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

Abstract:【Objective】Soil structure is the physical framework for various processes in soils and is of great importance for quantitative studies of soil physical, chemical and biochemical processes. Existing methods for quantifying soil structure are overly dependent on laboratory techniques, resulting in them being limited by factors such as sample size, resolution and cost. 【Method】To overcome these limitations, this study utilizes digital imaging techniques to quantify ped shapes using high-resolution soil profile images. 【Result】The results show that typical structural classifications and subjective descriptions can be transformed into quantitative morphometric (circularity, roundness, major-axis ellipse angle,aspect ratio, solidtity, width-to-height ratio) data.Also, the average circularity, roundness, and width-to-height ratio of ped in the topsoil layer in the nine soil profiles (0.79, 0.74, and 1.05) were higher than those in the heart soil layer and the parent soil layer (0.64, 0.68, and 0.94), and their average aspect ratio and major-axis ellipse angle (1.35 and 42.73) were lower than those of the heart soil and parent material layers (1.79 and 49.33).【Conclusion】Therefore, the use of digital imaging techniques can accurately quantify and visually characterize the morphology of ped shape, and the technology elucidates the law that the shape of ped gradually transforms from blocky structure to granular structure in the process of soil formation.

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

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

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

Abstract:【Objective】Fungal decomposition plays a key role as the primary driving force of the nutrient cycling and energy flow in the soil. However, the response characteristics of fungal communities to different types of straw carbon inputs and the key environmental factors at the aggregate scale are not yet clear.【Method】In this study, corn straw was used as the experimental, and three treatments were set according to the equal carbon content of straw returning: regular crushed straw (RS), decomposed straw (DS) and straw biochar (BC). A control group without straw application (CK) was also set up. The study aimed to investigate the effects of different carbon types from straws on the diversity, composition, and distribution of fungi in soil macroaggregates (>0.25 mm) and microaggregates (<0.25 mm), as well as the interactions within fungal communities. Furthermore, key environmental factors influencing the variation of soil fungal communities were explored.【Result】The results of a 2-year field experiment indicate that RS treatment significantly reduced fungal α diversity (P < 0.05) in microaggregates (< 0.25 mm) and macroaggregates (> 0.25 mm). The top three dominant phyla in each treatment were Ascomycota, Mortierellomycota, and Basidiomycota, while the top three dominant genera were Plectosphaerella, Chaetomium, and Mortierella. Compared to different aggregate size fractions, the treatment with straw carbon significantly induced differentiation in fungal community structure (P < 0.01), with notably distinct fungal community structure observed in the RS treatment compared to the other treatments. Also, analysis of fungal co-occurrence network showed that BC treatment increased the number of nodes (10.08%) and modularity (5.55%) while DS treatment increased the number of nodes (11.17%), the number of edges (32.57%) and the average degree of nodes (19.27%) included in the co-occurrence network, and all of which improved the structural stability of the fungal network of soil aggregates. The Mantel test analysis found that ammonium nitrogen (AN) and pH were the key environmental factors affecting the fungal community structure of soil aggregates, with the fungal community in the RS treatment being the most influenced by soil environmental factors. The prediction analysis of fungal community function showed that the input of straw carbon could reduce the relative abundance of pathogenic fungi and reduce the occurrence of soil-borne diseases in farmland. 【Conclusion】Our results reveal that in the short term, different soil aggregates of fungi are more susceptible to the influence of straw carbon types, leading to differentiation. The addition of decomposed straw and straw biochar can increase soil AN content, thereby increasing the complexity of the fungal network, thus, promoting fungal community stability. Therefore, for practical applications, it is advisable to consider appropriately increasing the input of decomposed straw or straw biochar to promote the stability of soil ecological functions.

Abstract:【Objective】The Sichuan-Yunnan ecological barrier area is an important ecological function area in China. To reduce the increasing ecological degradation and soil erosion, it is important to research soil erosion and soil conservation functions. 【Method】The Integrated Valuation of Ecosystem Services and Trade-offs (InVEST) model was used to characterize the spatial distribution of soil erosion and soil retention in 2000, 2010, 2015, and 2020. The GeoDetector was applied to detect the main controlling factors of soil erosion. 【Result】The results showed that the soil erosion modulus and the total amount of soil erosion in the four phases showed a trend of decreasing and then increasing. The erosion intensity was dominated by mild erosion, accounting for about 85% of the whole area, and mainly distributed in the eastern part of the area. The light and more than light erosion intensity were mostly distributed in the western part. Soil conservation modulus in 2000, 2010, 2015, and 2020 were 4.0×103, 3.5×103, 3.5×103, and 4.5×103 tkm-2, respectively, and soil conservation amount were 9.6×108, 8.3×108, 8.2×108, and 1.1×109 t, respectively. The influence degree of each influencing factor on soil erosion in descending order was as follows: land use type, elevation, fractional vegetation cover, soil erodibility, erosivity, and slope. The interaction effects between factors on soil erosion were greater than that single factor, and the interaction between land use type and soil erodibility had the strongest effects on soil erosion.【Conclusion】Although soil erosion in the Sichuan-Yunnan ecological barrier area shows a worsening trend, soil conservation is gradually improving, and soil conservation is stronger than soil erosion, and overall, the Sichuan-Yunnan area is developing in a better direction.

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

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

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