Abstract:The soil health status of arable land is related to national food security and ecological security. Current research on soil health assessment faces limitations such as the unclear definition of soil health and confusion of research scales. There are also drawbacks related to mainstream technology routes abroad. Based on literature research and expert interviews, we discussed the above issues from the perspective of conceptual deconstruction and proposed a research framework to provide a reference for the soil health assessment of arable land in China. Firstly, the concept of soil health based on soil functions and threats was constructed. The soil health of arable land was deconstructed theoretically into five types of soil functions:primary productivity, water purification and regulation, carbon sequestration and regulation, provision of functional and intrinsic biodiversity, provision and cycling of nutrients. Also, the idea of management and protection of arable soil health was identified. Secondly, based on the general principles of land evaluation, the soil health of arable land was divided into spatial scales, and four levels of arable soil health management goals, including field, county, province, and country, were proposed. Finally, from the above two aspects, the whole process research framework of arable soil health assessment was formed. The research framework can be summarized by the following five points:(1) the scientific connotation and assessment framework of soil health; (2) the relationship between arable soil health with soil functions and threats, and its description; (3) soil functions characterization and soil health assessment of arable land at different scales; (4) spatial differentiation characteristics and influencing factors of arable soil health at different scales; and (5) strategies and models for the management and protection of arable soil health. Nevertheless, this study is faced with the limitations of how to (i) define and quantify the supply-demand relationship between soil health status and soil functions of arable land (dry land, irrigated land, and paddy field), and (ii) scientifically select the indicators and characterization methods of soil functions to realize the expression from soil functions and threats to arable soil health? To answer these questions, more studies are recommended in this area of research.

Abstract:In China, N fertilizer use efficiency (NUE) is quite low as affected by its high-input intensive production mode in agriculture. A considerable portion of the nitrogen fertilizer applied to the cropping systems is lost to the environment as ammonia (NH₃), nitrate (NO₃), and nitrous oxide (N₂O) as greenhouse gas, thus raising agricultural production cost and aggravating environmental pollution. Nitrification is the key transformation process of nitrogen cycling in soil, and is closely related to nitrogen loss in farmland. Some plants can produce and secrete compounds that inhibit nitrification and are called biological nitrification inhibitors (BNIs). Thu use of such BNIs may be an efficient and environment-friendly nitrogen management strategy. Here, a review of recent key developments in the field of biological nitrification inhibitors at home and abroad was presented, elaborating significances, substance types, functions, secretion and mechanism of BNIs secreted by roots. Researches in the past, particularly with focus on tropical pasture grasses and sorghum, held that releasing of BNIs was a nitrogen-preserving survival mechanism plants used to adapt to low-nitrogen environments in natural ecosystems. This paper suggests that BNIs are equally important in the high-N-input agricultural ecosystems and that a certain number of food crop varieties also have high BNI activity. In addition, BNIs that are produced by plants may evolve as specific responses to nitrifying environments. The mechanisms of BNIs secretion under waterlogged and aerobic conditions are quite similar, but differ somewhat, for instance effect of the parts of the root system exposed to NH₄⁺ and pH. The hypothetic mechanism that BNIs released from plant cell membranes is proposed, for example, 1, 9-decanediol might be released via the ATP-binding cassette (ABC) transporter or members of the multidrug and toxic compound extrusion (MATE) transporter family. In terms of action targets, BNIs may regulate more ammonia-oxidizing microbial species and enzyme sites than the synthetic nitrification inhibitors (SNIs). Prospects of how to make use of BNIs in improving nitrogen utilization and reducing environmental pollution in agriculture are also discussed, such as high BNI-activity plants (such as pasture)-crop rotation, nitrogen fertilizer synergist, use of BNI traits for crop genetic improvement. For future researches, emphases should be laid on the following aspects:(1) to explore BNI functions and BNIs types in cultivation of important crops, and take into account interaction between BNIs substances; (2) to further reveal mechanism of known BNIs substances inhibiting nitrification, in addition to AOA and AOB, attention should be paid to response of the newly discovered Comammox, including other nitrogen transformation processes such as denitrification, and evaluation of potential loss of ammonia via volatilization caused by BNIs; (3) to investigate key genes and molecular genetic mechanisms regulating BNIs secretion through genome-wide association analysis (GWAS); and (4) to explore effects of BNIs in different soil conditions and with different crops in improving agriculture by field experiments, which hopefully may serve as reference for the developing of future BNIs technologies and products, improving the quality of agricultural produces, and promoting the green development of modern agriculture.

Abstract:Phosphorus (P) speciation in agricultural soils determines its transformation, transport as well as fate. A comprehensive and accurate assessment of phyto-availability and environmental risk of soil P, particularly in the long term, cannot be achieved based only on routine soil tests for total P or available P. Therefore, it is essential to fully characterize and accurately understand the speciation of soil P for sustainable P management. Past research on characterization of soil P using the technique of traditional sequential fractionation could reveal information of operationally-defined P pools only, while researchers are currently able to identify soil P species at the molecular level with the aid of advanced spectroscopic tools, among which, solution P-31 nuclear magnetic resonance (P-NMR) and synchrotron-based X-ray absorption near-edge fine structure (XANES) spectroscopies are nowadays state-of-the-art techniques. These advanced techniques substantially facilitate our understanding of the various forms of organic, and inorganic P including P associated with Fe oxides, Al oxides and Ca minerals. Based on citation network analysis using Histcite software, this paper summarized key achievements of great significance during the development of the research on soil P characterization, reviewed development context of the research in this field over the last 30 years (from 1990 to 2019). It was found that the initial understanding of molecular P speciation, particular for organic P, in soils was mainly based on the technique of P-NMR, then more comprehensive understanding of soil P speciation at the molecular level was achieved once the technique was used in combination of synchrotron-based XANES and X-ray microprobe. Finally, this review presented a perspective on future trends of the application of multiple spectroscopic techniques in the research on soil P molecular speciation.

Abstract:Soil is one of the most important reservoirs of virus genetic diversity. Due to the limitation of currently-available method for isolating and cultivating soil microorganisms, the overall diversity and function of the soil viruses remain largely unknown. Thanks to the development in the viral metagenome analysis, it is possible to directly obtain viromes from soil samples through high throughput sequencing, splicing assemble, ORF prediction, and protein annotation, which greatly enrich the understanding of soil viral functions. This review briefly summarizes the analytical methods that are extensively used in the soil virus metagenomic studies, including soil virus DNA extraction, sequencing and virus identification, functional gene annotation and etc. Meanwhile, the research progress in the phage genomes harbored in the culturable bacterial strains, and the viral metagenomes in terrestrial ecosystems were reviewed as well. This work highlights the significance of integrating currently-available virus analytical techniques, building standard viral analysis procedures, and optimizing the virus relevant databases.

Abstract:There are still some problems with the diagnostic criteria for Andisols in the "Chinese Soil Taxonomy (3rd edition, CST)", which call for further revision. To this end, evolution courses of the descriptions, diagnostic criteria, classification retrieval, and type division of Andisols in the "World Reference Base for Soil Resources (WRB, 1998-2014 edition)", the "Keys To Soil Taxonomy (KST, 3th~12th edition, 1987-2012)" and the "Chinese Soil Taxonomy (1st scheme ~3rd edition, 1991-2001)" were collated and compared in this paper. On such a basis, amendments were proposed to revise the diagnostic criteria, classification and retrieval of Andicols in CST.

Abstract:This paper was oriented to explore soil formation characteristics and classification by soil taxonomy of the soils at the south piedmont of the Tianshan Mountains in Xinjiang.A total of 8 typical soil profiles were prepared in the study area. Through profile observation and stratified sampling analysis, it was found that soil formation of the soils in the area changed in process with elevation, exhibiting a sequence of original soil forming process, organic matter accumulating process, latentizating process, maturing process and salt accumulating process.According to the "Chinese Soil Taxonomy (Third Edition)", the soils of the eight typical profiles changed with elevation from Cambosols to Gleyosols, Anthrosols, Cambosols and Aridosols from the southern foot of the Tianshan Mountains to the edge of the Tarim Basin. In line with the Taxonomy, the soils could be sorted into 4 order, 6 suborder, 7 group, 7 subgroup, 8 soil family and 8 soil series.By reference to the "Chinese Soil Taxonomy", "Chinese Soil Genetic Classification", "USA Soil Taxonomy", and "World Soil Resources Reference Base", ascription of the 8 typical soil profiles shows that the "Chinese Soil Taxonomy" puts more emphasis on characteristics of the soils in China, and hence brings forward some China-specific soil types.

Abstract:[Objective] Generally, root is the main organ of a plant to absorb water and nutrients in soil, and how it grows and distributes is an important indicator of a crop in growth and development. The commonly used methods for monitoring crop root growth, such as the soil drilling and excavation methods, are what we call destructive sampling methods. Although they are usually quite high in accuracy, they are not suitable for in situ monitoring of root growth. Therefore, the minirhizotron technique is recommended as an effective method for in-situ monitoring of crop root growth thanks to its rapid and non-destructive approach.[Method] In order to reveal impacts of salt stress on root growth of wheat, a pot culture experiment was conducted, with soil salt content varying along a gradient from 0.61(CK), 1.61(S1), 2.61(S2), 3.61(S3), 4.61 (S4) to 5.61 g·kg^-1 (S5). And the minirhizotron technique was used to- collect digital images of the roots at tillering, reviving, jointing and booting growing stages. Then root length, root length density and their distribution in the soil as affected by salt stress were determined with the aid of the digital image processing technology.[Result] Results show that with the aid of the minirhizotron technique, growth and development progresses of the wheat root in the experiment could be intuitively monitored. In the experiment the root length density obtained with the technique was found to be significantly and positively related with that with the soil drilling method (r=0.91), especially at the jointing and booting stages of the crop. Moreover, comparisons of the root images with the root parameters analysis relative to growing stage of the crop revealed that wheat root distributed mostly in the 0-10 cm soil layer and decreased with soil depth, and that root length decreased with rising soil salt content at all growing stages. For example, at the tillering stage, the root length in treatment S5 (S5, 6.61 g·kg^-1) was less than half of that in CK, and at the booting stage it was only one-third of that in CK, indicating that the wheat root growth was greatly inhibited by salt stress. The worst occurred at the booting stage, especially in the treatments with soil salt content higher than 3 g·kg^-1. It was mainly because high soil salt content caused the root rust and dead, and the higher the soil salt content was, the more obvious this phenomenon was.[Conclusion] Thus, the minirhizotron technique combined with the image processing technique could be used as a more effective method for obtaining root growth parameters as compared with traditional destructive sampling methods. This paper provides a theoretical basis and technical support for in situ monitoring intuitively of crop root growth in saline soils.

Abstract:[Objective] Biochar is an effective soil carbon sequestrator. In this study, a one year field experiment was carried out to explore variation of content and chemical structure of the humic substances (HS) in salt stress fluvo-aquic soil under wheat-corn rotation.[Method] The experiment was designed to have four treatments, that is, CK (control, no fertilizer);T1 ((NH₄)₂HPO₄ at 750 kg·hm^-2);T2 (peanut shell derived biochar 15 t·hm^-2 plus (NH₄)₂·HPO₄ at 750 kg·hm^-2);T3 (wood derived biochar 15 t·hm^-2 plus (NH₄)₂HPO₄ at 750 kg·hm^-2).[Results] Results show that biochar amendment increased the content of HS in the soil. Compared to the wheat growing season, the corn growing season had humin (Hu) increased in content by 0.54 g·kg^-1 and 0.35 g·kg^-1 in Treatments T2 and T3, respectively, and absorption peaks of the humic acid (HA), fulvic acid (FA) and Hu increased, too, in relative intensity at the 2 920 + 2 850 cm^-1 band, while it had relative area of the absorption peaks of HA and FA at the 1 630 cm^-1 band decreased by 2.46% and 5.77% in Treatment T2. Compared to Treatment T3, Treatment T2 had relative area of the absorption peak of Hu at the 1 630 cm^-1 band increased by 0.33% in the corn growing season. The peanut shell derived biochar used in this experiment was relatively higher in content of aromatic groups than the wood derived biochar. Hu increased in condensation degree, while decreased in oxidation degree in Treatment T2, however, it acted reversely in Treatment T3.[Conclusion] Biochar was conducive to increasing of the content of HS, especially Hu, and it increased Hu in condensation degree and decreased Hu in oxidation degree with the experiment going on. Application of biochar could also increase relative contents of methylene and methyl in HS. The biochars derived from different materials are different in chemical structure, which in turn affects chemical composition of the HS in the soil.

Abstract:[Objective] Cow dung is commonly used as organic manure in agricultural production. It comes up to be an important issue whether application of cow manure coupled with biochar or biochar-amended cow manure could increase net carbon transformation rate of the organic materials in soil as to high-efficient use of organic materials.[Method] In this study, a one-year field experiment was conducted to explore effect of application of biochar amended cow manure on net carbon transformation rate and structure of humic substances (HS) in soil by comparison. The experiment was designed to have four treatments, that is, M1 (cow manure at a normal rate), M2 (cow manure twice the normal rate), CBM1(M1 amended with biochar) and CBM2(M2 amended with biochar).[Results] Results show that compared with Treatment M1 and M2, Treatment CBM2 increased the content of humic acid (HA), fulvic acid(FA) and humin (Hu) up to 1.36 g·kg^-1, 2.50 g·kg^-1 and 5.03 g·kg^-1, respectively, and the net carbon transformation rate of HA and FA by 1.18% and 3.67%. Compared with the application of cow manure alone, the application of cow manure amended with biochar was much higher in relative content of aliphatic functional groups and polysaccharide in HA, FA and Hu. The amendment of biochar increased the relative content of aromatic functional groups of HA and Hu in Treatment CBM2, but decreased that of FA in Treatment CBM1.[Conclusion] All the findings show that CBM treatments are better than M treatments, forming more HS. Moreover, it also favors formation of aliphatic and polysaccharide functional groups. Biochar amendment increases the aromatic function groups of HA and Hu. In the treatments amended with biochar Hu and FA increases in condensation degree, while decreases in oxidation degree, but HA responds reversely.

Abstract:[Objective] It is very important to know how extracellular enzyme activities (EEAs) vary and what are their driving factors in reddish paddy soil under long-term fertilization. The knowledge may serve as a certain theoretical basis for improvement of soil fertility and rational fertilization in the region. To that end, this study was unfolded.[Method] Based on a long-term fertilization field experiment that was started in 1981 and designed to have four treatments, that is (CK, without fertilization), NPK (fertilizer N, P and K), HNPK (double dosage of fertilizer N, P and K), NPKM (NPK fertilizers plus organic manure), soil samples were collected separately in each plot of the treatments after the later rice was harvested in 2017 for analysis of microbial biomass and soil chemical properties. Six soil extracellular enzymes involved in C, N and P cycling, were investigated with the microplate fluorometric assay method. For exploration of the distribution characteristics of soil EEAs and their relationship with soil nutrients and microbial biomass carbon and nitrogen in the reddish paddy soil, principal component analysis (PCA) and redundancy analysis (RDA) were performed.[Result] Results show that long-term fertilization increased soil nutrient content and rice yield. Compared with no fertilization control (CK), treatment NPKM increased soil microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) significantly or by 60.2% and 60.4%, respectively, and soil AG, BG, NAG and ACP activities by 12.7%, 41.1%, 36.2%, and 50.0%, respectively, but reduced POX activity by 29.7%. The variations of EEAs were closely related to soil nutrient factors, among which soil total nitrogen (TN) and MBC might be the key determinants, accounting for 34.3% and 20.9% of the variation of EEAs, respectively.[Conclusion] It can be seen that the combined application of chemical fertilizer and organic manure is beneficial to improvement of soil fertility, microbial biomass and soil extracellular enzyme activity, and considered as the best fertilization management practice to maintain crop yield and improve soil quality.

Abstract:[Objective] Soil organic carbon (SOC) varies sharply with time and space, as it is always subject to influences of various soil-forming factors, natural environmental factors and human activities. So to determine how an appropriate number of sampling sites could affect accuracy of the prediction of SOC in different time periods is the basis for formulating a scientific strategy for high-efficient soil sampling.[Method] In this study, a tract of upland (3.93×10⁴ km²) in North Jiangsu was delineated and selected as a case area, and the Ordinary Kriging interpolation method commonly used in soil science was adopted in analyzing influences of numbers of sampling sites on prediction and mapping of SOC in different time periods. The study was designed to have 20 treatments, which were set in accordance with the principle of 5% decrease in number.[Result] Results show that with the number of soil sampling sites decreasing from 100% to 5%, correlation coefficient (r) between the predicted value and the measured value of SOC in 1980 and in 2008 varied in the range of 0.15-0.56 and 0.24-0.63 and root mean square error in the range of 2.09-2.63 and 2.11-2.62 g·kg^-1, respectively. As in 1980, the SOC in the studied region varied quite slightly in spatial autocorrelation and quite drastically and locally, its prediction improved slowly and unsteadily in accuracy, and around 563 samples were needed to make the prediction relatively reliable. However, in 2008, the SOC in the region varied quite sharply in spatial autocorrelation, but mildly locally, and hence its prediction was very sensitive in accuracy to variation of the number of sampling sites. So 526 soil sampling sites were enough to ensure stable prediction accuracy. Standard root mean square errors of the 20 treatments in terms of number of sampling sites varied in the range of 0.34-0.43 and 0.20-0.25 g·kg^-1, in 1980 and in 2008, respectively, and spatial prediction was higher in 2008 than in 1980 in accuracy when the numbers of soil sampling sites were the same.[Conclusion] Results of this study indicate that the optimal number of soil sampling sites and their prediction accuracy in the same area are not fixed, but determined in the light of spatial variability of soil attributes, distribution and spatial layout of the sampling sites in each time period. As environment, climate and farmland management practices all vary with time period, SOC content does too in spatial structure and layout, which will greatly affect the optimal number of sampling sites relative to time period.

Abstract:[Objective] Soil aggregates are the basic units structing soils, and their stability is an important index for evaluating soil breaking-down resistance under external forces. However, the current methodologies commonly used to analyze stability of soil aggregates rarely take into account influences of native soil particles on stability of soil aggregates relative to breaking-down mechanism. The purpose of this study was to fill up the gap by conducting an in-lab experiment.[Method] For the experiment, five undisturbed soil samples, 0-20cm in depth, were collected randomly using the S-shaped sampling method from each of the two tracts of land different in soil texture, one slope farmland of loamy sand soil in Shenmu County of Shaanxi Province, China and one newly established citrus orchard of sandy clay loam in Zigui County of Hubei Province, China. Following the LB (LeBissonnais) method listed in the international standard, the whole soil samples were pretreated separately with fast wetting (FW), slow wetting (SW), and mechanical breakdown by shaking after pre-wetting (WS) for analysis of breaking-down mechanisms of soil aggregates. At the same time, attempts were made to separate native soil particles from soil aggregates of various particle size fractions, so as to eliminate the influence of the former on fractionation of soil aggregates. Then soil aggregates in each fraction were treated with hydrogen peroxide to remove organic matter, and with sodium hexametaphosphate to separate native soil particles from skeletal materials of each fraction. The net mass of soil aggregates was obtained by substracting the mass of the soil aggregates of each particle size fraction in the soil samples treated with hydrogen peroxide and sodium hexametaphosphate from the mass of the soil aggregates in the soil samples before dispersion.[Result] Results show that two soils differ quite sharply in particle size distribution with the treatment. Mean weight diameter (MWD) was higher for the sandy clay loam soil than for the loamy sand soil regardless of breaking-down mechanisms. The two soils both followed an order of MWDfw < MWDws < MWDsw. Treatment FW is the most significant in affecting breakdown of soil aggregates, which is mainly attributed to pressure of the air enclosed in soil pores, and Treatment WS and Treatment SW follows. Based on the findings in this study, a new aggregates determination method is developed to verify the calculation results of the two selected regions. The influence of native soil particles on soil aggregate stability depends on soil texture and aggregates breaking-down mechanism and is much greater in the loamy sand soil than in the sandy clay loam, and exhibits an order of FW > WS > SW, in terms of breaking-down mechanism. The proportion of aggregate (>0.05 mm) to the total soil mass content (AR) before dispersion of the soil could hardly reflect stability of the soil aggregates. Variation of the AR before and after the influence of native soil particles is removed indicate that the influence of native soil particles is far more greater in the loamy sand soil than in the sandy clay loam.[Conclusion] The influence of native soil particles on aggregates varies sharply with soils type and treatment method. After eliminating the influence of native soil particles, AR can better reflect stability of the soil aggregates.

Abstract:[Objective] Once surface runoff gets coupled with subsurface water flow, severe soil erosion would be triggered off. As one of the key parameters of soil erosion, sediment transport capacity is of important theoretical significance to perfecting the knowledge about soil erosion process as affected by subsurface water flow.[Method] With the aid of certain experimental methods and devices, an experiment was designed and carried out with nozzles laid out at different locations under an artificial slope of purple soil to supply water from the bottom, so as to simulate subsurface water flow. Through a series of tests, sediment transport capacity of rill flow was determined as affected by water saturation depth (5, 10 and 15 cm) in the subsurface, flow rate (2, 4 and 8 L·min^-1) and slope gradient (5°, 10° and 15°). A multivariate nonlinear equation was used to analyze effects of flow discharge, slope gradient, subsurface water saturation depth and their interaction on sediment transport capacity.[Result] Experimental results show that the maximum volume of sediment increased with increasing subsurface water saturation depth, but it increased more when the saturation depth reached 5-10 cm than when it did 10-15 cm. When the subsurface water saturation depth increased from 5 to 15 cm, the increment rate of rill sediment transport capacity varied from -6.67% to 43.24% on the slope of 5°, from 2.22% to 15.37% on the slope of 10°, and from 0.99% to 11.54% on the slope of 15°, which indicate that rill sediment transport capacity increased as subsurface saturation depth increased, but with the increment rate declining and gradually leveling off in the end. And the determination coefficient of the equation fitting sediment transport capacity with subsurface water saturation depth was 0.87-0.99, but when the flow discharge was 2 L·min^-1 on the slope of 5°, the determination coefficient was only 0.35, because there was no interaction between subsurface water flow and surface runoff. Moreover, a nonlinear correlation equation was established for fitting relationships between slope gradient, flow discharge, subsurface water saturation depth and sediment transport capacity with a determination coefficient of 0.98. Compared with the slope gradient, the flow discharge was a more important factor affecting sediment transport capacity.[Conclusion] Sediment transport capacity is positively related to slope gradient, flow discharge and subsurface water saturation depth, but as it is rising on, it is losing its momentum gradually. Subsurface water saturation depth is an important factor affecting sediment transport capacity, exhibiting an exponential relationship. With the presence of subsurface water flow, flow discharge and slope gradient interacts significantly with each other, and subsurface water saturation depth and flow discharge does too. All the findings in this experiment may provide a certain theoretical and scientific basis for elucidating the mechanism of the coupling of surface runoff and subsurface water flow affecting soil erosion. Therefore, in the study on erosion control on slope farmlands of purple soil and related soil erosion prediction models, it is essential to recognize the importance of subsurface water flow in the effort to improve rationality of the prevention and control measures and accuracy of the prediction models.

Abstract:[Objective] The impact of crop cover and management on soil erosion is usually expressed as C, which comes from the US Universal Loss Equation (USLE). It is an important factor that must be thoroughly studied for effective control of soil erosion. At present, China has a large number of models for calculating C numerically by vegetation coverage, and their relationships are various in form. However, vegetation coverage is only one of the indicators characterizing surface crop coverage, and it does not reflect any impact of field management measures on soil loss. Moreover most of the modeling methods are just based on direct regression analysis.[Method] Therefore, in this study, the crop of soybean was taken as the research object, and artificial rainfalls were simulated outdoor. A C estimation model was designed with vegetation coverage as its key factor, and plant height, crust thickness, and surface roughness as adjustment factors for zeroing approximation errors.[Result] The obtained model formula goes like:C=-0.595ln0.01V×(-0.779x₁+0.439x₂+0.061h-0.357). In the formula, V stands for vegetation coverage (%); h for plant height(cm); x₁ for crust thickness (mm); and x₂ for surface roughness (dimensionless). Of the model, R²=0.935, and the root mean square error is only 0.089.[Conclusion] The findings of this study may serve as a theoretical reference for continuous improvement of the C factor model for agricultural soil in the Loess Plateau.

Abstract:The knowledge about chemical weathering characteristics of the loess-paleosol sequence is of great significance for understanding how inland Asia aridifies, East Asian monsoon evolves and how global carbon cycle goes. However, very little is known about chemical weathering characteristics of the loess-paleosol sequence in Harbin, which is located at the easternmost end of the Eurasian loess belt and the forefront of the eastward movement of the aridification process of inland Asia.[Objective] This study is to explore chemical weathering characteristics and paleosol formation environment of the Huangshan rock core in Harbin.[Method] Samples of the loess-paleosol sequence were collected and analyzed for elemental geochemical properties, magnetizability and heavy mineral contents.[Result] The color of the paleosol in Harbin is grey-brown and grey-black, which is dramatically different from those(brownish red) in other areas. The loess-paleosol sequence is 68-74(on average 72) in CIA(Chemical Index of Alteration), which suggests that the sequence is moderate in chemical weathering. However, compared with the loess layers, the paleosol layers do not show any signs of higher degree of chemical weathering, but are quite close to or even lower than the loess layers in chemical weathering degree. The S1 and S3 paleosol layers were the lowest even among the loess-paleosol sequence. The loess layers in Huangshan rock core contain mainly SiO₂(61.02%), Al₂O₃(19.51%), Fe₂O₃(4.19%) and K₂O(3.03%), together amounting to 87.75% of the total of the loess layer in mass, while the paleosol layers contain SiO₂(65.85%), Al₂O₃(19.33%) and Fe₂O₃(4.23%), amounting to 89.41%. In terms of α^Al index characterizing element migration ability, the elements in the loess-paleosol core follow an order of α^Al_Ca(6.2) > α^Al_Na(2.8) > α^Al_Sr(2.0) > α^Al_Fe(1.53) > α^Al_Mg(1.51) > α^Al_K(1.46) > α^Al_Ba(1.28) > α^Al_Rb(1.23) > α^Al_Ti(0.91) > α^Al_Cs(0.75), showing relative depletion of element Ca, Na, Sr, Fe, Mg, K, Ba and Rb and relative enrichment of Ti and Cs elements in the process of chemical weathering. Magnetic susceptibility and heavy minerals analyses show that the paleosol is significantly lower than the loess in magnetic susceptibility(MS), and in content of ferromagnetic minerals too. as the ferromagnetic mineral in the paleosol is mainly magnetic hematite-limonite that does contain magnetite, while that in the loess is magnetite. The Huangshan core is 0.4 and 0.1 in average return coefficient(BA) and ba value(Bc), respectively, and the paleosol layer is higher than the underlying loess layer in Rb/Sr ratio, indicating that the paleosol layers were formed under a wet climate.[Conclusion] The Huangshan rock core has experienced moderate chemical weathering. Although the paleosols in Harbin were the products of the interglacial climate, they formed under cold and wet climate, thus keeping the paleosols less chemically weathered than the loess. Moreover, the cold and wet soil-forming environment also caused reduction and decomposition of the magnetite in the paleosol layer, thus making the paleosol layers relatively lower than the loess layers in MS. The soil forming environment of Harbin paleosol is similar to that of the Heilongjiang black soil, which, hence, can be called paleo-black soil.

Abstract:[Objective] As clayey soil contains much clay and clay loam, it is rather complex in dielectric polarization. However, not much study has been done on mixed dielectric models for measurement of water content.[Method] In this study, based on the theory for bilinear dielectric measurement, dielectric spectra were determined, separately of soil samples, 0, 5%, 10%, 15%, 20%, 25%, and 30% in volumetric water content, prepared out of each of the 4 clay soils different in texture were determined, separately, within the frequency band of 0.001~3 GHz.[Result] Dielectric value (the real part of complex dielectric constant and apparent dielectric constant) is relatively stable within 300.4~2 952 MHz, but varies sharply with volumetric water content. The band of 1 050~1 503 MHz is the ideal frequency band in the frequency domain for predicting clay water content, and 1503 MHz is the optimal frequency point. At this point, two empirical models for predicting water contents in clayey soils in the frequency domain were constructed. In analyzing clay samples and validation samples, comparisons of the values predicted with the real part of the complex dielectric model with the measured values of water content show that the predictions are all higher than 0.9600 in R², lower than 0.0190 in RMSE, and higher than 5.000 inn RPD. In analyzing clay soil samples, comparisons between the values predicted with the apparent dielectric model formula and the measured values show that R²=0.9669, RMSE=0.0176, and RPD=5.515. Compared with the Topp model, Roth model and Malicki model, the apparent dielectric model yields values much closer to the measured value. In analyzing verification samples, comparison between the values predicted with the apparent dielectric model and the measured values show that R²=0.9537, RMSE=0.0208, and RPD=4.602.[Conclusion] The bilinear theory is quite high in applicability to the measurement of clay soil moisture content with the dielectric method. The two empirical models constructed in this paper are fairly high in accuracy in predicting water content in soils clayey in texture.

Abstract:[Objective] As one of the major species that have invaded into China, Spartina alterniflora(S. alterniflora) significantly affects the carbon storage and carbon cycle process in the coastal wetlands it has colonized. Close monitoring of spatiotemporal variation of soil organic carbon (SOC) in S. alterniflora invaded wetlands will facilitate scientific evaluation of impacts of this species on wetland ecosystems. The objective of this study is to investigate potential of the visible and near infrared reflectance spectroscopy in predicting soil organic carbon content in this kind of coastal wetlands. It is expected to provide certain important evidence of the impacts of the invasive S. alterniflora on wetlands.[Method] A soil survey was carried out in a tract of S. alterniflora invaded wetland typical of the coastal Jiangsu for acquisition of detailed soil——vegetation information with the space-for-time substitution method. In the surveyed area, 15 soil profiles were prepared randomly over the area for collection of soil samples, 3 each at different depths (0-30, 30-60, 60-100cm) in line with the stratified random sampling strategy, making up a total of 45 samples. The soil samples were analyzed in the lab for soil reflectance spectrum (R) and SOC content. With the aid of the partial least squares regression (PLSR) method, SOC prediction models were built up based on six forms of spectral transformation(R, R', R'', 1/R, (1/R)', (1/R)''), evaluated for performance by root mean square error(RMSE), coefficient of determination(R²) and residual predictive deviation(RPD), and analyzed for influence of auxiliary variables(like S. alterniflora invasion history and soil depth) on prediction accuracy.[Results] SOC content increased significantly in the surface soil after the invasion of S. alterniflora, and declined with depth. In the study area, mean SOC content was 7.37 g·kg^-1 in the 0-30 cm soil layer, with variation coefficient being 18.13%, and fell down to 4.39 g·kg^-1 in the 60-100 cm soil layer, with variation coefficient being 36.26%. Spectral curves of the soil samples appeared to be quite similar in shape, with three distinctive absorbance valleys, separately, at 1 400, 1900, and 2 200 nm. Relative to the models containing spectral information only, the hybrid models established by amendment of auxiliary variables were much higher in prediction accuracy. At the same time spatio-temporal variables could explain, to a certain extent, spatial heterogeneity of the spectral features of the soil. Cross validation shows that the PLSR models with spectra and their transformation forms as its single auto-variable was quite limited in prediction capacity, with R² varying between 0.41 and 0.58 and RPD between 1.12 and 1.31 obtained with two validation methods. Once the PLSR models were established with auxiliary variables amended, their evaluation parameters ought to be improved to a varying extent.Among the tested models, the hybrid model based on spectrum transformation was the highest in prediction accuracy with R² being 0.68 and an RPD being 1.6. A small sample size used in the study was probably one of the causes leading to relatively low prediction accuracy.[Conclusions] All the findings in this study demonstrate that the visible-near-infrared spectroscopy can be used to effectively predict soil organic carbon content in the coastal salt marsh colonized with S. alterniflora. The amendment of spatio-temporal auxiliary variables, like soil depth and plant invasion history, may improve the models in prediction accuracy to a certain extent, and the utilization of the spectral technology may help realize real-time monitoring of soil carbon dynamic in coastal wetlands invaded by S. alterniflora. Moreover, this study may be of certain reference value to using relevant auxiliary variables in guiding soil sampling for accurate prediction of soil properties.

Abstract:[Objective] Adsorption-desorption of Sb on micro-interfaces of soil colloids deeply affects its mobility, transformation and fate in the soil environment. Various soil minerals, organic matter (OM), microbes and soil colloids often combine with each other to form complicated mineral-organic complexes, which vary in properties (e.g., surface charge, particle size and the functional groups) with their composition and hence affect adsorption-desorption of the trace element differently. So far, though much have been done on the behaviors of antimony binding to single soil components, little attention has been paid to adsorption processes of Sb to mineral-organic composites and its mechanism.[Method] In this study, a batch adsorption experiment was carried out to investigate Sb (V/Ⅲ) adsorption behaviors on the interfaces of typical aluminum oxide-bacteria composites different in component ratio (30:70 and 70:30), with the aid of spectroscopic techniques and to validate whether bacteria affect Sb oxidation on mineral surfaces and to explore underlying mechanisms.[Result] Nano-sized particles of α-Al₂O₃ over on the surface of Bacillus cereus form an incomplete "mineral film", which may suggest that some of the available adsorption sites on either the mineral or the bacterial cells are covered or blocked. The Langmuir model can adequately describe Sb adsorption isotherms with a goodness of R²>0.98; α-Al₂O₃ adsorbs much more Sb (~50 mg·g^-1) than bacterial cells(15-24 mg·g^-1), which may be explained by difference in surface charge property, i.e., bacteria are negatively charged whereas α-Al₂O₃ is positively charged; the binding of Sb to α-Al₂O₃-bacteria composites does not follow the "component additive rule", i.e., the sum of the individual adsorptivities, but is significantly enhanced compared to the predicted assuming additivity. Scanning electron microscopy-energy spectrum analysis shows that the elemental distribution of Sb is highly correlated to that of Al rather than C, suggesting that Sb is mostly bound to minerals in the binary composites; and XPS analysis shows that the AlOH group of α-Al₂O₃ and the COOH and NH₂ groups of bacteria are all involved in binding Sb in the binary composite, possibly through formation of strong inner-sphere type complexes; moreover, bacteria inhibit oxidation of Sb (Ⅲ) on the surface of α-Al₂O₃, probably indirectly by hindering electron transfer between Sb and α-Al₂O₃.[Conclusion] All the findings in the study suggest that bacteria affect not only the quantity of Sb adsorbed onto Al minerals, but also oxidation-reduction of the element, therefore mineral-organic interaction should be taken into account in predicting transformation, translocation and fate of antimony in soils.

Abstract:[Objective] Phenol is a common organic pollutant that comes along with wastewater discharged from chemical industries. Clay minerals are abundant in reserve and high in adsorptivity, and hence have good prospects in application as adsorbents. The technology of magnetization and amphoteric modification can keep clay minerals capable of adsorbing organic and heavy metal pollutants and separating solid from liquid as well, which is conducive to material recycling. However, so far little has been reported about researches on comparison between different types of magnetized and modified clay minerals in adsorption of phenols and its mechanism, which though has certain practical significance for the application of amphoteric modified magnetic clay minerals to treatment of organic wastewater pollution.[Method] Magnetic sepiolite (MST), magnetic zeolite (MZT) and magnetic attapulgite (MAT) were prepared using the co-precipitation method, and then modified separately with the amphoteric surfactant dodecyl dimethyl betaine (BS-12). X-ray diffraction (XRD) was performed to characterize these adsorption materials, and then batch method was adopted to compare the three BS-12 modified magnetic clay minerals in phenol adsorption characteristics, while effects of temperature, pH, ionic strength and modification degree on the clay minerals adsorbing phenol were also investigated.[Result] Results show that in terms of phenol adsorption capacity of the three natural clay minerals and the three magnetized clay minerals exhibited an order of NAT > NST > NZT, and MAT > MST > MZT, respectively, and magnetization had the highest effect on the phenol adsorption capacity of attapulgite, which is highly related to the high Fe₃O₄ coverage on attapulgite. Once modified with BS-12, the three modified magnetic clay minerals increased in phenol adsorption capacity with increasing modification degree, showing a consistent trend; Among the three magnetic clay minerals, magnetic sepiolite increased the most phenol adsorption capacity in response to the BS-12 modification, which is related to its higher BS-12 modification rate. The increase in temperature or pH was not conducive to phenol adsorption on the BS-12-modified magnetic clay minerals, but the increase in ionic strength did have some positive effect.[Conclusion] Phenol adsorption on BS-12-modified magnetic clay minerals is dominated by hydrophobic partitioning, and phenol adsorption capacity of the minerals depends on organic carbon content. Among the three BS-12 modified magnetic clay minerals, BS-12 modified magnetic attapulgite has the highest phenol adsorption capacity as it has the highest organic carbon content, and it capacity is rarely affected by temperature, pH and ionic strength.

Abstract:[Objective] Organo-mineral complexes(OMC) in red soil vary significantly in mineral composition and surface properties, and have a profound impact on the environmental chemical behavior of heavy metals (HMs) in the soil. Though a large volume of researches have been done using models to predict pollutant behaviors in actual soil systems, it is still difficult to make accurate prediction due to the complexity of OMC. In this study, efforts were made to investigate elemental composition and mineral composition of the particulate organic matter (POM) and organo-mineral complexes (OMC) fractions, obtained from an actual red soil from Qiyang of Hunan, and furthermore, Cu (Ⅱ) adsorption behaviors, element micro-distribution and molecular binding mechanism of the Cu (Ⅱ) on the bulk soil(BS) and OMC, so as to specify Cu (Ⅱ) adsorption capacity of and molecular binding mechanism of Cu (Ⅱ) to the OMC in the actual soil system.[Method] POM and OMC were obtained from the bulk soil through density fractionation. X-ray diffraction analysis was performed to determine mineral compositions of the BS and OMC. Free Fe oxides were extracted with the DCB method and amorphous Fe oxides with the acidic ammonium oxalate method, and then determined with ICP-OES. C and N contents were measured with the Elementar Vario MACRO. Moreover, theoretical maximum Cu (Ⅱ) adsorption capacity of the samples were investigated through batch adsorption experiments. Then Cu (Ⅱ) adsorption in the samples were measured with the Scanning transmission X-ray microscopy(STXM) to specify micro-distribution of target elements (C, Fe, Cu, Al and Si) and molecular mechanism of Cu (Ⅱ) immobilization.[Result] Element analysis shows that the OMC is the main component of soil, and has organic matter with lower C/N ratio than the BS. XRD shows that the OMC consists mainly of clay minerals. The Cu isothermal adsorption curves of the OMC and BS could be well fitted with the Langmuir and Freundlich equations. Both the OMC and BS exhibit similar Cu adsorption curves, and equivalent theoretical maximum Cu (Ⅱ) adsorption capacities, which indicated that Cu (Ⅱ) adsorption is determined mainly by OMC in the red soil. With the aid of STXM, micro-distributions of Cu, C, Fe, Al and Si in BS and OMC of the adsorption samples are characterized on the submicron scale. The results indicated that the distribution of Cu in red soil is spatially heterogeneous, and Cu is mainly combined with the OMC formed by organic faction with carboxylic carbon and iron oxide.[Conclusion] Red soil is mainly composed of the OMC, which mainly determine the distribution and adsorption behavior of Cu (Ⅱ) in the red soil. The carboxylic carbon and iron oxides of the OMC serves as the binding sites of Cu (Ⅱ). Therefore, the OMC of the red soil predominantly controls Cu (Ⅱ) adsorption, and thus determines the availability and mobility of Cu (Ⅱ) in the red soil.

Abstract:[Objective] Soil fauna are an important indicator for quality assessment and monitoring of contaminated soils. However, few studies have been reported in the literature in China on community structure of Collembola and variation characteristics of certain specific species in soils contaminated with heavy metals in mining areas. In order to explore relationship between heavy metal pollution in soil and community structure of Collembola, toxic effects of the pollution on collembolan and law of the response of collembolan to the pollution, in an attempt to provide a scientific basis for assessing and monitoring soil quality.[Method] In this paper, on the farmlands around the Lanping lead-zinc mining in Yunnan Province, four sample belts, A, B, C and D were laid out, varying in distance from the mining. Among them, A, B and C were belts of contaminated farmlands and D the one free of contamination as CK. And in each belt, 3 sampling points were arranged at the same intervals along a line vertical to the river running through the belts. Point 1 was the closest to and Point 3 the farthest away from the river. So a total of 12 sampling points were specified for soil sampling, and three soil samples were collected quantitatively from each sampling point for identification and count of collembolan and analysis of soil heavy metals, physicochemical properties and heavy metals in collembolan, separately, and each soil sample was divided into 5 portions as replicate for the analysis of species diversity and community structure of collembolans, heavy metal content in their bodies and heavy metal content and physicochemical properties of the soils.[Result] A total of 1 445 collembolan individuals of 26 species were acquired, belonging to 2 orders, 6 families and 15 genera and reaching 12 042 ind·m² in average population density. The Collembola community was characterized by apparent dominancy with specific groups and relative deficiency in diveristy. The farther the sample points from the mining or the river, the lower the content of Cd, Pb and Zn in the soil, the lower the content of heavy metals in the collembolan body, and the higher the species richness(number of species), richness index and abundance of collembolans(density). And responses of the animals were greater to the content of available heavy metals than to the total heavy metals, especially in species richness and heavy metal content of collembolans. Onychiurus sp. was negatively related to the content of available Pb in population density. The three species of Isotoma were all negatively related to both total and available Cd. and Isotoma sp. 3 was negatively related to total and available Zn. Lepidocyrtus sp. was positively related to total Cd, Pb and Zn. Besides, Onychiurus sp. and Onychiurus folsomi were positively related to soil organic matter. Hypogastrura yosii was positively related to soil pH. Isotoma sp.1 was positively related to soil pH and soil bulk density.[Conclusion] Structure of the Collembola community and distribution of certain species in the farmland system around the lead-zinc mining area were significantly affected by heavy metal pollution:The collembolan community responded greatly to heavy metals in species richness, richness index and abundance, and was more sensitive to available heavy metals than to total ones. So the contents of available heavy metals are good indicators reflecting change in Collembola community. Onychiurus sp., the three species of Isotoma and Lepidocyrtus sp. possess the potential to act as indicator for assessment of heavy metal pollution and so do Onychiurus sp., Onychiurus folsomi and Isotoma sp.1 for assessment of soil quality.

Abstract:[Objective] Watermelon is susceptible to infection of Fusarium oxysporum, which causes it to wilt. Colonization of Arbuscular mycorrhizae (AM) on roots of the plants can not only effectively promote plant nutrient uptake, but also help prevent diseases. However, direct inoculation of arbuscular mycorrhizae in the field may in most cases affect its infection efficiency and ecological effects.[Method] In this study, Rhizophagus intraradices (R.i), was inoculated directly to watermelon seedlings in nursery to culture arbuscular mycorrhizae inoculated watermelon seedlings, some of which were then transplanted into pots for observation of how the inoculation helped the seedling to resist wilt disease and for analysis of its mechanism. Meanwhile activities of wilt-resistance related enzymes and their encoded gene expression were determined for analysis of mechanism of AM helping the seedlings resist wilt disease. Besides, some of the inoculated seedlings were transplanted into fields for exploration of effect of the inoculation helping the plants resist wilt disease and improve P nutrition in the field.[Result] Results show that watermelon seedlings inoculated with arbuscular mycorrhizae in nursery maintained their mycorrhizal colonization after transplanting, and even up-regulated the expression of chitinase-encoding genes of ClPR4 and ClPR5 and the expression of β-1,3 glucanase gene ClGlu3 and Phenylanlanine ammonia-lyase encoding gene ClPAL4 and ClPAL11 in their root systems. Chitinase activity in rhizosphere of the watermelons increased significantly, but β-1,3 glucanase and phenylalanine ammonia-lyase activities were unchanged. Meanwhile, the inoculation significantly reduced the number of pathogens in watermelon rhizosphere soil, increased the number of arbuscular mycorrhizal spores, and improved the watermelon root system environment, thus reducing wilt incidence of the plants by 22.22%, and disease index by 23.15%, and consequently increasing the disease controlling effect up to 36.23%. Moreover, the inoculation enhanced the activity of acid phosphatase in the rhizosphere soil, thus increasing the availability of phosphorus in the soils, optimizing phosphorus nutrition of the soil and eventually improving disease resistance of the crop.[Conclusion] When watermelon wilt disease occurs, colonization of AM fungi can increase activities of the disease resistance-related enzymes by increasing the expression of ClaPR4, ClaPR5, ClaGlu3 and ClaPAL4 in the watermelon root system, thereby improving disease resistance of the watermelon; inoculation of seedlings with arbuscular mycorrhizae can improve microbial environment of the plant root, and promote hydrolysis of insoluble phosphorus by stimulating the activity of acid phosphatase in the rhizosphere soil, thus increasing the content of available phosphorus in the soil and promoting absorption of the nutrient by watermelon, and eventually improving disease resistance of the crop, reducing the incidence index of watermelon wilt. It is, therefore, concluded that inoculation of the seedlings of watermelon with arbuscular mycorrhizae can effectively prevent occurrence of Fusarium wilt.

Abstract:[Objective] To tackle the present problem of fertilizer response modeling being generally low in success rate, this paper was devoted to discussions about strategies to optimize modeling and to improve its success rate.[Method] Based on collation and analysis of the following four modeling methods, i.e. nonlinear least-squares (NLS) modeling method for ternary non-structured fertilizer response model (TNFM), and ordinary least squares (OLS) method, principal component regression (PCR) method and feasible generalized least squares regression (FGLS) method for ternary quadratic polynomial fertilizer response mode l(TPFM), for adoptability and 1122 NPK fertilizer field experiments conducted in paddy fields and open vegetable gardens, an optimal modeling technology was designed and brought forth for comprehensive application of ternary fertilizer response models.[Result] Results show that ternary fertilizer response modeling using different functional equations and different modeling methods varied significantly in adoptability. The OLS modeling method for TPFM reached only 19.8% on average in proportion of typical models, while the PCR and FGLS modeling methods that had overcome the impacts of multicollinearity and heteroscedasticity, did up to 34.0% and 27.1%, respectively, and the NLS modeling method for TNFM after overcoming the obstacles of model specification bias and multicollinearity simultaneously rose further up to 41.4%, which improved the success rate of modeling. Using the classical OLS modeling method for TPFMs, the modeling had 28.7% failing the Duncan test, 30.1% having unreasonable model coefficient symbols, 15.2% missing maximum yield points and 6.1% extrapolating fertilization recommendation. However, the PCR modeling method reduced significantly the proportion having unreasonable coefficient symbols and increased that extrapolating fertilization recommendation, and the FGLS modeling method brought down to zero the proportion failing the Duncan test, but increased by a large margin in the proportion having unreasonable coefficient symbols. The ternary non-structural fertilizer response model significantly reduced the proportion having unreasonable coefficient symbols or missing maximum yield points, while increasing the proportion of non-typical models extrapolating fertilizer recommendation. Since agricultural production goes on in conditions of extreme complexity and diversity, it is certain that the curve or curved surface that reflects crops response to fertilization diversifies. Therefore, in the light of the applicability of the models and their modeling methods, a four-step modeling method is brought forth herewith for comprehensive application of the ternary fertilizer response model, which may raise the proportion of typical models up to 57.5%, and minimize the differences between double-cropping rice, single-cropping rice and vegetable crops in relevant proportion.[Conclusion] The four-step modeling method is an effective technical method to improve success rate of the modeling for ternary fertilizer response models.

Abstract:[Objective] Rice paddy soil has long been an important soil resource for farming and developed into various types under the impact of long-term anthropogenic actions. Yet, little is known about microbes in the paddy soils. To determine factors affecting soil microbial communities in the paddy soils, soil samples of four types of paddy soils (Sublayer Shajiang soil, Red soil, Black soil and Purple soil) were collected from major rice-production regions (Jiangdu of Jiangsu, Yingtan of Jiangxi, Changchun of Jilin, and Yanting of Sichun, respectively).[Method] To explore abundance of the soil microbial community in the soil samples, the real-time quantitative PCR was used, and to characterize diversity and composition of the soil microbial community, the 16S rRNA genes high-throughput sequencing was performed. With the aid of the field-based ¹⁵N₂-labeling technique, biological nitrogen fixation (BNF) rates in the four types of paddy soils were assessed.[Result] The number of 16S rRNA gene copies in paddy soils ranged from 1.8×10⁷ to 6.7×10⁹ copies·g^-1 dry soil. Statistical analysis shows that the number of 16S rRNA gene copies in Red soil was significantly higher than those in the other soils (P<0.05). A total of 666 738 raw sequences were obtained from 12 samples with the technique of 16S rRNA genes sequencing and were normalized to 38 715 per sample for the downstream analysis. These sequences were clustered into 13 097 OTUs. Taxonomic analysis shows that the bacterial communities in the four types of paddy soils were dominantly Proteobacteria, Actinobacteria, Chloroflexi and Cyanobacteria. Results show that observed OTU number and Chao 1 and PD indices of the soil bacteria were much lower in Red soil than in the other soils. Correlation analysis of abundance and diversity of soil bacterial communities and soil properties shows that 16S rRNA genes copies, observed OTU number, Chao 1 and PD indices of soil bacteria were significantly related to soil organic carbon and alkaline nitrogen content (P<0.01). Non-metric multidimensional scaling (NMDS) ordination shows that the bacterial community structures in the four types of paddy soils varied significantly (Stress<0.001). Among the soil properties analyzed, soil pH might play a key role in determining soil bacterial community structure (P<0.01). Biological N₂ fixation rate was significantly and positively related to soil pH (P<0.01). The highest biological N₂ fixation rate was found in Purple soil (3.2±0.7 mg·kg^-1·d^-1), and Leptolyngbya might be a major contributor to the BNF in Purple soil.[Conclusion] All the finding in this study highlight the influence of soil properties on soil microbial communities in paddy soils and suggest that regulation of soil pH and microbes might be a strategy to increase the BNF in paddy soils.

Abstract:[Objective] Soil labile organic carbon (LOC) is a soil component that is quite quick in turnover and quite sensitive to soil management practices. However, it is not clear how application of organic materials or manures LOC and their microbial mechanisms.[Method] In this study, a field experiment was designed to have wheat and maize planted in rotation and conducted to explore effects of returning wheat straw (R) and applying woody peat (MT) for two years in a row on potential carbon mineralization (PCM), microbial biomass carbon (MBC), dissolved organic carbon (DOC), readily oxidizable carbon (ROC) and particulate organic carbon (POC) in fluvo-aquic soil at the harvesting stage of the second maize crop.[Result] Compared with CK without any organic manure, Treatment R (returning of wheat straw) and Treatment RMT (returning of wheat straw plus application of wood peat) was 30.33% and 31.46% higher in DOC and 104.86% and 64.78% higher in POC, respectively. However, the treatments did not have much effect on PCM, MBC and ROC. High-throughput sequencing analysis shows that the treatments did not have much impact on soil bacterial community composition, but did have on fungi, which was mainly attributed to changes in POC, DOC and . Correlation analysis shows that DOC and POC were significantly and positively related to invertase activity. Both DOC and invertase increased significantly in Treatment R and were significantly and positively related to the abundance of Ttrichoderma peltatum and Trichoderma aerugineum. At the same time, DOC was significantly and positively related to the abundance of Pyrenochaeta unidentified, capable of promoting formation of root secretions, and Pyrenochaeta unidentified increased significantly in Treatment RMT. Both POC and invertase were significantly and negatively related to Cladorrhinum flexuosum and Basidiobolus ranarum, both of which decreased significantly in Treatment MT, while only Cladorrhinum flexuosum did in Treatment RMT. POC and invertase were also significantly and positively related to Chaetothyriales unidentified, and increased significantly in Treatment RMT.[Conclusion] All the findings demonstrate that both returning of wheat straw and application of woody peat alter the content of labile organic carbon, regardless of type, which may be attributed to the effects of the two practices affecting, separately, composition of the fungal community, thus altering abundance of the functional microbes and activity of relevant enzymes.

Abstract:[Objective] Soil nitrogen transformation is a microbially-mediated biogeochemical process that though strongly influenced by global climate change, is an effective indicator of soil. Nitrogen supplying capacity and soil nitrogen availability of a terrestrial ecosystem. Therefore, the study of characterizing soil nitrogen transformation helps to thoroughly and deeply understand the productivity and nitrogen cycling process in an ecosystem. Biocrusts, making up over 40% of the total area of the land surface cover in the arid region, is an important type of earth surface cover in desert, and a major compositions of the desert surface landscapes in the semi-arid and arid regions as well, so it plays a vital regulatory role in nitrogen cycling in arid area. This study aimed to explore responses of nitrogen transformation rate, microbial biomass carbon and nitrogen and enzyme activity in the crust-covered soil system to global warming, and reveal mechanisms of the responses from different levels (functional gene→microbial biomass→enzyme activity) in an attempt to provide a theoretical basis for studies in future to identify ecological functions of moss crusts in soil nitrogen cycling in temperate desert ecosystems under the background of climate warming.[Method] This study explored responses of soil nitrogen transformation rates, microbial biomass, enzyme activities and functional genes to warming in temperate desert ecosystems with undisturbed soil columns with moss crust cover on the surface collected from the field.[Result] Results show that soil net nitrogen transformation rates (net ammoniation rate, net nitrification rate and net nitrogen mineralization rate), enzyme (N-acetyl-β-D-glucosidase and urease) activities, abundance of microbial biomass carbon/nitrogen transformation function genes (gdh, hao and amoA) responded significantly to warming and soil type, and interactions between the two were apparent. Compared with CK, warmed moss covered soil was 49.5%, 63.2%, and 59.7%, respectively, lower in net ammonification rate, net nitrification rate, and net nitrogen mineralization rate and lower in enzyme (N-acetyl-β-D-glucosidase, leucine aminopeptidase and urease) activities. Microbial biomass carbon and nitrogen, and in abundance of ureC, hao and amoA, too (gdh exclusive). Moss crust covered soil was higher in net nitrogen transformation rate, enzyme activity, microbial biomass carbon and nitrogen, and nitrogen transformation function gene abundance than mossless soil under the same treatment.[Conclusion] To sum up, warming significantly inhibits soil nitrogen transformation process by decreasing enzyme activity, microbial biomass, and functional gene abundance, while degradation of the moss crust weakens its role in regulating the soil environment, thus accelerating the process.

Abstract:It is of great significance to compare exotic plants with their respective indigenous plants in growth and effect on soil properties for studies on mechanism of their successful invasion. Subtropical and tropical soils are often strongly weathered and hence low in phosphorus availability. Why can invasive plants, such as Wedelia trilobata, successfully invade South China, where the soil is deficient in phosphorus? An answer to this problem is of great significance for exploration of mechanism of the invasive plants flourishing in infertile soils. However, so far few reports on this topic have been found in the literature. This paper laid its focuses on soil organic phosphorus mineralization, and activities of acid phosphomonoesterase and alkaline phosphomonoesterase in the soils under W. trilobata, native plant W. chinensis and their hybrid in South China. A controlled field experiment using randomized complete block design was laid out in July 2016. The plots in the experiment were planted with W. trilobata, native plant W. chinensis and their hybrid, separately for comparison between the plots in microbial biomass phosphorus, activity of acid and alkaline phosphomonoesterase and soil organic phosphorus mineralization, and for analysis of underlying mechanisms of any possible differences. Results show that Treatment WT (W. trilobata) was higher than Treatment WC (W. chinensis) in soil dissolved organic carbon. In all the three treatments Labile-P accounted only for 2.2%~6.3% of the soil total phosphorus. Treatment WT and Treatment H (hybrid) was higher than Treatment WC in Labile-P, but lower in organic phosphorus, residual phosphorus, total phosphorus and microbial biomass phosphorus. Microbial biomass phosphorus made up 14.3%, 41.2% and 25.7% of the total phosphorus in Treatments WT, WC and H, respectively. The ratio of soil total carbon to organic phosphorus reached well beyond 200, indicating that soil phosphorus was a major limiting factor in the studied region. Soil organic phosphorus, as an important fraction in soil total phosphorus, accounted for 28.7%, 17.6% and 25.0% of the total phosphorus in Treatments WT, WC and H. Correlation analysis shows that Labile-P was significantly and positively related to alkaline phosphomonoesterase, but negatively to alkaline phosphomonoesterase. Treatments WT and H were higher than Treatment WC in activity of alkaline phosphomonoesterase, but did not differ much in activity of acid phosphomonoesterase. So, changes in organic phosphorus fractions were mainly driven by alkaline phosphomonoesterase. The findings suggest that both the invasive and native plants suffer from phosphorus deficiency, and alkaline phosphomonoesterase decomposing soil organic phosphorus may be the major mechanism of the invasive plants adapting to phosphorus limitation in the region. It is expected that this study may help understand the general rule of plant invasion in habitats poor in resource from the new perspective of soil organic phosphorus mineralization.