Abstract:Soil microbial biogeography is a discipline that aims to study the spatial distribution pattern of soil microbial community and their changes across time, and is research frontiers in the fields of soil biology and microbial ecology. In recent years, despite the tremendous progress in the study of soil microbial biogeography, there are still many difficulties and challenges. This mini-review will briefly review the development of soil microbial biogeography and emphatically introduce the recent progresses of soil microbial biogeography in forest, grassland and farmland ecosystems in China. This mini-review further elaborates the current international frontiers of soil microbial biogeography, including the spatial distribution of microbial communities and their driving mechanisms, community assembly processes and co-occurrence network, the relationship between microbial geographic distribution and ecosystem functions, and the prediction of microbial community under global change scenarios. Finally, this mini-review outlooks the future developments in the study of soil microbial biogeography, and emphasizes the importance of clear microbial species definitions, temporal dynamics of microbial communities, multiomics approaches and synthetic biology, and the prediction modelling with high accuracy in the study of soil microbial biogeography.

Abstract:Soil contamination by heavy metals (HMs) is an important eco-environmental problem in China. It is essential to understand the mechanisms of HMs interacting with solid-phased fractions of soil for effective control and remediation of HMs polluted soils. Due to the complexity and heterogeneity of soil as well as the varied sizes of soil particles ranging from millimeter to nanometer, microsites with different micro-structures and surface properties control the speciation, transformation and bioavailability of HMs. Therefore, it is of great importance to deeply understand the microscale interaction mechanisms of HMs within soil microsites in order to effectively predict and control environmental behaviors of HMs in soils. Synchrotron-based microprobe and scanning transmission X-ray microscopy (STXM), and nano-scale secondary ion mass spectrometry (NanoSIMS), with micro- and nano- scale spatial resolutions, provide a unique platform to investigate the microscale interaction mechanisms of HMs within soil microsites at environmental meaningful spatial scales. This review first gives a brief overview of the birth and development of environmental soil chemistry (ESC) of HMs, points out the bottleneck of the current development of ESC due to inherent complexity and heterogeneity of the soil, and summarizes the aforementioned three advanced techniques and their application in the investigation of microscale soil chemistry of HMs, and finally gives a perspective on future development in this field.

Abstract:Suitable pH and oxy-reduction conditions in paddy induced by flooding supply optimal conditions for diazotrophs to do N₂ fixation. Paddy biological N₂ fixation makes paddy be different from upland. Paddy can sustain certain productivity under no N fertilization, while upland productivity decreases year by year. Along with an increase of chemical active N application, environment becomes severely polluted. To secure food production and decrease environmental pollution, biological N₂ fixation is urgently to be increased to reduce chemical N fertilizer application. In order to better explore capacities of paddy biological N₂ fixation, we make the reviews on progresses of quantification techniques, controlling factors, enhancement techniques and perspectives in paddy N₂ fixation. We hope this review can offer some helps for further studies on paddy N₂ fixation.

Abstract:The Qinghai-Tibet Plateau is an important ecological barrier in China, and plays an important role in maintaining climate stability, carbon balance and water resources. It is known as the "Asian water tower" and the "regulator" of the environment of Asia and even of the northern hemisphere. Under the background of global warming and population growth, the Qinghai-Tibet Plateau is very sensitive to climate changes. As the Qinghai-Tibet Plateau is highly diversified in landform, its climate is very complex. Therefore, there are many kinds of erosion forces, such as freezing-thawing, wind, water and gravity. The existing researches made use of RS and GIS, wind tunnel simulation, runoff plot monitoring and other experimental methods to study causes and temporal and spatial distribution of the different types of soil erosion. Some scholars also conducted experiments on soil erosion control in some regions, and evaluated effectiveness of the measures. Findings of these researches provide some valuable information for studies on soil erosion in the Qinghai-Tibet Plateau. However, compared with other parts of China, the Qinghai-Tibet Plateau is relatively new in the study on soil erosion. This paper collated and analyzed what has been done in the research on freeze-thaw erosion, wind erosion, water erosion and gravity erosion in the Qinghai-Tibet Plateau, and found out some issues that call for attention. Firstly, divergence exists in definition of freeze-thaw erosion: e.g. freeze-thaw erosion should encompass the factors of wind, water, and gravity, or not? Secondly, geological erosion is confused with soil erosion in concept. Thicker humus layers are found in chestnut soil and mountain shrub soil in the Qinghai-Tibet Plateau except for in Huangshui Valley, Qinghai Lake basin, Hefei Long Qu Valley and Lhasa River Valley, and the two types of soils are relatively mature. However, soils in the other areas contain many coarse gravels or gravels. Geological erosion is a natural process that carries not only includes soil particles, but also rocks and weathered rocks from slopes and banks. So, in the Qinghai-Tibet Plateau where gravels dominate in the surface layer, what happens more, soil erosion or geological erosion? And thirdly, the topic of soil erosion still lacks basic research. For example, temperature and soil moisture data are the basis for the study of freeze-thaw erosion, however, at present, changes in soil temperature are generally reflected by air temperature data, and soil moisture data of a large area are derived from remote sensing data, and measured data in field are very limited. Consequently, the model for evaluating freeze-thaw erosion is not very accurate; Runoff and sediment monitoring data are important information for exploring law of the water erosion on slopes at a watershed scale, however, besides the measured data of the areas of the Qinghai-Tibet Highway slope and Three-river Source, of other areas very limited data are available; and soil and vegetation data are the basic ones needed for evaluation of regional erosion, but little is measured. In the future, the study in this area should dedicate more effort to basic work, such as soil erosion monitoring, pay more attention to influence of changes in temperature on soil erosion, and attach more importance to prevention and control of soil erosion, so as to provide certain scientific basis for decision-making to protect the ecological barrier in China.

Abstract:The meaning of soil quality (SQ) and the scale for SQ assessment varies with goal of the practices of using and managing soils, and the latter has become an important perspective in the research of SQ assessment (hereinafter referred to as “the research”). Existing researches in this aspect focus mainly on SQ assessments on small and medium spatial scales under a specific land use type or farming conditions, while little has been done on the research on large spatial scales.【Objective】In order to identify core content of SQ assessment, and to analyze methodological characteristics and development trends of the research on large spatial scales.【Method】In this paper, a conceptual cognitive framework for SQ assessment was built up based on concepts discrimination, and specific scopes of the large spatial scales of the research were defined via literature statistics, and then a review was presented of some representative theoretical studies and practice in various countries.【Result】 Results show: (1) The scope of a large spatial scale for SQ assessment may vary from global to continental, national and regional scales; the research basically follows the technical route of “set goals – specify objects and related soil functions (SFs) – select indicators and models – output results”; in specifying goals, objects and indicators, focuses were laid on natural resource attributes of soils; data were obtained through soil surveys, soil sampling and sample analysis; comprehensive assessment models were often used; generally, the assessment index system encompasses the inherent quality indicators that reflect background properties of soils, and the total number of indicators is small (about 6~12). (2) Decomposition and expression of SFs has gradually become cores of SQ assessment; mapping of assessment goals to soil properties and processes based on SFs drives multi-dimensional and multi-scale development of the research. (3) SQ and arable land quality belongs separately to environmental quality and management tools, and the connotations of the two are essentially different and should be clearly distinguished.【Conclusion】At present, for large spatial scales assessment, identification of goals and acquisition and integration of data still need to have certain breakthroughs, and call urgently for deployment: (1) to characterize spatial variability of the soil resources corresponding to the composite management goals, and to realize unified spatial SQ assessment over a wide area; (2) to identify corresponding soil threats, to evaluate land suitability and to recommend strategies for zoning of wide-ranged spatial soil resources for utilization or protection, in the light of SFs distribution, soil type characteristics and land use patterns; (3) to specify occurring conditions, processes, influencing factors and mechanism of SQ evolution over a large spatial scale of area, and to explore scale effects of SQ assessment by collaborating the research on small, medium and large spatial scales through integration of multi-source geoscience datasets and based on the development of SFs assessment models. Under the new scenario of unified management of natural resources, China should absorb the experiences of other countries, unfold the third national soil survey as soon as possible, and establish a national scale soil quality assessment system.

Abstract:【Objective】Yellow soil, an important arable land resource, is extensively distributed in Chongqing. However, so far, little is known about its pedogenetic process and attribution in the Chinese Soil Taxonomy. The aim of the study was to make up the missing knowledge in this aspect. 【Method】In this study, 5 soil profiles were prepared in 4 plots of yellow soils developed separately from different parent material (Quaternary Pleistocene old alluvial deposits, sandstone weathering of Xujiahe Formation, limestone weathering and purple rock weathering) for analysis of soil forming environment, morphological characteristics and physico-chemical properties, to determine pedogenetic processes of the soils. 【Result】Results show that in the Chongqing area, yellow soil that developed from sandstone of Xujiahe Formation was quite high in desilication and aluminumation degree of soils, followed by the soils developed from purple rock, and those developed from Quaternary Pleistocene old alluvial deposits and limestone were relatively low in desilication and aluminumation. Comparatively, soils developed from sandstone weathering of Xujiahe Formation were more typical, which distributed in the altitude of 350~1 300 m. Correlation analysis of pH with clay SiO2/Al2O3 shows the coefficient was 0.71, reaching up to a significant level (P<0.05), which meant that pH would regulate desilication and aluminumation of the yellow soils. And Fed/FeT in the soil was 50%~60%, this may because the climate in Guizhou was more humid and cold. 【Conclusion】By referring to “Keys to the Chinese Soil Taxonomy (third Edition)”, the 5 profiles were found to have the following diagnostic horizons and characteristics: ochric epipedon, cambic horizon, argic horizon, udic soil moisture regime, redox features, mesic soil temperature regime, ferric property and alic evidence. The 5 profiles could tentatively be sorted into the soil orders of argosols and cambosols, and further into 3 suborders, 5 groups and 5 subgroups. Reference studies of the 5 soil profiles between various soil classification systems shows that the Chinese Soil Genetic Classification and the Chinese Soil Taxonomy (CST) do not have any simple one to one corresponding relationships, as for yellow soil in the Chinese Soil Genetic Classification, certain discriminations begin to appear at the genus and species levels, while CST demands soil information more quantified, and hence is more accurate in classification. And the reference between CST and World Reference Base for Soil Resources (WRB) shows that the soils belonged to argosols of CST were Luvisols and Alisols in the first level of WRB separately, and the soils belonged to Cambosols of CST were also Cambisols of WRB.

Abstract:【Objective】Farmlands on long gentle slopes of black soil in Northeast China is the main source of soil erosion. Soil erodibility is an important factor affecting soil erosion. The soil erosion process in the black soil region of Northeast China is characterized by overlapping and/or coupling of wind-hydraulic-gravity-freeze-thaw, multiple in force and in process. In spring, freezing and thawing accompanies melting water, and temperature fluctuation and freezing and thawing are the dominant factors affecting soil properties, while in summer and autumn, water erosion is the main form of erosion and rainfall runoff and dry-wet alteration are the two leading factors. However, so far little has been reported in the literature about field experiments on soil erosion resistance in the black soil region under the multi-forced compound erosion, thus making it hard to effectively implement the task of controlling the multi-forced compound erosion. 【Method】On a typical cultivated long gentle slope in the Keshan Farm in Heilongjiang Province, a 150 m long section of the slope was delineated along the same direction as the farmland ridges go from south to north. Soil samples were collected from the 0～30 cm soil layer of the slope at sampling sites 30 m apart along the slope. Soil shearing force of undisturbed soil was determined in April and September 2018. At the same time, the collected soil samples were analyzed for content of water-stable aggregates with the Le Bissonnais method via slow-setting and mean weight diameter (MWD), geometric mean diameter (GMD) and mass fractal dimension (D) of the soil aggregates were measured in an attempt to characterize soil erodibility parameters of the long gentle slope of black soil.【Result】Results show that in terms of shearing force, MWD, GMD, D and content of >0.2 mm soil aggregates, the sampling sites exhibited a decreasing order of 0 m > 30 m > 150 m > 60 m > 120 m > 90 m in spring, and generally an order of 30 m > 0 m > 150 m > 120 m > 60 m > 90 m in fall, which indicate that the soils in the middle of the slope at 60 m, 90 m and 120 m are quite low in soil erosion resistance, and that the slope varies with posiiton of the sampling site in strength of soil erosion, sediment transport and deposition. And soil anti-erodibility increases with soil depth. MWD and GMD is 1.27 times and 1.37 times as high in fall as in spring, respectively, and the content of >0.2 mm soil aggregates and shearing force is higher in autumn than in spring, but D is in a reverse trend, which suggest that the soil erosion resistance of the long gentle slope of black soil is higher in fall than in the spring. The correlations between the indices of water-stable aggregates were significant, but they have nothing to do with shearing force. Soil water-stable aggregates can be used as a stable index to assess soil erodibility. Shearing force is not so good when used as an index for the assessment because it is not stable, which is mainly attributed to its variability with soil properties, susceptible to and complex in change, especially under the influence of freeze-thaw erosion force. As the change of soil erodibility has certain uncertainties, it calls for further in-depth studies on impacts of soil shearing force on soil erodibility on long gentle slopes of black soil in Northeast China.【Conclusion】To control soil erosion in cultivated slopes of black soil in the region, focuses should be laid on adoption of erosion controlling practices in spring, like reducing length of the slope and adopting corresponding soil and water conservation measures in the middle of the slope. Soil water-stable aggregates can be used as a stable index in assessing soil erodibility in the black soil region of Northeast China. Shear force is not so good as soil water stable aggregates when used as index. The findings of this study may be used as a scientific basis for prevention and control of compound erosion in cultivated long gentle slopes of black soil in Northeast China.

Abstract:【Objective】 Change in soil moisture of a collapsed wall is one of the main factors leading to occurrence and development of collapse therein. Rainfall can cause unstability and eventually collapse of the wall. During this process, the swell-shrink characteristics of the solum as affected by soil water content play an important role in mound collapsing. In the past, studies paid most attention to effect of water content on the swelling-shrinkage characteristics only in a single soil layer. 【Method】 With the collapsing mounds or walls typical of Anxi County of Fujian as object, effect of water content on the swell-shrink characteristics of a solum or a mound relative to soil layer was studied via indoor tests on no-loading expansion rate and linear shrinkage rate. 【Result】 Results show that no-loading expansion rate of the soil, regardless of layer, decreased with increasing initial water content, while linear shrinkage rate was in a reverse trend. Initial water content exhibited an obvious exponential decreasing relationship with soil unloading expansion rate in all soil layers and the relationship could be fitted with a regression equation of δ_e=ae^{(-ω /b)} +cwith R²＞0.96. But initial water content did have a significant exponential increasing relationship with linear shrinkage rate of the soil, regardless of soil layer, and the relationship could be fitted with a regression equation of δ_sl =ae^{(ω /b)} +c with R²＞0.96 in all soil layers. So initial water content had a good exponential relationship with no-loading expansion rate and linear shrinkage rate. In the same soil layer, the expansion varied more greatly than the shrinkage did in extent. Comparison between soil layers in extent of the variation of expansion and shrinkage rates shows that the red soil layer was 2.58% and 3.33% higher than the sandy soil layer, and 3.61% and 4.67% higher than the detritus soil layer, respectively. 【Conclusion】 These irreversible phenomena of swelling-shrinking might be the main cause to form cracks in the solum, which then eventually lead to soil collapse. This work is of certain important significance to understanding the causes and mechanism of collapsing of mounds.

Abstract:【Objective】Red soil slope farmlands are an important cultivated land resource in South China. Because of long-term unreasonable tillage measures and uneven spatial and temporal distribution of precipitation, resultant serious soil erosion on slope farmlands in this area has led to a sharply declining productivity and low and unstable crop yields, thus seriously restricting development of the agriculture in South China. Reasonable tillage measures play an important role in improving soil structure, increasing water use efficiency, preventing soil erosion, improving ecological environment, building up land productivity and raising crop yields. In this paper, a tract of red soil slope farmland in Yunnan Province was taken as research object. Farmlands under different tillage measures were compared in soil quality. This study was conducted to explore mechanisms of tillage measures affecting erosion resistance and production performance of the cultivated-layers of the farmlands, in an attempt to provide certain scientific basis for quality evaluation of the cultivated-layers of red soil slope farmlands and improvement of conservative tillage technologies for red soil slope farmlands.【Method】In this study a total of 15 experimental plots were set up and cultivated for comparison between different tillage measures or treatments, i.e. CK (traditional tillage), NT (no-tillage), P20 (tillage 20 cm in depth), P20C (tillage 20 cm in depth + compaction), and P20S30 (tillage 20 cm + subsoiling 30 cm in depth), in soil quality of the cultivated layer, and one-way ANOVA and soil quality index method were used to analyze the experimental data.【Result】Results show:（1）The impacts of tillages on erosion resistance of the cultivated-layers in red soil slope farmlands. Compared with Treatment CK, Treatment P20S30 increased by 28.13% in average mass diameter of water-stable aggregates. Treatment NT was the highest in shear strength (12.12 kg·cm^-2), and in soil saturated hydraulic conductivity (1.27 mm·min^-1) as well. Treatment P20 was the highest in content of >0.25 mm water-stable aggregates, in mean weight diameter of water-stable aggregates and in geometric mean diameter of the aggregates, reaching up to 69.64%, 1.74 mm and 0.77 mm, respectively;（2）The impact of tillage on productivity of the cultivated-layer in red soil sloping farmland varied with treatment. In Treatment NT, soil bulk density significantly increased, and soil organic matter and available phosphorus concentrated in the surface layer. In Treatment P20 and P20S30, the cultivated-layer was significantly thicker, and the soil organic matter and available phosphorus contents increased significantly;（3）And the effect of tillage on soil quality of the cultivated-layer and on the suitability of the diagnostic indices varied with treatment. Treatment P20S30 was the highest in soil quality index (0.58); and Treatments P20 and P20S30 varied within the range of suitability in thickness, bulk density and available phosphorus index of the cultivated-layer. Treatment P20 was the highest in organic matter content.【Conclusion】All the findings in this study may serve as reference for selection of suitable tillage measures, and evaluation and construction of a rational cultivated-layer in red soil slope farmlands.

Abstract:【Objective】According to the International Plant Protection Convention (IPPC), it is estimated that soil carbon loss contributes to the global atmospheric CO₂ concentration by about 30%~50%, and about 50%~70% of the loss is caused by soil erosion. Therefore, the loss of soil carbon through soil erosion has an important impact on carbon recycling and exchanging between terrestrial ecosystems and the atmosphere, and it plays a significant role in balancing the global CO₂ concentration and climate warming. Most studies on nutrient loss in China focus mainly on that in the loess plateau region and the purple soil region and pay attention mainly to nitrogen and phosphorous loss or TC loss with slope surface runoff, but almost neglect effects of the two factors, slope gradient and rainfall intensity, on TC loss with interflow in soil, let alone dynamic process of TC loss distribution in slope surface runoff and interflow. Therefore, this study was done to explore characteristics of soil total carbon (TC) loss with slope surface runoff and interflow on bare slopes of the soil derived from weathered granite in the Zhejiang-Fujian hilly region, China.【Method】 In this study an artificial rainfall simulation experiment was carried out to explore TC loss with slope surface runoff and interflow and its processes as affected by slope gradient and rainfall intensity and to analyze effects of the two on TC loss. So it was designed tot have 3 levels of rainfall intensity (60, 90 and 150 mm•h^-1) and four levels of slope gradient (5, 8, 15 and 25°), performed on two three-dimensional monitoring simulator runoff flumes, arranged in parallel. TC loss from each flume was monitored and calcuated.【Result】Results show that variation of the TC loss process with slope surface runoff was not much affected by slope gradient or rainfall intensity, and the TC loss rate variation curve was extra-significantly correlated with the mass concentration curve. That is to say, TC loss rate was affected mainly by TC mass concentration. In soil interflow, TC mass concentration curve peaked up rapidly and then declined and leveled off. In the experiment, TC loss with runoff increased with rising rainfall intensity, regardless of slope gradient, while TC loss with interflow decreased. No apparent linear relationship was found between TC loss with runoff and slope gradient under high rainfall intensities, while a linear relationship was looming between slope gradient and TC loss in the interflow. The influence of rainfall intensity on total TC loss and TC loss with runoff was more significant than that of slope gradient, but a reverse trend was observed in interflow. TC loss with runoff was found to be significantly and linearly related to rainfall intensity, slope gradient and runoff volume per rainfall event, with R² being higher than 0.800. 【Conclusion】In summary, TC loss increases gradually with rising slope gradient and rainfall intensity. Slope surface runoff is the main factor affecting TC loss, but interflow is one that can not be ignored. This study provides a calculation method for estimating TC losses with surface runoff on bare slopes of the soil derived from weathered granite in the Zhejiang-Fujian hilly region, China.

Abstract:【Objective】 The purpose of this study is to explore how to rapidly predict soil organic matter in red soil so as to meet the needs of smart agriculture and precision fertilization. 【Method】 This paper took the northern part of Fengxin County in the Northwest Jiangxi Province as its research area and used the 1 km×1 km standard grid method to divide the study area for soil sampling. A total of 248 red soil samples were collected and dried for spectral measurement. Three different mathematical transformation methods, including fractional order derivatives, were used to analyze the soil spectra. In the tests the 350~399 nm and 2 451~2 500 nm bands were removed because they were very susceptible to environmental noises. And noises in the remaining bands were removed with Daubechies(DB) wavelet. Then samples were collected from the pretreated spectral bands at 10 nm intervals to form a 205-band so as to reduce data dimensions and data redundancy. The 800~1 000 nm band, which was liable to the impact of iron oxide, was ruled out of the experiment. The bands used to construct the model were filtered by the P=0.01 significance test. A model was built up with the partial least squares regression (PLSR) in combination with BP neural network for prediction of soil organic matter content. And the model was tested. 【Result】 Results show that the prediction using the PLSR-BP composite model was the best after the soil spectral data was transformed with the 1.5 order fractional derivative, with R²=0.89 and RMSE=4.68 g∙kg^-1 for the training dataset and R²=0.87, RMSE=5.55 g∙kg^-1 and RPD=2.75 for the validation dataset. 【Conclusion】 The transformation of red soil spectral data with the 1.5 order fractional derivative better highlights characteristics of organic-matter-related information, which is helpful for prediction of organic matter contents. And the PLSR-BP composite model is higher than any single models in prediction accuracy, and can be used to predict organic matter content in red soil very well. So it can also serve as a new approach to predicting quickly organic matter content in red soil for precision agriculture.

Abstract:【Objective】 Soil salinization is the major obstacle restraining high quality and high yield of cotton in South Xinjiang, and rated irrigation can effectively alleviate soil salinization. EM38-MK2 can be used to obtain real-time dynamical soil salinization data, monitor in-situ soil salinization in time, and provide a digital basis for rated irrigation in cotton fields. 【Method】 In this study, different soil sampling schemes were designed in line with the designing of the transmitting coil and receiving coil of the electromagnetic sensor(EM38-MK2), and soil apparent electrical conductivities (EC_a) and soil samples from corresponding soil profiles were collected in the same field in six different time periods for analysis of, effects of soil sampling scheme and soil moisture content on accuracy of the apparent EC model, and specification of factors for building apparent EC models for different soil layers. Moreover, comparison was done of the local model based on data of a single period with the model based on overall data of the six periods in inversion accuracy.【Result】 Results show that the model based on single point sampling at the site of the transmitting coil of the EM38-MK2 was higher in sensoring accuracy and stability than the others and hence could effectively minimize the error caused by sampling. When soil moisture content was less than 10%, the correlation between apparent EC and measured EC was low, with determination coefficient being 0.58 and the inversion model could only roughly estimate EC; When it was more than 10%, apparent EC displayed a good relationship with measured EC, with determination coefficient being 0.80 and the inversion model could make an estimation of EC close to the measured one. The EMH+EMV model was built on the equation of EC_h0.375 +(EC_h0.75 +EC _v0.75)/2+EC_v1.5 defined as modeling factor and much higher than the EMH or EMV model in inversion accuracy with predicted apparent EC being very approximate to measured EC. The local models for predicting ECs in various soil layers different in depth were all higher than the overall one in inversion accuracy and their RPDs were more than 2.0, which indicate that they have high prediction ability. 【Conclusion】 All the findings in the study demonstrate that sampling under the transmitting coil is conducive to stability of the sampling, which may guide future utilization of the equipment, and open up new ways of thinking and server as reference for monitoring soil salinization dynamically with the electromagnetic sensor technology on the field scale.

Abstract:【Objective】 In the arid, semi-arid and coastal regions where freshwater resources are scarce, while underground brackish water/saline water resources are abundant. In order to ensure food security and sustainable development of the agriculture development, it is necessary to use brackish water/saline water for reasonable irrigation to alleviate the pressure of shortage of freshwater resources. However, the use of brackish water/saline water for irrigation will certainly cause accumulation of salts in the soil, and trigger secondary salinization of the soil, thus affecting growth of the crops therein. Moreover, it will also alter chemical composition of the soil solution and stability of the soil structure, leading to degradation of soil physical properties and change in chemical reaction in the soil. 【Method】 In this paper, an indoor soil column percolation experiment was conducted to investigate effects of the salts in irrigation water, relative to kind and concentration, on permeability of and transport of salt cations in the soil. In the experiment, to prepare soil columns, plexiglass cylinders, 40 cm in height and 6 cm in diameter, were used, and for irrigation water containing NaCl, MgCl₂ and CaCl₂, separately, at 3, 5 g·L^-1 (as brackish water) and 10 g·L^-1 (saline water). A total of 9 treatments were designed, and each had two replicates. 【Result】 It was found that soil relative permeability coefficient K/K₀ (K stands for permeability coefficient calculated at each time, and K0 for initial permeability coefficient) decreased with the increasing of Na⁺ concentration, and permeability declined faster in the topsoil than in the lower soil layers; and Ca²⁺ and Mg²⁺ behaved similarly during the process of infiltration, that is, both increasing soil permeability by a rate rising with the increase in Ca²⁺ and Mg²⁺ concentration and in soil depth. The effect of Ca²⁺ was more significant than that of Mg²⁺. Relative permeability coefficient of the whole soil column was in quadratic relationship with time and ion concentration. In terms of conductivity of soil effluent , the treatments followed an order NaCl > CaCl₂ > MgCl₂, while in terms of pH, an order of NaCl > MgCl₂ > CaCl₂. In the columns treated with NaCl solution, both Ca²⁺ and Mg²⁺ increased in the soil with rising NaCl concentration in the solution and soil depth. 【Conclusion】 Na⁺ migration in the soil will leads to decrease in soil permeability; while Ca²⁺ and Mg²⁺ migration in the soil does reversely; and the effects of the three ions are more significant in the surface soil layer than in the lower layers. Salt content in the soil depends on kind and concentration of the infiltration water. Irrigation with saline/brackish water tends to lead to accumulation of salts in the soil. The higher the salt concentration in the irrigation water, the higher the salt accumulation. When using saline/brackish water for irrigation, it is advisable to arrange irrigation reasonably in the light of water quality and properties of the soil to be irrigated, coupled timely with certain soil amelioration measures, when necessary, so as to avoid any adverse impacts of the irrigation on soil permeability and crop growth.

Abstract:【Objective】 Aiming at the common problem of arsenic (As) /cadmium (Cd) pollution and declining soil fertility in paddy fields in South China, organic manure is used to improve soil fertility, while dissolved organic carbon (DOC) is amended as metabolic substrate for sulfate-reducing bacteria to promote reduction of SO₄^2- into S^2- and subsequent formation of As/Cd sulfide deposit in flooded soil. This way of thinking may provide a useful solution to the common problem.【Method】 A systematic research was carried out to analyze effects of organic manure (OF) and amendment of sulfate (SOF) on solubility, bioavailability and chemical conversion of As and Cd in As/Cd compound polluted paddy soil.【Result】 Treatment OF (application of organic manure) reduced the concentration of As(III) in soil porewater by 9%~64% and increased that of Cd in porewater by 4~12 times during the first 10 weeks of flooding, as compared to CK. Sequencing extraction of solid As/Cd by fraction shows that Treatment OF increased the content of amorphous hydrous Fe oxides-bonded As, low in environmental stability, and specifically-sorbed As by 4%~5% and reduced soil Fe oxide-Cd and carbonate-Cd by 55% and 11%, respectively. Treatment SOF (application of organic manure amended with sulphate) did not have much effect of reversing solubility and transformation of soil As/Cd between solid fractions, but did promote reduction of SO₄^2- into S^2- that raised the content of soil arsenic sulfite by 71%. The pot experiments done in the research show that Treatment OF reduced As accumulation in the stems and roots of rice seedlings by 44%~ 47%, but increased total As in brown rice and inorganic As in white rice at the mature stage by 22% and 12%, respectively. And Treatment OF significantly enhanced Cd accumulation in rice seedlings and multiplied Cd content in brown rice Cd by 1.2 times. Treatment SOF significantly reversed the trend of Treatment OF increasing As content in brown rice, but did not have much effects on Cd accumulation in brown rice and increase in inorganic As in white rice.【Conclusion】 Application of organic manure has a serious risk of increasing As/Cd accumulation in rice, and even amendment of sulfate has only some mild effect of controlling bioavailability of soil As/Cd. Therefore, the potential threat of application of organic manure to quality and security of rice cultivated in As/Cd contaminated paddy fields has aroused great concerns.

Abstract:【Objective】Soil-borne diseases are important factors affecting yield and quality of crops. In order to understand the current research status and trends of soil-borne diseases, we conducted a bibliometric analysis. 【Method】Based on the core collection database of the Web of Science, bibliometric analysis was conducted using the CiteSpace knowledge map analysis tool, VOSviewer visual analysis software and HistCite Citation Analysis Tool, for number of publications and their distributions in disciplines, contributor countries (regions) and institutions, carrier journals, authors and main scholars involved, hotspots and trends in the field of soil-borne crop diseases.【Result】(1) During the period between 1990 and 2018, the number of research papers addressing the topic of soil-borne disease increased. It is important to continue supporting soil scientists in their research on soil-borne diseases; (2) The United States, China, Australia and France are the major contributors of academic articles in this field, and have established close cooperation relationships with each other in recent years; (3) “Phytopathology” and “Plant Disease” are the top two journals in local citation frequency. “Soil Biology & Biochemistry”, “Plant Disease”, “Plant and Soil”, and “Applied Soil Ecology ” are the main journals that have high impacts in the field of soil-borne diseases in the recent 5 years; (4) Qirong Shen, Christopher A Gilligan, Mark Mazzola, David M Weller, Aocheng Cao, and Zucong Cai are the most productive scholars in this field; (5) Biocontrol is a research hotspot in this field. The most typical soil-borne pathogenic microorganisms studied are Rhizoctonia solani , Verticillium dahliae, Fusarium oxysporum , and Ralstonia solanacearum; (6) The research in this field tends in future to focus mainly on relationships between soil microbial diversity and soil-borne diseases and between host plants and pathogenic microorganisms, and development of management practices effective to prevent and control those soil-borne diseases.【Conclusion】This paper is based on bibliometric data of the researches in the field of soil-borne disease. In recent years, intensive studies have been conducted on soil-borne diseases. With the aid of the high-throughput sequencing technology, the knowledge of soil microbial communities and rhizosphere microorganisms has been greatly expanded. Application of the next generation sequencing technology to the study of soil-borne diseases will help us explore interactions between pathogenic microorganisms and soil microbial communities, and develop more effective methods to control soil-borne diseases.

Abstract:【Objective】Soil alkalinity is a widespread environmental problem that limits crop yield. Up to 831 million hectares of land are under salt stress on the earth, and about half are being alkalinized. Under alkali stress, plants are exposed to both salt and high pH. Moreover, high pH stress is a more significant factor in limiting plant growth than salt stress. High pH stress inhibits plant growth by imposing adverse effect on roots, such as increasing ion imbalance, disrupting cellular pH stability and decreasing nutrient solubility. However, it remains unknown how transcription responds to high pH stress for regulation and its mechanism. Therefore, this paper tries to elucidate molecular mechanism of high pH tolerances of Arabidopsis with the aid of high throughput biotechnology. The research is essential to breeding high and stable yield crops. 【Method】 In recent years, high throughput sequencing has been rapidly developed and used in genome-wide gene expression profiling of Arabidopsis, rice and soybean. In this paper, a stable pH experiment system was established and transcriptional profiling of the root of Arabidopsis cultivated in high pH medium for 7 days was conucted using RNA-seq. Then differently expressed genes (DEGs) in response to high pH stress were presented and annotated. In the end, important high pH responsive genes and their putative upstream transcription factors were identified.【Result】The following findings were obtained. It was found that under high pH stress, growth of the primary root of Arabidopsis was significantly limited. Transcriptome sequencing of Arabidopsis root under normal pH (6.0) and high pH (8.0) were performed. Of the 1129 DEGs analyzed, 329 were identified as up-regulated genes and 800 as down-regulated genes. GO (Gene Ontology) functional categorization shows that these DEGs are highly related to abiotic stimulus, transcription, cell organizations and biogenesis, ion transport, protein metabolism and signal transduction. In addition, several genes were determined to be responsive to high pH identified. For example, water channel gene PIP2;4 and PIP2;5 , Al-activated malate transporter gene ALMT1 , K+ transporter gene HAK5 and calcium exchanger gene CAX7 were down-regulated after high pH treatment. Several encoding calcium binding proteins and calmodulin protein genes, such as MSS3, CBL7, CML23, CML37, CML38, were also down-regulated under high pH stress. Auxin responsive genes SAUR16, SAUR40, IAA4 and transport genes PIN5, PIN-LIKES7 and cytokinin biosynthesis genes LOG2 , LOG5, LOG6, LOG9 were expressed differently under high pH stress, suggesting that auxin and cytokinin play important roles in response to high pH. Meanwhile, identification of 97 differently expressed transcription factors (DE TFs) under high pH condition was performed. These DE TFs were included in 20 TF families, such as AP2/EREBP, MYB, WRKY, NAC, bHLH. Then a transcriptional regulatory network between DE TFs and important high pH responsive genes was constructed. It was found that DE TFs belonged to AP2/EREBP, WRKY, NAC and MYB TF families, such as DREB2A, WRKY45 , NAC045 and MYB107 acted as the hub genes in this high pH responsive network.【Conclusion】In this paper, a comprehensive overview was presented of the transcriptomes of Arabidopsis root under high pH stress. Among them a total of 1129 genes were identified as high pH responsive DEGs, and frequently involved in transcription regulation, ion transport, cell wall organizations, Ca²⁺ signaling and hormones pathway. Furthermore, regulatory relationship between the DE TFs and high pH responsive genes were predicted. DE TFs belongimg to AP2/EREBP, WRKY, NAC and MYB families played core roles in this regulatory network, suggesting that these TFs play important roles in high pH stress response in Arabidopsis. Overall, all the findings in this study may serve as a important theoretical basis for breeding of alkaline-tolerant crops.

Abstract:【Objective】This study aimed at exploration of effects of application of organic materials on composition of humic acid functional groups in primary saline-alkali soils.【Method】A field experiment was carried out in a field of original saline-alkali soil in Da""an City, Jilin Province. The experiment was designed to have CK and four treatments, that is, CK (control without application of any organic material), Treatment KL (application of granular straw), Treatment JG (application of normal corn stalk), Treatment MC (application of forage grass), and Treatment YF (application of sheep manure). Humic acids extracted from the soil of each treatment were analyzed with a fourier transform infrared spectroscopy (FTIR) and the principal component analysis technique and infrared spectra obtained were characterized relative to treatment. 【Result】Results show that the treatments increased the relative content of fatty carbon and aromatic carbon in soil humic acid, but reduced the content of carboxyl carbon as compared with CK. With the exception of KL, all the treatments increased the relative content of amino compounds in soil humic acid. In addition, all the treatments increased the ratios of aliphatic carbon/carboxyl carbon and aliphatic carbon/aromatic carbon in soil humic acid, which indicates that the application of organic materials reduces the structural condensation degree and oxidation degree of soil humic acid, while enhancing aromaticity. The structure of humic acid also tended to be aliphatic, simple, and young. Comparison between KL and JG shows that KL was higher than JG in relative content of aliphatic carbon in humic acid, but lower in relative content of carboxy-carbon and aromatic carbon in humic acid. Furthermore, JG increased the relative content of amino compounds in soil humic acid, while KL slightly reduced it. Judging from the ratio of I₂₉₂₀/I₁₇₂₀ and I₂₉₂₀/I₁₆₂₀ in humic acid, KL treatment is more conducive to formation of humic acid, younger, simpler and more aliphatic in structure in the soil. The principal component analysis indicates that the applied organic materials are one of the main sources of aliphatic carbon, aromatic carbon and amino compounds in soil, which provides a basis for exploring sources of humic acid functional groups. Via FTIR infrared spectroscopy, it was found that soil humic acid functional groups varied in composition with treatment or type of the organic material applied. This provided a theoretical basis for studying mechanism of the application of organic materials affecting humic acid properties in the soil.【Conclusion】In summary, the applied organic materials are one of the major sources of aliphatic carbon, aromatic carbon and amino compounds in the soil. As affected by the application, humic acid in the soil was lowered in structural condensation degree, oxidation degree and aromoticity, while enhanced in aliphaticity. Consequently the humic acid tended to be aliphatic, simple, and youngin structure. The effects on composition of humic acid in the soil varied with treatment or type of the organic material applied. As such, granulated straw is more conducive to the formation of humic acid, younger, simpler and more aliphatic in structure in the soil.

Abstract:【Objective】Moso bamboo (Phyllostachys heterocycla) is an important non-timber forest resource in subtropical China. Intensive bamboo forest management, beginning in the 1980s, has enormously increased the area of moso bamboo plantations and economic return for farmers. However, these long-term management practices, such as removal of understories and excessive application of nitrogen fertilizers combined with tillage, have already brought about some negative impacts, such as significantly altering soil microbial communities and increasing N₂ O emission, of which the latter possibly reflects changes in the population of denitrifying bacteria. To explore this possibility, investigations were made of abundance of denitrifying bacteria in moso bamboo plantations under long-term intensive management. 【Method】Soil samples were collected from the surface (0~20 cm) and subsurface (20~40 cm) soil layers of moso bamboo plantations receiving 0 (CK), 10, 15, 20 and 25 years of intensive management, for analysis of abundances of denitrifying communities (nirK-, nirS - and nosZ-denitrifiers). In addition with the aid of real-time quantitative PCR, and for analysis of soil physicochemical properties in an attempt to determine major factors that contribute the most to alteration of denitrifying bacteria in abundance. 【Result】It was found that the abundances of soil denitrifying bacteria in the moso bamboo plantations (1.45×10⁶～3.03×10⁸ copies•g^-1 dry soil) were generally higher than those reported for other ecosystems, except in the case of nirS in farmland. Abundances of the three functional genes in both soil layers increased or remained unchanged during the first 10 years of intensive management. With the exception of nirS in the surface soil, all three functional genes then decreased somewhat after either 15 or 20 years of intensive management. Eventually however, and with the exception of nosZ in the surface soil, abundances of the other genes recovered or even exceeded the level in control after 25 years of intensive management, indicating a resistence of denitrifying bacteria to disturbance caused by intensive management practices. The abundances of nirS and nosZ in the surface soil samples were significantly higher than those in the subsurface soil samples, but nirK showed an a reverse trend. This phenomenon possibly reflects the observed decreases in pH and dissolved organic carbon excreted by bamboo root in the subsurface soil. Correlation analysis between soil physicochemical properties and functional genes reveals that the denitrifying genes, nirK, nirS, and nosZ, were positively related to total N, available P, and organic carbon in the surface soils. Additionally, nosZ was also positively related to C/N. However, in the subsurface soils, all the three denitrification genes as a group were significantly and positively related to organic carbon. Redundancy analysis demonstrates that the impacts of intensive management significantly on denitrifying bacteria were main reflected in the comprehensive effects of soil nitrogen and organic carbon on activities and functioning of the bacteria. 【Conclusion】In summary, all the findings in this study indicate that long-term intensive management substantially alters both soil physicochemical properties and associated denitrifying bacterial communities. But the effect varies with soil layer, which means that depth of the soil is also a key factor affecting composition of the denitrifying bacterial community. Compared to some other ecosystems, the intensively managed moso bamboo plantations are relatively higher in abundance of denitrifying bacterial functional genes. Active participation of these bacteria in nitrogen recycling leads to increased emission of N₂O. Therefore, it is suggested that growers should use slow-release N fertilizers to reduce the concentration of ammonium nitrogen in the soil solution, thus encourage plant to absorb ammonium before it is nitrified. This strategy is believed to be able to decrease production of nitrate and hence denitrification and N₂O emissions.

Abstract:【Objective】Biochar has been considered as a promising strategy to improve soil carbon (C) sequestration and soil fertility. The aim of this study was to investigate effects of amendment of maize stalk biochar and returning of maize stalk on soil organic carbon fractionation and microbial activities in an unfertilized field of upland red soil, in an attempt to provide certain theoretical guidance for using biochar as soil amendment to improve soil fertility and enhance soil C storage in agricultural soils. 【Method】A field experiment was carried out to investigate changes in soil organic carbon pools, activities of the enzymes involved in C, N and P cycling, and microbial substrate utilization rates as affected by amendment of biochar and/or returning of straw. The biochar used in the experiment was prepared out of maize stalk via pyrolysis at 450~500 °C near anaerobically, and amended with or without straw returned in the experiment upland field of Ferralsol low in fertility. Soil samples were collected from the experiment for analysis of soil labile and recalcitrant C fractions with the two-step sulfuric acid hydrolysis method, and for soil enzyme activities and microbial substrate utilization rates with the microplate fluorimetric assay and MicroResp, respectively. 【Result】Results show that 9 months after the experiment started, soil labile C content increased in the treatment of straw returning alone, but no much changes were observed in soil pH, total organic C and recalcitrant C contents. Soil organic C and recalcitrant C increased significantly in content in the treatments of amending biochar alone or with straw returned. β-glucosidase activity was enhanced by straw returning, but not by amendment of biochar. Soil basal respiration and microbial utilization rates of glucose, asparagic acid and syringic acid were significantly increased by straw returning, but were not much affected by biochar amendment alone or in combination with straw. Significant interactions were observed between biochar and straw on labile C content and soil basal respiration rate. Significant and positive correlations were also found of soil basal respiration with labile C content, β-glucosidase activity and microbial utilization rate of glucose. 【Conclusion】To sum up, all the findings in this experiment suggest that compared with straw returning, amendment of the biochar derived from maize stalk improves soil stable C pools and reduces soil C emission.

Abstract:【Objective】Soil Phosphorus Storage Capacity (SPSC) is an index developed on the basis of the degree of phosphorus saturation (DPS), and can be used to effectively assess and monitor the status and release potential of soil phosphorus storage. Therefore, based on a long-term (1988—) fertilization experiment in a field of upland red soil, this paper tracked variations of the SPSCs in the red soil and its various fractions of soil aggregates and discussed impacts of soil P input on the SPSCs.【Method】A total of 33 soil samples were collected from the surface soil layers of the 11 treatments of the experiment, i.e. NK, NPK, NP, PK, NPKCa NPKCaS, CK, PS (1/2NPK + peanut straw), RS (1/2NPK + rice straw), FR (1/2NPK + fresh radish) and PM (1/2NPK + pig manure), for fractionation into soil aggregates ( > 2 mm, 2.0 ~ 1.0 mm, 1.0 ~ 0.25 mm and 0.25 ~ 0.053 mm) with the wet-sieving method, analysis of SPSCs in the soil and aggregates, exploration of effects of P input on SPSC, discussion on relationships of SPSC with soil total phosphorus (TP) and available phosphorus (Bray-P). In the end, the risk of soil phosphorus loss was assessed and “safe life” of the soil continuing to accommodate exogenous phosphorus.【Result】Among the inorganic treatments, Treatment NK was the highest in SPSC, reaching up to 265 mg•kg^-1, which was 1.9, 1.6, 1.9, 2.0 and 2.4 times that respectively of treatment NPK, NP, PK, NPKCa and NPKCaS. The fractions of soil aggregates exhibited an high to low order of 1 ~ 0.25 mm, 0.053 ~ 0.25 mm, > 2 mm, 1 ~ 2 mm in rate of contribution to the soil total SPSC. So, based on the current phosphorus application rate, it was estimated that the upland of red soil might remain safe for 30 years. Among the combination treatments, Treatment PM displayed a negative value in SPSC, reaching up to -333 mg•kg^-1. In this case, P application should be stopped immediately or fertilizer application rate should be adjusted. Treatment PS, RS and FR remained to be positive in SPSC value and did not vary much between them and followed an high to low order of 1 ~ 0.25 mm, > 2 mm, 0.053 ~ 0.25 mm, 1 ~ 2 mm in SPSC contribution rate of soil aggregates. So based on the current phosphorus application rate, the soil under the treatments might remain safe for 41, 30 and 14 years, respectively. However, the soil under Treatment CK may remain safe for 51 years.【Conclusion】According to the correlation analysis of SPSC, TP and Bray-P, when SPSC stay exceed 10 mg•kg^-1, application of phosphorus in the upland of red soil upland is absolutely "safe"; if it is in the range of -10 mg•kg^-1 ~ 10 mg•kg^-1, phosphorus in the red soil is extremely unstable and extremely liable to get leached into the surroundings or water; when SPSC stay below -10 mg•kg^-1, urgently calls for immediate halt of P application and readjustment of fertilization schemes so as to lower the risk of P polluting the environment.

Abstract:【Objective】This paper is oriented to study rational application of pig manure and its effect on soil fertility in upland red soil.【Method】A 3-year stationary field experiment on application of pig manure was carried out for the study. The experiment was designed to have 5 different application rates for pig manure, that is, 0, 7.5, 15, 30 and 45 t∙hm^-2. Samples of the soils and the crops, i.e. spinach and maize were collected from the plots with different manure application rate for analysis biomass of the shoots, relevant soil physico-chemical properties, and activity of the enzymes involved in C, N and P recycling with the microplate flurimetric assay method. 【Result】Results shown that soil organic matter, total N, P and K, readily available P and K and biomass of spinach and maize shoots all increased linearly with increasing pig manure application rate. In the plot applied with 45 t∙hm^-2 of pig manure, the highest average biomass of shoots reached 11.48 and 20.84 t∙hm^-2 in spinach and maize, respectively, organic matter, total nitrogen, total phosphorus rise up to 14.6, 1.07 and 0.73 g∙kg^-1 and available nitrogen, alkalyzable phosphorus and readily available potassium did up to 85.47, 106.9 and 411.7 mg∙kg^-1, respectively; But there was no significant differences in soil nutrient elements contents between 15, 30 t∙hm^-2 of pig manure treatments and 45 t∙hm^-2 of pig manure treatment. Moreover, activities of the 6 kinds of soil enzymes involved in C, N and P cycling (β-1,4-Glucosidase, βG; β-1,4-Xylosidase, βX; Cellobiohydrolase, CBH; Leucine amino peptidase, LAP; β-1,4-N-Acetyl-glucosaminidase, NAG; Acid phosphatase, AP) were linearly related with pig manure application rate, especially in the plots applied with 30 or 45 t∙hm^-2 and remarkablely or extreamly remarkablely and positively related to contents of soil organic matter and soil nutrients. In the plot applied with 45 t∙hm^-2 of pig manure, βG, βX, CBH, LAP, NAG and AP enzymes reached up to 105.3, 17.49, 36.63, 47.76, 55.31 and 77.38 nmol∙g^-1∙h^-1, respectively. C/N did not much in plots applied with different rates of pig manure, βG/(NAG+LAP) decreased with increasing application rate of pig manure, while (NAG+LAP)/AP exhibited a reverse trend. 【Conclusion】Soil organic matter, nutrient content and enzyme activity of the soil increase with application rate of pig manure in the red upland soil, and crop yield does linearly. Attention must be paid to problems, such as increased nitrogen and phosphorus loss, as a result of excessive available nutrients in the soil.

Abstract:【Objective】This paper aimed at understanding the relationship between continuous monocropping of vegetable and soil-borne diseases, which will contribute a lot to development of green ecological agriculture. 【Method】Based on the important role of rhizodeposition in plant-soil functional feedbacks, a field experiment was carried out to study incidence variation of root knot nematode diseases and explore its relationships with rhizospheric soil properties, especially composition of rhizodeposits in tomato fields under monocropping for 2, 6 and 8 seasons and the same cultivation management. 【Result】Results show that compared with the plot of 2 season, the plots of 6 and 8 seasons were significantly lower in soil pH (P< 0.05), and significantly higher in concentration of soil total organic carbon and nitrate nitrogen. Root knot index of the tomato and incidence of the root knot nematode disease increased with the monocropping going on. A total of 150 kinds of rhizodeposits were identified with the gas chromatography/time of flight mass spectrometry (GC/TOF-MS) metabolomics, including alcohols, organic acids, amino acids, carbohydrate, terpenes, alkaloids and steroids compounds. Meanwhile, with the monocropping going on, composition and relative contents of the components of the rhizodeposits varied significantly, and the amount and relative abundance of organic acids, such as 3-(3-hydroxyphenyl) propionic acid, salicylic acid, thymol, succinic acid, lauric acid, as main components of the rhizodeposits increased, too. The network architecture analysis of soil chemical properties, rhizodeposits and root knot index shows that the network was reducing in complexity, but intensifying in modularization after continuous tomato monocropping. The compounds in the rhizosphere were quite closely related to soil chemical properties and root knot index of the tomato. Among them, 3-(3-hydroxyphenyl) propionic acid, salicylic acid and succinic acid were negatively related to soil pH, and 3-(3-hydroxyphenyl) propionic acid, salicylic acid and atropine were positively to concentration of soil NO₃^--N. The relationships between root knot index and other nodes were strengthened with the monocropping going on. 【Conclusion】In the plot of 8 season, the root knot index was negatively related to content of lauric acid but positively to concentration of soil NO₃^--N, atropine and ergosterol. The findings shows that the monocropping of tomato aggravates root knot nematode disease, which is closely related to soil chemical properties, especially variation of the rhizodeposits. Therefore, more efforts should be made in future studies, based on screening of key differential compounds, to specify, through simulation of the composition of the rhizodeposits, functions of specific compounds in the rhizosphere and their synergic effects with biological and abiotic factors on incidence of root knot nematode diseases.

Abstract:【Objectice】To investigate dynamic characteristics of the soil macrofauna community in farmlands different in corn stalk returning rate, a field survey was carried out.【Method】Soil fauna were captured by hand-sorting during the maize growth period from June to September 2016.【Result】A total of 2 681 large soil fauna were captured, belonging to 41 groups. Variance analysis shows that Treatment SR4 (13 500 kg•hm^-2 in corn stalk returning rate) increased the number of individuals of soil macrofauna significantly (P<0.05), while Treatment SR3(12 000 kg•hm^-2 in corn stalk returning rate) increased the number of macrofauna groups significantly (P<0.05). With growth of the corn in the farmland diversity index and richness index of the macrofauna varied, displaying a trend of rising first and then declining, and evenness index a downward trend, while dominance index did reversely, following a trend just opposite to that of the diversity index, that is, declining first and then rising. With growth of the corn, soil macrofuana in the 0~10 cm soil layer tended to migrate downwards to the 10~20 cm soil layer. Analysis of functional groups shows that the group of predacous macrofauna increased first and then decreased in number of individuals with growth of the corn, while. The groups of phytophagous and saprophagous fauna exhibited a trend rising with growth of the corn and in number of individuals with rising corn stalk returning rate too. However, the number of individuals of omnivorous macrofauna did not change significantly with growth of the corn by a certain degree. RDA analysis shows that the groups of soil macrofauna that were affected quite strongly by farmland soil environmental factors were mainly the dominant groups in the research area. The number of macrofauna individuals was closely related to the contents of soil organic matter and soil moisture. 【Conclusion】The dominant groups are affected by soil environmental factors. Return of corn stalk alters microenvironment of the surface soil, which in turn affects composition, distribution characteristics and functional groups of the macrofauna community. So return of corn stalk is beneficial to the development of functional groups of the soil macrofauna in farmlands.

Abstract:【Objective】 Soil aggregates, as basic units of the soil in structure, are of huge influence for water penetration and retention in soil, topsoil erosion and plant growth. Their stability is one of the main indicators in evaluation of soil anti-erodibility. Arbuscular mycorrhizal fungi (AMF) may adjust soil structure via influencing formation of soil macro-aggregates and stability of water-stable aggregates. To explore the effects and potential mechanisms of arbuscular mycorrhizal fungi (AMF) affecting formation and stability of soil aggregates in rhizosphere of mulberry, a pot experiment was carried out.【Method】In the experiment, mulberry trees were planted in the pots and the soil in the pots was inoculated with Funneliformis mosseae (F. mosseae) and Rhizophagus intraradices (R. intraradices), separately. After a certain period of cultivation, the soils in the pots were collected with the shaking off method, and separated into three aggregate fractions by particule size (0.25~5 mm，0.053~0.25 mm and <0.053 mm）using the dry and wet sieving method for analysis of composition and stability of soil aggregates, glomalin related soil protein (GRSP) and soil organic carbon (SOC) in the rhizosphere of mulberry to evaluate effects of the inoculation.【Result】 Results show that R. intraradices-inoculation expanded the fraction of macro-aggregates significantly in proportion, and increased mean weight diameter (MWD) and geometric mean diameter (GMD) of the aggregates and deceased their destruction rate (PAD), as compared to the control. Interestingly, F. mosseae-inoculation did not have much the effects. However, both F. mosseae- and R. intraradices-inoculations increased the content of SOC in micro-aggregates significantly. In addition, F. mosseae-inoculation reduced total GRSP (T-GRSP) significantly in macro aggregates, while R. intraradices-inoculatioin increased the content of T-GRSP and easily-extracted GRSP (EE-GRSP) significantly in both macro- and micro-aggregates. Inoculation of AMF had certain negative effects on overall SOC, of which T-GRSP accounted for 25.5%~76.5% and EE-GRSP did for 4.87%~5.93%, and the effects were more significant in R. intraradices-inoculted soils than in F. mosseae-inoculated ones. Moreover, the composition of soil aggregates was significantly and positively related to soil T-GRSP, EE-GRSP and SOC. Among them EE-GRSP was the main driving factor, and T-GRSP was the key factor affecting soil aggregate stability. 【Conclusion】 In short, all the findings suggest that AMF can significantly improve the composition and stability of soil aggregates in the rhizosphere of mulberry. R. intraradices was more effective than F. mosseae. The formation of soil aggregate depends mainly on EE-GRSP, while their stability is subject mainly to the influence of T-GRSP.