rice field process has not been clearly understood. 【Method】In this study, the complexation process between DOM and Cd2+ in rice-shrimp cultivation (RS) and rice monoculture (CK) systems was investigated using a comprehensive array of analytical techniques, including ultraviolet-visible absorption spectrum (UV-Vis), 3D fluorescence spectroscopy, synchronous fluorescence spectroscopy, parallel factor analysis (PARAFAC), 2D correlation analysis (2D-COS), and the modified Stern-Volmer binding reaction model. Herein, RS was taken as an example of integrated planting and breeding of rice fields.【Result】The PARAFAC analysis showed that soil DOM components of RS and CK were similar, including 1 tryptophan(C1) and 3 humus components (C2, C3, C4). Compared with CK, the proportions of C2 and C4 in soil DOM of RS were lower, while C3 was higher, and C1 was not significantly different. The UV-vis spectrum showed that DOM absorbance in CK was higher than in RS, with the absorption peak mainly located at 200-230 nm. With the increase of Cd2+, the change of UV-vis spectrum and UV254 was significantly different between RS and CK. Synchronous fluorescence spectra and 2D-COS analysis showed that paddy soil DOM fluorescence intensity changed with the increase of Cd2+, three absorption peaks were found by synchronous fluorescence spectra in DOM of paddy soil, which were the peak of tryptophan at 270 nm and the humus peak at 310 nm and 370 nm, respectively. The binding order between soil DOM and Cd2+ in RS was humus (310 nm), tryptophan, and humus (375 nm) , respectively. However, in CK, the binding order was tryptophan, humus (375 nm), humus (310 nm). In the Stern-Volmer binding reaction model, the fluorescence intensity of C1 and C4 decreased with the increase of Cd2+, but the fluorescence intensity of C2 and C3 was unstable, which showed that the complexation of humus components C2 and C3 with Cd2+ had instability. This also led to the failure of fitting C2 and C3 in the model. The complexation constants lgK of C1 and C4 in the soil DOM of RS were 4.25 and 5.03, which were higher than in CK.【Conclusion】The soil DOM in RS and CK mainly consisted of humus and the material composition ratio of soil DOM in RS was different. The complex process of DOM and Cd2+ in paddy soil belonged to static quenching and the aromatic structure affected the stability of DOM and Cd2+ complexation. Also, RS influenced the binding ability of tryptophan and fulvic acid DOM to Cd2+ whereas the instability of the complexation of humus with Cd2+ and the complexation of C4 with Cd2+ can enhance the bioavailability of Cd in soil. The results of this research can provide a scientific reference for the study of soil Cd pollution mechanism and pollution prevention in paddy fields.

• Effect of Canopy Nitrogen Deposition on Soil Phosphorus Fractions in a Moso Bamboo Forest

  WEI Jingwei, XIAO Xiangqian, ZHUO Shoujia, JIANG Wenting, SUN Hongyang, CHEN Youchao, LI Yongfu, YU Bing, CAI Yanjiang†

  DOI: 10.11766/trxb202309110372

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  Abstract:

  【Objective】Nitrogen (N) deposition is an important global climate change factor affecting soil phosphorus (P) cycling in forest ecosystems. However, understory N application typically applied directly to the ground, has been widely used to simulate N deposition in forest ecosystems in the past. This simulation method may neglect the retention and adsorption effect of the forest canopy, which cannot truly assess the effect of N deposition on soil P cycling. Moreover, organic N is another important component of atmospheric N deposition, but the ecological effect of the organic N deposition has not been fully studied.【Method】To evaluate the effect of atmospheric N deposition on soil P cycling, a field experiment was conducted involving six treatments: canopy control (CNA-CK), canopy inorganic N addition (CNA-IN), canopy organic N addition (CNA-ON), understory control (UNA-CK), understory inorganic N addition (UNA-IN), and understory organic N addition (UNA-ON) based on the Anji MosoBamboo Ecosystem Research Station of Zhejiang A&F University, in Anji County, Zhejiang Province. The N deposition rate was set at 50 kg·hm-2·a-1 (based on the atomic mass of N, the same as below). IN uses ammonium nitrate while ON uses a mixture of 25 kg·hm-2·a-1 urea and 25 kg·hm-2·a-1 glycine as the N source. The CK treatment involves adding an equal amount of water. Soil P fractions, microbial biomass P, acid phosphatase activity, P cycling functional gene abundance, and some physicochemical properties were measured to investigate the effects of different N deposition simulation approaches and N components on soil P fractions and their driving factors.【Result】The results showed that canopy N addition (CNA) significantly reduced soil total P, occluded P, and labile P concentrations compared to understory N addition (UNA) with the percentage of 15.1%-26.5%, 18.3%-21.5% and 9.7%-38.3%, respectively. However, soil P fractions did not differ significantly between CNA-ON and CNA-IN treatments, whereas UNA-IN treatment significantly reduced resin P and labile P content compared to UNA-ON treatment. Acid phosphatase activity and pH were the main factors affecting soil P fractions, but N deposition did not significantly influence soil P cycling functional gene abundance.【Conclusion】Therefore, it was suggested that simulating N deposition via CNA significantly reduced the contents of total P and P fractions such as occluded P and labile P of Moso bamboo forest soils, whereas simulating N deposition via conventional UNA underestimated this reduction effect. Soil P is closely linked to the cycling of soil carbon and N, which are vital for maintaining a balanced nutrient ecosystem. Consequently, future simulation experiments on N deposition should systematically consider the effects of N deposition simulation approaches and N addition components on soil carbon, N, and P cycling processes.

• Effects of Single Application of Organic Amendments and Their Combination with Biochar on Microbial Community Composition in a Red Soil

  XU Yimeng, ZHANG Lei, BAI Meixia, ZHOU Yan, QIN Hua, XU Qiufang, CHEN Junhui

  DOI: 10.11766/trxb202308200332

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  Abstract:

  【Objective】This study aimed to clarify the effects of different return methods of organic matter on the characteristics of soil microbial communities.【Method】The changes of soil microbial community abundance and structure under single application of maize straw, sheep manure and combined application with biochar were analyzed by quantitative PCR and high-throughput sequencing based on two years of field experiments in dry cropland red soil.【Result】The results showed that: (1) Compared with the control (no material), the soil pH and nutrient content of sheep manure alone increased significantly, while the single application of straw had no significant effect on them. Compared with straw and sheep manure alone, soil organic carbon content under the treatment of biochar co-application with straw or sheep manure was significantly increased by 133.5% and 81.47%, respectively. (2) The abundance of bacteria and fungi under the treatment of sheep manure treatment significantly increased by 448.7%and 1 709%, respectively, and the abundance of bacteria under the treatment with biochar was further increased by 35.34%. Straw alone only increased fungal abundance. Single straw application and its combination with biochar significantly reduced bacterial diversity and richness but had no significant effect on fungal diversity. (3) Straw, sheep manure and biochar alone changed the structure of bacterial and fungal communities, and there were significant interaction effects. Functional predictive analysis showed that the combination of biochar and organic materials reduced carbohydrate metabolism and the abundance of potential plant pathogens. Available phosphorus, pH, total nitrogen and available potassium were the main factors affecting the abundance and structure of soil microbial communities.【Conclusion】In summary, the combined application of sheep manure and biochar can effectively improve the fertility of dryland red soil, increase the abundance of soil microorganisms, and reduce the number of potential pathogens. Thus, the combined application of sheep manure and biochar can be used as an effective measure to improve the fertility of dryland red soil and maintain soil health.

• Properties and Aggregation Characteristics of Humic Acid in Surface Soil Under Two Forest Vegetations of Jinyun Mountain

  BI Linna, TIAN Rui†

  DOI: 10.11766/trxb202309280403

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  Abstract:

  【Objective】Soil organic carbon (SOC) pool, the largest C pool in terrestrial ecosystems, can achieve long-term C sequestration. SOC plays a vital role in the global C cycle and is a key link in achieving C peaking and C neutrality goals. Humic acid (HA) is one of the most important and more stable components of soil organic matter, representing a more stable soil C pool. The vegetation coverage type of regional soil affects the quantity, quality and composition of HA, and further affects its aggregation characteristics. In this study, HA in surface soil under bamboo forest (Altitude 580 m) and broad-leaved forest (Altitude 280 m) in Jinyun Mountain, Chongqing, was taken as the research object, and then surface properties and aggregation characteristics of these two HA were clarified. 【Method】The structural characteristics were evaluated by element analysis, thermal gravimetric analysis, and Fourier infrared spectroscopy. Combined with dynamic light scattering and zeta potential measurement, the aggregation kinetic characteristics of these two HA colloids induced by Na+, Mg2+ and Ca2+ were studied and compared. 【Result】It was found that HA in bamboo forest soil had higher C/N, C/H, stronger thermal stability and aromatic infrared absorption characteristic spectra, indicating HA in bamboo forest soil had more aromatic functional groups, more complex structure, and higher humification degree. The results of dynamic light scattering showed that the critical coagulation concentrations of Na+, Mg2+, and Ca2+ for the HA colloids of bamboo forest soil were 1 097.9 mmol?L-1, 8.6 mmol?L-1, and 5.1 mmol?L-1, respectively. The HA colloids of broad-leaved forest soil did not aggregate in the Na+ system, and the critical coagulation concentrations in Mg2+ and Ca2+ systems were 80.7 mmol?L-1 and 20.2 mmol?L-1, respectively. The zeta potential of HA in bamboo forest soil was much lower than that in broad-leaved forest soil. The absolute value of the zeta potential of HA in bamboo forest soil was 3.43 times that of HA in broad-leaved forest soil, which could be used to explain the difference in aggregation characteristics between the two. The sensitivity of the HA in bamboo forest soil to three cations is much higher than that of HA in broad-leaved forest soil, which can quickly aggregate and form larger particle sizes. 【Conclusion】The change of coverage vegetation types will cause the corresponding change of HA properties in surface soil. The humification degree of HA in high-altitude bamboo forest soil is higher, and the sensitivity to cations is also higher. The results of this study provide an important reference for understanding the formation and stability of HA after organic matter input into soil.

• Response mechanisms of soil microbial carbon use efficiencies to cropland management measures

  ZHANG Chenyang, SUN Liyang, XU Minggang, LIJianhua, CAI Andong

  DOI: 10.11766/trxb202309020351

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  Abstract:

  【Objective】Soil microbial carbon use efficiency (CUE) is an important indicator reflecting the regulation of the soil carbon cycle by microorganisms through their metabolism. However, the response and driving factors of soil microbial CUE to different management measures in cropland ecosystems are still unclear. This hinders a deep understanding of soil organic carbon turnover, rapid improvement of soil fertility, and effective mitigation of climate change.【Method】We collected published literature from around the world, and established 198 paired of relatively independent soil microbial CUE databases under different cropland management measures, including 13C-labeled substrate (CUE13C), 18O-labeled water (CUE18O) and stoichiometric model (CUEST) approaches. We quantitatively evaluated the response of soil microbial CUE to different cropland management measures under specific climate, soil properties, and experimental conditions by meta-analysis, combining Pearson and regression analysis to study the biotic and abiotic factors that control soil microbial CUE variation.【Result】(1) Compared with no biochar addition, biochar addition increased soil microbial CUE13C and CUE18O by 9.40% and 18.22%, respectively, while CUEST decreased by 40.01%. Compared with no fertilization, the application of chemical fertilizers could reduce soil microbial CUE18O (-4.71%), but increased soil microbial CUEST (28.20%), whereas straw amendments led to a decrease in soil microbial CUE18O and CUEST by 14.08% and 28.64%, respectively. Relative to conventional tillage, no or reduced tillage significantly increased soil microbial CUE13C, CUE18O, and CUEST (-2.12%-15.45%). (2) There were significant differences in the effects of cropland management measures on soil microbial CUE under different climates, soil properties and experimental conditions. Cropland management measures in semi-arid and humid areas reduced the soil microbial CUE13C by 8.80% and increased by 4.69%, but the soil microbial CUE18O decreased from 44.57% to -2.31%. When the soil organic carbon content was > 12 g·kg-1, cropland management measures increased the soil microbial CUE13C and CUEST by 7.79% and 12.87%, respectively. In the transition from acidic to alkaline soils, cropland management measures caused the soil microbial CUE13C to decrease from 12.74% to -7.51%. Also, as soil clay content increased, soil microbial CUE13C and CUEST decreased, while soil microbial CUE18O showed an increasing trend. With the increase of soil cation exchange capacity, soil microbial CUE18O and CUEST showed a decreasing trend. When the experimental duration was 3-10 years, cropland management measures increased soil microbial CUE18O by 43.49% while soil microbial CUEST decreased by 23.72%. (3) Soil microbial CUE13C increased with aridity index and decreased with soil pH. Furthermore, the soil microbial CUE18O increased with soil microbial growth rate and soil microbial biomass carbon. Soil organic carbon, β-glucosidase and N-acetyl-glucosaminidase were positively correlated with soil microbial CUEST (P < 0.05) whereas soil clay content was negatively correlated with soil microbial CUEST (P < 0.01). 【Conclusion】Considering climatic factors and soil chemical properties, and the response of microbial activity and function to cropland management measures at a specific site is conducive to adjusting the soil microbial CUE at the microbial community or cell level, thereby effectively promoting soil carbon formation and accumulation in cropland ecosystems.

• Long-term Observation Effects on Soil Salinity and Fertility in Saline-alkali Land Reclamation Under Drip Irrigation

  HUO Weige, PENG Yi, ZHANG Shaomin, LIU Shenglin, BAIDENGSHA Maimaiti, FENG Gu†

  DOI: 10.11766/trxb202309080368

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  Abstract:

  【Objective】The submembrane drip irrigation planting mode has been a major factor in the evolution of physicochemical traits after the reclamation of saline-alkali land in inland arid areas, especially the changes in soil salinity and available nutrient content. 【Method】In this study, the gray desert soil of Xinjiang was studied by continuous localization survey and observation of the sample plot. The sample plots of Manas in Xinjiang were selected for land reclamation in different years in 1996, and four surveys were carried out from 2010 to 2020. The dynamic changes of soil salinity and fertility traits of gray desert soil under the condition of submembrane drip irrigation cotton after reclamation were monitored at fixed points, and the differences of several plots after different planting years were compared.【Result】The main results suggest that the soil salinity in the topsoil (0-20 cm) was significantly reduced after the reclamation from uncultivated land to farmland, and the average salinity of various plots decreased to 3.71 g·kg-1 after 6-10 years of reclamation. The average annual decline rate was 1.41 g·kg-1·a-1, reaching the level of mild salinization, then with the continued reclamation (11-25 years), the soil salinity was maintained between 2.06-2.11 g·kg-1, and reaching the non-salinization level. The soil pH in different reclamation years showed a significant downward trend after reclamation. With continued reclamation (11-25 years), the average soil pH remained between 8.2 and 8.5, which was slightly alkaline. With increasing years of reclamation, the soil available phosphorus (P) increased significantly, after 11-25 years of reclamation and planting, the soil average available P level remained between 13.33, and 19.97 mg·kg-1. This indicates that the variation of soil fertility was different with the different reclamation years. The soil organic matter increased significantly after 6-10 years of reclamation while the soil available potassium slowly decreased after 1-5 years of reclamation but slightly increased after 6-10 years. Also, available potassium increased to the original level after 11-16 years and then remained stable. The content of soil inorganic nitrogen increased significantly after 6-15 years of reclamation and remained stable after 16-25 years.【Conclusion】Our study showed that the process of reclamation and utilization of uncultivated land into farmland had a significant effect on the improvement and cultivation of soil P fertility. The uncultivated land reclamation and utilization effectively reduced soil salinity and pH, and it took 6-10 years to change the good land after uncultivated land reclamation. This study provides a theoretical basis for the control of salt content and the improvement of fertilization and farmland productivity during the reclamation process of inland saline-alkali uncultivated land.

• Mechanism of Degradation of Typical Malodorous Benzene Congeners in Soil by Activated Persulfate with Sulfidized Nano-zero-valent Iron Loaded on Biochar

  LI Yanlu, YANG Xinglun, BIAN Yongrong, MA Zhiyong, GU Chenggang, SONG Yang, XIANG Leilei, WANG Fang, JIANG Xin

  DOI: 10.11766/trxb202310240433

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  Abstract:

  【Objective】The degradation of organic pollutants in soil by activated persulfate (PS) with nanoscale zero-valent iron (nZVI) or sulfidized nanoscale zero-valent iron (S-nZVI) is currently one of the research hotspots in in-situ chemical oxidation remediation technologies. Benzene, toluene, ethylbenzene, and xylene (BTEX) are typical odorous pollutants in petrochemical-contaminated sites. Thus, the discovery of remediation technologies aimed to achieve efficient removal of BTEX and the elucidation of the degradation mechanism is of great environmental significance.【Method】The study established a persulfate oxidation system using biochar-supported sulfidized nano zero-valent iron (S-nZVI@BC) as the activator, explored the degradation of BTEX under different conditions, and compared its effectiveness with other materials for PS degradation. Moreover, based on chemical probe experiments, electron paramagnetic resonance (EPR) experiments, and purge-and-trap-gas chromatography-mass spectrometry (PT-GC-MS), the degradation pathways of BTEX were indicated.【Result】The results showed that S-nZVI@BC/PS system had the best degradation efficiency on BTEX in the soil at pH = 3, S/Fe = 1/4, Fe/C = 1/2, S-nZVI@BC dosage of 0.01g•g-1soil, and PS concentration of 30 mmol•L-1. The degradation rates of benzene, toluene, ethylbenzene, and ortho-xylene in the S-nZVI@BC/PS system reached 96.7%, 98.5%, 96.9%, and 98.4% within 2 h, respectively. The S-nZVI@BC catalytic system showed the best performance among the five different catalytic systems studied in the order of PS < nZVI/PS < nZVI@BC/PS < S-nZVI/PS < S-nZVI@BC/PS. Also, S-nZVI@BC maintained good reaction activity in a wide range of pH 2-9. There were three active free radicals in the system: SO4˙-, HO˙, and O2˙-, among which SO4˙- was confirmed as the main active substance in the reaction process. Based on main free radicals and intermediates, it is indicated that BTEX may have two degradation pathways: Free radical addition and free radical hydrogen extraction reaction.【Conclusion】Sulfur modification and biochar loading effectively improved the stability of nZVI catalytic performance, and S-nZVI@BC/PS can efficiently degrade BTEX. This study provides theoretical support for the establishment of efficient degradation technology for odorous pollutants in soils.

• 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

  Abstract(143) HTML(0) PDF(492.32 K)( 499) Collect

  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.

• 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.