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    • Research Progress on the Microstructure and Constituents of Fe-Mn Nodules in Soil

      WANG Yi, HUANG Laiming

      2023,60(2):317-331, DOI: 10.11766/trxb202107130360

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      Abstract:

      Ferromanganese concretions (or Fe-Mn nodules), as a specific type of soil neoformations, are formed during pedogenic processes. The structure of concentric rings in soil Fe-Mn nodules can be used to reconstruct paleoclimatic conditions and soil-forming environments. The constituents of soil Fe-Mn nodules can provide nutrients and energy for microbial metabolism that in turn affect the transformation, fixation and mobilization of soil nutrients and heavy metals. This article reviewed the research progresses on soil Fe-Mn nodules during the past several decades, including(i) the formation mechanism and process of Fe-Mn nodules and the associated influencing factors; (ii)differences in the microstructure and constituents of Fe-Mn nodules in different regions; and(iii) effects of Fe-Mn nodules on nutrient transformation and heavy metal sorption. Future research priorities include(a) study of the formation rates and environmental thresholds of Fe-Mn nodules during different stages of soil development; (b) establishment of the evolution models of Fe-Mn nodules in different soil-forming environments; and(c) elucidation of the mechanisms of stabilization and release of soil nutrients and heavy metals by Fe-Mn nodules. This will facilitate understanding of the pedogenic processes and elemental biogeochemical cycling in the Earth’s Critical Zone and provide a basis for quantitative evaluation of soil quality and function under changing environments.

    • Research Progress on Microbial-Mediated Mitigation of Nitrous Oxide Emissions from Agricultural Soils

      SHEN Weishou, XIONG Ruonan, ZHANG Huanhuan, YANG Siqi, GAO Nan

      2023,60(2):332-344, DOI: 10.11766/trxb202106170315

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      Abstract:

      Nitrous oxide(N2O), an important greenhouse gas, has a global warming potential of 265 times higher than that of an equivalent concentration of carbon dioxide. The N2O has a long atmospheric lifetime and does deplete the ozone layer in the stratosphere. Agricultural soil is an important source of N2O, which has a characteristic of diverse generation paths, multiple impact factors, and complicated regulation processes. Mitigation of N2O emissions from agricultural soils has long been the hotspot of research in this field. N2O-reducing bacteria harboring N2O reductase can reduce N2O to dinitrogen(N2), which is the only known sink of N2O consumption as a primary substrate in the biosphere. The direct use of microorganisms to decrease N2O emissions from agricultural soils is an emerging technology. We elaborated on the biological sources and sinks of N2O emissions from agricultural soils in detail, paying special emphasis on the screening and application strategies of microorganisms that can mitigate N2O emissions. There are three strategies for the direct use of microorganisms to decrease N2O emissions from agricultural soils: (1) application of the prepared microbial inoculum directly to the agricultural soil; (2) combination of the prepared microbial inoculum with fertilizers or other carriers before being applied to the soil; (3) construction of the microbial community with N2O mitigation effect, and then direct application to the soil or in combination with a carrier before being applied to the soil. We summarized two ecological mechanisms of microbial-mediated mitigation of N2O emissions from agricultural soils. One mechanism involved employing N2O-reducing bacteria containing nosZ gene to directly convert N2O to N2 in order to mitigate N2O emissions from agricultural soils. The other mechanism utilizes plant growth-promoting rhizobacteria to alter the community composition, abundance and activity of the N2O-reducing bacteria and indirectly mitigate N2O emissions from agricultural soils. We also discussed the environmental factors that affect the reduction of N2O to N2 by directly using microorganisms and the potential challenges. The biological process of reducing N2O to N2 is affected by many environmental factors, including the availability of NO3- and carbon sources, oxygen concentration, moisture content, temperature, pH and copper concentration. Among them, Cu availability and pH are some of the most important factors that determine the activity of N2OR. Several issues need to be addressed in future studies. For example, there are only a limited number of strains that have been screened with N2O mitigating effects. It remains unknown whether the inoculum colonizes roots or survive in the environment after the inoculation. The microbial ecological mechanisms are poorly understood; such as, how the inoculum achieve their beneficial effects in environments. Moreover, we lack effective technical means to regulate the inoculum to fully exploit their beneficial effects. Further, the methods to evaluate N2O mitigating effects also need to be improved. Finally, prospects on the application of microbial-mediated mitigation of N2O emissions from agricultural soils were suggested. The review provides an important technical reference for achieving the agricultural carbon neutrality strategic goal in China.

    • Promising Applications of Artificial Humification and Its Products in Agricultural Production

      LI Shunyao, QI Xuemin, CHEN Meihua, YANG Wei, SUN Kai, LI Yucheng

      2023,60(2):345-354, DOI: 10.11766/trxb202110080469

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      Abstract:

      Humic substance (HS) is the major component of soil organic matter and chemically can be depicted as a collection of diverse, relatively low-molecular-mass components of organic molecules, forming dynamic associations and stabilized by hydrophobic interactions and hydrogen bonds on the nanometer scale. The physiological effects of HS are widely documented and summarized as a result of enhancing nutrient use efficiency, aiding assimilation of both macro and micronutrients, and stimulating plant growth by induction of carbon, nitrogen, and secondary metabolism. Based on the formation mechanism and multifunctional properties of natural HS, scientists have applied HS to extracellular electron transport, environmental repair, cellular stress, and plant growth promotion. However, due to the limited supply of natural extraction sources of HS such as lignite, weathered coal, and peat, the market supply-demand of HS is increasing year by year. Given that the molecular structures of lignin and its derivatives are similar to natural HS, it is important to ask the question of whether artificial humification methods can be used to accurately control the oxidative decomposition of large-molecular lignin and/or the radical coupling of its small-molecular derivatives to synthesize humic-like products. Another important factor to consider is whether the synthesized products can match and even surpass the effects and functions of commercial HS. This creative idea has great commercial value and application prospects for realizing a continuous increase in agricultural production and income in China. In this review, the sources, structure characteristics, and functional attributes of natural HS were briefly generalized. The latest concept, mode, and mechanism of artificial humification by the use of macromolecule lignin and its derived-small phenolics are discussed, and the differences between artificial humification products and natural HS are also compared. It is confirmed that both artificial humification products and natural HS have C, H, O, N, and S elements, but the content of N in natural HS is higher than that of artificial humification products. In addition, they both contain phenolic -OH, -COOH, and aromatic components. Compared with artificial humification products, natural HS has more aromatic structures, but fewer oxygen-containing groups. Moreover, the application values of artificial humification products in agricultural production were explored. The agronomic effects of artificial humification products are extremely significant. On the one hand, artificial humification products can ameliorate soil physicochemical properties, increase soil fertility and water-holding capacity. On the other hand, these humic-like products are also able to serve as plant nutrient pools for promoting crop growth and development, improving nutrient use efficiency and crop yield. Therefore, the practical applications of artificial humification products are of great significance for agricultural production. At present, artificial humification techniques such as chemical oxidation, hydrothermal reaction, bio-composting, Fenton reaction, and fungal laccase-catalyzed oxidation have displayed a great application potential in the precise control of humic-like substance synthesis. In particular, fungal laccase exhibits unique advantages in humic-like substance synthesis due to its dual mechanism of oxidative decomposition and radical coupling. The humification reactions induced by fungal laccase have the characteristics of high catalytic efficiency, simple and controllable operating conditions, low energy requirements, and environmental protection, thus can be used to synthesize a variety of humic-like products. Also, the advantages and disadvantages, process paths, and main control factors of these humic-like substance synthesis technologies are summarized. Hence, this study provides theoretical support and technical guidance for researchers to conquer the artificial humification of lignin and its derivatives and the technology bottleneck of its large-scale application.

    Research Articles
    • Spatiotemporal Variation of Fertility Quality of Chinese Paddy Soil Based on Fuzzy Method in Recent 30 Years

      HUANG Jing, HAN Tianfu, SHEN Zhe, LIU Kailou, MA Changbao, WANG Huiying, QU Xiaolin, YU Zikun, XIE Jianhua, ZHANG Huimin

      2023,60(2):355-366, DOI: 10.11766/trxb202107050343

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      Abstract:

      【Objective】The spatiotemporal variation characteristics and driving factors of fertility quality of paddy soils in China were studied. 【Method】 Based on the long-term monitoring data (1988-2017) of the Ministry of Agriculture and Rural Affairs in the main rice areas in China, the fertility quality of paddy soil in the main rice areas was evaluated by the fuzzy mathematics (Fuzzy) method, and combined geo-statistics with machine learning. 【Result】In the recent 30 years, the soil fertility index (SFI) of the rice area in China increased significantly (P < 0.05). From the prophase (1988-1999) to the interim (2000-2009) and from the interim to the recent (2010-2017), the national paddy field SFI increased by 6.9% and 17.7% on average, respectively. The characteristics of SFI varied in different time stages in the main rice regions. The rice regions in southwest China and the middle reaches of the Yangtze River showed a significant increasing trend of slow in the early period (from prophase to interim) and fast in the later period (from interim to recent) (P < 0.05). Also the rice fields in South China and the Yangtze River Delta showed a rising trend of fast in the early stage (from prophase to interim) and stable in the later stage (from interim to recent). There was a decreasing trend in the earlier period (from interim to recent) and increasing in the later period (from interim to recent) in the Northeast rice region. At the recent, the distribution of paddy SFI in China showed a trend of higher in the north and lower in the south, higher in the east and lower in the west. The area with SFI exceeding the national average (0.61) accounted for 50.2%. Compared with the SFI of the rice region in the interim, the SFI showed an overall upward trend in the recent. The increased area accounted for 69.3%. The relative importance of soil organic matter and total nitrogen to SFI change (19.4%-60.3%) was much higher than that of other indexes (0.1%-13.3%) in all rice areas in the prophase and interim (except the middle stage of the northeast rice region). The relative importance of soil Olsen-P, available potassium and soil pH (except the northeast rice region) increased in all rice regions, and the relative importance of soil Olsen-P content increased to the maximum in the middle reaches of the Yangtze River. However, the relative importance of soil total nitrogen and soil organic matter content was greater in all rice regions.【Conclusion】In conclusion, the spatiotemporal variation characteristics of soil fertility quality and the changes of key driving factors at different stages and in different rice regions should be comprehensively considered. The balanced fertilization measures should be optimized to prevent and control soil acidification and to improve the fertility quality of paddy soil.

    • Acidification Resistance of Tobacco-planting Soils Derived from Different Parent Materials in Wuling Qinba District, China

      SHI Renyong, WANG Changjun, YAN Jing, LAI Hongwei, CHEN Zhenguo, LI Decheng, XU Renkou, SUN Jingguo

      2023,60(2):367-377, DOI: 10.11766/trxb202107010339

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      Abstract:

      【Objective】 This study aimed to investigate the effects of parent materials and initial soil pH on the resistance of soils to acidification. 【Method】 Twelve soil samples derived from different parent materials under tobacco-cultivation were collected from Wuling Qinba District, China. The pH buffering capacity (pHBC) of the different soil samples was determined by acid-base titration in the pH range 4.0 to 7.0. Additionally, the changes of soil pH, soluble Al and exchangeable Al following acid input were investigated through simulated acidification with HNO3. 【Result】 The results showed that soil pHBC was significantly affected by parent materials and initial soil pH. Due to the depletion of buffering substances in soils by acidification, the pHBC of weakly acidic yellow-brown soils and yellow soils (11.79-45.15 mmol·pH-1·kg-1) was lower than that of neutral yellow-brown soils and yellow soils (23.74-141.53 mmol·pH-1·kg-1). Therefore, the decrease in soil pH and increase in soil active Al in neutral yellow-brown and yellow soils were slow during the simulated acidification, indicating a weak acidification potential. Among the neutral yellow-brown soils and yellow soils, the soil pHBC increased with an increase in carbonate content in soils. The soils derived from limestone and carbonate parent materials reserved more carbonate (21.14 and 1.18 g·kg-1), which led to a higher pHBC than soils derived from quartzite and siliceous parents. However, the opposite tendencies were observed in the weak acid yellow-brown soils and yellow soils. In weak acid soils, the exchangeable base cations played the major pH buffering role due to the exhaustion of carbonate. Compared with the soils derived from limestone and carbonate parents, soils derived from quartzite and siliceous parents contained more clay and organic matter, which provided more H+ exchangeable sites and was thus beneficial to buffer exogenous acid and slow down the activation of soil aluminum during acidification. Among the 12 tested soils, the acidic yellow-brown soil derived from pelite was extremely sensitive to exogenous acids due to the lowest pHBC (11.79 mmol·pH-1·kg-1). When 6 mmol·L-1 HNO3 was added, the pH of the acidic yellow-brown soil derived from pelite was lower than that of the acid yellow-brown soils derived from carbonate parents and siliceous parents (by 0.74 and 1.10 pH units, respectively). Correspondingly, the soluble Al and exchangeable Al in the acid yellow-brown soil derived from pelite were significantly higher than those in the acid yellow-brown soils derived from carbonate parents and siliceous parents. 【Conclusion】 The acid yellow-brown soil derived from pelite presented the highest potential acidification risk. Thus, it is necessary to pay more attention to the acidification trend of soils derived from pelite and improve the resistance of these soils to acidification through the application of organic fertilizer. These findings provide significant guidelines for the management of soil acidification during continuous tobacco cultivation in the Wuling Qinba region, China.

    • Dewaterability of Frozen-melt Brackish Water and Its Soil Salt Leaching Efficiency Based on HYDRUS-1D

      WANG Ruiqi, LI Xianwen, ZHENG Na, JIANG Simin, CHEN Junying, YAN Baowen, HE Yujiang

      2023,60(2):378-389, DOI: 10.11766/trxb202105250272

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      Abstract:

      【Objective】Soil salinization is of growing concern in China since it severely restricts agricultural development and poses ecological and environmental risks in arid and semi-arid regions. High soil salinity causes deterioration of soil physical and chemical properties and inhabits plant growth. Given the wide distribution of brackish groundwater in arid and semi-arid regions, brackish irrigation is an effective approach to mitigate the shortage of freshwater resources. In addition, the naturally low air temperature in winter makes it possible to combine brackish irrigation and freeze-melt processes to enhance salt leaching and thus help reduce soil salinity. 【Method】 To reveal the dewaterability of frozen brackish water, the melting rates and temporal changes in water quality of ice blocks frozen from brackish water were compared under two air temperatures(10 ℃, 15 ℃)and four initial salinity gradients(freshwater, 0.5 g·L-1, 2 g·L-1, and 4 g·L-1). Furthermore, to evaluate the salt leaching efficiency through saline soil by melted brackish water, the HYDRUS-1D model was applied to simulate the one-dimensional soil water and salt transport patterns under two scenarios: direct infiltration using brackish water and infiltration using desalinized water melted from brackish ice frozen at different initial salinity gradients.【Result】 Our results show that: (1)The amount of melting water per unit time of brackish water ice body increased first and then decreased, and the melting rate was faster and peaked at higher value when the initial salinity was greater; (2)Freeze-melt could effectively desalinize brackish water by selectively discharging brine with great salinity at the early stage of melting, and the dewaterability was greater at lower initial salinity with an average dewaterability > 75%; (3)The HYDRUS-1D simulations on saline soil illustrated a better leaching efficiency when infiltrated with water melted from frozen brackish ice than directly applying unfrozen brackish water, and the leaching effect of brackish ice meltwater was better at 10 ℃ than at 15 ℃.【Conclusion】 These findings proved the applicability and effectiveness of combining brackish groundwater with freeze-melt treatments, as a new water-saving and salt-controlling mode, to help mitigate freshwater shortage and reduce soil salinization risk in the arid and semi-arid of China.

    • Study of the Water Infiltration Processes using ERT and TDR in Layered Soils

      LIN Qing, XU Shaohui

      2023,60(2):390-398, DOI: 10.11766/trxb202104280227

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      Abstract:

      【Objective】Soil water is the link between surface water and groundwater, and the carrier of solute transport in soil, which plays a key role in the Soil-Plant-Atmosphere Continuum (SPAC) system. The movement of soil water is a very complex process, especially in the layered structure. Heterogeneity of texture and pore of layered soil changes hydraulic characteristics at the interface of the soil layer, and thus the soil water movement and solute transport differ significantly from that in homogeneous soil．【Method】To fully understand the process of soil water movement, infiltration was evaluated using electrical resistivity tomography (ERT) in soil with a stratified profile. A field infiltration test was performed on an 8.7-m-long transect and successive measurements using ERT allowed determining resistivity changes as infiltration progressed. In the meantime, the soil water content was measured by time domain reflectometry (TDR) at the point scale, and the quantitative relationship was established between resistivity and water content. In addition, the soil water contents derived by ERT were validated with the soil water content derived by the drying method. 【Result】Results showed that the Multi-electrode resistivity method can fairly monitor the process of soil water movement, identify the depth of water infiltration, 90 cm in our study, and quantitatively retrieve the profile water content. The movement of soil water is mainly vertical downward with a weak horizontal flow. A good correlation between resistivity and soil moisture measurements revealed the capability of resistivity measurements to infer soil moisture spatial and temporal variability with root mean square error (RMSE) equal to 0.042 cm3·cm-3 for loam and 0.041 cm3·cm-3for clay loam. However, when the soil water content was lower than 0.15 cm3 cm-3, the electrical resistivity changed greatly with the increase in water content, while the soil water content was higher, the resistivity did not change significantly with water content. When the soil water reached the interface (~30 cm) between loam and clay loam, the soil water did not immediately move to the lower layer. According to the established relationship between resistivity and water content, it is estimated that at the soil interface, when the mass moisture content reached 0.136 g·g-1 at the upper layer of the soil, the water infiltrated the lower layer. Unexpectedly, abnormally increased resistivity appeared under the area of the soil water infiltration, which was presumably caused by the significant difference in resistivity of soil adjacent layers during the infiltration process. 【Conclusion】 In comparison with TDR, the resistivity method gives information integrated on a greater volume of soil and the measurements are easier and quicker to be carried out without disturbing the soil. Therefore, this method can be considered as an alternative tool to be employed for qualitative and quantitative soil moisture monitoring in the field. Also, this study provides a new method for quantitative analysis of the movement of soil water at a layered interface.

    • Experimental Study on the Improvement of Soil Moisture Characteristics of Coal Mine Dump by Fly Ash and Arsenic Sandstone

      ZHENG Peng, DANG Tinghui, XUE Jiang

      2023,60(2):399-408, DOI: 10.11766/trxb202104140197

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      Abstract:

      【Objective】Reclaimed soil in an open-air coal mine is highly infertile due to its poor physical and chemical characteristics. The reclamation methods usually improve soil moisture content which has important theoretical and practical significance for the reclaimed mine soil.【Method】This experiment was conducted in the Heidaigou open-air coal mine in the Inner Mongolia Autonomous Region, in which the following treatments were applied; fly ash, arsenic sandstone and dump soil. A certain mass ratio gradient was set, including 13 blended treatments denoted as L3F1, L4F1, L5F1, L1S1, L2S1, L3S1, L4S1, L5S1, L1F1S1, L2F1S1, L3F1S1, L4F1S1, L5F1S1, in which the L, F, S represented three kinds of controlled treatments. The volumetric water content of each compound soil under different water suctions was measured by the centrifuge method for the drawing of the water characteristic curve using the Gardner fitting model. The specific water capacity, field water capacity, wilting coefficient and effective water content of each treatment were also calculated.【Result】The results showed that the Gardner model was appropriate to fit the water characteristic curves of the 13 compound soils. The addition of fly ash increased the content of fine soil particles (i.e., clay and silt) by 24.11% to 37.19%, respectively, and improved the water holding capacity and water supply of soil. Furthermore, the addition of arsenic sandstone improved the water holding capacity of soil but failed to improve the water supply performance. The water holding capacity of L1F1S1 treatment and water supply performance of L3F1 treatment was the best, which was 47.6% and 40.23% higher than that of the dump soil, respectively. The field water holding capacity and available water content of LF combined treatment and LFS combined treatment were enhanced with the increase of additive proportion. When the mass ratio of soil and fly ash in the dump was 3：1 (L3F1), the maximum field water holding capacity was 18.02%. On the other hand, the maximum available water content was 13.1% with the mass ratio of soil, fly ash and arsenic sandstone of 1：1：1 (L1F1S1).【Conclusion】Overall, the comprehensive utilization of fly ash and arsenic sandstone is beneficial to improve the soil water characteristics of coal mine dump, and the soil water holding capacity and water supply capacity is better when the clay and silt contents of the soil are within the range of 30%-35%. In this experiment, the mass ratio of 1：1：1 is the best.

    • Effects of Paddy Rice Cultivation History on Soil Physical Properties and Water/ Nitrogen Distribution in the Intermediate Zone between Paddy Field and Bund

      CHEN Lu, ZHANG Hailin, YI Jun, LIU Xiuyun, LIU Muxing, LI Shenglong, ZHOU Li

      2023,60(2):409-423, DOI: 10.11766/trxb202104150199

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      Abstract:

      【Objective】Lateral seepage around the paddy bund is an important pathway for water loss in the paddy rice field. Revealing the evolution process of soil physical properties and the characteristics of soil water and nitrogen distribution in the intermediate zone between paddy field and bund is important. This is crucial for understanding the mechanism of water and nitrogen loss in the intermediate zone. 【Method】The intermediate zone between paddy field and bund with a cultivation history of 2 y, 19 y, and >100 y was considered for this study. Soil properties, including soil bulk density, equivalent porosity, soil-water characteristic curve, saturated hydraulic conductivity (Ks), soil water content and soil nitrogen concentration were determined through field sampling and laboratory analysis. The evolution process of soil physical properties and the mechanism of water and nitrogen loss in the intermediate zone were evaluated. 【Result】The paddy rice cultivation history affected soil physical properties. With the cultivation history extending, the difference in soil bulk density between paddy field plow layer (PL) and paddy bund surface layer(SL), and between paddy field plow pan(PP) and paddy bund hard pan (HP) increased. The microporosity(with diameter <0.03 mm) in PL and SL increased with paddy rice cultivation history, while the macroporosity (with diameter >0.3 mm and >0.03 mm) decreased in other soil layers for both in paddy field and bund. This showed a quicker decrease rate in the paddy field than for the bund. Differences in soil water holding capacity (SWHC) between paddy fields and bund were identified in the measured water suction range (0~100 kPa). Similar SWHC was observed between PL and SL in both 2 y and 19 y paddy rice fields, while a much higher SWHC was found in PL than SL in >100 y paddy rice fields. Also, a similar SWHC between PP and HP were identified in both 2 y and 100 y paddy rice fields, while a much higher SWHC was found in PP than HP in the 19 y paddy rice field. A higher SWHC was observed in the paddy bund subsoil layer (BSL) than the paddy field subsoil layer (FSL) for both 19 y and >100 y paddy rice fields. With paddy rice cultivation history extending, the differences in Ks between PL and SL decreased, while it increased between PP and HP. For example, the Ks in PP was 1.10, 6.90, and 6.32 times that in HP for 2 y, 19 y, and >100 y paddy rice fields, respectively. Also, a much higher Ks was observed in bund than the field for >100 y paddy rice field, while no significant differences were observed for the other two fields. The soil water and nitrogen distribution patterns were affected by the evolution of soil physical properties in both paddy fields and bund. Also, a higher soil water content and soil nitrogen concentration were observed in 19 y and >100 y paddy rice fields than in 2 y paddy rice fields, which was mainly accumulated in the PL for both 19 y and >100 y paddy rice fields. 【Conclusion】For the young paddy rice field, soil water and nitrogen rapidly seepage from both paddy fields and bund identically. With the paddy rice cultivation history extending, soil water and nitrogen are expected to be lost more quickly from the paddy bund than the field. For >100 y paddy rice fields, the PP in the newly built bund will degrade with time, then the paddy bund will be the key site for soil water and nitrogen lose again. Therefore, the soil water and nitrogen loss from the paddy bund should be given more attention, and the focus should be more on old paddy than young paddy rice fields.

    • The Surface Properties of Lou Soil with Different Phosphorus Levels and Their Effects on the Loss of Phosphorus

      HU Liang, DU Wei, CHANG Bokun, CAO Gang, YANG Xueyun, Lü Jialong

      2023,60(2):424-434, DOI: 10.11766/trxb202107070349

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      Abstract:

      【Objective】This study was designed to identify the surface electrochemical characteristics of Lou soil with different phosphorus levels and to study the transportation processes of phosphorus in the soil solid-liquid phase. Also, the relationship with soil surface properties was investigated and the change of surface properties of Lou soil under controlled electrolyte concentration and its internal relevance with phosphorus loss were clarified.【Method】The number of soil particles and phosphorus loss of Lou soil under different electrolyte concentrations was obtained by rainfall simulation test. The surface chemical properties of the soil were determined by combined measurement and analysis of surface properties. Also, the surface electrochemical properties of Lou soil with different phosphorus levels and their effects on soil phosphorus loss under the condition of long-term localized application of phosphate fertilizer were studied. 【Result】The results show that: (1) The total phosphorus content of Lou soil treated with long-term application of phosphate fertilizer is 2.46 times larger than that of Lou soil treated without phosphate fertilizer. However, the former’s surface potential, surface charge density, surface electric field strength, specific surface area, and surface charge number were lower than those of Lou soil without the application of phosphorus; (2) For Lou soils with different phosphorus levels, the cumulative loss of soil particles and phosphorus tended to intensify with an increase in the surface potential (absolute value) of soil particles. There was a linear positive correlation between the cumulative loss of particulate phosphorus (PP) and the cumulative loss of soil particles; (3) The surface potential(absolute value)of Lou soil with lower phosphorus content was larger than that of Lou soil with higher phosphorus content, and the electrostatic repulsion between soil particles was larger, resulting in poor stability of soil aggregates and more cumulative loss of soil particles and their attached phosphorus; (4) Under the experimental conditions, the phosphorus loss in Lou soil was dominated by PP, accounting for 81%-99% of total phosphorus loss, and the proportion of dissolved phosphorus was extremely low.【Conclusion】Long-term application of phosphate fertilizer can change the surface properties of Lou soil, and effectively maintain the stability of soil aggregates and attached phosphorus during rainfall. This study provides a new idea for environmental risk prevention and control of the long-term phosphorus application soil.

    • Screening of Low-Cd-accumulating Rice Varieties and Derivation of Soil Cd Safety Threshold in Southern Jiangsu

      TU Feng, HU Pengjie, LI Zhenxuan, ZHANG Xumei, PAN Yunjun, KONG Cheng, SUN Yongquan, QIU Yige, WU Longhua, LUO Yongming

      2023,60(2):435-445, DOI: 10.11766/trxb202108140363

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      Abstract:

      【Objective】There are urgent requirements to solve the problem of cadmium (Cd) pollution in farmlands and rice. With the rapid economic development in Southern Jiangsu, Cd pollution in soil and rice caused by industrialization has significantly increased. The purpose of this study was to screen low-Cd-accumulating rice varieties from main cultivated varieties in Southern Jiangsu, and to deduce the local soil Cd threshold for the safe production of rice. 【Method】In this study, field plot experiments and field investigation were conducted at different sites and years. Eighteen local main cultivated rice varieties in Southern Jiangsu were selected, including 15 Japonica conventional varieties: Wuyunjing 30(WYJ30), Suxiangjing 100(SXJ100), Changnongjing 10(CNJ10), Nanjing 3908(NJ3908), Nanjing 5055(NJ5055), Changnongjing 12(CNJ12), Nanjing 46(NJ46), Changnongjing 11(CNJ11), Jiahua 1(JH1), Changxiangjing 1813(CXJ1813), Changnongjing 8(CNJ8), Wukejing 7375(WKJ7375), Zaoxiangjing 1(ZXJ1), Yangyujing 3(YYJ3), Zhennuo 19(ZN19), and 3 Japonica three-line hybrid varieties: Changyoujing 6(CYJ6), Changyou 4(CY4) and Changyoujing 11(CYJ11). The differences of Cd bioconcentration factor(BCF) in rice grains among these varieties were comprehensively compared, and the soil Cd safety thresholds at different pH ranges were deduced using the species sensitivity distribution(SSD) method. 【Result】The results showed that the order of grain Cd accumulation among tested varieties was consistent between field investigation and plot experiments. There were significant differences in Cd BCF among 18 main cultivated rice varieties, with a maximum difference of 4.7 times. The Cd accumulation in some varieties like NJ46 and NJ3908 was stably low. Based on the SSD method, the deduced safety thresholds of soil total Cd to protect 95% of rice varieties from exceeding the standard (0.2 mg·kg-1) (GB 2762-2017) under soil pH 5.0～6.5, 6.5～7.5 and 7.5～8.5 in southern Jiangsu were 0.52, 0.80 and 1.78 mg·kg-1, which were higher than the current risk screening value(GB 15618-2018). It was verified that the deduced thresholds remarkably improved the accuracy of Cd risk prediction of rice in Southern Jiangsu. 【Conclusion】Based on field plot experiments and field investigation, numerous local main cultivated rice varieties including NJ46 and NJ3908 were screened with stably low Cd accumulation capacity, stable yield and high quality, and therefore are suggested for cultivation in Cd contaminated paddy fields in Southern Jiangsu. The deduced local safety thresholds of soil total Cd to protect 95% of rice varieties from exceeding the standard were higher than the current risk screening value. The results have important implications for the safe utilization of Cd contaminated paddy fields in Southern Jiangsu.

    • Effects of Drying and Oxidation Stage on the Forms and Availability of Cd and As in the Soil-rice System

      ZHANG Yuting, ZHU Qihong, HUANG Daoyou, TIAN Yingbing, XU Chao, ZHU Hanhua, HE Lei, WANG Wei, ZHANG Quan

      2023,60(2):446-457, DOI: 10.11766/trxb202105190264

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      Abstract:

      【Objective】The chemical behavior of cadmium (Cd) and arsenic (As) in paddy soils is opposite to the change in biological efficiency. This presents serious challenges to the simultaneous control of Cd and As pollution in rice. Previous studies have found that continuous flooding of Cd polluted fields can reduce the bioavailability of Cd while reducing soil water content can mitigate the bioavailability of As. However, the forms and availability of Cd and As in the soil-rice system under the process of drying (oxidation) remain unclear. 【Method】In this study, continuous sampling during the process of drying (days 0, 3, 5, and 7 of the drying process) under tillering period of rice in a pot experiment was carried out. At the same time the soil samples were analyzed for pH, Eh, soluble organic carbon, available Cd and As, and the different forms of Cd and As. Also, the plant samples were analyzed for iron plaque in the rice roots and Cd and As concentration in the rice tissues. 【Result】 The results showed that: during the process of drying, the Cd concentration in all parts of rice tissues increased with a reduction in water content, and the Cd concentrations in roots and shoots were increased by 109% and 183%, respectively, under the second drying stage(drying for 5 days) compared with the control treatment (P < 0.05). The concentration of As in rice roots decreased firstly and then increased with the reduction of water content. Compared with the control treatment, the concentration of As in rice roots was decreased by 41.96 mg·kg-1(P < 0.05). Also, the shoot As concentration was decreased by 12% and 18%, respectively, under the second and third stages of drying (drying for 5 and 7 days) (P < 0.05). The Cd, As and Fe concentrations in the Fe plaque increased by 96%, 16% and 16%, respectively(P < 0.05). With the decrease of soil water content, soil Eh, soil soluble organic carbon, and soil available Cd extracted by DTPA were increased, but soil pH, soil available As, and soil available Fe extracted by DTPA were decreased. In addition, reducing soil water content promoted the transformation of residual Cd to acid extractable and reducible Cd, resulting in the increase of oxidizable As concentration. It was also observed that when the soil moisture content was 33.6%, the bioavailable Cd and As concentration remained relatively low. 【Conclusion】Reasonable water management practices can reduce the bioavailability of Cd and As in soil. This is due to the changing soil Eh, pH, soluble organic carbon and available Fe, and the promotion of adsorption and fixation of Cd and As by the iron plaque. However, it is worth noting that while exploring water management methods to reduce the bioavailability of Cd and As, the growth and development of rice cannot be ignored. Our study contributes to the wealth of knowledge aimed at improving the remediation of Cd and As contaminated soils.

    • Human Bioavailability and Health Risk Assessment of Heavy Metals in Soils from a Mining Area of Southwest China

      BAO Xinchen, MA Jiaoyang, XU Wumei, WANG Haoji, WANG Chengchen, XIANG Ping

      2023,60(2):458-468, DOI: 10.11766/trxb202107200287

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      【Objective】Ingestion of soil is a pathway of human exposure to several environmental contaminants, including several heavy metals. Risk assessment of soils has typically been performed on total concentrations of target heavy metals. However, it may overestimate the potential adverse effects. To refine exposure risk, bioaccessibility and bioavailability measurements have been employed in many studies. Bioaccessibility tests are used to measure the bioaccessible fractions of contaminants in soils while bioavailability evaluates the fraction of heavy metals that reach the systemic circulation. These tests are both considered accurate approaches to evaluate the potential health risk of contaminants. However, there are few studies on the health risk assessment of heavy metals from mining soils via bioavailability. 【Method】In this study, five soil samples from the mining area of Wenshan, Yunnan Province were collected and the levels of Cd, Pb, Zn and Cu were analyzed using inductively coupled plasma mass spectrometry (ICP-MS). The bioaccessibility of Cd, Pb, Zn and Cu was detected using in vitro digestion method (SBRC), and the relative bioavailability (RBA) of Cd was determined by BALB/c mice models. The health risks of the four heavy metals in mining soils were assessed based on total, bioaccessible, and bioavailable data, respectively.【Result】The results showed that Cd pollution in this study area was serious, with the content being 2.06 mg·kg-1, which was 9.36 folds higher than the limit of soil background value in Yunnan. The bioaccessibility of Cd, Pb, Zn and Cu in the gastric phase was 24.29%-50.55%, 7.68%-17.87%, 24.61%-32.18%, 7.75%-37.87%, respectively, while in intestinal phase, they were 22.78%-44.32%, 1.64%-5.22%, 14.10%-28.11%, 8.51%-31.49%, respectively. As evident, the bioaccessibility of Cd was the highest among the four heavy metals. The RBA of Cd measured in vivo was 1.31%-48.39% in the liver, 2.83%-8.58% in the kidney, and 4.60%-50.95% in the liver and kidney. Compared with a single endpoint, Cd-RBA in the liver and kidney provided better repeatability and were ideal target organs for the determination of Cd-RBA. In vivo-in vitro correlation showed that the bioavailability of Cd determined by SBRC had a poor potential to predict Cd-RBA in contaminated soils from the mining area in China. Health risk assessment of the mining soil based on the target heavy metals, bioaccessibility and bioavailability revealed that the assessment using the total heavy metals had greater human health risk, while the data based on bioaccessibility and bioavailability showed a significantly reduced risk. 【Conclusion】The health risks assessment based on the total heavy metals in soil may be overestimated, and the establishment of a new method based on the bioavailability data will be more accurate. Our results provide a scientific basis for the health risk assessment of contaminated soils in China.

    • Characteristics and Influencing Factors of the Catalytic Transformation of Ferrihydrite by the Structural Fe(II) in Reduced Montmorillonite

      LIAO Wenjuan, PENG Wei, WU Cong, NING Yaqi, WANG Shuai, CUI Haojie

      2023,60(2):469-478, DOI: 10.11766/trxb202111020410

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      【Objective】Fe(II)-induced transformations of amorphous ferrihydrite to more crystalline iron oxide phases is a widely occurring geochemical process in soils under reduced conditions, and play an important role in regulating the biogeochemical processes of nutrient elements and pollutants. As one of the main species of Fe(II) in soils, Fe(II)-containing clay minerals are ubiquitous in soils under reduced conditions. However, the catalytic properties of structural Fe(II) in clay minerals for ferrihydrite transformation and its influencing factors are still not fully understood.【Method】In this study, the transformation of ferrihydrite induced by the structural Fe(II) in reduced montmorillonite (rSWy-2), which was produced by a chemical method, were investigated at neutral pH under anoxic conditions. Also, the influencing factors including types of cations and anions, organic matter, and As(III) on the transformation were studied.【Result】The X-ray diffraction (XRD) and chemical extraction analyses results showed that the structural Fe(II) in rSWy-2 with low Fe content can catalyze the transformation from ferrihydrite to more crystalline lepidocrocite, and 83.3% of initial ferrihydrite converted to lepidocrocite after mixing reaction for 96 h. XRD, high-resolution transmission electron microscope (HRTEM), scanning transmission electron microscopy (STEM) and surface adsorbed Fe(II) content analyses showed that the processes of ferrihydrite transformation induced by the structural Fe(II) in rSWy-2 mainly included three stages: Firstly, positively charged ferrihydrite nanoparticles adsorption on negatively charged rSWy-2 surface through electrostatic interaction. Secondly, interfacial electron transfer from the structural Fe(II) in rSWy-2 to the adsorbed ferrihydrite and partly reducing Fe(III) to surface adsorbed Fe(II). Finally, the surface adsorbed Fe(II) catalyzed the transformation of ferrihydrite to more crystalline lepidocrocite phases. HRTEM analyses showed that the formed lepidocrocite phases presented nanoplates with a size range of 100～200 nm. XRD and chemical extraction analyses results showed that Na+ and Cl- ions in the mineral suspension had a weak effect on the catalyzed transformation from ferrihydrite to lepidocrocite phases by the structural Fe(II) in rSWy-2. In contrast, Ca2+, SO42-, organic matter, and As(III) all had obvious inhibition on the transformation due to their strong interactions with minerals.【Conclusion】The structural Fe(II) in rSWy-2 could catalyze the transformation of ferrihydrite to lepidocrocite at neutral pH under anoxic conditions, and coexisting divalent cations and anions, As(III), and organic matter could inhibit the transformation reaction. The results provide a theoretical basis for further understanding the role of iron-bearing clay minerals in regulating abiotic transformations of iron oxides in soils under anaerobic reduction conditions.

    • Effects of Iron Oxide on the Adsorption and Desorption of Se(Ⅳ)in Selenium-Rich Soils of Guangxi

      HUANG Jinlan, JIANG Daihua, WANG Mingshi, HUANG Xuejiao, DENG Huawei, HUANG Zhigang, DENG Yusong

      2023,60(2):479-490, DOI: 10.11766/trxb202110250434

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      【Objective】The influence of free iron oxide on the adsorption and desorption of Se(Ⅳ) in a lateritic red soil and red soil in the selenium-rich area of Guangxi was studied. 【Method】The adsorption and desorption characteristics of Se(Ⅳ) in the soil before and after removing free iron oxide were compared by isothermal adsorption and desorption experiments. Zeta potential, scanning electron microscopy and energy spectrum analysis and Fourier transform infrared spectroscopy was used to explore the influencing mechanism.【Result】The results showed that the adsorption process for Se(Ⅳ) fitted the Langmuir and Freundlich models, with correlation coefficients ranging between 0.920~0.995. After removing free iron oxide of red soil and lateritic red soil, the zeta potential became more negative and changed from -24.42 and -18.06 mV to -33.06 and-26.43 mV. Also, the specific surface area was decreased. This observation correlated with the lower adsorption capacities of the soils after the removal of free iron oxide. Hence, the order of maximum adsorption capacity was: lateritic red soil (1 399 mg·kg-1) > red soil (1 336 mg·kg-1) > DCB-treated lateritic red soil (444 mg·kg-1) > DCB-treated red soil (352 mg·kg-1). The desorption rates of the tested soils were between 2% and 7%, while that of DCB-treated soils were higher than that of the original soils. The FTIR peak fitting analysis showed that the soils reacted with selenium mainly through the oxygen-containing groups such as -OH, Fe-O and C=O. After the removal of iron oxide, the effect of Fe-O in the adsorption was weakened or disappeared.【Conclusion】Free iron oxide can significantly increase the adsorption capacity and strength of soil for Se(Ⅳ) and reduce the release of Se(Ⅳ) by its physical and chemical properties and surface groups.

    • Effects of Key-stone Microbe Based on Co-occurrence Networks on Wheat Yield in the Soils with Straw Returning

      QIU Lili, LI Dandan, ZHANG Jiabao, ZHAO Bingzi

      2023,60(2):491-502, DOI: 10.11766/trxb202107200372

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      【Objective】The mechanism of the inconsistent effects of straw application on crop yield is still unclear, and the main reason may be related to the insufficient understanding of the effects of straw application on soil microbial community composition and its abundance changes on crop yield.【Method】A pot experiment to study the growth of wheat was carried out using red and yellow-cinnamon soils. Three levels of straw application were set for each soil, namely 0, 10 and 30 g·kg-1 soil(S0, S10, S30). Based on bacterial-fungal co-occurrence networks, the Path analysis model was used to evaluate the contribution of microbial ecological clusters, enzyme activities and chemical properties to wheat yield. 【Result】The results showed that although the content of available nutrients, soluble organic carbon, microbial biomass carbon and enzyme activities(amylase, invertase, polyphenol oxidase, urease, acid phosphatase, dehydrogenase) increased significantly in both soils, the wheat yield increased with the increase in straw dosage in the red soil but decreased in yellow-cinnamon soil. Compared with S0, S10 and S30treatments increased wheat grain yield and above-ground biomass by 33%-44% and by 73%-85% in the red soil; and decreased wheat grain yield and above-ground biomass by 22%-25% and by 55% in the yellow-cinnamon soil, respectively. The abundance of two key ecological clusters within the bacterial-fungal co-occurrence network, enzyme activities and soil chemical properties had positive effects on wheat yield in red soil while the abundance of two key ecological clusters had a larger positive effect on wheat yield in yellow-cinnamon soil. The straw application significantly increased the abundance of Aspergillus, a key microorganism positively correlated with wheat yield in red soil, while significantly decreased the abundance of Bacillus, Burkholderia, and Basidiobolus, which were positively correlated with wheat yield in yellow-cinnamon soil.【Conclusion】The combined effects of straw application, an increase in key microbial abundance, enzyme activities, and improvement of soil chemical properties was responsible for improving wheat yield in the red soil. In the yellow-cinnamon soil, the decrease in wheat yield was mainly related to lower key microbial abundance, whose effect was superior to the potential positive effects of improved soil chemical properties and enzyme activities. These results suggest that the change in the abundance of key microorganisms has an important influence on the variation of crop yield after straw returning.

    • Seasonal Variations in Methane Production Potential and Methanogenic Pathway in a Permanently Flooded Rice Field

      ZHU Xiaoli, HUANG Qiong, SONG Kaifu, MA Jing, ZHANG Guangbin, XU Hua

      2023,60(2):503-511, DOI: 10.11766/trxb202107050347

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      【Objective】The mitigation of methane (CH4) emission has long been the focus of governments and researchers worldwide. Rice fields are an important source of CH4 emission, and CH4 production is the precondition of CH4 emission. It is mainly produced by acetate fermentation and CO2/H2 reduction. Substantial CH4 emissions are observed from the permanently flooded rice fields, thus leaving a high mitigation potential of emission. However, reports on the seasonal variation of the methanogenic pathway in these rice fields are limited.【Method】Fresh soil samples from four rice growth stages (tillering stage, booting stage, heading stage, and maturity stage) were collected from a permanently flooded rice field in Ziyang City, Sichuan Province, China. The CH4 production potential (MPP) was observed through anaerobic incubation experiments. Both stable carbon isotope technique and methyl fluoride (CH3F, 2%) inhibition method were used to quantify the carbon isotopic fractionation factor for the conversion of CO2to CH4(α(CO2/CH4)), as well as to quantitatively estimate the relative contribution of acetate-dependent methanogenesis (ƒacetate).【Result】The addition of CH3F significantly decreased the CH4 production, and the MPP reached the highest value at the maturity stage, ranging from 3.22 to 12.71 µg·g-1·d-1. The δ13C-value of produced CH4(δ13CH4) varied from -66.83‰ to -59.62‰, which was much more positive than that of produced CH4 with CH3Faddition (from -90.83‰ to -82.26‰). The α(CO2/CH4)reached its maximum and minimum values at tillering and booting stages, respectively, which was between 1.064 and 1.076. The ƒacetate(30%-61%) decreased sharply from 54%-61% at the tillering stage to 30%-35% at the booting stage and then increased to 54%-61% at the maturity stage. Further analysis showed that the seasonal variation of MPP was positively correlated with the variation of soil dissolved organic carbon (DOC) content, and the seasonal variation of ƒacetate was significantly related to variations of acetate content.【Conclusion】Distinct seasonal variations were observed in both MPP and methanogenic pathways of the permanently flooded rice fields, which was mainly affected by soil DOC content and acetate content, respectively.

    • Effects of Long-term Organic Fertilizer Instead of Chemical Fertilizer on Organic Carbon Stability of Paddy Soil

      MIAO Yulin, LIANG Feng, XIE Jun, ZHANG Qin, LIU Yiren, ZHAO Xiaomin

      2023,60(2):512-522, DOI: 10.11766/trxb202105260276

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      【Objective】The effects of long-term and different proportions of organic fertilizer on the content of labile/non-labile carbon components and the stability of the chemical structure of organic carbon in paddy soil were determined.【Method】This study selected a long-term positioning test of paddy soil developed by Quaternary red clay as the research object. Five treatments were selected: no fertilizer treatment (CK), chemical fertilizer treatment (100F0M), 30%, 50% and 70% of the nitrogen in chemical fertilizer treatment was replaced by organic fertilizer (70F30M、50F50M、30F70M). During the study, we measured the content of total organic carbon, labile/non-labile organic carbon pool, the chemical structure of organic carbon, and soil properties.【Result】 The contents of organic carbon, labile carbon and non-labile carbon in paddy soil were increased by different proportions of organic fertilizer instead of chemical fertilizer. The contents of labile carbon were 70F30M, 30F70M > CK, 50F50M, and the contents of non-labile carbon were 30F70M > 70F30M, 50F50M > 100F0M > CK. With an increase in the replacement proportion of organic fertilizer, the proportion of non-labile carbon gradually increased from 69.67% to 77.26%. Under different organic fertilizer substitution ratios, the chemical structure of soil organic carbon remained the same, and the relative content percentage shows the same trend: aromatic carbon (33.28% ~ 37.79%), alkyl carbon (27.81% ~ 31.19%), alkoxy carbon (16.19% ~ 20.10%), carbonyl carbon (10.35% ~ 12.07%), and carboxyl carbon (2.52%~ 5.75%).Alky, carbonyl, and carboxyl carbons made up the largest, second largest and lowest proportions, respectively.With the increase in the proportion of organic fertilizer instead of chemical fertilizer, the aromaticity increased from 0.40 to 0.44 while the ratios of aliphatic carbon/aromatic carbon and alkyl carbon/alkoxy carbon decreased, suggesting an increase in the stability of organic carbon. PH (P< 0.05) and Cation exchange capacity (CEC, P< 0.01) were the main influencing factors of activated carbon content. pH, CEC, Alkali hydrolyzed nitrogen (AN) and carbon input(organic fertilizer, rice root and rice stubble) (P< 0.01) were the main influencing factors of non-labile carbon content.【Conclusion】30F70M not only improved the content of labile and non-labile carbon but also increased the aromaticity of organic carbon, which is more conducive to improve the stability of soil organic carbon.

    • Responses of Soil Carbon Pool of Abandoned Grassland on the Loess Plateau to Two-years Warming and Increased Precipitation

      WANG Xing, ZHONG Zekun, WANG Jiayi, JIAN Junnan, YANG Gaihe, REN Chengjie, HAN Xinhui

      2023,60(2):523-534, DOI: 10.11766/trxb202106120307

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      【Objective】Global climate change has had a huge impact on the carbon pool of terrestrial ecosystems, and the changes in average temperature and precipitation patterns pose severe challenges to the management of terrestrial carbon pools. This is especially serious in the Loess Plateau where the ecological environment is fragile. Therefore, understanding the changes of different fractions of soil organic carbon pool and the stability of this carbon pool under the background of the warming and humid climate of the Loess Plateau is of great significance. This will be of importance in the sustainable development of the carbon pool in fragile ecological areas and the evaluation of regional ecological benefits.【Method】In this study, natural abandoned grassland in the loess hilly region was taken as the research object. Soil warming and increased precipitation were artificially simulated and the changes in vegetation community, soil carbon fractions content and distribution, carbon pool stability index under warming (W), precipitation (P50%) and their interactions (WP50%) were analyzed. 【Result】The results showed that: (1) P50% significantly increased the vegetation Gleason richness index, W and WP50% significantly reduced the Gleason richness index (P < 0.05) and the leaf organic carbon content under the WP50% was significantly higher than the control treatment. Both P50% and WP50% treatments reduced the Shannon-wiener diversity index and pielou evenness index. (2) Soil organic carbon (SOC), acid hydrolyzable organic carbon (AHC), easily oxidizable carbon (EOC), dissolved organic carbon (DOC) content and their distribution ratio of the two sampling years under P50% were significantly higher than the control treatment. Also, warming based on P50% can further increase soil EOC, microbial biomass carbon (MBC) content and distribution ratio. However, only the soil MBC showed a significant difference compared with the control under W treatment. Recalcitrant organic carbon (ROC) presents an opposite trend to AHC. The correlation analysis showed that there was a significant correlation between soil total organic carbon and each active carbon fractions (P < 0.05). (3) The soil carbon pool activity (CA), carbon pool activity index (CAI), and carbon pool management index (CPMI) under WP50% treatment were higher than other treatments. The sensitivity index of AHC and MBC was relatively high under the treatment of climate change.【Conclusion】In summary, the total organic carbon, the content and distribution ratio of active fractions of organic carbon, and the stability of the carbon pool in abandoned grassland of the loess-hilly area will be significantly improved under background warming and humid climate. This will contribute to the healthy development of the carbon pool. From a sensitivity point of view, AHC and MBC can be used as early important indicators of changes in soil organic carbon under warm and humid climates in the future. This study provides a theoretical and scientific basis for research on climate change and carbon pool management in fragile ecological areas.

    • Optimization of Denitrifier Method for Determination of Soil NO2--15N Abundance

      GUO Ru, WEN Teng, CAO Yacheng, ZHANG Jinbo

      2023,60(2):535-545, DOI: 10.11766/trxb202106070299

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      【Objective】NO2- is a key intermediate product of several nitrogen transformation processes in soil, with low concentration and fast transformation. The combination of denitrifier method and mass spectrometry technology has been widely used in the 15N isotope analysis of NO3- or NO2- in water. 【Method】This paper aims to optimize the culture and reaction conditions of Stenotrophomonas nitritireducens denitrifier method, and to realize the specific, rapid and accurate determination of NO2--15N abundance in soil extract. Thus, we will optimize the culture method and reaction conditions, and bacterial concentration of denitrifier method, then applied this method to the soil extract. 【Result】There was no significant difference in the 15N isotopic determination of NO2- samples between aerobic shaking with seed solution and microaerobic incubation of single colonies. The seed solution ensures the stability of different batches of bacteria and aerobic incubation reduces the incubation time from 7~8 days to 12~15 h. High purity N2 or He purging for 0.5 h can effectively remove O2 and blank nitrogen, but the cost of N2 purging is lower. The transfer of N2O gas to the dry gas cylinder did not affect the accuracy and precision of the determination results. However, it can prolong the sample preservation time and reduce alkali steam corrosion of the instrument pipeline. Also, using bacteria in logarithmic growth phase and adjusting the reaction system to an OD600 value of 0.3~0.9 will ensure their denitrification efficiency and reduce variation between batches. Using no more than 1 mol·L-1 KCl to extract the soil will ensure the extraction efficiency and reduce the impact on the viability of the bacteria.【Conclusion】The optimized method can accurately determine the 15N abundance of NO2- in different types of soil with a measurement accuracy of δ15N of 5~20 nmol and natural abundance value of NO2- between 0.1‰~0.9‰, with most values being less than 0.5. Also, the experimental period was greatly shortened, simplified steps and save cost.

    • Community Assembly and Functional Potential of Habitat Generalists and Specialists in Typical Paddy Soils

      LIU Hongtao, HU Tianlong, WANG Hui, ZHANG Yanhui, GUO Shiwei, XIE Zubin

      2023,60(2):546-557, DOI: 10.11766/trxb202105310284

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      【Objective】Great differences exist in the utilization of carbon and nutrients between habitat generalists and specialists, which play unique roles in the cycle of soil energy and nutrients. At present, the research on farmland microorganisms mainly focuses on the whole bacteria, fungi, archaea or other functional communities, and the understanding of habitat generalists and specialists in farmland ecosystems is still lacking. Therefore, this study was designed to explore the community structure, assembly mechanism and possible functions of habitat generalists and specialists in typical paddy soils in eastern and southwestern China. 【Method】Sixteen surface soil samples (0~20 cm) were collected from the eastern area (Jiangsu, Anhui, Shanghai) and southwestern area (Guizhou and Yunnan) of China according to the data of the second soil survey, and their physico-chemical properties and next generation high-throughput sequencing were analyzed. 【Result】The results showed that 3.28% of all OTUs were classified as habitat generalists while 9.07% as habitat specialists. There were significant differences in species composition between habitat generalists and specialists. At the level of phylum, the proportions of habitat specialists in Chloroflexi, Actinobacteria, Nitrospirae, Firmicutes and Planctomycetes were higher than those of habitat generalists. The analysis of the community assembly process based on the β diversity null model showed that habitat generalists and specialists were dominated by deterministic process. Compared with habitat specialists, habitat generalists were more affected by the stochastic process. The environmental factors driving the community structure variation of habitat generalists and specialists were different. pH, mean annual precipitation, clay content and total nitrogen were the main factors driving the community structure variation of habitat generalists, while the community structure variation of habitat specialists was dominated by pH and clay content. By analyzing the co-occurrence network and robustness of habitat generalists and specialists, it was found that the habitat specialists’ network had more connections, more complexed structure and stronger robustness. The functional prediction by FAPROTAX showed that biological nitrogen fixation mainly existed in habitat generalists. 【Conclusion】Information derived from the community structure, environmental driving factors, assembly process, co-occurrence network characteristics and related functions of nitrogen metabolism of habitat generalists and specialists, provides a theoretical basis for the evolution and regulation of bacterial communities in paddy fields.

    • Characteristics of Protist Community in Banana Rhizosphere Soil and Interactions between Protists and Pathogens of Fusarium wilt Disease

      REN Xiangyu, LIU Manyi, SUN Mingze, YANG Jinming, WANG Beibei, LI Rong

      2023,60(2):558-567, DOI: 10.11766/trxb202107140361

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      【Objective】As a serious banana disease and a significant limiting factor in banana production worldwide, banana Fusarium wilt disease is caused by the fungal pathogen Fusarium oxysporum f. sp. cubense race 4(FOC). The rhizosphere microbiome of plants is a key barrier that defends plant roots from an invasion of soil-borne pathogens. Most studies of the rhizosphere microbiome have focused on bacterial and fungal communities. However, as an important component of the rhizosphere microbiome, the rhizosphere protist community has been neglected in the regulation of microbiome and plant health. This study was conducted to explore the characteristics of the soil protist community in healthy and diseased plants and the interactions between protists and pathogens through field experiments of continuous cropping of bananas.【Method】In this paper, high-throughput Illumina MiSeq sequencing was applied to analyze the differences of soil protist community structure and composition among different treatments in field experiments.【Result】Results show that the relative importance of protists in predicting pathogenic Fusarium number was 47.19%, suggesting that protists might be the best predictor for pathogen number than culturable bacteria and fungi. The diversity and richness of the rhizosphere protist community decreased during plant growth and was lower in diseased plants. The composition and community structure of protists differed between healthy and diseased plants in rhizosphere soil. Also, the relative abundance of phagotrophic protists was highest compared to other functional groups in all soil samples, showing an increasing trend throughout plant development and enriched in diseased plants. Before the heading stage, the relative abundance of Bacillariophyta_X_unclassified, a phototrophic protist, was highest in healthy plants but decreased at a later stage. In healthy plants, the relative abundances of Group-Te and Cercomonas, phagotrophic protists, were higher at the heading stage. It was also observed that diseased plants showed a higher relative abundance of Pythium while phagotrophic protists, particularly Cercozoa protists, had significant correlations with Fusarium than other protistan communities. Group-Te and Cercomonas, two Cercozoa taxa, were negatively linked with the pathogen. In contrast, pathogens in diseased plants were positively linked with Pythium, which was a plant pathogenic protist. 【Conclusion】Protists in the rhizosphere soil demonstrated a greater impact on pathogens. The community characteristics of protists in rhizosphere soil changed in the process of plant growth and differed between healthy and diseased plants. Particularly Group-Te and Cercomonas were negatively linked with the pathogen, which might have potential in the prevention and control of banana wilt disease. Future research should focus on(i)the isolation and purification of phagotrophic protists negatively related to pathogens, (ii)exploring the mechanism of phagotrophic protists and pathogens, and(iii)investigating the internal connection with other beneficial microorganisms in rhizosphere soil to improve the efficiency of controlling banana wilt.

    • Contributions and Influencing Factors of Soil Fauna to Litter Decomposition under Different Land-use Patterns

      YUAN Fang, DENG Chengjia, TANG Jing, SONG Lihong

      2023,60(2):568-576, DOI: 10.11766/trxb202110090441

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      【Objective】Soil fauna play an important role in litter decomposition processes through activities such as burrowing and feeding. Besides the quality of litter, climate parameters have been identified as major factors affecting the role of soil fauna on litter decomposition. However, the contribution of soil fauna in litter decomposition and the role of climatic parameters under different land-use patterns are still not clear.【Method】In this paper, meta-analysis was used to quantify the effect sizes of soil fauna on litter decomposition rates. We established a meta-analysis database by collecting the results of 56 publications both in Chinese and English in China from papers published until May 31, 2021. The effect size of soil fauna on litter decomposition rates among three different land-use patterns (i.e., forest, grassland, and farmland), was further tested by a random-effects model. Correlations were tested between environmental factors -temperature, precipitation, litterbag size, latitude, and experimental duration -and the effect size of soil fauna on litter decomposition rates.【Result】Soil fauna increased litter decomposition rate by an average of 8.10%, reaching a significant level among different land-use patterns. Among the three different land-use patterns, the effect of soil fauna on litter decomposition rates was strongest in the farmland (12.36%). Environmental factors were closely correlated with the effect size of soil fauna on litter decomposition rates.【Conclusion】In the forest, effect size significantly increased with temperature, including the average temperature in January and July, and the mean annual temperature (P < 0.01). In grassland, however, the effect size of soil fauna decreased with temperature (P > 0.05). The effect size significantly increased with mean annual precipitation but significantly decreased with altitude (P < 0.01). Besides, with the increase of litterbag size and experimental duration, the effect size values of soil fauna on litter decomposition significantly increased and decreased, respectively.

    • Regulation of Phosphorus Levels on the Interaction Balance between Endophytic Fungus Phomopsis liquidambaris and Rice

      CHEN Man, ZHANG Yang, BAI Yanan, DAI Chuanchao

      2023,60(2):577-586, DOI: 10.11766/trxb202108030397

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      Abstract:

      【Objective】The interaction between endophytic fungi and plants is affected by many factors, among which the content of phosphorus in soil plays a key role in regulating the interaction between them. However, it is not clear whether and how phosphorus fertilizer in the environment affects the interaction between endophytic fungi and plants.【Method】In this study, the symbiont of Phomopsis liquidambaris(B3)and rice(Oryza sativa L.)was used as the experimental model. Three different phosphorus levels, i.e., low phosphorus(LP), medium phosphorus(MP), high phosphorus(HP), uninoculated endophytes treatment(E-), and inoculation endophytes treatment(E+)were designed in this experiment. Physiological indexes of rice and B3 colonization were detected under different phosphorus levels to explore how phosphorus regulates the interaction between B3 and rice in the outdoor experiment and greenhouse experiment.【Result】In the outdoor experiment, B3 significantly(i)increased the phosphorus uptake ability of rice, (ii)promoted rice growth in the whole growth period and the formation of rice grain in the mature stage, and(iii)increased the rice yield by 7.05% under LP treatment. In MP and HP treatments, the effect of B3 was weakened. In the greenhouse experiment, under LP treatment, compared with the uninoculated treatment, the root/shoot ratio of rice inoculated with B3 increased by 22.48%, and resulted in an enhanced phosphorus uptake ability of rice by 39.98%. There was a significant enhancement of photosynthesis in rice and the accumulation of carbon sources such as sucrose, glucose and fructose in rice roots. However, the colonization of B3 was significantly limited under this condition. Also, consistent with this result, the biomass of B3 cultured in the LP medium was significantly lower than that in MP and HP mediums, which meant that B3 would be significantly affected by the phosphorus concentration. In the MP and HP treatments, B3 had high colonization in rice roots, but had little effect on rice growth.【Conclusion】Phosphorus concentration affects the symbiotic relationship between B3 and rice. In LP treatment, B3 colonization was low in rice roots, but it significantly promoted plant growth. In MP and HP treatments, B3 had high colonization rates in rice roots but with no significant effect on rice growth. Understanding the influence of phosphorus fertilizer on the interaction between endophytic fungi and plants will be helpful to improve the utilization efficiency of phosphorus fertilizer and microbial resources, which will provide a new path for the sustainable development of agriculture.

    • Effects of Seawater Rice Rhizosphere Effect on Soil Ammonia-oxidizing Microorganisms in Coastal Saline-alkali Soil

      LI Gaoyang, HUANG Yongxiang, WU Weijian, CHEN Yijie, ZHANG Weijian, LUO Shuwen, LI Huijun, HUANG Fengcheng, LIN Zhong, ZHEN Zhen

      2023,60(2):587-598, DOI: 10.11766/trxb202109170340

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      【Objective】The special environment of coastal saline-alkali land restricts the transformation and utilization of soil nitrogen. Microorganisms in saline-alkali paddy environment mediate ammonia oxidation in rice rhizosphere in a key process of soil nitrogen cycling. However, due to research blindness and outdated technology, the effect of seawater rice rhizosphere effect on the microbial community structure of ammonia oxidation in coastal saline-alkali soil is rarely reported. 【Method】In this study, the saline tolerant rice species ‘Haidao 86’ was used as the experimental material for the pot experiment. The pot experiment was conducted with low (2 g·kg-1) and high (6 g·kg-1) salt concentrations. Soil physicochemical properties and microbial biomass were measured and analyzed, and high-throughput sequencing of ammonia-oxidizing microorganisms was conducted to analyze the effects of different treatments of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) community structure in the rice rhizosphere.【Result】Results showed that after 70 days of rice growth, pH of rhizosphere soil decreased by 0.82 and 0.70, soil organic matter (SOM) content decreased by 6.41 g·kg-1and 4.46 g·kg-1, humus (HU) content increased by 5.76 g·kg-1 and 4.45 g·kg-1, total nitrogen (TN) content decreased by 0.46 g·kg-1 and 0.37 g·kg-1 for low and high salt concentrations, respectively. Rice rhizosphere effect significantly increased soil microbial biomass carbon, microbial biomass nitrogen and microbial respiration intensity, reaching peak values on the 55th day of planting with 850.0 mg·kg-1, 72.2 mg·kg-1 and 231.9 mg·kg-1·d-1 for high salinity treatment and 546.1 mg·kg-1, 53.7 mg·kg-1 and 171.2 mg·kg-1·d-1 for low salinity treatment, respectively. The rhizosphere effect had no noticeable influence on the Chao1 index, Shannon index and Simpson index of AOA. At the genus level, the dominant bacteria of AOA were norank_c_environmental_samples_p_Crenarchaeota, unclassified_k_norank_d_Archaea, and Nitrososphaera. The rhizosphere effect of seawater rice significantly affected the richness, diversity and abundance of AOB in coastal saline-alkali soil. It can significantly increase the abundance of environmental_samples_f_Nitrosomonadaceae and Nitrosospira. Also, correlation analysis between the AOB community and soil environment showed that environmental_samples_f_Nitrosomonadaceae and Nitrosospira had a significant positive correlation with HU and a significant negative correlation with pH. 【Conclusion】The results of this study indicate that planting tolerant rice species can improve nutrient cycling in coastal saline-alkali land, and the rhizosphere effect of saline-alkali tolerant rice mainly affects the community structure of AOB in acidic soil.

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

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

        DOI: 10.11766/trxb202208300347

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

      • Effects of Potassium-Solubilizing Bacteria Loaded Biochar on Soil Enzyme Activity and Microbial Community Structure

        LI Changjun, LI Ting†, LI Lulu, MIAO Li, WEI Wei, WANG Zhiao

        DOI: 10.11766/trxb202206030294

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        【Objective】Biochar loaded bacteria is a practical application of microbial immobilization. Biochar is considered as the ideal carrier of microorganisms in recent years because of its large specific surface area, pore diameter and good absorbability. Biochar loaded with Bacillus and other exogenous functional microorganisms can increase crop yield, improve root activity, and improve soil enzyme and microbial activity. However, In the process of gradual potassium deficiency, it needs to be further explored that the impact of biochar-loaded potassium-solubilizing bacteria on soil enzyme activity and microbial community structure. Therefore, this paper aims to explore the effect of potassium-solubilizing bacteria-loaded biochar on soil microbial characteristics.【Method】Based on pot experiment with ryegrass and five treatments: control (CK), chemical potassium fertilizer (KCl), inoculation of potassium solubilizing bacteria (KSB), application of biochar (BC) and potassium solubilizing bacteria loaded biochar (BC-KSB), it was analyzed that the change characteristics of soil urease, acid phosphatase, invertase and catalase enzyme activities and microbial community structure, also the effects of biochar-loaded potassium solubilizing bacteria composite materials on soil nutrients, soil pH, microbial biomass carbon, microbial biomass nitrogen and ryegrass yield were discussed.【Results】The soil urease and acid phosphatase activity increased first and then decreased while the soil invertase and catalase activity decreased with an increase in the number of harvests for treatments with microbial agents or biochar. Compared with other fertilization treatments, BC-KSB was more conducive to the increase of soil urease, invertase, acid phosphatase and catalase activities. In terms of soil bacterial community, BC-KSB improved the species diversity and flora uniformity of soil bacteria, increased the abundance of soil beneficial bacteria (Chloroflexi, Actinobacteriota, Bacillus and Bradyrhizobium), and inhibited the reproduction of soil pathogenic bacteria (Proteobacteria and Rhodobacteria). Compared with CK, all fertilization treatments significantly increased the dry weight of ryegrass and BC-KSB treatment showed the largest increase. Also, compared with CK and KCl, BC-KSB treatment can significantly increase the contents of soil microbial biomass carbon, microbial biomass nitrogen, organic matter, total nitrogen and available potassium. However, the content of soil total potassium and total phosphorus in different treatments showed no significant difference. Furthermore, BC significantly increased soil pH compared to other treatments. Redundancy analysis showed that soil organic matter, available potassium, acid phosphatase, urease and microbial biomass nitrogen were the main influencing factors of bacterial community structure, whereas the growth of ryegrass was mainly affected by Burkholderia and Rhodobacteria.【Conclusion】KSB loaded biochar has a positive impact on ryegrass yield, soil nutrients, soil enzyme activity, and bacterial community structure, which provides profound significance for fertilizing soil and improving soil ecological environment.

      • Evaluations and Influencing Factors of Soil Available Fe, Mn, Cu and Zn Concentrations in Major Wheat Production Regions of China

        CHU Hongxin, DANG Haiyan, SUN Ruiqing, HOU Saibin, HUANG Qiannan, LI Xiaohan, WANG Zhaohui, HUANG Tingmiao

        DOI: 10.11766/trxb202205070236

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        【Objective】It is of great importance to clarify the current regional distributions and influencing factors of soil available iron (Fe), manganese (Mn), copper (Cu) and zinc (Zn) concentrations. This will improve understanding of the soil micronutrient supply abilities and guarantee high-yield and high-quality wheat in major wheat production regions of China.【Method】During 2016 to 2021, a successive 6-year in situ farm survey was conducted in combination with the collection of topsoil (0-20 cm) samples from 1 314 randomly selected farmland fields in 17 major wheat production provinces and regions in China. The soil-available Fe, Mn, Cu and Zn concentrations were determined to evaluate their abundance and deficiency status based on China’s classification criteria for soil-available micronutrients. Also, it was quantified the contribution of main soil chemical properties on Fe, Mn, Cu and Zn availabilities by random forest analysis.【Result】Results showed that the soil available Fe ranged from 1.8 to 611.9 mg?kg-1, with an average of 49.1 mg?kg-1, and 8.9% of samples had lower soil available Fe than the Fe deficiency threshold of 4.5 mg?kg-1. Soils with relatively low available Fe were usually observed in the provinces of Shanxi, Shaanxi and Gansu in northern and northwestern wheat production regions, while high-Fe soils were found in southwestern and middle and lower Yangtze River wheat regions. Also, soil available Mn ranged from 0.1 to 176.2 mg?kg-1, with an average of 22.1 mg?kg-1, and 6.9% of samples exhibited lower soil available Mn than the Mn-deficient threshold of 5.0 mg?kg-1. Mn-deficient soils were mainly distributed in Shanxi, Shaanxi, Gansu provinces and Inner Mongolia Autonomous Region in northern and northwestern wheat growing regions, while soils with high and very high available Mn often occurred in southwestern and middle and lower Yangtze River wheat regions. Soil available Cu ranged from 0.1 to 10.8 mg?kg-1, with an average of 1.9 mg?kg-1, and only 1.8% of samples had lower available Cu than the Cu-deficient critical value of 0.5 mg?kg-1. Soil available Zn ranged from 0.1 mg?kg-1 to 26.0 mg?kg-1, with an average of 1.4 mg?kg-1, and 14.3% of samples’ available Zn was lower than the Zn deficiency threshold of 0.5 mg?kg-1. Zn-deficient soils were mainly found in Shanxi, Shaanxi, Gansu provinces and Inner Mongolia Autonomous Region of northern and northwestern wheat production regions, and higher Zn concentrations were mainly observed in soils of Yunnan and Guizhou provinces of southwestern wheat regions. Among the investigated soil chemical properties, the pH was the most important influencing factor to available Fe and Mn, and available Fe contributed to the highest Cu availability, and available phosphorus, followed by Cu, was found to be the leading factor for soil available Zn in major wheat production regions of China. 【Conclusion】There were large regional variations in the soil-available Fe, Mn, Cu, and Zn concentrations in China’s wheat fields. Deficiencies of soil available Fe, Mn and Zn were serious problems on calcareous soils in the northern part, and higher supplies of these micro-elements occurred in the southern part, while almost all of the wheat fields were not identified as Cu-deficient soil in China.

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

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

        DOI: 10.11766/trxb202208210462

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

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

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

        DOI: 10.11766/trxb202207120379

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        Abstract:

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

      • Progress of soil temperature prediction equation

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

        DOI: 10.11766/trxb202210220581

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        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.

      • Nanoscale Observations of Formation of Sugar-Clay Microaggregates and The Mediation for Phosphorus Adsorption Capability

        Chi Jialin, Jia Chonghao, Zhang Wenjun

        DOI: 10.11766/trxb202206090217

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        【Objective】Sugar-clay aggregates play important roles in the transformation of nutrient elements such as phosphorus in soils. However, few studies have paid attention to the initial formation of microaggregates and subsequent adsorption of phosphorus mediated by the molecular weight of sugar in the nanoscale. 【Method】In this experiment, a model clay, laponite, and representative sugars including glucose and dextran with different molecular weights were selected to serve s the research objects. The formation of aggregates mediated by sugars with different molecular weights was observed by Raman spectroscopy and atomic force microscopy (AFM), and then the differences in interactions of laponite and sugar with different molecular weights were measured by single molecular force spectroscopy (SMFS). Finally, the content of phosphorus adsorbed by microaggregates was compared via the measurement of sorption isotherms of phosphate by laponite or sugar-laponite complexes. 【Result】The molecular weight of sugar was important for interaction with laponite and the size of sugar-clay microaggregates increased with molecular weight, suggesting stronger interactions of laponite with the sugars. Phosphate adsorption was increased for sugar-laponite microaggregates compared to laponite because of an increase in the content of hydroxyl and surface zeta potential of microaggregates. Also, the amount of phosphate adsorbed was observed to decrease with an increase in the molecular weight of sugar due to the greater particle size of high-molecular-weight sugar-laponite microaggregates. 【Conclusion】The results showed that sugars with high molecular weight promoted the formation of microaggregates but disfavored the adsorption of phosphorus by microaggregates. These nanoscale observations will provide a new method and theoretical basis for understanding the biogeochemical cycle of phosphorus involved in microaggregates in soils.

      • Soil microbial community stability of different fertilization strategies under drought disturbance

        Zhang Zhou, Chen Ruirui, Wang Xiaoting, Yu Bingqian, Lin xiangui, Feng Youzhi

        DOI: 10.11766/trxb202206210261

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        Abstract:

        Revealing soil microbial community stability of different long-term fertilization strategies is helpful to guide field fertilization management and ensure soil health and sustainable development of agroecosystems. Based on the long-term stationary field experiment on nutrient balance in the Fengqiu National Agro-ecological Experimental Station of the Chinese Academy of Sciences, the experiments of drought disturbance and rewet recovery were carried out on three different fertilization strategies of Fluvo-aquic soils. The microbial community stability (resistance and recovery) was quantified and compared in terms of dehydrogenase activity, bacterial alpha diversity, key taxa, community structure and molecular ecological network. The results showed that compared with no fertilization (CK) and mineral NPK fertilizers (NPK), organic manure plus mineral NPK fertilizers (OM) significantly increased the resistance and recovery of the microbial community. After rewet treatment, soil alpha diversity recovered faster than community function and structure. Soil alpha diversity, the abundance of key taxa and network topology parameters recovered to the initial level, while dehydrogenase activity and community structure did not recover completely. This study quantified and compared the microbial community stability of three different fertilization strategies from a variety of microbial community response indexes. The results showed that the application of organic manure plus mineral NPK fertilizers could significantly improve the stability of the microbial community, which is a good fertilization management strategy to ensure the soil health and sustainable development of the farmland ecosystem.

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

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

        DOI: 10.11766/trxb202208210463

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

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

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

        DOI: 10.11766/trxb202207270413

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

      • Responses of Soil Organic Carbon Components to Long-term Nitrogen Addition in the Stipa baicalensis Meadow Steppe

        WU Zhendan, MA Shangfei, LU Junyan, YANG Dianlin, HONG Mei

        DOI: 10.11766/trxb202204230204

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        Abstract:

        【Objective】This study aimed to analyze the response of soil carbon composition to long-term nitrogen addition in the Stipa baicalensis meadow steppe. 【Method】A nitrogen addition experiment was designed in the meadow steppe of Ewenke Banner, Hulunbuir City, Inner Mongolia in 2010, and 8 nitrogen treatments were set as 0 (N0), 15(N15), 30(N30), 50(N50), 100(N100), 150(N150), 200(N200) and 300(N300) kg?hm-2?a-1(calculated as N). Soil samples were collected in August 2019 and soil organic carbon and its fractions were measured to investigate the changes and drivers of soil organic carbon and its fractions after 10 years of nitrogen addition. 【Results】The results showed that: (1) Compared to the control, soil organic carbon (SOC) content and soil recalcitrant carbon (RP-C) did not change significantly under long-term nitrogen addition. The content of soil labile organic carbon (LP-C) increased, among which labile carbon fraction I (LPⅠ-C) and II (LPⅡ-C) increased by 0.48%-15.59% and 1.94%-8.41%, respectively. Soil easily oxidized organic carbon (EOC) did not respond, whereas the contents of dissolved organic carbon (DOC) and microbial biomass carbon (MBC) changed significantly. The overall soil carbon composition was more sensitive to N addition at the level of 30, 50 and 100 kg?hm-2 ?a-1; (2) The responses of sensitivity index (SI) of soil organic carbon to nitrogen addition showed that MBC was more sensitive to long-term nitrogen addition, which could be used as an indicator suggesting the changes in organic carbon component in the region; (3) Structural equation modeling (SEM) indicated that soil carbon fractions were regulated mainly by plant biomass and soil pH under long-term nitrogen conditions. 【Conclusion】Nitrogen addition increases soil labile carbon content in Stipa baicalensis and the changes in soil organic carbon and its fractions are mediated mainly by soil pH and plant biomass.

      • Effects of Long-term Straw Returning on Organic Carbon and Extracellular Enzymes in Paddy Soil Aggregates

        LI Xinyue, LI Bing†, WANG Changquan, HUANG Rong, XIE Ningyi, MO Taixiang, WANG Nanxi, ZHANG Qingwei

        DOI: 10.11766/trxb202206170325

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        Abstract:

        【Objective】Soil aggregate organic carbon and extracellular enzymes play an important role in improving soil structure and carbon sequestration, which are easily affected by agronomic management practices. In order to study the effects of long-term straw returning combined with chemical fertilization on organic carbon components and extracellular enzymes in soil aggregates, a 35-year field positioning experiment was carried out. 【Method】The field experiment was designed to have three treatments in a rice-wheat rotation system: no chemical fertilizer (CK), chemical fertilizer only (NPK), and straw plus chemical fertilizer (NPKS). The contents of soil organic carbon (SOC) and its labile components (dissolved organic carbon (DOC), easily oxidizable organic carbon (EOC) and microbial biomass carbon (MBC)) in soil aggregate were analyzed, as well as the activities of extracellular enzymes related to carbon cycle (β-1,4-Glucosidase (BG), β-1,4-Xylosidase (BX) and β-D-Cellobiohydrolase (CBH)). 【Result】The contents of SOC, DOC and MBC in >0.25 mm aggregates were significantly higher than those in <0.25 mm aggregates, and their contents of NPKS treatment were the highest. This showed that NPKS promoted soil macro-aggregates organic carbon regeneration. The values of MBC/SOC and DOC/SOC in each particle size aggregate were relatively stable, which indicated that dynamic change trends of MBC and DOC were consistent with that of SOC. Thus, MBC and DOC could be used as sensitive indexes to evaluate soil organic carbon. The 2-0.25 mm aggregates were the main carriers of extracellular enzymes, and their activities in NPKS treatment were the highest. However, the enzymes activities in >2 mm aggregates had no significant difference among treatments. The soil organic carbon components and extracellular enzymes in soil aggregates promoted each other, in which the contents of SOC, DOC and MBC in aggregates were mainly affected by CBH, followed by BG; while EOC was only positively affected by CBH. These two extracellular enzymes (CBH and BG) could promote soil organic carbon turnover and the interaction was enhanced in 2-0.25 mm aggregate. 【Conclusion】Long-term application of straw returning combined with chemical fertilizer could increase organic carbon regeneration and turnover rate, and increase soil organic carbon content, which is an important agronomic way for sustainable carbon sequestration in paddy soil.

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

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

        DOI: 10.11766/trxb202205230266

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        Abstract:

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

      • Cadmium Adsorption Characteristics of Different Biochar and Their Regulatory Effects on Soil Cd Pollution, in Yunnan

        WANG Yikun, LIANG Ting, ZHOU Guopeng, CHANG Danna, GAO Songjuan, FU Libo, FAN Hongli, CAO Weidong

        DOI: 10.11766/trxb202205300286

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        Abstract:

        【Objective】Cadmium (Cd) is a harmful element to the human body and can cause many serious diseases. At present, many soils are faced with serious Cd contamination. For example, the soil in Yunnan Province highly polluted by Cd, and necessary steps need to be taken to remedy this situation. The application of biochar to soils is a common way to remedy soil Cd contamination, therefore, this research is designed to study the properties of biochar from different plant sources and evaluate their application effect on Cd pollution in the Dongchuan area, Yunnan Province. 【Method】The isothermal adsorption-desorption and adsorption kinetic characteristics of rice straw biochar (RBC), wheat straw biochar (WBC), corn straw biochar (MBC), hemp straw biochar (HBC), sesbania biochar (TBC) and peanut shell biochar (PBC) were studied; Through pot experiments, the effects of the above biochar on Cd fraction in Cd-contaminated soil and Cd uptake by Lactuca sativa L. in Dongchuan were analyzed. 【Result】Fitting results of adsorption models showed that Langmuir adsorption isotherm and the pseudo-second-order model could better simulate the adsorption process of Cd by biochar. TBC’s maximum saturated adsorption capacity was the highest, 37.1 mg?g-1 in the isothermal adsorption model and 27.9 mg?g-1 in the adsorption kinetic model, respectively. The desorption rates of WBC, RBC and TBC were lower than those of MBC, HBC and PBC, and no more than 10% under each concentration gradient. Fourier transform infrared spectroscopy (FTIR) analysis showed that TBC contained more oxygen-containing functional groups (OH-, C=O etc.). Also, the XRD analysis showed the biochars were mainly composed of C and Si elements, while different biochars also had some different elements (e.g. Fe, Mn etc.). Compared with the treatment without biochar (CK), WBC, MBC, HBC, TBC and PBC treatments significantly reduced the content of soil available Cd. Among them, the maximum decrease was observed for TBC (24.32%). At the same time, the Cd fraction changed from an acid soluble state to a reducible state, oxidizable state and residual state. Compared with the treatment without biochar, WBC, MBC, HBC and TBC treatments significantly reduced the Cd content in the aboveground parts of Lactuca sativa L. (P<0.05), and the maximum decrease occurred in HBC (26.40%). In addition, WBC and HBC treatments significantly reduced the translocation factors of Cd in Lactuca sativa L., which were 0.662 0 and 0.692 8 respectively. The results of ABT(aggregated promoted tree) analysis showed that soil soluble organic carbon (DOC) and soil pH were the main influencing factors of soil available Cd, with a significant negative correlation, and the contribution rates were 33.0% and 21.9% respectively. 【Conclusion】In conclusion, all the biochars from different plant sources can reduce the availability of Cd in Cd-contaminated soil in Dongchuan, change the Cd fraction in soil, and reduce the absorption and transport of Cd by plants. There are differences between different biochars. Moreover, TBC can be selected to remedy Cd-contaminated soil in the Dongchuan area through the results of the isothermal adsorption test, adsorption kinetics test and pot experiments.

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

        XU Zhe, YANG Jinling, ZHAO Yue, ZHANG Ganlin

        DOI: 10.11766/trxb202207280415

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        Abstract:

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

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

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

        DOI: 10.11766/trxb202109300537

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        Abstract:

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

      • Three Dimensional Changes of Soil Organic Carbon Content and Its’ Key Factors in Cultivated soils of Henan Province During the Recent 30 Years

        ZHAO Yanfeng, LI Yixin, MA Panpan, CHEN Jie, LI Yuanyuan, YANG Qiong, CHENG Daoquan

        DOI: 10.11766/trxb202201290041

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        Abstract:

        【Objective】The information of temporal-spatial variation of soil organic carbon content (SOC) with high resolution and high precision is the base for assessing the capability of soil in sequestrating carbon. Though there had been much research on the changes in topsoil SOC, research on SOC of deeper soil layers is still rare. To reduce the gaps in understanding of the ability of deep soil to sequestrate carbon, our research sought to investigate the sensitive area where SOC had changed significantly, the depth where SOC had changed significantly, and the factors that drive SOC change. Thus, research on the temporal-spatial changes of SOC of 0~15 cm, 15~30 cm, 30~60 cm and 60~100 cm of cultivated land in Henan, China from 1982-2010 was conducted and the SOC accumulation rate in this area was compared with that of the COP21 target .【Method】The legacy soil data that was collected from the second national soil survey carried out in 1982 and the recent topsoil data and soil profile data that were sampled in 2010 were used in this research. Digital soil mapping technology with the aid of a quantile random forest algorithm (QRF) and 26 environmental covariates was used to produce SOC maps. For every soil layer in both 1982 and 2010, 500 SOC distributions with equal probability were produced by QRF, and then the SOC map pools for both 1982 and 2010 were derived. Then, stochastic sampling with replacement was repeated 1 000 times from both SOC map pools, respectively, and each time, a subtraction of the two SOC maps was performed to get a SOC change map. So, 1 000 SOC change maps with equal probability were got and based on that the uncertainties of SOC change were assessed. Only those SOC changes with a probability above 0.66 were received as significant results and were used to calculate SOC storage change in the next step. To better understand the mechanism of SOC change, SOC changes among soil types were compared, and the Pearson correlation coefficient between SOC change and primitive SOC content, some climate variables, crop yields, straw returning amount, soil texture, and soil pH were analyzed. 【Result】It was revealed that the significant increase of SOC in 0~15cm, with a magnitude of 2~4 g∙kg-1, had taken place across the plain and basin regions of Henan province. Nevertheless, the increase of SOC in 15~30 cm soil layers with a magnitude of 0~2 g∙kg-1 mainly took place in the Fluvo-aquic soils that were distributed alongside the Huang river and scattered to the Cinnamon soils and Paddy soils. The changes of SOC in soil layers below the 30 cm depth were low in probability. Overall, the total storage of SOC in 0~1 m depth of soils across the cultivated land of Henan province increased by 7.04% in the past 28 years with a mean annual rate of 2.43‰, which was far from the expected value of COP21 4‰. It was also found that the effects of bio-climate variables were more important than soil variables in SOC change. Except for single-cropping rice areas with a fallow period every year, SOC significantly or extremely significantly correlated with biomass input. The mean annual temperature range (the difference between the mean hottest month temperature and the mean coldest month temperature) was positively correlated with SOC accumulation, while climate warming had a negative effect on it. Probably due to the differences in the environment and soil properties, the relationships between SOC change and soil texture, between SOC change and soil pH in different soil types were high variable. The initial SOC values were negatively correlated with SOC change in 0~15cm in two of five soil categories, so was that in 15~30 cm in all the five soil categories, which may be implied a slowing rate for the SOC accumulation in the future. 【Conclusion】The SOC accumulating rate in Henan province will be difficult to meet the object of COP21 in the future. Thus, it is suggested not to overestimate the effects of agricultural soil on carbon sequestrating and much attention should be paid to reducing net carbon emission.

      • Coupled Effects of Film Mulching and Straw-derived Carbon Inputs on Soil Aggregate Characteristics and Crop Yields in Semiarid Areas

        WANG Yuhao, PANG JinWen, WEI Ting, GAO Fei, LIU Enke, JIA Zhikuan, ZHANG Peng

        DOI: 10.11766/trxb202203230129

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        Abstract:

        【Objectives】This study aimed to provide a scientific basis for optimizing appropriate film mulching practices to improve productivity and protect the environment in dryland farming.【Methods】A complete random two-factor field experiment was conducted in Pengyang, Ningxia Province to investigate the coupled effects of mulching (started in 2012) with different straw-derived carbon inputs on the soil aggregate characteristics, organic carbon content, and maize yield. Specifically, the mulching method was the main factor and the straw return form was the sub-factor. Six treatments were established as follows: straw return with film mulching (PS), biochar return with film mulching (PC), no-return with film mulching, straw return without mulching (TS), biochar return without mulching (TC), and no return without mulching.【Results】The results indicated that each straw and biochar return treatment significantly (P < 0.05) improved the soil aggregate distribution and stability of each particle size, and the aggregate content > 0.25 mm increased significantly (P < 0.05) by 47.32% on average. Compared with the no-mulching treatment, the mean weight diameter and geometric mean diameter of the soil particles increased by 9.19% and 4.15%, respectively, under the double ridge-furrow mulching treatments. The organic carbon content of the 0-60 cm soil layer increased significantly (P < 0.05) under each straw and biochar return treatment compared with the no-return treatments, where the contents were 2.60% and 2.73% higher under PC and TC than PS and TS, respectively. The aggregate organic carbon contents under each treatment increased as the aggregate particle size increased. Also, the straw and biochar return treatments significantly increased the organic carbon content of aggregates, whereas the contents decreased under double ridge-furrow mulching treatments. Structural equation modeling showed that the straw return form, mulching method, and soil organic carbon content could significantly promote yield increases, while the straw and biochar return treatments significantly increased (P<0.05) the corn yield in film-mulched fields by 14.6% on average. However, the yield increase did not differ significantly between the straw return treatments and biochar return treatments.【Conclusion】In conclusion, double ridge-furrow mulching and straw carbon input treatments significantly improved the soil stability, soil organic carbon content, crop yield, and the coupled effect of the double ridge-furrow mulching and biochar return had a positive effect on improving the farmland soil quality and fertility.

      • Review on Quantification of Root-induced Change of Soil Hydraulic Parameters

        LU Jianrong, LI Yunliang, TAN Zhiqiang, JI Mingfei, YANG Lei, B. Larry Li

        DOI: 10.11766/trxb202204190188

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        Abstract:

        【Objective】Plants roots are known as an important driving force for the change of soil structure and soil hydraulic parameters (SHP). However, there is a lack of appropriate modelling approaches to root-pore-SHP interactions with quantitative descriptions, which has led to knowledge gaps in the effects of roots on SHP at larger scales. A consequence of this gap is the bias in the simulation and prediction of hydrological processes such as infiltration, runoff and evaporation in catchments. 【Method】In this paper, available literature are reviewed and used to quantify the changes and effects of plant roots on SHP. In addition, its relationships with plant and soil type are proposed. The quantitative expression of SHP and their prediction models under the dynamic growth of plant roots are summarized. This paper also analyzes problems and future research directions of the quantitative research on root-permeated soils. 【Result】This study points out that the current research on SHP affecting roots focused on small-scale control experiments, ignoring the interference of soil spatial heterogeneity and environmental factors at large scales. Previous studies found contrasting root effects (on SHP) depending on which processes are dominant, including root growth (or decay) and the density and diameter of roots. Meanwhile, root-induced change of SHP was species (root characteristics), soil type, and time-dependent. Also, related studies indicated that the model’s accuracy and reliability would be improved when considering the temporal dynamics of roots induced by land cover/land use change and seasonal variations in SHP. Few efforts have been undertaken to incorporate root variables into soil function to predict SHP based on roots occupying the soil pore space, changing soil pore size distribution and soil pore network model. 【Conclusion】Neglecting root-induced change of SHP in hydrologic simulation may lead to high uncertainties. As the root-related dominant process at a larger scale is different to that in small-scale control experiments, there remain significant knowledge gaps that impede the development of quantitative guidance on root-induced change of SHP at a larger scale. It is highlighted that the importance of root effects and associated parameters related to soil structure, and it is becoming a part of hot topic about coupling hydrological and water quality models.

      • Effects of Microbial Model Parameter Optimization on the Spatiotemporal Dynamics Modelling of Soil Organic Carbon

        ZHANG Xiu, XIE Enze, CHEN Jian, PENG Yuxuan, YAN Guojing, ZHAO Yongcun

        DOI: 10.11766/trxb202205080237

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        Abstract:

        【Objective】 Soil organic carbon (SOC) forms the basis of soil fertility, food production, and soil health, and plays a key role in climate change via mediating greenhouse gas emissions. Consequently, accurate characterization of SOC spatiotemporal dynamics is extremely important for the sustainable management of soil resources, ecosystem stability maintenance, and mitigation and adaptation to climate change.【Method】A total of 399, 413, and 407 cropland topsoil (0 ~ 20 cm) SOC data in 1980, 2000, and 2015 were collected from the southern Jiangsu Province of China, respectively, and the microbial-explicit SOC model MIMICS (Microbial-Mineral Carbon Stabilization) was used to model the spatiotemporal dynamics of SOC. The Sobol global sensitivity analysis was applied to identify the sensitive parameters of the MIMICS model, and then, two-parameter optimization schemes, one batch (using all SOC observations in a batch mode to optimize the parameters) and site-by-site (using SOC observations at individual sites to optimize the parameters site by site), were used to optimize the sensitive parameters of the MIMICS model through Markov Chain Monte Carlo (MCMC) approach, respectively. The coefficient of determination (R2), root mean squared error (RMSE), and mean absolute error (MAE) that were calculated from the independent validation of SOC in 2000 and 2015 were used to compare the performance of different parameter optimization schemes.【Result】Results show: (1) The net increment of SOC density between 1980 and 2000 was 0.89 kg∙m–2, while the net decrement was 0.44 kg∙m–2 between 2000 and 2015, representing a net increment of 0.45 kg∙m–2 over the period of 1980–2015; (2) The MIMICS model with parameters optimized by either One batch or site-by-site method can represent the overall trends in topsoil SOC dynamics during the period of 1980–2015, but the model with parameters optimized by the site-by-site method presents more local details on the variability of the SOC change rate; (3) Compared with the default parameter values and the One-batch optimized parameter values, the MIMICS model with site-by-site optimized parameter values had the best performance in modeling the spatiotemporal dynamics of SOC in the study area, with the RMSE decreasing by 22.2% (the independent validation in 2000) and 14.7% (the independent validation in 2015) in comparison with the MIMICS model with default parameter values. Yet, its prediction accuracy in 2015 was still relatively low (R2 = 0.13, RMSE = 1.22 kg∙m–2). 【Conclusion】The optimization of sensitive parameters can improve the space-time SOC prediction accuracy of the MIMICS model, and the representation of local details on the spatiotemporal patterns of SOC dynamics. Although the MIMICS model with the spatially heterogeneous parameter values optimized by the site-by-site method had the best performance, its prediction accuracy in 2015 was still relatively low, which indicated that the MIMICS model still has limitations in representing the responses of SOC to anthropogenic activities such as changes in land use and agricultural management practices. Thus, further improvement of the MIMICS model structure and enhancing the spatiotemporal resolution of model input data are still significant challenges for regional scale modeling of SOC spatiotemporal dynamics through microbial-explicit SOC models.

      • Effects of Potassium Addition on Physiological Characteristics and Grain Yield Under Drought Stress Condition in Different Growth Stages of Rice

        XIONG Zhihao, YANG Cheng, ZHANG Geng, LI Xuchun, LI Xiaokun

        DOI: 10.11766/trxb202205230267

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        Abstract:

        【Objective】As one of the most important food crops in China, rice (Oryza sativa L.) is the staple food for more than half of the country""s population. With the development trend of global warming and frequent occurrence of extreme weather such as sustained high temperature, drought on farmland is becoming a more frequent and urgent problem. Thus, this study seeks to clarify the effects of drought stress on rice at different growth stages, the regulation of potassium on drought stress and its mechanism, and to provide a theoretical basis for the management of potassium and efficient water use in rice.【Method】A two-factor pot experiment of K and water treatments at different periods was carried out in 2021. Potassium management was two levels of 0.15 (+K) and 0 (?K) g?kg?1 soil(calculated as K2O), moisture management was four levels of drought stress at the tillering stage (TD), drought stress at booting stage (BD), drought stress at milking stage (MD) and well-watered treatment (WW), to explore the effects of K fertilizer on rice yield and physiological characters under drought stress at different growth stages. 【Result】Results showed that drought stress significantly decreased rice yield. Compared with the WW treatment, TD, BD and MD treatments decreased rice yields by 53.9%, 45.2%, and 7.6% under K deficient conditions, respectively, while under K sufficient conditions, rice yields reduced by 28.3%, 16.5% and 5.9%, respectively. The degree of influence of drought stress on yield in different growth stages was: TD > BD > MD, and K deficiency aggravated the negative impact of water deficit on rice yields. Similarly, drought stress also caused a decrease in canopy transpiration rate, leaf water potential, leaf net photosynthetic rate, and limited dry matter accumulation. Compared to the WW treatment corresponding to the same period, TD and BD treatments reduced leaf biomass by an average of 42.9% and 31.2%, respectively. The stem sheath biomass decreased by 43.8% and 38.0%, respectively, and the effect of water deficiency on biomass in different growth stages was: TD > BD. Potassium deficiency resulted in a reduction in net photosynthetic rate, leaf area and chlorophyll content, which restricted the ability of plants to receive light radiation and produce dry matter. Compared with the K-sufficient treatment, the leaf biomass of the TD and BD and WW treatments at the same stages decreased by 52.6%, 32.7%, 42.1%, and 31.2%, respectively. Also, under potassium deficient conditions, stem sheath biomass decreased by 55.3%, 63.6%, 52.2%, and 28.0%, respectively. Drought stress exacerbated the negative effects of potassium deficiency. 【Conclusion】Our results indicated that drought stress could limit the net photosynthetic rate and leaf water potential, resulting in the reduction of rice yield, which affects the tillering stage and booting stage more than the milking stage. Potash application significantly increased leaf area, increased chlorophyll content, enhanced the ability of rice to intercept light radiation, improved rice photosynthetic efficiency, and increased rice dry matter accumulation, while reducing canopy transpiration rate, improving water use efficiency, alleviating the decline of leaf water potential, thereby enhancing the drought resistance of crops.

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

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

        DOI: 10.11766/trxb202206200329

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        Abstract:

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

      • Effect of Exogenous Rice Straw on Water Dispersible Colloidal Metals in Polluted Soil Under Redox Change

        ZHANG Yu, WANG Jiajia, XIA Bing, LUO Xueting, HU Pengjie†, WU Longhua, LUO Yongming

        DOI: 10.11766/trxb202204110168

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        Abstract:

        【Objective】Soil colloids, especially water-dispersible colloids (WDC), as pollutant carriers, play important roles in heavy metal adsorption, migration, and biological absorption. The purpose of this study was to explore the effect of exogenous rice straw and redox change on the distribution of heavy metals in the aqueous phase of the soil and water-dispersible colloids. 【Method】In this study, soil microcosm experiments were conducted for 70 days, in which 0-40 days was the reduction period, and 41-70 days was the oxidation period. The experiment comprised two treatments: (i) no straw added (CK), (ii) rice straw added (1% of the soil weight, S). The different chemical parameters in the aqueous phase of the soil were comprehensively compared, and the particle size classification and elemental composition of WDC during the redox process were characterized by asymmetrical flow field-flow fractionation (AF4) coupled to UV and ICP-MS (AF4-UV-ICP-MS) method. 【Result】The results showed that in anaerobic conditions, exogenous rice straw increased aqueous concentrations of dissolved organic carbon (DOC), arsenic (As), iron (Fe), manganese (Mn), calcium (Ca), potassium (K), silicon (Si), aluminum (Al), and magnesium (Mg), while it decreased aqueous redox potential (Eh) and the concentrations of copper (Cu) and lead (Pb). In aerobic conditions, exogenous rice straw increased aqueous concentrations of Pb. Results from AF4-UV-ICP-MS indicated that the size of WDC was mainly distributed at three size ranges, 0.3-3 kDa, 3-40 kDa, and 130 kDa-450 nm with different complexes of organic matters, inorganic clay minerals, and ferriferous minerals. A significant proportion of heavy metals in the aqueous phase were bound to WDC particles, which indicated that WDC played an important role in the environmental behavior of these pollutants. WDC with different particle sizes tended to combine different kinds of heavy metals. Exogenous rice straw affected the distribution of heavy metals in WDC particles and this effect was related to the nature of the elements. Also, exogenous rice straw promoted the transformation of Fe and As from WDC state to the dissolved state, while promoting the transformation of cadmium (Cd) and Cu from dissolved state to the WDC state. 【Conclusion】Water-dispersible colloids were important carriers for heavy metals in the aqueous phase of the soil. Exogenous rice straw and redox change affected the behavior of WDC associated heavy metals related to the nature of elements. This study is important as it reveals the interface mechanism of how agricultural activities affect the migration, transformation, and bioavailability of heavy metals.

      • Effects of long-term different tillage practices on chitin degrading microbial communities and chitinase activity in farmland black soil

        Sui Pengxiang, Luo Yang, Li Ruiping, Zheng Hongbing, Yuan Ye, Zheng Jinyu, Wang Hao, Liu Wuren

        DOI: 10.11766/trxb202203180120

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        Abstract:

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

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

        li jie, wang qiang, luo meng, jiang xiang ting, sun yuan peng, zhang li zhi

        DOI: 10.11766/trxb202204290220

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        Abstract:

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

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

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

        DOI: 10.11766/trxb202206200331

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        Abstract:

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

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

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

        DOI: 10.11766/trxb202206060235

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        Abstract:

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

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

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

        DOI: 10.11766/trxb202203160112

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        Abstract:

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

      • Rapid Diagnosis and Assessment of Heavy Metal Pollution in Greenhouse Vegetable Production Soils Based on Portable X-ray Fluorescence Spectroscopy

        DENG Yuan, FAN Yanan, WU Qiumei, HU Wenyou, YU Yueming, WANG Hua, ZHU Chunwu, LI Xun, TIAN Kang, HUANG Biao

        DOI: 10.11766/trxb202206130187

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        Abstract:

        【Objective】Guangdong is a major province of vegetable production and consumption in China, and is also an important vegetable production base for Hong Kong, Macao, and the "Southern Vegetables and Northern Transportation". Therefore, rapid diagnosis and assessment of soil heavy metal pollution is the premise of soil pollution prevention and control and risk management. This study aimed to investigate the applicability of in situ and ex situ portable X-ray fluorescence spectroscopy (PXRF) for rapid detection of heavy metals in greenhouse vegetable production soils of Guangdong Province and to diagnose and evaluate heavy metal pollution in greenhouse vegetable production soils based on portable X-ray fluorescence spectroscopy. 【Method】A total of 110 greenhouse vegetable production soil sampling sites and 26 open-field soil sampling sites were set up in the study area. PXRF was used in situ to rapidly detect soil heavy metal contents (Cd, Cu, Cr, Pb, Zn, As, Ni and Hg). The accuracy of the PXRF method was verified by analyzing the correlation between the values of soil heavy metals measured by the PXRF and the traditional laboratory analysis and based on this, the soil heavy metal pollution status was quickly diagnosed. The risk of soil heavy metal pollution was evaluated by the single factor pollution index and the Nemerow composite pollution index method. 【Result】The results indicated that: (1) the concentrations of Cd, Cu, Cr, Pb, Zn, As and Ni detected by the ex situ PXRF method were significantly correlated with those determined by traditional laboratory methods (P < 0.01), and the R2 were 0.69, 0.50, 0.56, 0.58, 0.47, 0.54 and 0.62, respectively. Also, the results of in situ determination of Pb and As in soil by the PXRF method were significantly correlated with those by traditional laboratory methods (P < 0.01), and the R2 were 0.73 and 0.74, respectively. (2) When the soil moisture content was 150 g?kg-1-200 g?kg-1, the results of in situ determination of Cr, Pb, Zn and As in soil by the PXRF method were significantly correlated with those by traditional laboratory methods (P < 0.01), and the R2 were 0.77, 0.94, 0.72 and 0.93, respectively. (3) Soil Cd and Cu pollutions were prominent in greenhouse vegetable production soils of Guangdong Province. The point exceeding rates were 20.9% and 10.0%, respectively, according to the Soil Environmental Quality Risk Control Standard for Soil Contamination of Agricultural Land (GB 15618-2018). In addition, the average content of Cd in greenhouse vegetable production soil was 0.21 mg?kg-1, which was 1.2 times greater than that in open-field soil. The contents of Cd, Cu, Cr, Pb, Zn, As and Ni in the greenhouse vegetable production soil in the Pearl River Delta were generally higher than those in other areas. (4) The single pollution index of Cd, Cu, Cr, Pb, Zn, As, Ni and Hg were all less than 1, and the order was Cd > Cu > Pb > Zn > Cr > As > Ni > Hg. The mean value of the Nemerow comprehensive pollution index was 0.69. From the overall average, the degree of soil heavy metal pollution was at a clean level.【Conclusion】In summary, PXRF is an effective method for the rapid diagnosis of heavy metal pollution in greenhouse vegetable production soils in Guangdong Province. Furthermore, Cd and Cu can be quickly identified as the primary pollution elements with high risk in greenhouse vegetable production soils of Guangdong Province. The results of this study will serve as a reference for the evaluation of soil environmental quality and sustainable development of greenhouse agriculture.

      • Progress and Prospect of Research on Constructed Technosols

        ZHENG Ruilun, ZHU Yongguan, SUN Guoxin

        DOI: 10.11766/trxb20226200209

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        Abstract:

        Urban green infrastructure is an effective way to solve many environmental issues caused by urbanization. As urban soils are generally not suitable for vegetation growth, a lot of soil resources needed for urban green infrastructure construction can only be excavated and transported from the exurban farmland and/or natural topsoil to urban areas, or in another way, urban soils are planted vegetation after fertilized with organic waste. These methods tend to be costly, destructive to arable land, induce large carbon emissions, and/or have a high cumulative risk of pollution. The huge amount of soil resources needed for the construction of urban green infrastructure is very scarce and this has to be addressed urgently. Constructed Technosols (CT) is a new soil created by using organic and inorganic solid wastes (including artefacts and also seminatural sediment and excavated deep soil-like things) for growing plants, which can be adjusted to meet the requirements of various vegetation types, land uses, site conditions (roof, balcony, street, etc.) in physicochemical properties and pollutant limit standards, and finally returned to the city for green infrastructure construction. CT can simultaneously alleviate the pressure of disposal of urban solid waste and solve the issue of soil shortage in urban green infrastructure construction. It features low carbon, low cost and low eco-impact, and can also produce economic benefits. In this paper, firstly, it was briefly stated the definition, classification and construction techniques of CT. And, the research status and advances mainly in terms of roles in plant growth, carbon capture, biodiversity protection, runoff pollutant removal, and artificial biological intervention of CT were presented. Then, it was briefly described the production of solid waste in China, and according to the current research and application situation, it was proposed the application potential (such as ornamental plant breeding and cultivation, sod production and urban farming etc. in addition to the park, green buffers, green roof and brownfield remediation like things) and advantages of CT. Finally, based on comprehensive research progress, some problems in CT research were pointed out and some insights and suggestions were put forward. Meaningful research on the ecological risk of pollutants in CT, biochar (hydrochar or pyrochar) application to CT, soil heterogeneity design for plant diversity, biological regulation of CT good for human health, promotion of environmental function for CT, and role of carbon sequestration by CT were proposed and supposed. It was aimed that comprehensive reutilization of urban solid waste and more eco-friendly low-carbon development of urban green infrastructure will be able to be promoted, urban carbon sequestration will increase, and urban ecological environment and people""s health and well-being will be improved.

      • Effect of the Acidification Environment on Exchangeable Cations and Acid Buffering Capacity of Weathering Products of Purple Parent Rock

        LI Chunpei, LI Xue, WANG Xuan, LIU Gangcai, ZHAO Jixia, XIONG Junfen

        DOI: 10.11766/trxb202203200121

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        Abstract:

        【Objectives】This study aimed to analyze the influence of the acidification environment on weathering products of the typical purple parent rock. The weathering products of purple parent rocks from the Suining Group (J3s), Shaximiao Group (J2s), and Penglaizhen Group (J3p) were investigated under different acidification environments in the laboratory. 【Method】 The acid solutions used for acidification of purple parent rock samples were used to cycle soaking and simulate leaching experiment tests at pHs of 2.5, 3.5, 4.5, and 5.6. In addition, deionized water (pH = 7.0) was set as a control treatment (CK). 【Result】 The results showed that the exchangeable cations and content of total exchangeable cations of weathering products of these purple parent rocks decreased as the acidity of the acidifying solutions increased. The acid buffering capacity of weathering products had an extremely significant correlation with the content of the exchangeable K+, Na+, Ca2+, and Mg2+ and the content total of exchangeable cations (P < 0.01). Compared with the value at pH = 7.0 (CK), the total content of exchangeable cations of the weathering products of purple parent rock of the groups J3s, J3p, and J2s in cycle soaking experiment tests decreased by 8.75%-18.21%,10.83%-23.18%, and 5.85%-18.41%, respectively. When the amount of simulated rainfall at 24 times was compared with that at 12 times, the total content of exchangeable cations in J3s, J3p, and J2s decreased by 1.77%-24.85%, 8.99%-25.75%, and 8.05%-25.66%, respectively. In addition, the exchangeable cations characteristics of the weathering products were Ca2+> Mg2+> Na+ > K+ under the same acidity treatment. 【Conclusion】The acid buffer capacity, exchangeable salt ions, and total salt of weathering products under the soaking treatment in this experiment were lower than under the leaching treatment. It can be seen that the transport of minerals or nutrients on the slopes of hilly areas is dominated by leaching, while the transport of minerals or nutrients on the plains is dominated by leaching. Therefore, acid deposition may accelerate the occurrence of soil erosion on slopes to some extent, which in turn leads to an acceleration of the plain side process.

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

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

        DOI: 10.11766/trxb202205120170

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        Abstract:

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

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

        NIU Ben, WANG Yanling

        DOI: 10.11766/trxb202205160257

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        Abstract:

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

      • Composition Structure and Phosphorus Entrapment Capacities of Periphytic Biofilms in Paddy Fields in Different Regions in Eastern China

        LU Wen-yuan, SUN Peng-fei, XU Ying, LIU Jun-zhuo, WU Yong-hong

        DOI: 10.11766/trxb202203220002

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        Abstract:

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

      • Effects of Nitrogen and Phosphorus Addition on Organic Carbon Mineralization and Priming Effect in a Moso Bamboo Plantation Soil

        Yao Yihan, Zhang Shaobo, Zhou Jiashu, Liu Juan, Cai Yanjiang, Li Yongfu

        DOI: 10.11766/trxb202205060034

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        Abstract: 【Objective】Nutrients addition to soil have a significant effect on soil organic carbon mineralization. However, the response of soil organic carbon priming effect (PE) to the addition of different nutrients and its mechanism is still not clear.【Method】Urea and sodium dihydrogen phosphate were selected as exogenous nutrients and the effects of nitrogen addition, phosphorus addition and nitrogen combined phosphorus addition on soil organic carbon (SOC) mineralization, (PE), microbial function and soil physicochemical properties in a Moso bamboo plantation soil were investigated through an 80-day incubation experiment. 【Result】Nitrogen, phosphorus and their interaction significantly increased the cumulative CO2 emissions of native SOC mineralization (by 91.33%, 19.18% and 94.88%, respectively), resulting in a cumulative positive PE. The magnitude of positive PE induced by nitrogen and nitrogen combined with phosphorus was greater than that induced by phosphorus alone. The above three nutrient addition treatments all significantly increased soil pH, labile organic carbon pool (microbial biomass carbon, dissolved organic carbon and O-alkyl C), carbon-degrading enzyme (?-glucosidase and invertase) activities and cbhI and GH48 functional gene abundance, but inhibited the activity of polyphenol oxidase and RubisCO enzymes. Also, soil inorganic nitrogen content (NH4+-N and NO3--N) was enhanced under nitrogen and nitrogen combined phosphorus treatments but reduced under phosphorus treatment. Results of Spearman correlation analysis showed significant positive relationships between cumulative PE and soil pH, labile organic carbon, inorganic nitrogen content, carbon-degrading enzyme activities, cbhI and GH48 functional gene abundances, whereas the activities of polyphenol oxidase and RubisCO enzyme were negatively related to cumulative PE. 【Conclusion】The addition of nitrogen and phosphorus nutrients may have enhanced the rate of native SOC mineralization by affecting soil pH, the content of labile carbon and nitrogen, and stimulating the activity and function of microorganisms.

      • Advances in the Indicator and Assessment Approaches of Medium-low Yield Fields

        Bai Xueyuan, Zhang Jie, Cui Zhenling, Wang Guangjin, Lu Yujiao, Zhang Fusuo

        DOI: 10.11766/trxb202204070045

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        Abstract:

        China’s medium-low yield fields are widely distributed and have great potential for land productivity improvement. Improving the land productivity of medium-low yield fields is of great significant for ensuring food security and achieving sustainable development goals (SDGs). Assessing the quality and spatial distribution of medium-low yield fields is the prerequisite and basis for land improvement. This paper systematically reviewed the concept, evaluation indicators, and main evaluation methods of medium-low yield fields. Based on the research status of medium-low yield fields, this paper discusses the main problems and development trends of the assessing of medium-low yield fields in China. The existing concepts of medium-low yield fields focus on the area and quality of medium-low yield fields, and there are few studies on ecological aspect and sustainable development abilities. Furthermore, the indicators system and evaluation methods for medium-low yield fields are not uniform. In the future, the medium-low yield fields assessment should consider quantity, quality, and ecology aspects. The medium-low yield fields assessment should be focused on the multi-scale assessment indices system construction and multi-source data fusion assessment methods innovation. Analyzing the spatial and temporal pattern of medium-low yield fields in different scales is helpful to explore ways to increase the productivity of green, high-yield, and efficient agricultural production, ensure food security, and promote the realization of SDGs

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

        Xia Weiwei, Li Yikun, Zhang Meng, Sun Xiangxin, Wang Yufang, Jia Zhongjun

        DOI: 10.11766/trxb202203220126

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

      • Correlation Between the Stability and Function of Soil Microbial Community Driven by Reductive Soil Disinfestation

        Zhaojun, Zhangjingqing, Linyulan, Wangbaoying, Huangxinqi, Zhangjinbo, Caizucong

        DOI: 10.11766/trxb202205150254

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        【Objective】Reductive soil disinfestation (RSD) is an effective agriculture practice to conquer continuous cropping obstacles by the elimination of soil-borne pathogens, degradation of allelochemicals, improvement of soil microbial community structure, and restoration of soil microbial functions. However, the effects of RSD practice on the stability of the mono-cropped soil microbial community are still unknown. Moreover, the relationship between soil microbial community stability and functions also needs to be studied. Therefore, this study was oriented to explore the relationship between the stability and function of soil microbial communities driven by reductive soil disinfestation. 【Method】A field experiment, designed to have four treatments, i.e. CK (control without soil treatment); SB (RSD incorporated with 15 t·hm-2 organic substrate with C/N ratio of 122); BD (RSD incorporated with 15 t·hm-2 organic substrate with C/N ratio of 19); and SB+BD (RSD incorporated with 15 t·hm-2 organic substrates containing both high and low C/N ratios with equal mass), was carried out in a lisianthus mono-cropped soils in Shiping County, Yunnan Province. Biolog microplate method, quantitative real-time PCR, and high-throughput sequencing were used to analyze the microbial community stability, microbial metabolic activity and function diversity, and the abundance of nitrogen-related functional genes. 【Result】Results showed that RSD significantly reduced the stability of bacterial community composition and abundance as compared to CK, with the effects of SB+BD treatment being stronger than that of SB and BD treatment, whereas it had no significant effect on the stability of fungal community composition and abundance. Also, RSD significantly enhanced the stability of interactions between bacterial and fungal communities, and SB and BD treatments had greater effects on the improvement of stability of the interaction between microbial communities than SB+BD treatment. Regression analysis indicated that the stability of interaction relationship of soil microbial community was closely related to the stability of microbial composition and abundance. In addition, correlation analysis showed that soil microbial community stability was highly correlated with its activity, carbon metabolic function and denitrification capacity. 【Conclusion】Collectively, reductive soil disinfestation can improve the stability of interactions between microbial taxa by reducing the stability of microbial community composition and abundance, thereby promoting the restoration of soil microbial activity and improvement of community ecological function.

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

        Lai Zheng, Xiao Liting, Lai Sheng, Yang Huiling, Ni Caiying, YANG Wenjing, JIAN Min-fei

        DOI: 10.11766/trxb202205150255

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

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

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

        DOI: 10.11766/trxb202112010651

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        【Objective】Under the background of high-intensity soil resource utilization, digital soil mapping has become an effective method to obtain and characterize soil information quickly, efficiently and accurately. The accuracy and reliability of soil spatial prediction and digital mapping are restricted by multiple factors, such as soil sample size, sampling strategy, prediction model, the complexity of geomorphology and soil-forming environment in the target region, and quality of covariate data. 【Method】Choosing Henan Province as the study region, we applied five of the most representative machine learning (ML) algorithms to spatially predict and digitally map the topsoil pH of croplands. Afterwards, the impact of different sample sizes and sampling methods on the performance of the chosen ML models and the prediction accuracy of topsoil pH were compared. 【Result】The results showed that: (1) When the soil sample size increased from 200 to 2 000, the performance of all ML models and prediction accuracy of topsoil pH showed a general trend of rapid increase regardless of the sampling method. When sample size reached and exceeded 2 000, the performance of most ML models tended to be stable, and the prediction accuracy of topsoil pH increase rapidly slowed down, suggesting that a soil sample size of 2 000 might be the sample size threshold for these ML models to predict the topsoil pH of croplands in this area. (2) The performance of the five ML models and their topsoil pH prediction accuracy was significantly different. The tree-based ML models, namely Random forests (RF) and Cubist performed best. No matter which sampling method was used, when the sample size was more than 2 000, the archived coefficient of determination (R2) of the two models could be stable between 0.75 and 0.80, and the RMSE could be kept below 0.50. (3) When the soil sample size was large enough, the sampling method had little impact on the ML model performance. Also, the topsoil pH prediction accuracy and the sampling method gradually highlighted when the soil sample size was less than 2 000. Comparatively, Conditioned Latin hypercube sampling (clhs) had advantages when the sample size was small. When the sample size was 1 000, clhs sampling method could still keep the R2 of random forest and Cubist prediction at about 0.80. Even when the sample size was as small as 200, the R2 archived by all five ML models under the clhs sampling method was above 0.54. (4) The uncertainty analysis showed that 73.9% of the observed values of topsoil pH of the validation samples fell into the 90% Prediction Interval (PI) of the random forest model, indicating that the reliability of the model was slightly overconfident, but it was within the acceptable range. In addition, the data indicated that the uncertainty of model prediction was not significantly correlated with sample size. 【Conclusion】Tree-structured machine learning models Random Forest and Cubist stand out in this case. Improving the spatial prediction and digital mapping accuracy of soil target variables cannot be achieved simply by expanding the scale of sample points and increasing the density of sample points. It is necessary to improve the model prediction performance and covariate data quality at the same time. When the sample size is large enough, the sampling strategy has little effect on the performance of the ML model and the prediction accuracy of surface soil pH; when the sample size is smaller than a certain threshold, the sampling method has a significant impact on the model performance and prediction results.

      • Research Progress of Heavy Metal Biomineralization Induced by Iron and Manganese-Oxidizing Bacteria in Soils

        WU Chuan, LUO Yuxuan, XUE Shengguo, QIAN Ziyan, QI Yanting

        DOI: 10.11766/trxb202201070648

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        Abstract:

        The effects of iron-manganese oxidizing bacteria-induced mineralization on the environmental behavior of heavy metals were reviewed, including iron/manganese-oxidizing bacteria and biomineralization, iron/manganese-oxidizing bacteria-induced iron-manganese oxide precipitation coupled with heavy metal stabilization, and the effect of iron-manganese oxide on heavy metals in soils. The application of iron/manganese-oxidizing bacteria in the bioremediation of different heavy metals was further summarized from the aspects of the biological mineralization pattern of iron/manganese-oxidizing bacteria (direct or indirect catalytic mineralization of iron oxide protein/enzyme, dual electron transfer reaction of manganese oxidase dominated by polycopper oxidase and the mineralization induced by external factors), heavy metal stabilization mechanisms of iron/manganese-oxidizing bacteria biological mineralization in soils (precipitation/coprecipitation, adsorption/complexation and redox). The effects of extracellular polymers, temperature and pH, coexisting ions and other factors on the mineralization process were also analyzed, in order to provide theoretical references for microbial-induced mineralization to remediate heavy metal pollution. Future work should focus on the long-term stability of heavy metals generated by minerals, the regulation of different microbial species combinations on mineralization, and the application of iron/manganese-oxidizing bacteria in the remediation of soil multi-heavy metal contaminated sites.

      • The Change in Dominant Mycorrhizal Fungi Type Induced by Stand Transformation Affects Soil Organic Carbon Accumulation

        TU Jiaying, JIN Wenhao, SHENG Weixing, XING Jiajia, PENG Liyuan, CHEN Junhui, XU Qiufang, QIN Hua

        DOI: 10.11766/trxb202206210271

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        【Objective】Masson pine forest（Pinus massoniana Lamb.）is a typical ectomycorrhizal (ECM) dominant forest. However, in recent years, the ecological service function of the Masson pine forest decreased due to pine wood nematode disease, and the Masson pine forest was gradually replaced by an Arbuscular mycorrhizal (AM) dominant broadleaved forest. However, it remains unclear what influence could be exerted by the changes of dominant mycorrhizal types on soil organic carbon accumulation during the conversion of Masson pine forest to broadleaf forest in the subtropical region.【Method】In this study, the biomass of ECM fungi and AM fungi were determined by high-performance liquid chromatography (HPLC) and neutral lipid fatty acids (NLFA), respectively. At the same time, phospholipid fatty acids (PLFAs) technology was used to study the characteristics of the microbial community. The content of glomalin-related soil protein (GRSP) and the activities of soil extracellular enzymes was also determined in Masson pine and broadleaved forests in Jiande County, Zhejiang Province.【Result】The results showed that: AM fungi-dominated (AMD) broadleaved forest replaced ECM fungi-dominated (ECMD) Masson pine forest, soil organic carbon in AM fungi dominated broadleaved forest was significantly enhanced by 36.81%, microbial carbon use efficiency (CUE) significantly increased by 53.85%, and AM fungal biomass significantly increased by 25.57%. Moreover, compared with ECM fungi-dominated forests, the biomass of ECM fungi in AM fungi-dominated forests decreased significantly by 45.04%. The Masson pine forest, which was dominated by ECM fungi, was subjected to more severe microbial nitrogen limitation. Phospholipid fatty acids analysis showed that the gram-positive bacteria (G+) and the ratio of gram-positive bacteria to gram-negative bacteria (G+/G-) in Masson pine forest dominated by ECM fungi compared with the broadleaved forest dominated by AM fungi were significantly decreased by 21.47% and 6.46%, respectively. Redundancy analysis (RDA) results showed that there were significant differences in microbial community structure between forests dominated by AM fungi and ECM fungi (P<0.05), in which AM fungal biomass (R2=0.48, P=0.002) and soil organic carbon content (R2=0.47, P=0.003) were significantly correlated with the variation of microbial community structure (P<0.05).【Conclusion】The decrease of GRSP and the different recruit of microbial groups by different mycorrhizal fungi types were important reasons for the reduction of soil organic carbon content in forests dominated by ECM fungi compared to AM fungi dominated forests. Therefore, the substitution of broadleaved forest for Masson pine forest in the subtropical region increased the content of forest soil organic carbon and improved the function of the forest carbon sink.

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

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

        DOI: 10.11766/trxb202203220004

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

      • Research on the Carbon Sink Contribution of Subtropical Paddy Field Soil Under Different Straw Return Rates

        LUO Yuye, QIU Longxia, LONG Jun, CHEN Hanyue, WU Ting, LI Jing, XING Shihe, ZHANG Liming

        DOI: 10.11766/trxb202112280700

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        Abstract:

        【Objective】Straw returning is generally considered to be an effective way to increase soil "carbon sink" and mitigate climate change. China is rich in straw resources, but the rate of straw returning to the field is less than 20%, which is the main reason for a long-term deficit of carbon pool in farmland soils in China. There are many kinds of straw resources in subtropical region, which also account for about 30% of the total output of the country. Therefore, clarifying the quantitative relationship between the amount of straw returning and soil carbon sink in subtropical areas of China is an important basis for formulating carbon sequestration measures and implementing national strategies such as carbon neutralization.【Method】Paddy soil in Fujian Province, a typical subtropical region in China, was selected as our study area. The spatial database was constructed by the digitization of 1:50,000 soil map paper data from 84 counties (cities and districts) in Fujian Province during the second soil census in 1982. The soil attribute database is composed of 15,833 surface samples from the arable land fertility survey conducted by the Ministry of Agriculture and Rural Areas in 2016. ArcGIS software and the PKB method (Pedological Knowledge-Based Method) connect the spatial data and attribute data in a 1:50 000 soil database. Using the latest established 1:50000 soil database and DNDC (DeNitrification and DeComposition) model widely used in the agricultural ecosystem, the future dynamic changes of soil organic carbon under different rates of straw returned in Fujian Province were simulated.【Result】 Results showed that the average annual carbon sequestration rates can reach 173, 302, 478 and 838 kg·hm-2 , and the sequestration of carbon amounts were 11.56, 20.15, 31.90 and 55.95 Tg during the period of 2017-2053 under the treatments of conventional management (15%), straw returning of 30%, 50%, and 90%, respectively. Straw was returned to the field from the perspective of carbon sequestration rate, the average annual carbon sequestration rates of Acid sulfate paddy soils and Salinized paddy soils were the highest, which ranged from 220 to 920 kg·ha-1 under different straw returning rates. In terms of total carbon sequestration, the total carbon sequestration of Percogenic paddy soils and Hydromorphic paddy soils under different straw returning rates accounted for 81% of the total carbon sequestration over the whole province. Considering the administrative areas, the average annual carbon sequestration rate and total amount in Longyan and Quanzhou were relatively large, ranging from 202~937 kg·hm-2 and 1.55~8.34 Tg under different straw returning rates, respectively.【Conclusion】In general, the increase in straw returning ratio contributed significantly to the "carbon sink" of paddy soil in Fujian Province, which is worth promoting. However, under different straw returning rates, due to the influence of soil properties, climate, fertilization and other factors, the contribution of different soil subtypes and administrative regions in Fujian Province to carbon sequestration varies greatly. In the future, it is necessary to formulate reasonable management measures for carbon sequestration and emission reduction for different soil types and prefecture-level cities.

      • Effects of Root, Stem and Leaf of Maize Enriched by 13C on Brown Earth

        Yu yaxi, PEI Jiu-bo, LIU Wei, WANG Meng-meng, YIN Si-jia

        DOI: 10.11766/trxb202110300587

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        Abstract:

        Due to the differences in carbon chemical components among maize residues (root, stem and leaf), their return to cropland soils with different fertility levels will induce differences in soil respiration and priming.【Method】In order to explore these differences in the field, a 540-day in-situ field experiment with eight treatments of low fertilizer soil (LF+CK), low fertilizer soil + root (LF + R), low fertilizer soil + stem (LF + S), low fertilizer soil + leaf (LF + L), high fertilizer soil (HF+CK), high fertilizer soil + root (HF + R), high fertilizer soil + stem (HF + S) and high fertilizer soil + leaf (HF + L), was carried out at a long-term positioning station of brown earth in Shenyang Agricultural University using 13C labeled maize straw tracing method.【Result】Results showed that (1) the contribution rates of soil respiration flux and straw carbon to soil CO2-C emission showed downward trends over the in-situ incubation period. (2) Compared to the treatment without straw, the cumulative CO2-C released from low fertility soil with root, stem and leaf increased by 134%, 126% and 95%, respectively, while that from high fertility soil increased by 157%, 189% and 96%, respectively. (3) The contributions of root and stem to soil CO2-C emission in high fertility soil were significantly greater than that of leaf, but there was no difference in low fertility soil. (4) Different parts of maize straw returning to the field could cause the positive priming effects in both high and low fertility soils. Meanwhile, the priming effects of adding root and stem were significantly stronger than that of adding leaf, showing root and stem would cause more positive priming effects of soil CO2-C than the leaf. Moreover, there was no significant effect on the priming effect between straw parts and soil fertility.【Conclusion】Overall, this study enriched the theory of cropland soil respiration induced by straw returning, suggesting that the interaction of straw parts and soil fertility on soil respiration should be considered in straw returning.

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

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

        DOI: 10.11766/trxb202111020591

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        Abstract:

        【Objective】Improving the spatial prediction accuracy of soil attributes is of great significance for achieving accurate fertilization of farmland and protecting the ecological environment. 【Method】Soil organic matter (SOM) data was collected from 1773 samples from soil surface layer (0-20cm) of cultivated land in Luanping County, Hebei Province. The optimal environmental variables were screened through a stepwise regression analysis method. Multiple linear regression (MLR), ordinary kriging (OK), random forest (RF), Bayesian regularized neural network (BRNNBP), and the corresponding three integrated models combined with a geostatistical model (MLR-OK, RF-OK and BRNNBP-OK) were utilized to predict SOM content via the training set including 1426 sampling points. Also, the prediction accuracy of each method was compared with 347 sampling points of the testing set. Autocorrelation analysis was carried out based on the residual of the integrated model to evaluate the fitting effect of the model. 【Result】Results showed that the range of SOM content in the study area was 8.62~35.64 g·kg-1, and the coefficient of variation was 20.26%, which showed a moderate spatial variation. High concentrations of SOM were mainly distributed in the northeast and southeast areas with higher altitudes, while relative low concentrations of SOM were mostly observed in the southwest and central valleys of the study area. Elevation, slope and temperature selected by stepwise regression were closely related to SOM content (P<0.001). The lowest average absolute error and the root mean square error of the BRNNBP-OK model were 2.162 g·kg-1 and 2.801 g·kg-1, respectively. Compared with the OK, MLR, RF, BRNNBP, MLR-OK and RF-OK models, the goodness of fit of the BRNNBP-OK model increased by 1.81%～30.42%, making it an optimal model for SOM spatial prediction. Compared with the single model, the nugget coefficient of the integrated model residual was greater than 0.75, and the Moran"s I was less than 0 and numerically closer to 0, indicating that the spatial autocorrelation of the integrated model residual was weakened and the residual presented a more discrete spatial distribution. At the same time, the accuracy of all models was significantly correlated with Moran"s index of model residuals. 【Conclusion】In this study, the integrated model fitted more trends and the spatial aggregation of model residuals decreased and even tended to be discrete. Thus, the overall prediction accuracy of the integrated models was improved.

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

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

        DOI: 10.11766/trxb202112150675

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        Abstract:

        【Objective】 Wind activity and aeolian dust transportation are key terrestrial processes in dryland ecosystems. Biocrusts are photoautotrophic communities that consist of cyanobacteria, actinomycetes, mosses, green algae, fungi, and other organisms. As an important living skin and pioneer communities developing on surface soil in drylands, biocrusts strongly influence most soil processes (hydrological, ecological, biological, and chemical processes) and have a variety of essential ecological functions. Although biocrusts are usually relatively thin (a few millimeters or centimeters at most), these organisms have unique micro-structures which could positively influence the formation of aeolian soil parent material. In order to further explore the aeolian sedimentary effects of biocrusts on soil parent material, we conducted this study to understand the effects of biocrusts on dustfall retention and soil fixation, as well as their influencing factors.【Method】 In the north of Chinese Loess Plateau, the biocrusts developed on aeolian and loessal soils were sampled, and the analyses and simulated experiments were carried out in the laboratory. The amount of dustfall retention and soil fixation of biocrusts at different developmental stages (cyano crust, mixed crust, and moss crust) were measured. The variations of dustfall retention amount under different wind speeds, dustfall grain sizes, and dustfall amount were explored. We also explored the key influencing factors.【Result】 The dustfall retention amount of biocrusts was 1.1~4.8 times higher than that without biocrusts, and it increased with the developmental stages of biocrusts from cyano crust to moss crust. On average, the erosion reduction of biocrusts was 19.5~4892.7 t·km-2·a-1 under 1~8 m·s-1 wind speeds. Moreover, the dustfall retention amount increased with increasing soil water content, and these increases were positively correlated with wind speed. It was found that the dustfall retention amount was increased by 4.9%, 53.1%, 59.6%, and 72.3%, respectively, under 5~8 m·s-1 wind speeds when relative water content increased from 0 to 80%. Additionally, the dustfall retention amount was also significantly and positively correlated with the surface roughness of biocrusts. Similarly, the soil fixation amount of biocrusts also increased along with their developmental stages from cyano crust to moss crust. The soil fixation amount of moss crust was 1.4 times higher than that of cyano crust. At the same developmental stage, the soil fixation amount of biocrusts on aeolian sandy soil was significantly (F=30.74, P<0.003) higher than that on loessal soil. Furthermore, the soil fixation amount was positively correlated with the thickness of biocrusts and negatively correlated with the surface roughness. It firstly increased and then decreased with increasing soil water content.【Conclusion】 These findings show that biocrusts can significantly retain dustfall and fix soil due to their root, mycelium, exudates, and pore structures, and these biocrust functions are of great significance for the aeolian sedimentary process of soil parent material, the pedogenic process of primitive soil, and the primary succession of dryland ecosystem in the Chinese Loess Plateau. Additionally, this study demonstrates the important effects of biocrusts on the formation of aeolian soil parent material, and their key influencing factors are surface roughness, developmental stages, and water content of biocrusts. Therefore, it is essential to pay attention to the biocrust effects on dust retention and soil fixation in arid and semiarid climate regions.

      • Characteristics and Correlation of Fusarium oxysporum and Soil Nutrients around Banana Roots

        LIU Zexian, WANG Beibei, TAO Chengyuan, Ou Yannan, LV nana, SHEN Zongzhuan, LI Rong, SHEN Qirong

        DOI: 10.11766/trxb202112050660

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        【Objective】This study aimed to elucidate the characteristics and correlations between Fusarium oxysporum and soil nutrients in banana orchards with Panama wilt occurring through analyzing the number of F. oxysporum and nutrient contents in soils. This can provide a certain theoretical basis for the prevention and control of banana Panama wilt.【Method】Nine symptomatic and nine non-symptomatic banana plants in each orchard from 15 banana orchards in the main banana production areas in China and Laos were randomly selected for soil sample collection. Then real-time quantitative PCR and soil agrochemical analysis were used to explore the abundance of F. oxysporum and nutrient contents in the 270 sampled soils.【Result】The result showed that the abundance of F. oxysporum in the soil sampled near the symptomatic banana roots was significantly higher than that collected near the non-symptomatic banana roots, with an average copy of 5.5 as lg-transformed per gram of dry soil. However, there were almost no significant differences between the nutrient contents of soils sampled from symptomatic and non-symptomatic banana plants. The distribution of various indexes of soil nutrients in the studied banana orchards was different based on each factor. Among them, only the contents of organic matter and total phosphorus were distributed normally while the soil pH, and contents of total nitrogen and zinc were skewed normal distribution. Mantel test results further displayed that the overall soil nutrients were significantly correlated to the abundance of F. oxysporum. Specifically, the soil pH, and contents of iron, manganese, and copper were significantly and negatively correlated to the abundance of F. oxysporum revealed by the Spearman correlation analysis between the abundance of F. oxysporum and each soil nutrient. In addition, the correlation analysis between F. oxysporum and nutrients in soils with different degrees of acidity and different organic matter contents showed that in the weakly acidic banana garden soil (pH > 6.0), the number of F. oxysporum in soils was significantly negatively correlated with the contents of iron, manganese and copper. Meanwhile in soils where organic matter contents were not seriously lacking (> 1%), the abundance of F. oxysporum in soils displayed a significant negative correlation with soil pH and the contents of iron, manganese, copper and zinc.【Conclusion】In summary, banana orchards in the main banana production areas in China and Laos usually exhibit an acidification trend. Symptomatic banana soil showed an increase of F. oxysporum with a negative correlation to soil pH and the contents of trace elements, especially iron, manganese, copper and zinc.

      • Incorporation of Carbon and Nitrogen from Rice Straw into Particulate Organic Matter in Black Soil with Rice Planting

        Wu Yihui, Wagn hongfei, Zhang Rui, An Jing, zhangyuling, Yu Na, Zou Hongtao

        DOI: 10.11766/trxb202203030009

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        【Objective】Particulate organic matter is an important component of soil labile organic matter and a sensitive index to evaluate a change of the soil organic matter. The climate in Northeast China is very cold, so, paddy fields therein have a short flooding period and a long non-flooding period since the soil is frozen for most of the time. However, little research has been carried out on the incorporation of exogenous rice straw carbon (C) and nitrogen (N) into particulate organic matter in black soil with different rice planting years. 【Methods】A 300-day incubation experiment was conducted, in which dual-isotope-labeled (13C/15N) rice straw was added to a cultivation chronosequence of paddy soils ranging from 0 to 85 years (0 a, 12 a, 35 a, 62 a and 85 a). Flooding incubation experiments were conducted at a temperature of 20 °C and a 1 cm water-flooded layer in a laboratory for 150 days while the freezing incubation experiments were also carried out for 150 days under a soil temperature of -15 °C and water-saturated. 【Result】 Throughout the entire incubation period, the contents of particulate organic carbon (POC) and particulate organic nitrogen (PON) in all paddy soils from the samples with and without rice straw were lower than that in the control soil (0 a). The contents of POC and PON in all soils from the samples with rice straw increased after 5 days of flooding incubation, but they did not show a consistently increasing trend in the subsequent incubation period. For paddy soils of different rice planting years, the relative contribution of the added rice straw C (N) to POC (PON) was 0.2%-13.9% (0.4-3.8%). 0.7%-13.8% (1.4%-9.9%). At the end of freezing incubation, incorporation of the rice straw C into POC in control soil (0 a) and 12-year paddy soil (12 a) decreased significantly compared with that at the end of flooding incubation. Also, the added rice straw N into PON in control soil (0 a) and 85-years paddy soil (85 a) decreased while the added rice straw C (N) into POC (PON) in other rice cultivating years was still increasing. The incorporation of the added rice straw C into POC was significantly negatively correlated with soil organic C, total N and alkaline N, and significantly positively correlated with soil C/N, available phosphorus and microbial biomass C. In addition, the incorporation of straw N into soil PON showed a significant negative correlation with soil organic C content. 【Conclusion】The study showed that the longer the years of rice planting in a typical black soil of northeast China, the contents of soil organic C, total N and alkaline N were relatively low, while the soil C/N, available phosphorus and microbial biomass C contents were relatively high. The greater the incorporation of straw C and N into soil particulate organic matter, the more the response of soil particulate organic matter to rice straw addition.

      • Effects of environmental factors on rate and partitioning of dissimilatory nitrate reduction processes in paddy soils

        Jin Ke, Wei Zhijun, Ma Xiaofang, Li Chenglin, Shan Jun, Yan Xiaoyuan

        DOI: 10.11766/trxb202203090101

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        【Objective】Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) are the two competing nitrate reduction pathways that remove the available nitrate, both of which are affected by inter-related environmental factors. Understanding how environmental factors regulate nitrate partitioning in these two competing processes is of great significance for the optimization of nitrogen management in paddy fields.【Method】Using 15N-tracing technique in combination with membrane inlet mass spectrometer (MIMS), a series of laboratory incubation experiments were performed to investigate the effects of different environmental factors including temperature (5, 15, 20, 25, and 35 ℃), pH (5, 6, 7, 8.5, and 9.5), NO3– concentration (50, 100, 150, 200, and 300 μmol·L–1), C/N (0, 2.5, 5, 12, and 30), Fe2+ (0, 300, 500, 800, and 1000 μmol·L–1), and S2– (0, 50, 62.5, 100, and 125 μmol·L–1) on denitrification and DNRA rates and their partitioning in nitrate reduction in three paddy soils (Wuchang, WC; Changshu, CS; Ya’an, YA).【Result】Denitrification was the predominant pathway ( 87.97%?91.73%), whereas DNRA only contributed to 8.27%~12.03% of the total dissimilatory nitrate reduction in all treatments. Denitrification and DNRA rates increased exponentially with increasing temperature, as well as the DNRA/(Denitrification + DNRA) (RDNRA). The highest denitrification and DNRA rates occurred at the pH of 7 and 8.5, respectively, and RDNRA was higher in an acidic environment (6.24%?15.56%) than under an alkaline environment (4.92%?14.67%). The response of denitrification and DNRA rates to nitrate concentrations fitted well with the Michaelis-Menten relationship, in which the Vmax and Km of denitrification were larger than those of DNRA. In the three paddy soils, compared with the treatment without glucose addition, denitrification rates were significantly increased by 22%?35% at the C/N ratio of 2.5. Following the C/N ratio increased to > 2.5, DNRA rates were enhanced by 74%?199%. In terms of Fe2+ and S2– addition treatments, denitrification rates were the highest in the low levels of electron donors (300?500 μmol·L–1 Fe2+ and 50?62.5 μmol·L–1 S2–), whereas more electron donors (800?1000 μmol·L–1 Fe2+ and 100?125 μmol·L–1 S2–) were required when DNRA reached the peak rates.【Conclusion】By exerting different effects on rates of denitrification and DNRA, temperature, pH, NO3–, C/N ratio, Fe2+, and S2– concentration significantly changed the partitioning between denitrification and DNRA. Specifically, relatively high temperature, C/N, Fe2+, and S2– concentration favored nitrate partitioning to DNRA, while denitrification dominated the nitrate reduction process in environments with a relatively high NO3– concentration. Collectively, our results provide comprehensive information in terms of regulation of environmental factors on nitrate partitioning between DNRA and denitrification in paddy soils. This deepens our understanding of nitrate reduction processes and provides a scientific basis for increasing nitrogen use efficiency by favoring the nitrate partitioning to DNRA in rice fields.

      • Variations in the Diversity and Community Assembly of Arbuscular Mycorrhizal Fungi in Greenhouse Soils during the Growing Season

        LIU Lei, XIAO Guangmin, WANG Ling, RU Shuhua, ZHANG Guoyin, SUN Shiyou

        DOI: 10.11766/trxb202204210197

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        Abstract: 【Objective】This study aimed to understand the key processes that drive the changes in diversity and community assembly of arbuscular mycorrhizal (AM) fungi in greenhouse ecosystem. 【Method】Soil samples were collected during different growth stages (i.e., fallow period, flowering stage, fruiting stage) of tomatoes in a greenhouse. Illumina MiSeq high-throughput pyrosequencing was performed to investigate the changes in taxonomic and phylogenetic diversity and community structure of AM fungi. The relative importance of stochastic and deterministic processes in structuring AM fungal community at different growth stages was analyzed by phylogenetic structure analysis. 【Result】Results showed that both taxonomic and phylogenetic diversity of AM fungi varied significantly across different growth stages. Compared with the fallow period, OTU richness, Shannon diversity, Pielou evenness, phylogenetic diversity (PD) and mean pairwise phylogenetic distance (MPD) of AM fungi significantly decreased by 42.82%~59.18%、43.25%~48.31%、17.46%~25.40%、57.14%~67.86% and 50.00%, respectively, during the flowering and fruiting stages. In addition, the relative abundance of Glomus was promoted in the growing period, whereas the relative abundance of Claroideoglomus and Paraglomus decreased. Also the relative abundance of Archaeospora followed a unimodal pattern. Results of permutational multivariate analysis of variance (PERMANOVA) and non-metric multidimensional scaling analysis (NMDS) showed that, based on both taxonomic and phylogenetic data, the community structure of AM fungi in tomato soils during the fallow period was significantly different from that of the growing period, while the difference in community composition between the flowering and fruiting stage was not significant. According to the phylogenetic structure analysis, we found that the mean net relatedness index (NRI) across all samples was equal to zero at the fallow period, indicating phylogenetic random of AM fungal community, whereas the mean NRI was significantly greater than zero in both the flowering and the fruiting stages, indicating phylogenetic clustered. These results suggest that the primary ecological process structuring communities shifted from a stochastic process at early succession to a deterministic process at the tomato growing stage when local environmental filtering increased, which inference was also supported by the neutral community model (NCM) results. Mantel test showed that soil pH, soil nutrients (SOC, total NPK, and Olsen-P) and salt content, as well as soil temperature and humidity, significantly affected the seasonal changes of AM fungal community. 【Conclusion】The highly intensive production stress in the greenhouse vegetable ecosystem promoted the transformation of the primary ecological process of AM fungal community assembly from a random process to a deterministic process, leading to a decrease in diversity and a change in community structure. Our results reveal the degradation of soil quality and the evolution of the microbiome in the process of greenhouse vegetable cultivation.

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

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

        DOI: 10.11766/trxb202204060097

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        【Objective】Soil fertility is significantly influenced by plough layer thickness. However, it is still not clear how the transformation and fate of fertilizer nitrogen (N) in fluvo-aquic soils would be affected by plough layer thickness. 【Method】In this study, a soil column simulation experiment in the field was conducted throughout three crop cultivations. The experiment was performed in a completely randomized design with six treatments including two plough layer thicknesses (15 and 25 cm) and three soil textures (sandy loam, sandy clay loam and loamy clay). A 15N-labeled tracer technique was used to evaluate the dynamics of fertilizer-derived organic N, fixed NH4+ and mineral N in 0~40 cm soil layer and the fate of fertilizer N in soil-crop systems. 【Result】The transformation of fertilizer N in soil-crop systems was significantly affected by plough layer thickness, and showed the same varying tendency among different textural soils. The residual fertilizer N existed mainly in the form of organic N, which accounted for more than 83% of the total residual fertilizer N and played a pivotal role in the storage and supply of fertilizer N. Increasing plough layer thickness degraded the conversion of fertilizer N to fixed NH4+ pool, while increased the stocks of fertilizer-derived organic N in 0~40 cm soil layer. In the current season after fertilizer N was applied, the average value of fertilizer-derived organic N stock in soils with 25 cm plough layer thickness (PLT-25) was averagely 8.9% higher than that in soils with 15 cm plough layer thickness (PLT-15). The stocks of fertilizer-derived mineral N under PLT-25 treatments were also higher than that under PLT-15 treatments in the current and subsequent crop cultivations; promoting the fertilizer N uptake by crops. The N use efficiency under PLT-25 treatments in the first two crop cultivations was about 8.0% higher than that of PLT-15 treatments, while the current seasonal loss rate and cumulative loss rate of fertilizer N were 12.3% and 9.1% lower, respectively. The stocks of fertilizer-derived organic N in sandy clay loam and loamy clay were significantly (P < 0.05) higher than that in sandy loam, while the trend was the opposite for the stocks of fertilizer-derived fixed NH4+. And the fertilizer-derived mineral N stock was usually to be higher in sandy loam. Overall, the percentage of recovery of applied fertilizer N in crops and soil under sandy loam treatment was significantly (P < 0.05) lower than that in sandy clay loam and loamy clay. Also, the percentage of cumulative loss of fertilizer N in sandy loam was 18.8% and 20.8% higher than that in sandy clay loam and loamy clay, respectively. 【Conclusion】The fluvo-aquic soils with higher sand content have lower fertilizer N storage capacity, restricting the enhancing of N use efficiency. For fluvo-aquic soils with different textures, increasing plough layer thickness could improve the annual N use efficiency and the residual amount of applied fertilizer N in the current season. This, could be released for crop uptake in the subsequent crop cultivation. In typical fluvo-aquic soil areas, increasing the plough layer thickness may be a potential means for regulating the transformation and fate of applied fertilizer N, increasing fertilizer N retention, enhancing the fertilizer N uptake by crops and minimizing fertilizer N loss in soil-crop systems.

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

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

        DOI: 10.11766/trxb202111110611

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        Abstract:

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

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

        JIANG Pengju, WU Huawu, MIN Leilei, ZHANG Zhihua, SHEN Yanjun, Bi Huitao

        DOI: 10.11766/trxb202110180561

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        Abstract:

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

      • Study on Particle Distribution Characteristics of Soil Physical Crust Profile in Sloping Farmland

        CHEN Lin, WANG Jian, HUO Chunping, YANG Chang

        DOI: 10.11766/trxb202109110492

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        【Objective】 The response of runoff and erosion to soil physical crust has been extensively investigated in recent decades. However, there have been few attempts to quantify the effects of the profile of soil physical crusts on erosion processes. Thus, to explore the formation mechanism of soil physical crust in microtopography, artificial simulated rainfall and stratified soil treatment method were adopted to study the distribution and characteristics of soil particle size. 【Method】Soil plot (2.0 m long × 1.0 m wide × 0.5 m high) was set to a slope of 5°, filled with soil by contour tillage (20 cm ridges and 30 cm ditches). Simulated rainfall was designed for eight durations (5, 10, 12, 14, 16, 18, 20 and 30 minutes) and one intensity (100 mm h-1). The samples were taken out by a cutting ring (diameter 10 cm) and placed in a stratified sampling device. The bottom of the device was designed with a spiral rising bottom bracket. By turning the nut, the soil sample rises by 1 mm after turning one circle at a time with the bottom bracket. Each tier of soil sample is stripped with a soil sampling knife. Particles of samples in each tier of soil""s physical crust and the collected mud were analyzed by Mastersizer 2000. 【Result】The results showed that: (1) During erosion, the surface sand particles of structural crust (Cst), silt-containing sedimentary crust (Cscs) and silt-free sedimentary crust (Csfs) were dispersed, while the clay and silt particles were enriched, and the degree gradually increased with the duration of rainfall. (2) When the rainfall lasted for 30 min, from top to bottom of the profile, the content of sand and clay in Cst decreased by 4.61% and 1.73%, respectively, the content of silt increased by 1.83%. The content of sand and silt in Cscs and Csfs increased by 29.35% and 36.59%, 4.34% and 0.39%, respectively. The content of clay decreased by 16.30% and 14.34%, respectively. (3) In the process of crust formation, the dominant factor of Cst was raindrop dispersion, the dominant factor of Cscs and Csfs was raindrop dispersion in the early rainfall period, and sediment deposition in the late rainfall period. 【Conclusion】 Spatial location and rainfall factors are the important factors that lead to the difference in physical crust types and particle composition.

      • Elevational Distribution Pattern of Fungal Diversity and The Driving Mechanisms at Different Soil Depths in Mount Segrila

        SUN Yuanyuan, XU Meng, LI Yuefen, ZHANG Xubo

        DOI: 10.11766/trxb202109230511

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        【Objective】Unveiling the formation and maintenance mechanisms of fungal biodiversity is crucial to understand the biogeographic distribution pattern of soil fungi. However, knowledge of the elevational distribution pattern and its underlying mechanism of fungal communities in the deep layers of soil profile remains inadequate. 【Method】In the present study, topsoil (0～20 cm) and subsoil (40～60 cm) samples were collected along an elevational gradient of 3 300～4 600 m from Mount Segrila, Tibet. The variations in fungal diversity and community composition with elevation in the topsoil and subsoil and the driving factors were investigated by Illumina MiSeq high-throughput pyrosequencing of the ITS rDNA. Changes in the coexistence characteristics of soil fungal communities among different elevations and between top-and subsoil were further explored based on the calculation of niche properties. 【Result】We found that fungal communities collected from the topsoil and subsoil of Mount Segrila were dominated by Ascomycota (averaged relative abundance of 35%), Basidiomycota (46%) and Zygomycota (13%). Symbiotrophic fungi (62%) and saprotrophic fungi (33%) were identified as the major functional guilds by FUNGuild. In the topsoil, indices of fungal α-diversity (richness and Shannon diversity) decreased significantly with increasing elevation. In the subsoil, fungal richness decreased whereas Shannon diversity presented a hump-shaped pattern with increasing elevation. The dissimilarities in fungal community composition (β-diversity) increased significantly with increasing elevational distance in both topsoil and subsoil, suggesting a distance-decay pattern. The β-diversity of the fungal community was also positively correlated with environmental factors such as mean annual temperature (MAT), soil pH, the ratio of soil carbon to nitrogen, and soil moisture as suggested by the Mantel test. Results from distance-based redundancy analysis (db-RDA) suggested that pH was the driving factor for the variation in fungal community composition with elevation in the topsoil, whereas in the subsoil soil moisture was the most contributive factor. The community-level habitat niche breadth (Bcom) of soil fungi was significantly higher at 3 500 m and 3 689 m, indicating an increase in environmental fitness and a more metabolically flexible fungal community at lower elevations. However, the niche breadth of soil fungi became narrow at 4 420 m and 4 590 m, implying that soil fungi at higher elevations could be more vulnerable in response to climate change in the future. A greater degree of niche overlap (Oik > 8) between major fungal taxa was observed at lower elevations (3 356～3 689 m) and in the topsoil, whereas a lower degree of niche overlap (Oik ≤ 6) was observed at higher elevations (4 284～4 590 m) and in the subsoil. In addition, a greater degree of niche overlap was observed between Ascomycota, Basidiomycota and Zygomycota, suggesting fierce competition for resources or habitats among these taxa. The degree of niche overlap was lower between Glomeromycota, Chytridimycota and other taxa due to their symbiotic or parasitic relationships with plants. 【Conclusion】Overall, our study shows that the elevational distribution pattern of fungal biodiversity is distinctive between topsoil and subsoil, which is strongly related to the effect of environmental filtering and coexistence characteristics of specific taxa. These results may thus provide novel insights into the diversity and coexistence mechanisms of soil fungal communities in the alpine ecosystems of the Tibetan Plateau.

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

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

        DOI: 10.11766/trxb202201100014

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        Abstract:

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

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

        YANG Guang, WANG Yu, WANG Shenqiang, ZHAO Xu

        DOI: 10.11766/trxb202204060091

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        Abstract:

        【Objective】The objective of this study was to clarify the status of soil nutrient accumulation in the peach orchard of Taihu Watershed. It aimed to provide a guide for the green production mode of peach orchard. 【Method】In this study, a total of 66 soil samples were collected from 33 juicy peach orchards, with different cultivation years in the four main planting towns. Combined with field research and laboratory analysis, the fertilizer input status, soil nutrient content and ecological stoichiometry characteristics were analyzed. 【Result】The results showed that the average total nutrient inputs was N 527 kg?hm-2, P2O5 362 kg?hm-2 and K2O 545 kg?hm-2, and the proportion of organic inputs were 27.8%, 15.4% and 15.6% respectively. Here chemical fertilizer was mainly NPK compound fertilizer, while the types of organic fertilizer applied mainly included rapeseed cake, livestock manure, and composting straw. Over-application of fertilizer could aggravate soil acidification and nutrient accumulation, soil pH in 0-20 cm and 20-40 cm soil layers of planted >10 years peach orchard both decreased by more than 1.5 units, which belonged to strongly acidic soil (4.510 years peach orchard reached level 1. The soil NO3--N concentration of the peach orchard was up to 19.3-33.1 mg?kg-1. The annual apparent surplus of N, P2O5, K2O were 343 kg?hm-2, 238 kg?hm-2 and 240 kg?hm-1, respectively. 【Conclusion】The excessive nutrient input in the peach orchard has aggravated soil acidification and nutrient accumulation. A high concentration of nitrogen and phosphorus accumulated in the soil might increase the environmental loss risk. Therefore, it is necessary to put forward a green production model for the peach production.

      • Input-Output Balance-Based P Fertilization Approach for Achieving Target Crop Yield and High P Use Efficiency: A Case Study of Cotton (Gossypium hirsutum L.) with Mulched Fertigation

        PENG Yi, YANG Guojiang, GUO Xiuli, WANG Xiaofeng, EREL Ran, FENG Gu

        DOI: 10.11766/trxb202202030044

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        【Objective】Maintaining moderate soil phosphorus (P) supply intensity and determining the P application rate based on the P requirement of the crop target yield, and combining with acid, slow-release water-soluble P fertilizers and applied in the early stages of crop growth is a novel P management approach in cotton. Here we test the feasibility and effectiveness of this method and provide a basis for reducing the P fertilizer application amount and increasing its use efficiency. 【Method】A two-year field experiment was employed using cotton (Gossypium hirsutum) in the moderate Olsen-P soil (23.6 mg?kg-1) in Shihezi, Xinjiang. Based on the P requirement of the target lint yield of 2.7 t?hm-2, 52.4 kg?hm-2 was selected as the P application rate. Four treatments were set-up with three types P fertilizers: (1) no P fertilizer (CK); (2) monoammonium phosphate (MAP); (3) urea phosphate (UP); and (4) ammonium polyphosphate (APP). It was analyzed that the lint yield, P uptake and above-ground biomass of cotton in different treatments. The partial productivity of P fertilizer (PFP), agronomic efficiency (AEP), P utilization efficiency (PUE) and P recovery index (the ratio of shoot P uptake to the amount of P fertilizer application, PRI) were calculated. Through stratified sampling, soil Olsen-P and P fractions in different soil layers were tested. Those allowed us to clarify the relationships between the P spatial availability and cotton growth requirements with different P fertilizers. 【Result】The significant results were: (1) The average lint yield of P applied treatments in two years was 2.73 t?hm-2, which was classified as the high yield level in northern Xinjiang. Compared with the CK treatment, the lint yield of MAP, UP, and APP treatments were increased by 21%, 25%, and 11%, respectively. (2) The P surplus was 2.2-4.8 kg?hm-2 and the P use efficiency was 24% across P applied treatments. The P recovery index of MAP, UP, and APP treatments was 91.7%, 95.6%, and 94.8%, respectively. (3) P fertilizer applied by drip irrigation in the cotton bud and boll stages can move to the 10-20 cm soil layer, which may maintain the soil P supply intensity during the cotton-growing period. Compared with the CK treatment, the mean Olsen-P in P applied treatments were increased by 94%~302%, 104%~144%, and 42%~67% in the 0~5 cm, 5~10 cm, and 10~20 cm soil layers, respectively. 【Conclusion】In summary, our results indicate that maintaining soil available P near the agronomic thresholds and determining the P application rate according to the P requirement of the target yield, and combining with acid, slow-release P fertilizer and applied in the cotton bud and boll stages can improve lint yield and P use efficacy under balanced P input-output conditions. Furthermore, the P recovery index based on the balanced P input-output can better reflect the real P use efficiency.

      • Quantitatively Partitioning Organic Carbon Loss by Interrill and Rill Erosion on The Loess Slope

        ZHANG Fengbao, LI Xuantian, SHEN Nan, YANG Mingyi

        DOI: 10.11766/trxb202201290040

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        【Objective】The differences in soil detachment and transport mechanisms between interrill and rill erosion lead to the differences in organic carbon loss by interrill and rill erosion. However, few studies were conducted to explore the effects and contributions of interrill and rill erosion on organic carbon loss during the erosion process because of the limitation of research methods. Successful use of the radionuclide 7Be to document soil erosion provides a means of addressing this need. The objectives of this study were to first estimate the contribution of interrill and rill erosion to sediment yield and then quantitatively explore the effects and contributions of interrill and rill erosion on organic carbon loss on the loess slope. 【Method】The simulated rainfall experiments with five slope gradients (5°, 10°, 15°, 20°, 25°and 30°) were conducted under different rainfall intensities in the field to investigate soil and organic carbon loss and 7Be tracing technology was used to quantify the contribution rate of interrill and rill erosion on sediment yield and organic carbon loss for the loess slope.【Result】Interrill erosion is the main and the relative contribution of interrill erosion on sediment yield was 86% on the 5°plot. But rill erosion dominated on the plots with gradient greater than 5°. The relative contribution of rill erosion on sediment yield ranged from 61% to 71% and could even reach 96% during the rainfall. The average enrichment ratio of organic carbon of sediment from the entire plot and the interrill area was 1.16±0.15 and 1.50±0.50, respectively, during the rainfall. The enrichment could increase organic carbon loss rate of 0.008 to 0.028 g m-2 min-1. The relative contribution of rill erosion to organic carbon loss were between 55% and 62% on plots with gradient greater than 5°, which were lower than those of rill erosion to sediment production, but still dominated. Sediment yield from the entire plot and the interrill area could respectively explain 97% and 89% of the variations of organic carbon loss from the entire plot and the interrill area. 【Conclusion】The organic carbon enrichment ratio had less effects on organic carbon loss when rill erosion occurred severely. Sediment yield determined the amount of organic carbon loss. Severe rill erosion could enhance the enrichment ratio of organic carbon of sediment from the interrill area.

      • Proteomic Dissection of the Rice Shoots in Response to Iron Deficiency and Excess

        ZHANG Xin, WANG Ruonan, SHEN Renfang, LAN Ping

        DOI: 10.11766/trxb202203150109

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        【Objective】In calcareous soils, iron (Fe) generally exists in the form of oxides or hydroxides, which is not conducive to plant absorption and utilization, thus frequently causing Fe deficiency in plants. In flooded acidic soils, such as paddy soil, due to conditions of irrigation and drainage and alternate cultivation of water and drought, the redox potential of the soil is low and ferric Fe is reduced to be ferrous. The ferrous Fe is readily absorbed and utilized, resulting in excessive Fe absorption by plants. Fe deficiency and excess are limiting factors affecting rice yield and quality. Fe deficiency leads to chlorosis and reduces plant growth while Fe overload is toxic for plants, with a typical symptom of leaf bronzing. Several transcriptome analyses have been performed to investigate the responses under Fe stress. However, a comprehensive dissection of the entire Fe-responsive profile at the protein level is still lacking. It is necessary to analyze the rice responses under Fe deficiency and Fe excess using proteomic analysis. 【Method】In this study, a label-free proteomic analysis was performed on rice shoots grown in Fe-deficient (0 μmol?L-1), Fe-sufficient (40 μmol?L-1), and Fe-excess (350 and 500 μmol?L-1) conditions. 【Result】Results showed that 130, 157 and 118 differentially accumulated proteins (DAPs) were identified under Fe deficiency and two concentrations of Fe excess stresses, respectively, compared with Fe sufficient conditions. Gene ontology enrichment analysis of the DAPs revealed that primary metabolic process, organonitrogen compound metabolic process, response to stimulus, and oxidative stress responses were significantly enriched under both Fe deficiency and excess stresses. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that DAPs under Fe deficiency and Fe excess were commonly enriched in metabolic processes like the ribosome, photosynthesis, and oxidative phosphorylation. Notably, the abundance of proteins involved in phenylpropanoid biosynthesis and biosynthesis of cofactors was mainly affected by Fe deficiency, while the abundance of proteins involved in the biosynthesis of amino acids was mainly influenced by Fe excess. Under Fe excess stress, the abundance of enzymes involved in amino acid metabolism was decreased, indicating a reduction in the content of plant-synthesized amino acids. However, the increased abundance of transketolase involved in photosynthesis and secondary metabolism probably reduced the inhibitory effect induced by Fe stress. Ribosomal proteins S16, Os03g0798600 and RPL17 may play important roles in response to Fe deficiency and Fe excess stresses, but the exact functions of these proteins under Fe stress are still unknown. Several novel proteins which may play potential roles in rice Fe homeostasis were also predicted in this study.【Conclusion】Overall, our results indicate both Fe deficiency and Fe excess stresses affected photosynthesis and ribosomal metabolism. The synthesis of phenylpropane was mainly affected by Fe deficiency, while amino acid metabolism was mainly affected by Fe excess in the shoots of rice. The findings will provide some information for the exploration of key factors for the efficient absorption and utilization of Fe.

      • Effects of Vegetation Restoration on Functional Groups Related to Soil Carbon, Nitrogen and Phosphorus Cycles in Open-pit Mining Area of the Loess Plateau

        CHEN Fu, ZHAO Jiao, ZHU Yanfeng, LUO Zhanbin

        DOI: 10.11766/trxb202203170117

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        【Objective】The ecology of mining areas in the Loess Plateau is relatively fragile, while the vegetation restoration is closely related to soil microbe-mediated nutrient cycling. This study was designed to clarify the influence and regulatory roles of vegetation restoration on the functional groups related to soil carbon, nitrogen and phosphorus cycles, which are significantly important to rebuilding the ecological resilience and self-sustaining mechanism of mining areas.【Method】In this study, high-throughput qPCR chip technology, random forest model and structural equation model were used to reveal the changes and mutual feeding mechanism of soil characteristics, enzyme activities, carbon, nitrogen and phosphorus functional groups under different vegetation restoration modes of Antaibao open-pit reclamation waste dump on the Loess Plateau. 【Result】 The results showed that Caragana korshinskii (bushwood, BL), Pinus tabuliformis (coniferous forest, CF), Robinia pseudoacacia (broad-leaved forest, BF) and Robinia pseudoacacia + Ulmus pumila (mixed forest, MF) were superior to soil nutrient accumulation compared with Populus simonii forest (CK). Compared to CF, soil organic carbon (SOC) of BL, BF and MF increased by 82.26%, 168% and 56.65%, respectively. The total nitrogen (TN) of BL, BF and MF enhanced by 68.31%, 130% and 46.75% comparing with CF, while the available phosphorus (AP) contents increased by 10.41%, 27.65% and 20.89%, respectively. Nevertheless, these were still significantly lower than that of CK (P< 0.05). The soil catalase (CAT) activities of BL, CF, BF and MF increased by 95.6%, 101.0%, 46.4% and 120.0% respectively, and are significantly higher than that of CK (P<0.05). Also, the soil β-glucosidase (BG) and leucine aminopeptidase (LAP) activities decreased significantly (P<0.05). The β-glucosidase activities of BL, CF, BF and MF decreased by 66.5%, 67.0%, 58.9% and 59.8%, while the leucine aminopeptidase activities decreased by 57.8%, 67.7%, 78.0% and 67.7%, respectively. The different modes of vegetation restoration significantly changed the relative abundances of functional groups related to carbon, nitrogen and phosphorus (P<0.05), whereas the variation tendencies always keep a consistent correspondence. The functional groups related to carbon, nitrogen and phosphorus were significantly positively correlated with soil nitrate nitrogen (P<0.001), but they presented negative correlations with ammonium nitrogen (P<0.01). The functional groups involved in the carbon cycle, nitrification process and organic phosphorus mineralization were significantly positively correlated with available phosphorus (P<0.01). In addition, results of the structural equation model showed that vegetation restoration could directly affect CAT and AP, thereby regulating the carbon, nitrogen and phosphorus cycle. Otherwise, the vegetation restoration could affect soil AP indirectly, thereupon then regulating the abundances of carbon, nitrogen and phosphorus functional groups, together with other soil characteristics, such as nitrate nitrogen or ammonium nitrogen. 【Conclusion】 This study might help deepen the knowledge about soil microbiology mechanism of vegetation restoration, which will furtherly help the ecological restoration of damaged mines in the Loess Plateau.

      • Progress and prospect of biological salt removal from farmland under drip irrigation inarid area of northwest China

        suyuan, Tian Chang yan, Mai Wen xuan, Wanglei, Zhao Zhen yong, Zhou hong fei

        DOI: 10.11766/trxb202202150008

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        Abstract:

        Since the end of the 20th century, mulched drip irrigation technology has been widely promoted and applied in arid areas of northwest China, which has greatly pushed the development of oasis agriculture. However, the salt in water brought by drip irrigation cannot be discharged from the soil, which makes the sustainable development of oasis agriculture in arid areas challenging. Therefore, preventing and controlling secondary salinization of farmland to make use of the salt and alkali land resources widely distributed in the arid area of northwest China under conditions of water resource shortage is an urgent problem to be solved in order to promote sustainable development of agriculture. This article sorted literature on biological salt removal and the aspect of salt tolerance mechanism, growth and development of halophytes to salt, mutual feedback effects between salt removal of halophytes and reclamation of saline-alkali soil, and the effects of planting halophytes on soil water and salt dynamics. Also, this study points out the existing problems in the research of biological salt removal in arid areas of the northwest and suggests prospects for further research works. The study can provide decision bases for making reasonable, efficient and comprehensive salt removal systems in arid area agriculture and is of great significance for realizing salt balance in farmland, alleviating soil secondary salinization crisis and soil sustainable utilization.

      • Effects of residence time on 13C and 15N abundances of rice and rice derived-biochars after a dual isotope labeling

        Zhang Fangchao, Lu Weiwei, Zha Quanzhi

        DOI: 10.11766/trxb202203250133

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        Abstract:

        【Objective】To provide a basis for an advanced on the impacts of biochar on soil carbon and nitrogen cycling, the effects of residence time after isotope labeling on the δ13C and δ15N values of rice aboveground and underground tissues and biochars derived from these two tissues were studied. 【Method】Rice plants were labeled with 13C and 15N by pulse labeling of 13C-CO2 and foliar fertilization of 15N-urea, respectively. The residence time of 4 h, 6 h and 24 h was set after 15N isotope labeling. The labeled rice plants were divided into aboveground and underground tissues and four biochars were produced by pyrolyzing these two tissues at 300 ℃ and 500 ℃, respectively. The δ13C and δ15N values of rice tissues and their biochars were determined by isotope mass spectrometry. 【Result】With the increase in residence time, δ13C values of the aboveground tissues of rice plants gradually decreased from 872‰ to 578‰, while the δ13C values of the underground tissues gradually increased from 226‰ to 869‰. Unlike with the δ13C, the δ15N values in the aboveground tissues of rice plants first increased then decreased, and the maximum (1764‰) occurred at the residence time of 6 h, while δ15N values in the underground tissues first decreased and then increased. Overall, compared to rice tissues, the δ13C and δ15N values of the biochars decreased by 52.1% and 15.9%, respectively. Moreover, both the δ13C and δ15N values of the biochars were highest at the residence time of 24 h, especially for the 300 °C biochar. With the increase in residence time, the reduced proportion of the δ13C of hot water extractable dissolved organic carbon when compared with that of the residual solid increased from 4.14% to 11.0% for the 300 °C biochar, while it decreased from 32.3% to 18.9% for the 500 °C biochar. This indicates that increase in the residence time decreased and increased the uniformity of 13C of the 300 °C and 500 °C biochars, respectively. 【Conclusion】Our results demonstrate that the effects of residence time after labelling on δ13C and δ15N values of the rice plants were different, and the biochars did not retain the isotopic signature of the raw rice tissues. Residence time and pyrolysis temperature together affected the uniformity of 13C in rice biochars.

      • Response of nitrite-dependent anaerobic methane oxidation in paddy fields to slow increase of atmospheric CO2 concentration

        Jin Jinghao, Huang Hechen, Shen Lidong, Tian Maohui, Liu Xin, Yang Wangting, Yang Yuling, Liu Jiaqi, Ren Bingjie, Xu JiangBing, Hu Zhenghua

        DOI: 10.11766/trxb202111250641

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        Abstract:

        Nitrite-dependent anaerobic methane oxidation (n-damo) is a novel pathway for controlling methane emissions from paddy ecosystems. However, the contribution of n-damo to methane oxidation and its response to elevated atmospheric CO2 concentration are poorly known. Here, an ambient CO2 treatment (CK) and a slow increase of atmospheric CO2 treatment (EC: an increase of 40 μL·L-1 per year above CK until 160 μL·L-1) were set up based on the CO2 automatic control platform with open top chambers. The stable isotope tracer experiment, quantitative PCR and high-throughput sequencing were employed to investigate the n-damo activity, abundance, diversity and community composition of Candidatus Methylomirabilis oxyfera (M. oxyfera)-like bacteria in paddy soils across key rice growth stages (tillering, jointing and flowering stages) under different CO2 treatments. The results showed that EC treatment stimulated the n-damo activity and abundance of M. oxyfera-like bacteria, particularly at the jointing stage. Further, EC treatment significantly changed the community composition and diversity of M. oxyfera-like bacteria. The variations in soil dissolved organic carbon content and inorganic nitrogen content under EC treatment could probably cause the change of n-damo activity and the community structure of M. oxyfera-like bacteria. Taken together, our results showed a positive response of n-damo to the slow increase of atmospheric CO2 concentration, suggesting its active role in reducing methane emissions from paddy fields under the future climate conditions.

      • Molecular Characteristics of Soil Dissolved Organic Matter in Response to Decomposition of Organic Fertilizers from Different Sources

        CHEN Liming, WU Yueying, LI Caisheng, WU Zhipeng, HUANG Cheng, JI Hengkuan, HOU Zhengwei, FU Chuanliang, ZHAO Yidong, WU Weidong

        DOI: 10.11766/trxb202111290519

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        Abstract:

        【Objective】 Dissolved organic matter (DOM) derived from organic fertilizers may provide new insights into the potential applications of different commercial organic fertilizers.【Method】Herein, four different sources of organic fertilizers (biochar, WSB; sheep manure, SM; seaweed, SW; shrimp peptide, SP) with soils around the Changhua mine site were used to carry out a three-month incubation experiment. The subsequent effect of organic fertilizer amendment on molecular characteristics of soil DOM was investigated using multivariate spectral analysis. 【Result】Compared to the control, soil DOM concentrations significantly increased in response to organic fertilizers amendment during the whole incubation period, exhibiting the lowest increment in WSB treatment and the highest increment in SW treatment, respectively. The excitation-emission matrix with parallel factor (EEM-PARAFAC) showed that WSB increased the proportion of humic-like fluorophore of soil DOM while fulvic acid-like fluorophore decreased during the whole incubation period. Also, SM, SW and SP amendments lowered the proportion of microbially-transformed humic-like fluorophore and increased the proportion of fulvic-acid like fluorophore during 0-45 days, but increased the proportion of refractory humic-like fluorophore during 45-90 days. Two-dimensional correlation spectroscopy analysis on Fourier-transform infrared (2D-FTIR-COS) spectroscopy revealed that aromatic/carboxylic acid groups of soil DOM in the control and SP treatments and alkene/polysaccharide groups in the added WSB, SW and SM treatments had the fastest responses over time, respectively. In addition, Si-O-Al signals from soil nano-minerals functional groups exhibited a distinct response over time in the added WSB and SP treatments. The carbon near-edge X-ray absorption fine structure (C 1s NEXAFS) analysis showed that compared to control, the added WSB increased the proportion of oxygenated aliphatic fractions but reduced aromatic/phenolic fractions of soil DOM after incubation. Also, SW increased the proportion of aromatic and carbonyl fractions but reduced aliphatic and oxyalkyl fractions while SM and SP increased the proportion of phenolic, aromatic and aliphatic fractions but reduced the proportion of carboxyl, oxyalkyl and carbonyl fractions. 【Conclusion】The results of this study can enhance our understanding of how the decomposition of different sources of organic fertilisers affects the molecular characteristics of soil DOM. This is essential for assessing the ecological effects of the application of commercial organic fertilisers in soils.

      • Grazing Effect on Activity and Diversity of Soil Methanotrophs in Winter Pastures of the Loess Plateau

        WANG Yufang, CAI Yuanfeng, HOU Fujiang, BOWATTE Saman, JIA Zhongjun

        DOI: 10.11766/trxb202112080664

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        【Objective】Soil methanotrophs are the only biological sink of atmospheric methane (CH4). Grazing can regulate the methane oxidation activity of the soil by affecting the abundance and diversity of soil methanotrophs. 【Method】In this study, we collected soil samples in winter pasture from different intensities of continuous grazing on typical grasslands in the Loess Plateau and used laboratory incubation and high-throughput sequencing to determine methane oxidation activity, composition and abundance of soil methanotrophs.【Result】The results showed that the grassland was CH4 sink, and the medium grazing (MG) and high grazing (HG) intensity increased the rate of methane oxidation. Meanwhile, the mean abundance of methanotrophs in HG and MG also increased significantly compared with CK. The results of high-throughput sequencing showed that grazing had a significant impact on the diversity of methanotrophs, Upland soil cluster gamma (USCγ) was the dominant methanotrophic group under different grazing intensities, and a small amount of Methylocaldum and Methylocystis were also present. Pearson correlation analysis showed that methane oxidation rate (MOR) showed a significant positive correlation with soil moisture content and NO3--N content ( P< 0.05), and significantly positively correlated with the absolute amount of USCγ (P < 0.01), which indicated that USCγ played a major role in the process of methane uptake in this grassland.【Conclusion】This study proved that grazing can improve the methane sink function of typical grasslands in the Loess Plateau.

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

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

        DOI: 10.11766/trxb202203040090

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        Abstract:

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

      • Effect of Tillage Practices on Soil Pore Structure Characteristics in Shajiang Black Soil

        QIAN Yongqi, XIONG Peng, WANG Yuekai, ZHANG Zhongbin, GUO Zichun, SHAO Fangrong, PENG Xinhua

        DOI: 10.11766/trxb202201190027

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        Abstract:

        【Objective】Shajiang black soil is one of the major soil types with low or medium productivity in China and is mainly distributed in the Huai River North Plain. As the soil is high in clay content and its parent material is dominated by montmorillonite, it suffers from swelling/shrinkage, low infiltration and strong strength. Suitable tillage is widely considered an effective measure to improve soil structure. However, how tillage practice impacts the pore structure of Shajiang black soil is not clear. Therefore, the objective of this study was to assess the effect of different tillage practices on soil pore structure characteristics in Shajiang black soil. 【Method】Intact soil columns (20 cm height, 10 cm diameter) were sampled from three tillage treatments including no-tillage (NT), rotary tillage (RT) and deep ploughing (DP) at Longkang Farm in Anhui Province, and then were scanned using X-ray computed tomography at a voxel resolution of 60 μm, and followed by saturated hydraulic conductivity (Ks) measurement. After reconstruction of CT images, characteristics of soil macropore (>60 μm) morphology and networks were quantified with Image analysis. 【Result】Compared to no-tillage, rotary tillage and deep ploughing increased soil macroporosity by 192.7% and 261.1% (P < 0.05), respectively. Rotary tillage and deep ploughing significantly increased the hydraulic radius, compactness, fractal dimension and global connectivity of soil macropores (P < 0.05), but decreased the degree of anisotropy and Euler number (P < 0.05). The Ks was significantly improved under rotary tillage and deep ploughing. Deep ploughing improved soil structure and Ks better than rotary tillage did. A significant correlation was observed between Ks and macropore structure characteristic parameters (P < 0.05), in which the connected largest macroporosity was the highest (r=0.833**, P < 0.01). 【Conclusion】Deep ploughing enhanced pore hydraulic radius, connectivity and complexity, built a good soil pore morphology and network structure and consequently improved hydraulic conductivity and reduced structural obstacles of Shajiang black soil.

      • Distribution and Stabilization of Photosynthetic Carbon in Rice-soil System Under Long-term Multiple Cropping of Green Manure

        LIU Weimin, SHU Yeqin, XIA Yinhang, XIANG Hongkun, GAO Peng, ZHAO Ziwei, HUANG Jing, GAO Jusheng, ZHANG Zhenhua

        DOI: 10.11766/trxb202112060640

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        Abstract:

        【Objective】Winter multiple cropping of green manures such as Chinese milk vetch and rapeseed is a traditional system for improving soil fertility and crop yield in the rice field in southern China. Thus, it is of great importance to analyze the soil carbon (C) cycle and the ecological functions of green manure by exploring the distribution of photosynthetic C in a rice-soil system under long-term winter cropping of green manure. 【Method】In this study, based on a 38-year rice-rice-green manure cropping experiment, the 13C-CO2 pulsing labeling technology was used to study the distribution characteristics of photosynthetic C in a rice-soil system at the tillering stage of early rice season under long-term green manure (Chinese milk vetch, rapeseed and winter fallow). At the same time, the stability of 13C-photosynthetic C in soil was studied by measuring the content and distribution ratio of 13C in particulate organic carbon (POC) and mineral associated-organic carbon (MAOC). 【Result】The results showed that the biomass of rice at the tillering stage was not significantly changed but the root/shoot ratio was decreased by 12.6%-19.4% with the long-term multiple cropping of green manure. Compared with winter fallow treatment, the cropping of green manure promoted the distribution of 13C-photosynthetic C in the shoot of early rice, and the accumulation of 13C-photosynthetic C was increased by 19.9 mg?plant-1 and 80.6 mg?plant-1 in cropping of Chinese milk vetch and rapeseed treatments, respectively. The 13C-photosynthetic C accumulation in the root of early rice was decreased by 2.7 mg?plant-1 under Chinese milk vetch treatment, while it was not significantly affected by rapeseed treatment. This result infers that long-term multiple cropping of green manure increased soil nutrient supply and reduced the ratio of root to shoot of early rice, which allows the rice to distribute more biomass to the shoot. Meanwhile, the cropping of Chinese milk vetch and rapeseed treatments reduced the distribution of 13C-photosynthetic C in the soil by 7.6 mg?plant-1 and 7.8 mg?plant-1 respectively. The proportions of rice 13C-photosynthetic C to POC and MAOC were not significantly affected by the cropping of Chinese milk vetch, but the proportion of 13C-photosynthetic C in POC was increased by 35.3% with multiple cropping of rapeseed. 【Conclusion】The long-term multiple cropping of green manure promoted the accumulation of rice photosynthetic C in the plant-soil system. Compared with winter fallow treatment, the accumulation of photosynthetic C in the rice-soil system increased by 3.7%-28.0% in cropping of Chinese milk vetch and rapeseed treatments. On the other hand, the long-term multiple cropping of green manure increased the distribution of photosynthetic C to the shoot of rice and reduced the proportion of photosynthetic C to the root of rice and soil. Moreover, the stability of rice photosynthetic C in soil was weakened by multiple cropping of rapeseed treatments. From the perspective of increasing the total organic carbon and the stability of photosynthetic carbon, the cropping of Chinese milk vetch treatment is a better system for winter multiple cropping of green manures.

      • Medicinal Liquid Diffusion and Weed Control Effect Based on Drip Irrigation System under Maize Film

        GUO Zhijie, ZHANG Haiying, LI Jianjun, XU Shengjun, JING Zhuoqiong, LÜ Heping

        DOI: 10.11766/trxb202112270633

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        Abstract:

        【Objective】This study aimed to explore the possibility of herbicide application in a drip irrigation system. To do this, the relationship between the application technology of soil closed herbicide and the control effect of weeds in the field were studied by using a drip irrigation system under film.【Method】Under three different drip irrigation belt spacing, 40% ethyl atrazine emulsion was applied in three ways. After the drip application, the herbicide concentration in soil samples in different distribution areas was evaluated. In order to provide a scientific basis for rational application of drip irrigation weed control technology in a maize field and enrich drip irrigation application theory, the control effect was investigated in the stage of weed occurrence. 【Result】The results showed that the distribution of herbicide in soil after it was applied was not related to the laying distance of drip irrigation belt, but was related to washing time of water after the last application. The longer the washing time, the lower the concentration of acetochlor in soil, the obvious vertical settlement, and the shorter the radial diffusion distance. Through drip application, the control effect of weed plant and fresh weight was the best after 15 min of drip irrigation, 30 min of drip irrigation and 5 min of drip irrigation. 【Conclusion】It is feasible to apply soil sealing herbicide with drip irrigation in a mulched maize field, which can save time, labor and energy, and provide a new method for early weed control in a maize field. Nevertheless, it is necessary to carry out practical technology optimization research according to different pesticide types and properties.

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

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

        DOI: 10.11766/trxb202112010590

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        Abstract:

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

      • Effects of Soil Hydrothermal Response and Pools of Carbon and Nitrogen Under Straw Cover Rotation on Slope Farmland of Low Mountains and Hills

        WANG Genlin, DUAN Yan, LIU Zhengyu, WANG Nannan, GAO Yang, LI Yumei†, MENG Xianghai, WANG Wei, CAI Shanshan, SUN Lei

        DOI: 10.11766/trxb202112170583

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        Abstract:

        【Objective】The main forms of soil erosion are water, wind and freeze-thaw erosion in the black soil area of Northeast China, and slope farmland is the main source of soil erosion. Human factors such as long-term plowing and straw burning or leaving the field untended and heavy use of light farming or other factors have led to the loss of surface soil, shallow cultivated layer, soil infiltration and erosion resistance of sloping farmland. This would aggravate surface runoff and soil water erosion in summer during severe rainfall. To improve the straw return rate in sloping farmland, a suitable farming method based on planting and cultivating land was proposed. 【Method】Field experiments were used to study the effects of straw mulching and rotation tillage technology (including this season straw mulching and fallow, last season straw mulching and rotary tillage) and conventional farming (straw removal and rotary tillage) on soil water and heat changes and carbon and nitrogen accumulation.【Result】The results showed that: water content in the 20-40 cm soil layer in the early stage of planting could significantly be increased with straw mulching, and the mulching fallow and mulching rotary tillage treatments increased by 26.02% and37.49%, respectively, compared with conventional tillage. At the same time, the 20-40 cm soil bulk density in mulching rotary tillage treatment was higher than that of conventional tillage and mulching fallow, which were reduced by 6.52% and 13.04%, respectively. Compared with mulching and rotary tillage, mulching and fallow could reduce the soil temperature of 0-20 cm and 20-40 cm in the early stage of crop growth by 1.57℃-1.63℃, while the soil moisture content increased by 15.25%-24.41%, which provided conditions for crop emergence and early growth. Combining straw mulching fallow tillage and mulching rotary tillage technologies increased the carbon and nitrogen content of 0-20 cm soil layer, and the organic carbon and total nitrogen reserves were increased by 11.36% and 20.51% compared with conventional tillage.【Conclusion】All of this provide a scientific basis for the implementation of protective farming techniques on slope farmland in the low mountain and hilly areas. In the future, the optimized combination of crop varieties and dwarfing and maturity promotion would promote the increase of productivity in slope farmland when implementing conservation tillage technology.

      • Changes in Soil Heterotrophic Respiration and Its Microbial Diversity during Restoration of Pinus massoniana Plantations in Eroded Red Soil Area

        JIANG Yongmeng, DENG Cui, LYU Maokui?, XIONG Xiaoling, LI Jiayu, XIE Jinsheng

        DOI: 10.11766/trxb202110240498

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        Abstract:

        【Objective】The accumulation rate of soil organic matter directly restricts the improvement of productivity of Pinus massoniana (Masson pine) in the process of vegetation restoration in eroded red soil area. The way to solve this problem has been an inevitable development process of Masson pine in eroded red soil area. Heterotrophic respiration, an important part of soil carbon emission, is a key factor affecting soil organic carbon accumulation. Therefore, it is of great significance to study the effects of Masson pine plantation restoration on heterotrophic respiration and its temperature sensitivity in eroded red soil areas. This will enhance our understanding of the carbon output process and effectively increase soil organic matter accumulation in eroded red soil areas. 【Method】In this study, Masson pine plantations with different restoration years (Y0, Y14, Y31) were selected as the research objects. The effects of vegetation restoration on soil heterotrophic respiration were studied by separating and measuring different respiration components and combining with soil factors such as soil organic carbon, total nitrogen, soil temperature, water content and litter. The structural equation model of heterotrophic respiration between litter, soil temperature, soil nutrients, soil microorganisms and heterotrophic respiration were established to analyze the correlation between heterotrophic respiration and environmental factors in the process of vegetation restoration, and to explore the main factors affecting heterotrophic respiration. 【Result】The results showed that the heterotrophic respiration (RH) of the pine forests with different recovery years differed significantly. The RH in site Y31 was significantly higher than that in site Y14 and Y0. The RH in site Y0 was only 0.99 μmol?m-2?s-1, while in sites Y14 and Y31 it was 2.20 and 2.80 μmol?m-2?s-1, respectively. Temperature was the main influencing factor of the seasonal variation of heterotrophic respiration, explaining 40.6% (Y0), 62.2% (Y14) and 66.6% (Y31) of the seasonal variation, respectively. During the restoration process, the temperature sensitivity (Q10) of relative humidity increased significantly, which was 1.58, 1.93 and 1.82, respectively. The relative contributions of RH to total soil respiration in different recovery years are 77.94% (Y0), 70.84% (Y14), and 77.35% (Y31). The structural equation model showed that soil organic carbon (SOC), temperature and soil microbial diversity were the main factors affecting soil RH during the restoration of Masson pine. SOC and soil microbial abundance significantly correlated with RH, and soil temperature varied with vegetation restoration which significantly and negatively correlated with RH. 【Conclusion】The results of this study indicate that the accumulation of SOC and lack of effective physical protection during Masson pine vegetation restoration increase the decomposition of SOC by microorganisms; On the other hand, the reduction of soil environmental temperature, a continuous increase of bacteria and fungi abundance, and an increase of Proteobacteria, Ascomycota and Acidobacteria in the community further aggravate the microbes to the original strength of soil organic matter decomposition. Consequently, the continuous increase of heterotrophic respiration related carbon emissions limits the improvement of carbon sequestration efficiency of Masson pine forests. Therefore, the strong soil heterotrophic respiration in the eroded and degraded red soil area may be the key factor limiting further improvement of soil organic matter.

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

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

        DOI: 10.11766/trxb202112030656

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        Abstract:

        【Objective】Reclaimed soil in an open-air coal mine is highly infertile due to its poor physical and chemical characteristics. The reclamation methods usually improve soil moisture content which has important theoretical and practical significance for the reclaimed mine soil.【Method】This experiment was conducted in the Heidaigou open-air coal mine in the Inner Mongolia Autonomous Region, in which the following treatments were applied; fly ash, arsenic sandstone and dump soil. A certain mass ratio gradient was set, including 13 blended treatments denoted as L3F1, L4F1, L5F1, L1S1, L2S1, L3S1, L4S1, L5S1, L1F1S1, L2F1S1, L3F1S1, L4F1S1, L5F1S1, in which the L, F, S represented three kinds of controlled treatments. The volumetric water content of each compound soil under different water suctions was measured by the centrifuge method for the drawing of the water characteristic curve using the Gardner fitting model. The specific water capacity, field water capacity, wilting coefficient and effective water content of each treatment were also calculated.【Result】The results showed that the Gardner model was appropriate to fit the water characteristic curves of the 13 compound soils. The addition of fly ash increased the content of fine soil particles (i.e., clay and silt) by 24.11% to 37.19%, respectively, and improved the water holding capacity and water supply of soil. Furthermore, the addition of arsenic sandstone improved the water holding capacity of soil but failed to improve the water supply performance. The water holding capacity of L1F1S1 treatment and water supply performance of L3F1 treatment was the best, which was 47.6% and 40.23% higher than that of the dump soil, respectively. The field water holding capacity and available water content of LF combined treatment and LFS combined treatment were enhanced with the increase of additive proportion. When the mass ratio of soil and fly ash in the dump was 3:1 (L3F1), the maximum field water holding capacity was 18.02%. On the other hand, the maximum available water content was 13.1% with the mass ratio of soil, fly ash and arsenic sandstone of 1:1:1 (L1F1S1).【Conclusion】Overall, the comprehensive utilization of fly ash and arsenic sandstone is beneficial to improve the soil water characteristics of coal mine dump, and the soil water holding capacity and water supply capacity is better when the clay and silt contents of the soil are within the range of 30%-35%. In this experiment, the mass ratio of 1:1:1 is the best.

      • Stoichiometry of Base Cations and Silicon of Cambosols Derived from Different Parent Materials as Leached by Simulated Acid Rain

        ZHAO Yue, YANG Jinling, XU Zhe, ZHANG Ganlin

        DOI: 10.11766/trxb202202110053

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        Abstract:

        【Objective】The soil acidification rate in current environment is the basis for controlling soil acidification. However, the accurate estimation of soil acidification rate is difficult due to the buffer effect of soils. The soil consumes exogenous H+ and releases base cations through mineral weathering (compensating for base cations loss and inhibiting soil acidification) and the cation exchange process (increasing exchangeable H+ and inducing soil acidification). Nevertheless, it is difficult to distinguish these processes, which leads to large errors in estimating soil acidification rate. Since silicon (Si) only comes from mineral weathering reaction and has nothing to do with cation exchange, the stoichiometry of base cations (BC: K+, Na+, Ca2+, Mg2+) and silicon release (BC:Si) during soil mineral weathering can quantify the H+ consumed through mineral weathering, which is helpful to determine accurate soil acidification rate. The purpose of this research is to explore the BC: Si difference and its causes in Udic Cambosols derived from three parent materials of Mica schist, Gneiss and Andesite. 【Method】 First of all, the physical, chemical and mineralogical properties of test soils were measured. To avoid the influence of the base cations adsorbed by soil colloid on stoichiometry of the mineral weathering process, soil exchangeable base cations were washed by elution experiment. Then, the release of base cations and silicon of soils derived from three parent materials were obtained by leaching of simulated acid rain. 【Result】The results showed that content and distribution in the profile of clay, pH, organic matters, exchangeable base cations (K+, Na+, Ca2+, Mg2+), cation exchange capacity (CEC) and mineral compositions were significantly different for different parent materials. During simulated acid rain leaching, BC:Si values of base-uneluted soils were three times more than that of base-eluted soils. Only when the exchangeable base cations adsorbed by soil colloid were eluted can obtain accurate BC:Si values. The smallest BC:Si value was in the humus surface horizon (Ah) in the same soil profile with different soil genetic horizons and the largest BC:Si value was in the parent materials horizon (C). BC:Si value of Udic Cambosols derived from different parent materials soils followed: Gneiss > Mica schist > Andesite. The mineral proportions of plagioclase, illite, chlorite, and vermiculite in soils controlled the BC:Si values. 【Conclusion】Therefore, only on the basis of corresponding BC:Si, the response degree of Cambosols with different parent materials to the acidification process can be accurately evaluated. The results can provide data support for soil acidification rate evaluation regionally.

      • Effects of Nitrogen Fertilization Combined with Straw Incorporation on Soil Protist Community

        LI Shengjun, LI Yujie, ZHAO Jianning

        DOI: 10.11766/trxb202111090520

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        Abstract:

        Long-term chemical fertilization (especially nitrogen fertilization) under intensive land-management practices in agriculture is of great concern globally due to its adverse influence on the environment and human health. Returning the eco-friendly crop residues to farmland is a promising way of reducing chemical fertilizer input and alleviating environmental problems.【Objective】Protists are unicellular eukaryotes with enormous abundance and diversity, and play versatile functional roles to improve soil fertility and agricultural productivity. Thus, they comprise an integral component of soil microbiota in the agroecosystem. However, little is known about the responses of the soil protist community to nitrogen fertilization in combination with straw incorporation.【Method】Here, a fixed field trial with 2 × 4 full-factor interaction was performed to examine the variations in diversity, composition, and potential function of the protistan community using Illumina high-throughput sequencing under eight different fertilization treatments (2 straw returning groups × 4 nitrogen gradients)，Also, the key forces driving the variation in soil protistan community were determined in combination with edaphic property analysis.【Result】The phyla Chlorophyta, Conosa, Cercozoa and Ciliophora were dominant in the soils for all treatments. Nitrogen fertilization diminished the diversity of soil protists, whereas straw returning in general modified such impacts, with more pronounced effects under higher nitrogen application rates. Regardless of whether straw was added, the relative abundance of Chlorophyta exhibited an overall decrease with increased nitrogen gradient. Cercozoa and Ciliophora presented an increase in proportion with the amount of nitrogen fertilizer in the straw returning group. In the current study, the protistan functional community was predominated by phagotrophs in all treatments. Compared to treatments without straw addition, the implementation of straw returning enhanced the relative abundance of phagotrophs, but suppressed the proportion of phototrophs. Protistan parasites preferred a high nitrogen input under exclusive nitrogen fertilizer, with highest proportion in N300 treatment, which was significantly higher than those in all other treatments,. Soil properties were important environmental factors determining the shifts in soil protist community, with soil organic matter and pH exhibiting the most intensive influences as revealed by redundancy analysis (RDA) and Pearson’s correlation analysis.【Conclusion】This study provides experimental evidence that nitrogen fertilization coupled with straw incorporation have consequences for the soil protist community, It also shows that the phylogenetic and functional taxa of protists are responsive to such agricultural management regime alterations. Future studies should aim at deciphering the trophic associations among microorganisms, as well as constructing agricultural soil microhabitat beneficial for crops based on reasonable fertilization regimes and utilization of biotic resources like protists.

      • Contrasting Effects of Biochar and Ca(OH)2 on Alleviating Plant Aluminum Toxicity during Soil Acidification: A Simulation Study

        LAI Hongwei, NI Ni, SHI Renyong, DONG Ying, YAN Jing, NKOH Jackson Nkoh, LI Jiuyu, CUI Xiumin?, XU Renkou

        DOI: 10.11766/trxb202111250567

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        Abstract:

        【Objective】 With the input of acid, the lime effect of ameliorants on acidic soils is gradually weakened resulting in soil re-acidification and aluminum toxicity. As a new alternative amendment material for acid soils, the performance of biochar on alleviating aluminum toxicity during soil re-acidification is still unclear. To investigate the effect and mechanisms of biochar on alleviating aluminum toxicity during soil acidification, a comparative study between biochar and Ca(OH)2 was conducted through a simulated soil re-acidification test.【Method】 Cyclic acid leaching with HNO3 was used to rapidly simulate the soil acidification process. A root elongation experiment with maize was used to investigate the response of plant roots to soil acidification. The change in soil pH, soluble Al3+ and base cations (K+, Ca2+ and Mg2+) during soil acidification were also studied. 【Result】Cyclic acid leaching effectively simulated the process of soil re-acidification. With the increase of cyclic acid leaching time, soil pH decreased and the maize root elongation was inhibited. Compared with Ca(OH)2 treatment, biochar significantly inhibited the acidification process and alleviated adverse effects on plant roots. When acid input was simulated for 12 years, the relative elongation of maize root in biochar treatment was 18.6% higher, and the relative absorption of Evans blue was 19.6% lower than that in Ca(OH)2 treatment. On the one hand, biochar slowed down the decrease of soil pH during re-acidification through the protonation of surface anionic functional groups, and thus inhibited the activation of soil aluminum. As a result, the soil pH and the soluble Al3+ concentration in biochar treatment were 0.12 units higher and 33% lower than that in Ca(OH)2 treatment with simulated 12-year acid input, respectively. On the other hand, biochar released Mg2+ continuously during soil re-acidification. In the simulation of 12-year acid input, the concentration of Mg2+ in soil solution and uptake of Mg2+ by maize in biochar treatment was more than twice higher than that in Ca(OH)2 treatment. A higher concentration of Mg2+ can help alleviate the symptoms of aluminum toxicity in maize by regulating the physiological response of plants to Al3+. 【Conclusion】 Compared with Ca(OH)2, biochar presented more long-term potential in ameliorating acidic soils under continuous acid input. These results are of important significance for management of soil acidification.

      • Cultivated Land Quality Evaluation Method and Demonstration Based on Improved Grey Target Model

        NIE Yan, HE Xinying, WANG Pu, YIN Chen, YU Lei

        DOI: 10.11766/trxb202109170501

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        Abstract:

        【Objective】Cultivated land is a special public resource and the most precious natural resource, which has a fundamental and guaranteeing role in national food security. As an important means to measure the internal basic conditions and external utilization level of cultivated land, cultivated land quality evaluation is the basis for grasping the status quo of cultivated land quality and promoting sustainable use of cultivated land resources. 【Method】Based on the needs of the “triad” protection of cultivated land, we applied the Criteria Importance Though Intercriteria Correlation(CRITIC) method to improve the gray target evaluation model. Also, we proposed a new method for the evaluation of county-level cultivated land quality based on the triple quality dimension including soil quality, ecological quality and management quality. The Chibi City was taken as the case study. 【Result】Results show that the organic matter content and 17 others indicators can characterize the multi-functional quality level of cultivated land under the triple quality dimensions of soil, ecology and management. The quality of cultivated land in Chibi City was at an upper-middle level, and the range of bullseye was 0.66～0.85. Furthermore, the regional spatial difference of cultivated land quality was large and the quality grade of cultivated land in Chibi City was mainly two and three, accounting for about 80.49% of the total cultivated land area. The cultivated land with a higher quality level was mainly distributed in the northwest and east of Chibi City while with a lower quality level was predominant in the central and northern urban areas and Shenshanzhen in the northeast. The difference in cultivated land management quality in Chibi City was small, soil quality and ecological quality were more restrictive to the comprehensive quality of cultivated land. 【Conclusion】The evaluation results of this study were consistent with the existing cultivated land quality grade evaluation results. This indicate that the improved gray target evaluation model was not only more objective in the weighting and evaluation process, but also conducive to measuring the single-dimensional quality of cultivated land. The improved gray target evaluation model was an important supplement to the existing cultivated land quality evaluation methods. This research can provide theoretical and methodological references for the evaluation of cultivated land multi-functional quality, which is in line with the new perspective of cultivated land quality evaluation in the new era.

      • Desorption and Migration Characteristics of Cu/Cd Composite Contaminated Soil under different pH/Ionic Strength

        LI Jing, LIN Qing, XU Shaohui

        DOI: 10.11766/trxb202108080413

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        Abstract:

        【Objective】Some changes in the external environment are often observed after the remediation of heavy metal polluted soils with solidification stabilization technology. Thus, an important scientific question worth discussing is whether the inactivated heavy metals will be released again and migrate in the soil, causing pollution risk, and under what conditions.【Method】In order to reveal the effects of different chemical factors on the activation and migration of heavy metals in contaminated soil, the desorption and migration behavior of Cu2+ and Cd2+ in soil under different ionic strength, pH and cation types (Ca2+, Na+) were studied by laboratory soil column experiments.【Result】In general, the peak leaching concentration of Cu2+ and Cd2+ increased with the increase in ionic strength. Using CaCl2 as a leaching agent, the desorption capacity of Cu2+ and Cd2+ increased at 0.005, 0.01, 0.05 and 0.1 mol·L-1 CaCl2, and the desorption capacity of Cd2+ was higher than that of Cu2+. However, 0.5 mol·L-1 CaCl2 inhibited the desorption of Cd2+ and the desorption of Cu2+ was higher than that of Cd2+. When pH decreased, the desorption of Cu2+ and Cd2+ increased, that is, the acidic environment was conducive for the desorption of Cu2+ and Cd2+. However, the concentration peak of Cu2+ and Cd2+ at pH 3 was smaller than that at pH 4 and 5. Ca2+ was more favorable for the desorption of Cu2+ and Cd2+ than Na+, but NaCl solution was more favorable for the desorption of Cu2+ at 0.005 mol·L-1. Also, the concentration of Cu2+ in the leaching stage with deionized water was higher than that in the leaching stage with CaCl2. In addition, soil particles exhaled at 0.005, 0.05 and 0.5 mol·L-1 NaCl, and the flow rate decreased at 0.05 and 0.5 mol·L-1 NaCl.【Conclusion】The increase in ionic strength, decrease in pH and presence of divalent cations were beneficial to the desorption and migration of heavy metals in soil. This study provides a theoretical basis for soil remediation and heavy metal release after soil remediation.

      • Application of Generalized Linear Geostatistical Model for Digital Soil Mapping in A Typical Subtropical Hilly Area

        HAO Chenkai, SUN Xiaolin, WANG Huili

        DOI: 10.11766/trxb202107290386

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        Abstract:

        【Objective】Digital Soil Mapping (DSM) is receiving more attention and becoming widely used. Its methods mainly include environmental correlation-based models, spatial auto-correlation based models, and a mixture of these two kinds of models. The mixed model is expected to be advantageous over the single models. A generalized linear geostatistical model (GLGM) is a kind of mixed model. Compared with the commonly used mixed model, i.e., regression kriging (RK), GLGM has advantages such as having random effects to account for the non-stationarity of soil variability. However, GLGM is seldomly used due to its major disadvantages, i.e., complicated computation. 【Method】In this study, within a small hilly area (3.03 km2) in Gaofeng Forest of Nanning, Guangxi, generalized linear mixed model (GLMM) and its combination with ordinary kriging (OK), i.e., GLGM, were used to predict the spatial distribution of soil organic carbon (SOC), pH, clay and cation exchange capacity (CEC). Performances of the two models were then compared with commonly used models, including multivariable linear regression (MLR), geographically weighted regression (GWR), regression forest (RF), OK, RK and generalized additive model (GAM). 【Result】The results showed that GLMM had higher accuracy in predicting clay, while GLMM and GLGM had medium accuracy in predicting CEC. Further, GLMM and GLGM had lower accuracy in predicting SOC and pH. 【Conclusion】Based on the adjusted R2 of the linear regression model, nugget effect and global Moran’s I, it is concluded that GLMM and GLGM are appropriate when there is a low adjusted R2 of linear soil-landscape regression (less than 5%), weak spatial auto-correlation of soil (nugget-to-sill ratio large than 71%), and strong local spatial variability of soil (Moran’s I less than 0.09), e.g., clay in this paper. Otherwise, GLMM and GLGM are not appropriate, e.g., for SOC and pH in this paper. For the high spatial heterogeneity and multi-scale variability of soil, we think that GLMM and GLGM are promising for DSM, although more studies are needed to improve the efficiency of GLMM and GLGM modelling.

      • Soil Texture Grading and Zoning for Tobacco Planting in Yuxi at 100 m Spatial Resolution

        XIE Xinqiao, LU Junping, TIAN Yutian, YANG Jizhou, LI Xiangwei, SUN Weixia, SONG Zhengshan, SHI Xuezheng

        DOI: 10.11766/trxb202109280526

        Abstract(433) HTML(0) PDF(1.30 M)( 200) Collect

        Abstract:

        【Objective】The development of soil texture grading and zoning is of practical significance for improving tobacco quality. 【Method】Based on the soil profile data recorded in the soil species records of Yunnan province (prefecture and county), combined with GIS technology and geostatistics, this study carried out a high-precision division of soil texture and quality for a tobacco plantation in Yuxi City. A spatial database of soil texture at 100 m spatial resolution level was built, and the quality grade of soil texture of the key soil factors for tobacco zoning was scientifically divided. 【Result】The results showed that the soil texture and quality suitable for tobacco planting in Yuxi varied greatly. According to soil texture and quality, the areas of grade I to grade V were 9.87%, 36.08%, 11.7%, 21.38% and 20.97%, respectively. The most suitable grade I soil for tobacco planting was mainly distributed in Eshan and Huaning counties, with an area of 26.2 km2 and 25.2 km2, respectively. Also, suitable second class soils were mainly distributed in Xinping, Yuanjiang and Jiangchuan, with an area of 87 km2, 58.6 km2 and 55.5 km2, respectively. There were obvious differences in soil texture and quality for tobacco plantation soils at different altitudes. The main suitable tobacco plantation area was at the altitudes of 1600 ~ 2000 m. 【Conclusion】The spatial distribution of soil texture at 100 m spatial resolution level in Yuxi was as detailed as village scale, which greatly improved the precision and practicability for tobacco plantation zoning. These results can provide a theoretical basis for high-quality tobacco production, long-term zoning and scientific management of soils.

      • Effects of Long-term Fertilization on Phosphorus Adsorption Characteristics of Fluvo-aquic Soils

        YANG Jiao, XIN Xiuli, ZHONG Xinyue, DING Shijie, ZHAGN Xianfeng, REN Guocui, ZHU Anning

        DOI: 10.11766/trxb202108060406

        Abstract(501) HTML(0) PDF(918.98 K)( 248) Collect

        Abstract:

        【Objective】The availability of soil phosphorus (P) usually limits the productivity of fluvo-aquic soil. In order to provide a scientific basis for improving P use effectivency and rational fertilization in fluvo-aquic soils, the adsorption characteristics of P and its relationship with soil properties under long-term fertilization were studied.【Method】We selected seven treatments: no fertilizer (CK), no P fertilizer (NK), no potassium fertilizer (NP), no nitrogen fertilizer (PK), mineral fertilizer NPK (NPK), half compost plus half mineral fertilizer NPK (1/2OM) and compost alone (OM) in a long-term fertilization experiment at Fengqiu, to determine soil properties and P adsorption capacity. The Langmuir and Freundlich equations were used to fit the isothermal adsorption curves. Furthermore, the maximum adsorption capacity (Qm), adsorption constant (K), maximum buffer capacity (MBC), P adsorption saturation (DPS), Freundlich adsorption constant (a) and adsorption index (b) were calculated. Correlation analysis and redundancy analysis (RDA) were used to explore the vital factors affecting the soil P adsorption characteristics.【Result】The results showed that P adsorption in fluvo-aquic soil fitted both the Langmuir (R2≥0.80) and Freundlich (R2≥0.89) isotherms. With the increase of P concentration in the equilibrium solution, P adsorption capacity rapidly increased at first and then slowly afterwards. Compared with CK and NK, Qm and MBC of NP, PK and NPK increased by 15.62%~23.60% and 2.94%~23.46%, respectively, however, K and MBC of 1/2OM and OM reduced by 39.60%~49.57% and 36.09%~56.15%, respectively. Correlation analysis and RDA results showed that organic matter (SOM), pH, free Al oxides (Ald) and C/P were the main factors affecting P adsorption characteristics of fluvo-aquic soil. In addition, the DPS of 1/2OM was 30.92% lower than that of OM.【Conclusion】Long-term combined NPK fertilizer with compost can increase the content of SOM, reduce P adsorption capacity and reduce the risk of P loss compared with OM.

      • Effects of Nitrogen Form and Phosphorus Fertilizer on Phosphorus-solubilizing Bacteria and Phosphatase of Maize Rhizosphere in Acidic Red Soil

        GUO Long, FENG Tongyu, XUE Zhuangzhuang, WANG Chao, SHEN Renfang

        DOI: 10.11766/trxb202108250454

        Abstract(415) HTML(0) PDF(633.74 K)( 247) Collect

        Abstract:

        【Objective】Low phosphorus (P) availability limits the increase in the productive capacity of acidic soils. The bacteria phoC and phoD genes encode acid and alkaline phosphatase (ACP and ALP), respectively, which mineralize organic phosphorus (P) to inorganic P, are affected differently under different fertilization regimes. However, the combined responses of phosphorus-solubilizing microorganisms (PSM) to fertilization strategies and the rhizosphere effect are still unclear.【Method】In this study, we evaluated the response of maize to the interaction of different nitrogen forms (ammonium nitrogen and nitrate nitrogen) and phosphate fertilizer levels. The phoC and phoD genes, separately coding for acid and alkaline phosphatase productions, were used as molecular markers to investigate the effects of fertilization strategies and rhizosphere effect on soil phosphatase activities and associated functional microbial communities in acidic soil.【Result】The rhizosphere effect significantly increased soil phosphatase activities in the rhizosphere. ALP activities in the rhizosphere under nitrate-nitrogen treatment were lower than in the corresponding ammonium nitrogen treatment. Also, the strength of the rhizosphere effect was greater than that of nitrogen forms and phosphate fertilizer levels. Nitrogen forms, phosphate fertilizer levels and rhizosphere effect all significantly affected the operational taxonomic units (OTU) number and Shannon index of phoD-harboring bacteria, but only nitrogen forms and rhizosphere effect affected the OTU number of phoC-harboring bacteria. Principal coordinate analysis (PCoA) and PERMANOVA analysis showed that the rhizosphere effect exhibited more influence on the phoC- and phoD-harboring bacterial community composition than nitrogen forms and phosphate fertilizer levels, with more effects on the phoD-harboring bacterial community. The stimulation of soil phosphatase activities in the rhizosphere was closely related to the increase in soil organic matter. Additionally, changes in the composition and structure of phoC-harboring bacterial community were mainly related to the changes in rhizosphere nutrients, while the changes of phoD-harboring bacterial community structure may be attributed to combined effects of root exudates and nutrient changes.【Conclusion】The rhizosphere showed more influence on soil phosphatase activities and associated functional bacterial communities than nitrogen forms and phosphate fertilizer levels in acidic soil. However, the strength of the effect strongly relied on the fertilization strategies.

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Supervisor： Chinese Academy of Sciences

Sponsor：Soil Science Society of China

Editor-in-Chief：Xu Renkou

Address：71 East Beijing Road, Nanjing 210008, P. R. China

Zip Code：210008

Phone：+86-25-86881237

Email：actapedo@issas.ac.cn

ISSN：0564-3929

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