Abstract:Soil can exert both positive and negative impacts on human health. In this paper, three aspects of the relationship between soil and human health are discussed: 1) supply of essential mineral nutrients from soil to humans; 2) human’s exposure to toxic heavy metals and metalloids via their transfer from soil to the food chain; and 3) the spread of antibiotic resistance genes in soil. Although soils, through the food chain, are a main source of many essential mineral nutrients for humans, for some nutrients the supply may not meet the requirements of humans, especially those elements that are required by animals but not by plants. Selenium is a typical example, which is deficient in the diets of many people due to low levels of this element in the soil. Agronomic biofortification through additions of selenium in fertilizers is an effective way to increase selenium intake in the population living in the low selenium areas. Human activities have caused contamination of soil with various types of organic and inorganic contaminants. Heavy metals and metalloids such as cadmium and arsenic can be transferred readily from soil to the edible organs of crop plants, posing a risk to human health. Soil contamination coupled with soil acidification has resulted in increased availability of cadmium in soil and elevated accumulation of this toxic metal in food crops. A number of strategies can be used to reduce the accumulation of heavy metals and metalloids in food crops, including methods to immobilize contaminants in soil, cultivar selection, breeding and genetic engineering to reduce heavy metal uptake or translocation in crop plants, phytoextraction of heavy metals and metalloids with hyperaccumulators to clean up contaminated soil. Overuse of antibiotics in humans and in animal production has resulted in increased antibiotic resistance in microorganisms in the environment, which may lead to the evolution of superbugs of human pathogens. Animal manures may contain high levels of antibiotic resistant microbes and resistance genes, which can disseminate into agricultural soil via manure applications. Urgent actions should be taken to control the overuse of antibiotics in animal production. Effective methods are also needed to decrease the abundance and diversity of antibiotic resistance microbes and genes in animal manures before application to soil. It is recognized that the impacts of soil on human health are uneven across the whole population; people living in poor areas or having a low income are often more vulnerable to the negative effects of soil on human health. The relationship between soil and human health will become more prominent in the future with the dual challenges of increasing population and global climate changes. Options to alleviate the negative impacts of soil on human health and future research directions are also discussed.

Abstract:Soil erosion under forest is a typical phenomenon of hydraulic erosion in red soil hilly regions of South China. It not only causes decline of soil quality and affects productivity of forest soils, but also destroys local ecological environment and hinders development of regional economy. This study firstly analyzed causes of the soil erosion under forest in this region, reviewed progresses in current researches on prevention and control of the soil erosion under forest and then explored in depth effects and application scope of the measures so far adopted for prevention and control of soil erosion under forest on soil and water conservation, soil fertility improvement and revegetation. At the end, the paper specified deficiencies of the current researches on prevention of soil erosion under forest in this region, and presented prospects of the researches in future. The paper suggests that future efforts should be devoted to renovation of the mode for control of soil erosion under forest, development of a technology system for comprehensive prevention and control of the erosion, intensification of technical guidance on implementation of soil and water conservation measures for control the erosion, and construction of a comprehensive evaluation index system for the soil erosion control measures. It is expected that the paper may serve as a theoretical basis for selection and application of appropriate measures for prevention and control of soil erosion under forest in red soil hilly regions of South China.

Abstract:Phosphorus is a nutrient element essential to plant growth and a key one linking biological and abiotic interactions in ecosystems. An in-depth knowledge of sorption mechanism of phosphate on mineral surface is helpful to understanding the speciation, translocation, transformation, and bioavailability of phosphate in terrestrial and aquatic environments. In this paper, a review is presented of progresses in researches on phosphate sorption on mineral surface and its mechanism. Various analytical techniques or methods, such as quantitative analysis of OH- released, Zeta potential measurement (electrophoretic mobility measurement), isothermal titration calorimetry, atomic force microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy, nuclear magnetic resonance spectroscopy, X-ray absorption spectroscopy, surface complexation model, and quantum chemical calculation have been used to analyze adsorption mechanism of phosphate on mineral surface from different angles. Adsorption of phosphate on the surface of minerals (e.g., iron and aluminum oxides) is usually accompanied by exchange of aqueous and hydroxyl groups. It is generally believed that phosphate mainly forms bidentate binuclear, monodentate mononuclear inner-sphere complexes on the surface of minerals, which is greatly affected by pH. Both pH and adsorption density of phosphate on the surface of minerals affect its protonation state. Under special conditions (i.e., low pH, high phosphorus concentration, high reaction temperature, long adsorption duration, and adsorption by weak crystalline mineral), phosphate adsorbed on the surface of minerals may transform into phosphate-containing surface precipitates, thus resulting in mineral dissolution and conversion, and further decrease of phosphate bioavailability. In the end, prospects are discussed about hot spots and orientation of future researches related to phosphate sorption on the surface of minerals.

Abstract:With new antibiotics slowing down in development and antibiotic resistant genes (ARGs) popping up and spreading rapidly, antibiotic resistant bacteria (ARB) and ARGs have become imminent threats to public health and a global problem urgently calling for solution. Nowadays, the industry of livestock breeding still abuses the use of veterinary antibiotics in concentrated feeding operation in an attempt to improve growth and control diseases. It is estimated that approximately 30%~50% of the administered antibiotics are excreted with waste instead of being absorbed by animals. Manure is commonly used as a substitute for inorganic N and P fertilizers for agricultural crops, especially in organic farming. In 2013, a total of 54 000 tons of 36 antibiotics was excreted in China, 54% into the soil and 46% into the water environment. The antibiotics involved include sulfonamides, tetracycline, fluoroquinolones, macrolides, β-lactam, etc. The ARGs contained in the ARB excreted with manure, generated in microbes as a result of accumulation of antibiotics in soil, and multiplied with the proliferation of ARGs-containing microbes stimulated by manure are the main sources of ARGs in the soil. Bacterial communities in manure and in soil vary sharply in structure. The bacteria in feces can survive in soil for weeks to months, depending on soil and environment, however, horizontal gene transfer from these bacteria to indigenous soil bacteria might rely on persistence of ARGs in soil. As one of the largest and most diverse microbial habitats on earth, soil has been the source of most discovered ARGs, supplying ARGs to water environment, crops, and animals and human through food chain. Once ARB and their corresponding suite of ARGs enter the soil, water and crops, their persistence and fate depend on nature and viability status of their host bacteria and their living environment. Both natural factors, like temperature, rainfall, time and soil type, and human factors, like content and specie of antibiotic, type and treatment of manure, content of heavy metal and biochar addition, could affect persistence and diffusion of ARGs in soil. However, the impacts of manure application contaminating the soil with ARGs on environmental quality and human health still remain unclear. It is, therefore, suggested that studies should be intensified on modelling, source tracing, biogeographical distribution, rules of ARGs transferring from sources to environmental media, measures to reduce and mechanisms of reducing the transfer, which will help to recycle animal waste safely and control pollution of ARGs in the environment effectively.

Abstract:【Objective】Soil organic carbon content in China and its variation plays a very important role in the global carbon cycle and variation of atmospheric carbon dioxide concentration. Even minor changes in soil organic carbon content may affect the global carbon budget, atmospheric carbon dioxide concentration, and long-term sustainability of the ecosystem. Moreover, soil spatial information at the national scale is the basis for the study of changes in soil carbon storage and agricultural macro-decision-making. The processes of soil formation, development and erosion are subject to impacts of the complex and volatile environmental factors in the surroundings of the soil, so soil organic carbon is of strong spatial variability and dependence. Due to invisibility and concealment of soil properties, traditional field sampling methods require a lot of manpower and material resources, and can hardly obtain sufficient information to characterize continuous spatial distribution of soil organic carbon. Therefore, soil environment models are the main approaches to the research on digital soil mapping. However, most of these studies focus on small-scale and small-sized watersheds, while for large-scale areas the traditional area product method is still used in most cases. How to establish correlations between environmental variables and soil organic carbon on the national scale is the main research content of this paper. 【Method】Based on the data of soil organic carbon contents in the surface layers of 2 473 soil profiles collected during the Second National Soil Survey, this paper explored influences of factors, like topography, vegetation and climate on spatial distribution of soil organic carbon; With the ordinary Kriging method as control, geographically weighted regression, geographically weighted regression Kriging, multiple linear regression and regression Kriging were used separately to modeling for spatial prediction of soil organic carbon; indices, like mean absolute estimation error (MAE), mean relative error (MRE), root mean square error (RMSE) and Pearson correlation coefficient (r) were used to evaluate performance of these models; and soil organic carbon spatial distribution prediction maps were drawn separately. 【Result】Results show: (1) Soil organic carbon varied in the range from 1.62 g•kg ^-1 to 223.88 g•kg ^-1in content and averaged to be 22.28 g•kg ^-1in the country. Its variation coefficient reached 96.10%, which indicates that organic carbon in the soil varies very sharply in range, and is of strong spatial heterogeneity; (2)Soil organic carbon content was significantly related to annual mean precipitation, ≥10℃ annual accumulated temperature, elevation, slope, aspect, normalized difference vegetation index, annual average temperature, topographic wetness index, topographic position index and topographic roughness index. Among them, slope, elevation, aspect, topographic roughness index, annual average precipitation and normalized vegetation index were positively related, while topographic position index, topographic wetness index, annual average temperature and ≥10℃ accumulated temperature were negatively related; (3) Multiple linear regression coefficients might reflect influences of the environmental variables on soil organic carbon globally, whereas the geographically weighted regression coefficient map might do clearly those of different environmental variables on soil organic carbon in different geographical locations; (4) The mean absolute estimation error, root mean square error, mean relative error and Pearson correlation coefficient of the model were used as model validation indices and indicated that the geographically weighted regression is higher than the other models in prediction accuracy, and hence can be used to plot soil organic carbon spatial distribution characteristics maps of large scales areas; and (5) Areas relatively high in soil organic carbon content were mainly distributed in the northeast and southwest of the studied region, and patches in the southeast, while areas relatively low were in the northwest. 【Conclusion】The geographically weighted regression is higher than the ordinary Kriging, multiple linear regression, regression Kriging and geographically weighted regression Kriging in prediction accuracy. In this paper, efforts have been made to explore correlations between soil properties and environmental variables on large scales in an attempt to provide certain solutions and ideas for soil properties spatial mapping.

Abstract:[Objective]Sichuan is the area the most representative of purplish sandstones and shales distribution in China. The purpose of this article is to verify whether the hue of "L.C. of purplish sandstones and shales" in Chinese Soil Taxonomy(Third Edition) is reasonable. [Method]In this paper, a total of 45 samples of the parent rocks of typical purplish soils in Sichuan were collected and analyzed for hue in the light of the "Chinese Standard Soil Color Charts" (hereinafter referred to as Chinese Color Charts), and "Japanese Revised Standard Soil Color Charts"(hereinafter referred to as Japanese Color Charts) and with the aid of a spectrophotometer. And then, the data were compared against the purple (RP) definition for "L.C. of purplish sandstones and shales" in the Chinese Soil Taxonomy (Third Edition). Based on this, relevant revisions were suggested. [Result]Results show that when the color of the parent rock samples in block was measured with the Chinese Color Charts and the Japanese Color Charts, the number of the samples conforming to the RP hue reached up to 20.0% and 33.3%, respectively. And when the color of the parent rock samples in powder (ground to pass a 10 mesh sieve), only 2.2% of the samples matched the RP hue in the Chinese Color Charts. When measured with a spectrophotometer the parent rock samples, either in block or in powder were RP-free, and most of them were of YR hue. [Conclusion]Therefore, taking into account the definitions of purplish soil and red soil set by other scholars, it is suggested that the color definition for "L.C. of purplish sandstones and shales" should be revised as follows: hue of 2.5RP ~ 10RP; or hue of 2.5R ~ 5YR, dry value of 3 ~ 6, and dry chroma of 2 ~ 4. Once the revised standard is used, 62% ~ 75% of the samples meet the definition of purple, which is much closer to the traditional understanding of the color of purplish soil. In addition, it is necessary to further improve the soil color charts system, or to use a portable colorimeter that can objectively, accurately and automatically read Munsell color information in measuring soil color. And it is essential to observe more attentively the "purple" color of purplish sandstones and shales during the field investigation so as to avoid negligence of the soil with "L.C. of purplish sandstones and shales".

Abstract:【Objective】Soil shear strength is an apparent indicator of how easily shear deformation occurs under the action of external force, and a major index to characterize soil mechanical properties, as well as an important parameter of the process-based soil erosion model for prediction of hydraulic erosion, so it is very closely related to soil erosion. However, soil structure, water regime, biomass and particle size composition of a collapsing mound varies sharply with development of the collapse. So far, little has been reported on soil shear strength at each collapse developing stage. The purpose of this study is to (1) investigate variation of soil shear strength with the process of soil erosion on typical collapsing mounds; (2) determine influences of basic physical and chemical properties on soil shear strength; and (3) establish an equation for prediction of variation of soil shear strength with development of collapsing.【Method】The experiment lot was set up in the Jingouxing watershed in Tiancun Town of Gan County, where there are quite a number of collapsing mounds, diverse in erosion type. Three adjacent collapsing mounds of granite different in collapse developing stage (initial stage, active stage and stable stage) were selected for the experiment and a total of 15 sampling sites were set in the pattern of “Plum Blossom” or a pentagram for mixed sampling on each mound. Topsoil samples from the 0～20 cm soil layer of each mound and relevant environmental variables, were gathered, separately, for analysis of basic soil properties and soil shear strength. The data were processed with the classical statistic method for spatial variation of soil shear strength and variation of saturated shear strength with developing of collapse was predicted with the stepwise regression equation.【Result】(1) The physical properties of the soil in the collapse system are relatively poor with bulk density of the top soil layer varying in the range of 1.02～1.40 kg•m^-3 and declining with the position lowering along the slope, particle size composition coarsening, soil organic matter content lowering and root density ranging from 0.27 to 3.57 kg•m^-3, all of which demonstrate typical features of soil degradation with developing collapse; (2) Soil cohesion and internal friction angle, regardless of position along the slope, varies quite similarly, that is, both in a declining trend with development of the collapse, peaks at collecting areas, and bottoms in ditches. When collapse develops into a stable stage, restoration of vegetation promotes formation of root-soil complexes, which in turn increases soil cohesion and hence soil shear strength by a certain degree; (3) Statistical analysis shows that the contents of gravels, silt and clay are the optimal parameters to characterize soil internal friction angle of a collasping mound and their relationships can be well-described with a power function. Besides, a good linear correlation between root density and soil cohesive was observed; and (4) The experiment used root density and particle size composition to characterize shear strength of the soil under saturation, and established the equation (R²=0.891, P<0.01) for predicting soil shear strength of a developing mound.【Conclusion】All the findings listed above demonstrate that collapsed systems are generally poor in soil quality. With developing collapse, soil properties degrade obviously. Soil saturated shear strength varies significantly with soil particle-size distribution and root density across the collapsing erosion area, and is affected jointly by soil texture, topography, moisture and land use at the regional scale. It is recommended to use the functional equation based on parameters like particle-size and root density to predict soil shear strength, particularly for soil layers below 20 cm in the collapsed erosion areas in South Jiangxi. The study has discovered the main factors controlling soil shear strength in the South Jiangxi granite collapsing areas at different development stages, and provided certain theoretical foundations for further researches on mechanisms of soil shear strength responding to soil properties in expection of providing data of reference value and practical significance to future researches on control of soil erosion and rehabilitation of ecosystems in collapsing erosion areas.

Abstract:[Objective] Haloxylon ammodendron is the main species of shrubs planted to establish a sand-fixing vegetation in the arid region of Northwest China. Evolution of the sand-fixing vegetation system after Haloxylon ammodendron is planted, is influenced by soil development. [Method] To explore how the soil develops under the Haloxylon ammodendron forest in that region, plots of Haloxylon ammodendron forests along an age sequence, i.e. of 0-, 3-, 6-, 9-, 16- and 40-year-old, in the edge of the Pingchuan Oasis in Linze County in the middle of the Hexi Corridor were selected in the study and soil samples were collected from the plots for analysis of soil properties. And then discussion was made of plant-soil interactions and their influences on evolution of the vegetation ecosystem. [Result]Results show that soil clay and silt, soil organic carbon (SOC) and soil total nitrogen (TN) all increased in content or concentration gradually with the vegetation living on, but the phenomenon became obvious only in the 0~20 cm surface soil, 9 years after the vegetation was established. However, salt accumulation occurred throughout the whole soil profile (0~100 cm in depth), especially significant in the 20~80 cm soil layer. SO₄^2-,Ca²⁺ and Na⁺, the main components of soil salt, increased with the age of the plantations and accumulated significantly in the soil profiles of the 16- and 40-year-old plots. In comparison with non-vegetated land of shifting sand, the Haloxylon ammodendron planted plot, 16 and 40 years old, was 3.3 time and 5.7 times, respectively, higher in SOC concentration in the 0~10 cm surface soil layer, and 5.4 and 6.5 times higher in mean salt content in the 0~100 cm soil profile. [Conclusion] All the findings in this study suggest that soil salt accumulates faster than SOC and soil nutrients in the soils under Haloxylon ammodendron in its growing and developing process. Such a salt accumulation rate may affect setting-up and development of herbaceous plants, and in turn influence stability of the artificial vegetation system. Along the 40-year-long age sequence, the soil under Haloxylon ammodendron plantation developed from Aridic Psamments to Aridic Orthents and will eventually turn into Calciorthids as affected by the continuous salt accumulation and calcafication process. Hence further observations and studies are needed to verify development of the soil.

Abstract:【Objective】 Measurement of soil heat flux is pivotal to researches on budgeting of surface heat. To measure soil heat flux, there are several ways, one of which is the heat flux plate method, simple and easy to handle, but unpredictable in accuracy.【Method】 In this study, an indoor experiment was carried out in combination with computer simulation to determine errors of the measurement with the soil heat flux plate method and explore its influencing factors. In this paper, with soil deemed as homogenous medium and the heat flux plate as composite material, influences of the composite material on temperature field of and heat flux distribution in the homogenous medium. In addition, analysis was done of applicability of the modificatiton equation Philip put forth in 1961. 【Result】 Results show that when the soil and the plate is quite approximate in heat conductivity measurement error of the method is low and Philip’s equation is relatively low in applicability under transient conditions.【Conclusion】 The study shows that due to difference in thermal conductivity between the heat flux plate and the soil, the heat flow will distort at the edge of the plate, thus leading to occurrence of errors in the measurement. As Philip’s equation simplifies computation in the derivation process, difference is still found between calibrated value and theoretical value when soil temperature varies with time, which indicates that its application is limited in range.

Abstract:[Objective] The primary cause of eutrophication of landscape water is too much N and P in the water body. It is, therefore, key to control of landscape water eutrophication to reduce N and P concentrations in the water body. Studies have shown that total nitrogen(TN) and total phosphorus(TP) in landscape water can be effectively removed with the complex of purple parent rock and polymeric ferric sulfate (PFS). However, it is still unclear how the complex looks like in micro-structure and how it removes TN and TP from landscape water. [Method]Morphological structure of the complex of J₃p purple parent rock and ferric sulfate (J₃p+PFS) was explored with electron microscopic scanning, energy spectrum analysis, infrared spectrum analysis and X-ray diffraction, and mechanism its removing total nitrogen and total phosphorus through analysis of isothermal curves of the adsorption of total nitrogen and total phosphorus by J₃p, zeta potential of the system, fractal dimension, and changes in content of chlorophyll a.[Result] Electron microscopic scanning and energy spectrum analysis shows that once J3p and PFS formed into complex, larger in agglomerate structure, more fluffy in surface and roughly the same as J₃p in elemental structure, but changed in content of metal elements. Infrared spectroscopy and X-ray diffraction shows that changes occurred in composition of its internal material and functional groups, thus turning the complex into new hydroxyl-bridged iron polymers. Isothermal adsorption experiments show that TN adsorbed on J₃p was in the form of a monolayer on the surface, while TP adsorbed mainly in the form of a monolayer, with maximum theoretical adsorption capacity being 0.259 mg•g^-1 and 0.619 mg•g^-1, respectively. Zeta potential of the system increased dramatically after it was treated with J₃p + PFS, but still below 0, which indicates that the use of J₃p + PFS integrates the advantages of PFS neutralizing charges, and of J3p adsorbing N and P. Once landscape water was treated with J₃p, PFS, or J₃p + PFS, TN, TP and chlorophyll-a concentrations in the water all reduced. However, J₃p + PFS shows the highest capacity of removing TN, TP, and chlorophyll-a. Moreover, fractal dimension of the system was higher after treatment with J₃p + PFS than after treatment of J₃p or PFS. All the findings demonstrate that J₃p+ PFS promotes aggregation of chlorophyll-a, which precipitates in tiny particles in the water, thus reducing the content of chlorophyll-a and hence the contents of TN and TP. [Conclusion] The complex of J₃p+PFS integrates the effect of PFS neutralizing charges and that of J₃p adsorbing N and P, so it can achieve rapid and efficient removal of total nitrogen and total phosphorus from landscape water. The complex can removal of TN and TP from landscape water by 53.53% and 86.48%, respectively, in 3 hours after the treatment.

Abstract:【Objective】Selenium (Se) is an essential micronutrient for human and animals. Ingestion of either an inadequate or excessive amount of Se tends to cause hazard to their health. Bioavailability of Se in soil depends on its forms. Iron oxide is an important component of soil and may interact with Se through desorption/adsorption. Iron and manganese oxides in soil are often cemented together forming binary metal oxides or Mn-doped iron oxides, thus significantly affecting translocation and transformation of nutrient elements and contaminants in the soil. However, so far little has been reported in-depth in the literature about effects of Mn-doped iron oxides on speciation and bioavailability of Se in soil. 【Method】Samples of pure goethite (Goe) and Mn-doped products (G-Mn_0.1、G-Mn_0.2、G-Mn_0.3和G-Mn_0.5) were prepared under set hydrothermal conditions and were characterized with the aid of X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen physical adsorption, Zeta potential analysis and potentiometric titrations. Moreover, selenite (Se(IV)) and selenate (Se(VI)) adsorption characteristics of the samples were investigated through batch adsorption experiments. 【Result】 Mn-doping at a low rate with R_Mn/Fe (Mn(II)/Fe(III) molar ratio being 0.1～0.2) promoted significantly formation of goethite crystals along Axis b, in the form of flat needles big in length-to-diameter ratio instead of short spindles, whereas Mn-doping at a high rate, 0.3-0.5 in R_Mn/Fe , which means increased Mn(II) content, inhibited significantly formation of goethite crystals along Axis b, while promoting their growth along Axis a by a certain degree and moreover making them tenuous. Additionally, a mass of Mn-doped magnetite appeared in the samples. Of Goe, G-Mn_0.2 and G-Mn_0.5, the specific surface area was 36.78、53.22 and 71.33 m²•g^-1; the surface fractal dimension D, 2.31, 2.53 and 2.59; the mean pore diameter, 13.73, 15.59 and 6.92 nm; the isoelectric point, 7.36, 6.58 and 5.31; and the surface zeta potentials at pH=5.0 40.5, 35.3 and 4.92 mV, respectively. In terms of surface hydroxyl content, the three types of the samples followed the order of Goe < G-Mn_0.2 < G-Mn_0.5. At pH=5.0, the Langmuir model was found to be more suitable for use to describe isotherm adsorption data of Se(IV) and Se(VI) in the samples (R² =0.966~0.996). The Langmuir adsorption capacity (Q_max) of Goe, G-Mn_0.2 and G-Mn_0.5 was 11.6, 16.8 and 20.4 mg•g^-1 for Se(IV) and 7.6, 8.5 and 9.2 mg•g^-1 for Se(VI), respectively. The adsorption affinity for Se(IV) slightly effect by the Mn content, which dramatically increase the adsorption affinity for Se(VI). 【Conclusion】At R_Mn/Fe =0.1-0.2, the formation of Goe is accelerated by Mn(II), and at R_Mn/Fe =0.3-0.5 Mn-doped magnetite is observed in the products. As of Goe, G-Mn_0.2 and G-Mn_0.5, specific surface areas and surface fractal dimension D increases in turn, while isoelectric point, surface zeta potentials at pH=5.0 and surface hydroxyl contents decreases gradually. Q_max increases with rising Mn(II) content for both Se(IV) and Se(VI), and Q_max of Se(IV) was higher than that of Se(VI), and their isotherm adsorption model is mainly kind of homogeneous surface mono-layer adsorption.

Abstract:【Objective】Soil nanoparticles are organic-mineral complexes. It is of great practical significance to study stability of the suspension of natural soil nanoparticles. However, so far little attention has been paid to effect of organic-mineral complexes on stability of soil nanoparticles, and let alone its mechanism. 【Method】 In this study soil nanoparticles were extracted, separately, from soil samples of Lou soil and cinnamon soil before and after soil organic matter was removed with the aid of the ultrasonic dispersion method and the Stokes’ law based high-speed centrifugation method for analysis of particle size distribution, zeta potential, critical coagulation concentration (CCC) in NaCl and CaCl2 solutions and characterized with the dynamic light scattering technique. Furthermore, Hamaker constants of and interaction energies between the soil nanoparticles were calcuated in line with the DLVO (Derjauin-Landau-Verwey-Overbeek) theory, mechanism of organic matter removal affecting stability of soil nanoparticle suspensions explored and role of organic-mineral complexation in stabilizing soil aggregates explained. 【Result】 Results show that the Lou and cinnamon soil nanoparticles were 94.00 nm and 88.20 nm, respectively, in average diameter and the OMR (organic matter removed) loess nanoparticles slightly higher than 100 nm; the obtained loess nanoparticles were all of the polydisperse system and quite approximate to each other in ploydispersity. The nanoparticles in the all the four types of loess soil samples carried negative charge on the surface and their zeta potential increased with rising pH of the solution in absolute value due to deprotonation of the functional groups on the surface of the organic matter. As the soils varied in clay mineral property, the nanoparticles in the cinnamon soil varied more sharply in surface zeta potential than those of the Lou soil; the cinnamon soil contained more variably-charged kaolinite, while the Lou soil contained more permanently-charged illite. The functional groups on the surface of organic matter, like alcoholic hydroxyl, phenolic hydroxyl and carboxyl, are the main sources of soil negative charges. Compared with the nanoparticles in the Lou and cinnamon soils, those in the OMR Lou and cinnamon were lower in absolute value of the zeta potential as they were lower in organic organic matter. The nanoparticles in the Lou and cinamon soils were 1.70 mmol·L^-1 and 1.51 mmol·L^-1, respectively, in CCC while those in the OMR Lou and cinnamon soils were 10.58 mmol·L^-1 and 11.69 mmol·L^-1; Obviously, removal of organic matter enhanced stability of the nanoparticle suspension. Based on DLVO-based simulation, the nanoparticles in the Lou and cinnamon soils in vacuum were 6.86 × 10^-20 J and 9.73 × 10^-20 J, in Hamaker constant and those in the OMR Lou and cinnamon soils were only 3.14 × 10^-20 J and 3.40 × 10^-20 J. Apparently, the Hamaker constants of the latters were lower than the formers and so were their van der Waals attractive potential energies. Lower absolute values of the zeta potentials of the nanoparticles in the OMR loess soils resulted in reduced electrostatic repulsive potential energies. Therefore, the removal of organic matter reduced both the van der Waals attractive potential energies and electrostatic repulsive potential energies of the nanoparticles in the loess soils. But the decrements in van der Waals attractive potential energy were higher in magnitue than those in electrostatic repulsive potential energy. Further calculations demonstrate that the nanoparticles in the OMR loess soils were higher in total potential energy than those in the Lou and cinnamon soils, which resulted in higher CCCs and higher dispersion stability of the suspensions. 【Conclusion】 The presence of organic matter affects stability of the nanoparticles in loess soils through adjusting both attractive and repulsive potential energies. The complexation of organic-mineral alters soil nanoparticle composition, which in turn determined their Hamaker constant. Removal of organic matter reduces Hamaker constants of the nanoparticles in loess, leading to low attractive potential energy between nanoparticles in OMR Lou and cinnamon soil. Therefore, it is concluded that organic-mineral complexation may enhance stability of soil aggregates through increasing Hamaker constant.

Abstract:【Objective】In recent years, the study on heavy metal pollution in soil has become popular. Although quite a number of scholars reported achievements in this field, they have not overcome the defects in regional background value and evaluation method, especially in salt lake basins in the arid region. So, it was difficult for them to achieve accurate results. The objective of this paper is to characterize spatial distribution and determine environmental background values of heavy metals pollutants, to evaluate soil quality using different methods, and to investigate sources of heavy metals pollution in salt lake basins, in an expectation to provide certain scientific reference for researchers in studies on accumulating basic data, determining environmental capacity, setting up soil environmental standards, protecting soil environment, eliminating soil environmental risks, rationalizing utilization of soil resources and so on and for government policy-makers in all these fields. 【Method】The Jilantai Salt Lake Basin, located in the arid region of Northwest China, was selected as the object for the study. Soil samples were collected from topsoil (0 to 10 cm), subsoil (50 cm) and substrate (100 cm) in the study area using the random arrangement method. Heavy metals (e.g. Cr, Hg and As) for analysis of chemical composition in the Inner Mongolia Key Laboratory of Water Resources Protection and Utilization. Spatial distribution of Cr, Hg and As was characterized through geo-statistical interpolation maps and background values of the elements in the soil environment were determined as benchmarks for evaluation of soil quality. Six commonly used methods (i.e. single factor index, geo-accumulation index, ecological risk index method, Nemero index, potential ecological risk integration index and pollution load index) were used to evaluate soil quality for comparison analysis. 【Result】Results show that the three heavy metal elements, Cr, Hg, and As, in the Jilantai Basin, were on the whole quite similar in spatial distribution characteristic; the background value of Cr, Hg and As in the soil of the basin was 27.89 mg•kg^-1, 0.039 mg•kg^-1and 12.83 mg•kg^-1, respectively; Cr was higher in the Bayinwula Mountain Region, the Wulanbuhe Desert Region, and the hilly southwestern part of the study area; Hg was higher only in the northeastern and the hilly southwestern parts of the study area; and As was higher areas near the lake, the Helan Mountain Region, the Bayinwula Mountain Region, and the Wulanbuhe Desert Region. The evaluation based on background value reveals that the three pollution elements in the topsoil of the study area followed a decreasing order of Hg > Cr > As in pollution level; the evaluation using the simple factor index method shows that Cr, Hg and As were all light in pollution level in the study area; the evaluation using the ecological risk method indicates that Hg was higher than Cr and As in ecological risk; and the evaluation using the comprehensive pollution index method suggests that the pollution of the three elements, when talked about separately, was slight in the topsoil, but their comprehensive ecological risk was high. The pollution level evaluated with the simple factor index methods was higher than that evaluated with the comprehensive pollution index method, Furthermore, the correlation coefficients of the evaluations using the two methods, simple and comprehensive, reached over 0.80 and 0.65 (a=0.01), respectively. In evaluating Hg, all the evaluations using the three comprehensive pollution index methods were significantly correlated with those using the three simple factor index methods, with correlation coefficient being 0.53 (a=0.01), while no significant correlations were found with the other two heavy metal elements.【Conclusion】It can be concluded from the spatial distribution characteristics and the evaluations that the presence of Cr, Hg and As in the surface soil of the salt lake basin is subject to the comprehensive impact of soil-forming parent material, natural hydro-geochemistry and climatic conditions, and partially to the disturbance of human activities.

Abstract:【Objective】This study is oriented to explore effects of thermal-disturbed vermicompost on soil quality and crop growth in expectation that all the findings may help guide large-scale processing and application of the manure and promote high-efficient recycling and utilization of organic waste. 【Method】 Fresh vermicompost was placed into an incubator for 20 hrs of incubation under a set temperature (30, 40, 50, 60, and 70 °C) separately, The incubated vermicomposts were sampled for analysis of changes in basic property, and then packed into pots separately for pot experiment in a well-lit greenhouse to explore effects of the incubated vermicompost on soil properties and tomato growth.【Result】Results show that with the temperature in incubation rising from 30 ℃ to 70 ℃, pH, and the contents of dissolved organic carbon and ammonium in the vermicompost increased and reached the highest at 70 ℃, but the content of nitrate and available potassium declined and the activities of the enzymes involved in carbon and nitrogen recycling did, too, while microbial biomass carbon and nitrogen increased first (at 40 ℃) and then declined (at 70 ℃). Microcosm study shows that compared to CK (vermicompost incubated at room temperature (30 ℃), the vermicomposts incubated at higher temperatures significantly increased shoot and root biomasses of the tomato in the pot experiment by about 200% and 56% ~ 115%, respectively. With incubation temperature rising, the plant uptake of NPK increased steadily. NKP supply (the sum of soil available nutrients and effective nutrient uptake of the plant) of the vermicompost increased first and declining with the incubation temperature rising, and was the highest in Treatment 50 (where the vermicompost was incubated under 50 ℃). Soil pH and dissolved organic carbon in the vermicompost increased gradually with rising incubation temperature. Soil microbial biomass carbon and nitrogen increased first and then declined and was the lowest in Treatment 70. Activities of the soil enzymes involved in carbon and nitrogen recycling varied from treatment to treatment, but on the whole did exhibit a rising trend.【Conclusion】To sum up, thermal disturbance may cause vermicompost to decline in bio-activity, but increase in nutrient availability. So application of thermal disturbed vermicompost can significantly promote plant uptake of NPK. Obviously thermal disturbance may help vermicompost bring its nutrient availability into full play. It is, therefore, concluded that thermal disturbance of vermicompost is beneficial to building up of soil fertility in a short term and to plant growth as well. However, future studies should shift their focus on long-term effect of the application of thermal-disturbed vermicompost on larger spatial and temporal scales.

Abstract:【Objective】 Fluvo-aquic soil is widely distributed in the North China Plain. The soil is very low in organic matter, which is hard accumulate therein. Maybe, this is the main cause preventing high crop yields. Application of extraneous organic materials (i.e. straw and woody peat) is a common agricultural strategy to improve soil organic matter（SOM）content in this agricultural region. However, so far only limited information is available in the literature about effects of applying crop straw and/or wood peat on crop yield and soil fertility, and it is not clear whether it is superior to direct straw returning to the field. 【Method】 In this study, a field experiment, designed to have four treatments, that is, CK (Do not apply any organic material, only chemical fertilizer), R (Chemical fertilizer and 7 500 kg·hm^-2 of straw), MT (Chemical fertilizer and 7 005 kg·hm^-2 of the wood peat), and RMT (Chemical fertilizer, 7 500 kg·hm^-2 of straw and 7 005 kg·hm^-2 of the wood peat) was conducted in a field of Fluvo-aquic soil in Fengqiu, Henan. Crop yield and soil fertility indices, such as SOM, total nitrogen(TN), available phosphorus(AP), Nitrate (NO₃^--N) and carbon nitrogen ratio (C:N) of the soil were measured. High-throughput sequencing was employed to characterize diversity and composition of the bacterial community in the soil, FAPROTAX database was used in prediction of bacterial functions. 【Result】 Results show that there was no significant difference between Treatments R and RMT and CK in aboveground biomass, but Treatment R and RMT was 40% and 64% respectively, higher than CK in average respiration rate in the whole growth period of maize. However, Treatment MT was 10% lower than CK in aboveground biomass, and did not differ much in average respiratory rate. On the other hand, the treatments varied in effect on soil fertility. Compared with CK, Treatment R was 23.56% lower in AP, while Treatment MT was 79.30%, 39.12%, 43.63% and 86.50% higher, respectively, in SOM, AP, NO3-N and C:N. Through high-throughput sequencing and function prediction, it was found that the bacterial communities in Treatments R and MT differed significantly from that in CK in composition and function, while that in Treatment RMT was similar to that in CK, and the soil bacterial communities in Treatments R and MT were significantly higher than that in CK in diversity. Compared with CK, the relative abundances of Chloroflexi, Gemmatimonadetes, Arthrobacter, Dactylosporangium and Rubellimicrobiu that could decompose and utilize fresh straws were significantly increased in Treatment R, but the functions of Chemoheterotrophy, Aerobic chemoheterotrophy and Ureolysis were decreased, while in Treatment MT, the relative abundances of Agrobacterium, Cellulosimicrobium, Devosia, Niastella, Nocardioides and Rubellimicrobiu that could degrade macromolecular organics were significantly increased and the function of Cellulolysis was strengthened and that of Aerobic chemoheterotrophy was weakened. In addition, the predicted functions of the soil microbial communities in Treatments R and MT were significantly different from those in CK, but thoese in Treatment RMT were similar to those in CK. In addition, the predicted functions of the soil microbacterial communities in Treatments R and MT were significantly different from those in CK, while those in Treatment RMT were similar to those in CK. 【Conclusion】 In conclusion, in the Fluvo-aquic soil area, although applying woody peat alone can rapidly increase SOM, it may lead to decrease in crop yield temporarily or in a short term, which may be relative to changes in the soil microbial community in composition and function, thus affecting nutrient recycling and transformation. Combined application of straw and woody peat is beneficial to building up of soil fertility, and maintaining the soil microbial community in structure and function.

Abstract:【Objective】 This paper was oriented to explore effects of cultivation, relative to duration, on gross and net N transformation rates in black soil in Northeast China. 【Method】 Two tracts of upland farmlands of typical black soils, different in cultivation history, 2 and 30 years, were selected in Northeast China for the study. Soil samples were collected for in-lab incubation using the ¹⁵N pair-labeled technique. Gross N transformation rates in the soils were calculated using the numerical algorithm model (FLUAZ), and net mineralization rates and net nitrification rates were by duration of the incubation and variation of the samples in inorganic nitrogen content or nitrate nitrogen content with the incubation. 【Result】 The soil of the farmland, 30 years in cultivation, was 20.8% and 16.0% lower, respectively, than the one 2 years in cultivation in organic C and water soluble organic C content, and only 62.6% and 42.1% of the latter, respectively, in gross mineralization and immobilization rate. However, the former was significantly higher than or 1.77, 2.00, and 7.29 times as high as the latter, respectively, in gross nitrification rate, net nitrification rate, and net mineralization rate. The gross nitrification rate was 1.15 and 1.02 times as high as the net nitrification rate, respectively, in the latter and former, and the immobilized ammonium nitrogen accounted for 60%~97% of the total inorganic nitrogen during the whole incubation period, indicating that little nitrate nitrogen was immobilized by soil microorganisms in these two soils. The values of m/i (the ratio of gross N mineralization rate to immobilization rate) and n/ia (the ratio of gross nitrification rate to ammonium immobilization rate) of the former were both significantly higher than 1, while those of the latter were approximate to 1. 【Conclusion】 The processes of mineralization and immobilization of nitrogen in the soil, 2 years in cultivation, were coupled tightly, posing little risk of nitrogen loss to environment, whereas the amount of mineralized nitrogen was much higher than that of immobilized nitrogen in the soil 30 years in cultivation, thus providing substrate for nitrification and increasing denitrification and leaching risk of nitrate.

Abstract:【Objective】 Imidacloprid, a new type of neonicotinoid insecticide with high pest control efficiency, is widely used in recent years. As this chemical insecticide has a long residual period (about 25 days), it is necessary to evaluate risks it might pose to beneficial microbes in the soils. 【Method】 Solid and liquid incubations were carried out simultaneously to investigate effects of the insecticide on growth, reproduction, and phosphorus (P) dissolving capacity of inorganic phosphate-solubilizing bacteria (IPSB), such as Burkholderia Yabunchi B05, B07 and B09, relative to concentrations of imidacloprid (0, 5, 10, and 20 mg•L^-1). 【Results】 Imidacloprid inhibited to a varying extent the growth and reproduction of all the three strains of IPSB, with the diameter of bacterial colonies decreased by 39.81%~55.45% in solid incubation. The tested bacteria varied in solubilization of tricalcium phosphate in response to imidacloprid. B09 was lowered in diameter of P-dissolving halos and index in the presence of imidacloprid, but B05 and B07 behaved otherwise, with the diameter of P-dissolving halos and index reaching as high as 9.72% ~19.44% and 40.69%~106.94%, respectively. In liquid incubations, imidacloprid also inhibited growth and reproduction of the three strains of IPSB, with the bacterial density decreased by 49.87%~65.28% in culture solutions. P solubilization capacibility of the bacterial strains varied with imidacloprid concentrations. Imidacloprid, regardless of concentration, stimulated P solubilization of B05. P solubilization of B07 varied in solutions low or mediumin concentration of imidacloprid, but increased in those high in imidacloprid concentrations compared with CK (without imidacloprid). B09 showed a similar tread to B07 in variation of P dissolving capacity in solutions low in imidacloprid concentrations, while it decreased greatly in solution medium or high in imidacloprid concentrations. All the three strains of bacteria were able to excrete protons, oxalate, and citrate. Oxalate and citrate accounted for 67.65%~83.28% of the total organic acids excreted. In addition, acetate was detected in culture solution with B05 and B07, malate with B09, and succinate with B07. Excretion of the organic acids was affected by not only imidacloprid concentration, but also strain of bacteria and type of organic acid. Furthermore, imidacloprid inhibited bacterial proton secretion by a varying degrees. The amount of P dissolved from tricalcium phosphate was positively related to the excretion of total organic acids (r = 0.876, P < 0.05, n = 12) and to that of protons (r = 0.823, P < 0.05, n = 12) as well. 【Conclusion】It could be concluded that imidacloprid inhibites growth and reproduction of the IPSB by a varying degree in the soil, thus affecting the effects of the bacterial excreting organic acids and protons, and hence the effect of promoting or inhibiting and P solubilization. So in pest controlling application of a large amount of imidacloprid could influence the activities, numbers, and functions of IPSB to a various extent, depending on type of the soil and group of IPSB.

Abstract:【Objective】 It is very important to study how soil K-solubilizing bacteria (KSB) vary and its driving factors in the red soil of South China under long-term fertilization, so as to lay down a certain theoretical basis for management of soil potassium (K) resources and rational application of K fertilizer in the region. 【Method】 Based on a long-term fertilization field experiment in red soil that started in 1986, which was designed to have four treatments, that is CK (no-fertilization), NP (nitrogen and phosphorus fertilizers applied), NPK (nitrogen, phosphorus and potassium fertilizers applied), NPKM (NPK fertilizers plus organic manure). Soil samples were collected from the rhizosphere of the maize plants in the plots of the treatments during their florescence for analysis of strains of K-dissolving bacteria and their K-dissolving abilities and organic acids and hormones contents, and for exploration of key factors affecting KSB in upland red soils in relation to properties of the maize root system and physico-chemical properties of the rhizosphere soils. 【Result】Results show that Treatments NP, NPK and NPKM were significantly higher than CK in root length, root surface area and root volume, and so in content of soil organic matter, non-exchangeable K and exchangeable K. Treatment NPKM was the most significant in the effect and 112.3%, 174.4%, 32.43% and 291.5% higher than Treatment NPK in root length, root surface area, root diameter and root volume, respectively; and 0.67 unit, 29.50%, 19.34% and 53.89% higher in pH and content of soil organic matter, Non-exchangeable and exchangeable K, respectively, in rhizosphere soil. KSBs were found in the rhizosphere soils of all the treatments. The KSBs in CK and Treatment NP were of Paenibacillus, while those in Treatments NPK and NPKM were of Cellulosimicrobium. Compared with CK, Treatment NP, NPK and NPKM was 162.4%, 139.0% and 105.6%, respectively, higher in K-dissolving efficiency, showing obviously that Treatment NP was the highest. Moreover, analysis with the the partial least squares path model shows that root and fertilization are that two factors that regulate simultaneously KSB K-dissolving efficiency. Furthermore, redundancy analysis shows that soil KSB characteristics are closely and positively related to root length and root surface area (P<0.05). 【Conclusion】 In the upland red soil, long-term fertilization can not only affect development of the maize root system and physico-chemical properties of the rhizosphere soil, but also alter soil KSB communities and their K-dissolving abilities. Within the root system, root length and root surface area are the two key factors regulating KSB in the rhizosphere soil of maize.

Abstract:【Objective】 To explore potential causes of the occurrence of potassium deficiency symptoms in the middle and upper leaves, rather than lower leaves, of normally fertilized tobacco plants in the field during their growth, a field experiment was carried out in this study. 【Method】 The field experiment was laid out in a tobacco field of sandy loam planted with flue-cured tobacco of variety K326, designed to have three treatments, i.e. K0 ( plants applied with N P at the conventional rate and without K, 0 kg·hm^-2 K₂O), CF (plants applied with NPK at the conventional rate, 364 kkg·hm^-2 K₂O, and only those among the plants exhibiting potassium deficiency symptoms during the middle and late stages were sorted as Treatment CF), and CK (sharing the same plants with Treatment CF, applied with NPK at the same rate, and only those free from any potassium deficiency symptoms during the middle and late stages were sorted as Treatment CK). Observation of the plants began after their transplantation for growth and possible appearance of potassium deficiency symptoms in leaves). Leaves were sampled timely for determination of dry matter and potassium content, and rhizosphere soils were for analysis of available potassium content. 【Result】 (1) The tobacco plants in Treatments CF and K0 did not show any symptoms of potassium deficiency during the first 33 days after transplanting. However, when soil available potassium in the root zone was gradually depleted and dropped below 99.86 mg·kg^-1 in content on D42, symptoms appeared one by one on the 8th ~ 15th leaves of the plants in Treatment K0 ; and when soil available potassium in the root zone was lowered down below 131.1 mg·kg^-1 on D57, symptoms appeared one by one on the 12th ~ 16th leaves of the plant in Treatment CF, but not on the other leaves; (2) During the first 42 days after transplanting, dry matter and potassium accumulation significantly increased in Treatments CK and K0, but the trend of the total weight of the tobacco plants in Treatment K0 getting lower became more and more apparent; and the two indexes kept on rising till D57, and during this period of time, the two treatments exhibited a rising trend in dry matter accumulation, similar to that Treatment CF did, but Treatment CF was a bit lower than Treatment CK in potassium during the first 42 days after transplantation; (3) From D42 to D57, net potassium export was significant from the upper and middle leaves of the plants in Treatment CF and the upper leaves in Treatment K0, while net potassium import was in the stems, and potassium in the other organs or parts was generally kept in balance or slightly increased; and in Treatment CK, potassium stayed in balance in the upper leaves of the tobacco plants and slightly increased in the other organs; and (4) During the growth period, potassium content increased with rising position of the leaf but declined in overall in the plants of Treatment CK; similar patterns were observed Treatments K0 and CF in the early stage, but Treatment K0 showed a “rise-decline-rise” trend after D42 and D57, while Treatment CF did a “decline-rise” trend after D57. 【Conclusion】 All the findings indicate that the appearance of potassium deficiency symptoms in the middle leaves of the plants in Treatment K0 on D42 was attributed to (1) insufficient potassium absorption as a whole and (2) high net export of potassium in the upper leaves in the later stage. The appearance of potassium deficiency symptoms in the middle and upper leaves rather than lower leaves of the tobacco plants in Treatment CF was because (1) the on-going fast dry matter accumulation diluted potassium in the plants in the later stage; (2) potassium accumulation of the whole plant declined instead of going on in the later stage and (3) the net potassium export increased in middle and upper leaves of the plants.

Abstract:【Objective】In this study, effects of dry-wet alternation on diversity, abundance and structure of the soil microbial community in the black soil of a long-term stationary field experiment in Dehui of Jilin on tillage modes, no-tillage or ridge tillage, were investigated. So far few reports were detected in the literature about responses of the soil microbial community in the soil subjected to drying-wetting alternation under no-tillage or ridge tillage. In this paper, soil samples were collected for analysis by means of high-throughput sequencing in laboratory. This research was expected to be of great significance to prediction of impacts of drought on soil functions under different tillage practices. 【Method】No-tillage and ridge tillage plots in the field experiment had been cultivated with maize (Zea mays L.) for 13 years. Soil samples were collected with a T sampler, ground to pass a 4-mm sieve, and then packed separately into PVC pipes with a sealing film at the bottom of each pipe to make the soil in the pipe the same in bulk density as that in the plot under no-tillage or ridge tillage. The amount of soil packed into the pipe for no-tillage was 115.75 g and for ridge tillage, 113.04 g. Five dry-wet treatments different in frequency and intensity were designed and implemented: (1) CK as control; (2) MDW1, one round of moderate dry-wet alternation; (3) VDW1, one round of very dry-wet alternation; (4) MDW3, three rounds of moderate dry-wet alternation; and (5) VDW3, three rounds of very dry-wet alternation. Soil microbial communities were investigated by means of Illumina Miseq sequencing. Soil available phosphorus and available potassium were determined with conventional analysis methods. Soil pH was determined with a composite electrode. And soil water ratio was set as 1:5. For measuring carbon and nitrogen, a part of each treated soil sample was ground to pass a 0.85 mm sieve. Total carbon and total nitrogen of the soils were determined with the Vario Max produced by the German Elementar Company. 【Result】Results show that dry-wet alternation significantly reduced microbial diversity in the soils under no-tillage, and the effect was amplified with rising frequency and intensity of the dry-wet alternation. However, dry-wet alternation did not affect microbial diversity in the soils under ridge tillage. Compared to the control, the treatments under dry-wet alternation significantly increased the relative abundances of Planctomycetes and Verrucomicrobia in the soils under no-tillage and significantly reduced the relative abundances of Saccharibacteria and Parcubacteria in the soils under either no-tillage or ridge tillage, and increased the relative abundance of Gemmatimonadetes in the soils under ridge-tillage. Relative abundances of Proteobacteria and Acidobacteria were significantly lower in the soils under ridge tillage than in the soil under no-tillage, while that of Actinobacteria was significantly higher in the soils under ridge tillage. Relative abundances of Firmicutes and phyla in the “Others” did not vary much between the two tillage modes. Frequency of dry-wet alternation did affect structure of the soil microbial community. However, intensity of drought in the treatments did not have much effect on structure of the soil microbial community. So soil microbial community structure is significantly altered by frequency of the alternation, but not by intensity of the drought in the dry-wet alternation. Redundancy analysis was conducted with available phosphorus, readily available potassium, total N, total C and pH of soil as explanatory variables and 11 phyla of microbes in the soils under no-tillage and ridge tillage as response variables. Readily available potassium was the main environmental factor affecting the distribution and quantity of soil microorganisms. 【Conclusion】Dry-wet alternation has certain significant effects on soil microbial communities, but such effects are dependent on tillage practices and frequency of the dry-wet alternation. This study is expected to provide a theoretical basis for predicting effects of arid climate on soil ecological functions.

Abstract:【Objective】 It is of great significance to vegetation restoration in and eco-remediation of saline-alkali soils to unfold researches on microbial community diversity in the rhizospheres of salt-tolerant plants in saline-alkali soils. 【Method】In this research, the biolog ecoplate technology was used to study soil enzyme activities and metabolic function diversity of the microbial communities in the rhizospheres of six salt-tolerant species of plants species in saline-alkali soils North Yinchuan. 【Result】Results showed physical and chemical properties and enzyme activity of the rhizosphere varied somewhat with species of the plant. Compared with bare soil, rhizosphere soils of the salt-tolerant plants were significantly higher in soil enzyme activity, especially the rhizosphere soil of Medicago sativa in the activity of three kinds of soil enzymes. In general, the average well color development (AWCD) of the rhizosphere soils increased with the processing of culture and in terms of AWCD, the five species of plants followed an order of Medicago sativa (MX), Achnatherum splendens (JJC), Tamarix chinensis (CL), Panicum virgatum (LZJ), Sophora alopecuroides (KDZ), Lycium barbarum (GQ), all being much higher than that in the bare soil (CK) (P <0.05). The soil microbial community in the rhizosphere soil of Medicago sativa was the highest in Simpson index, Shannon index and McIntosh index, and followed by that of Achnatherum splendens, and the two differed significantly from that of the others (P <0.05). Soil microbial community in the rhizosphere soil varied with species of the plant in ability to utilize carbon resources. The one in the rhizosphere soil of Medicago sativa was significantly higher than that of the others in carbon utilization ability (P <0.05). Carbohydrates were the main carbon source for soil microbes in rhizosphere soil, and followed by amino acids and carboxylic acids, and amines the last. Principal component analysis demonstrates that the main carbon sources that differentiated between PC1 and PC2 were carbohydrates and carboxylic acids. 【Conclusion】All the findings demonstrate that all the indices are higher in the rhizosphere soil than in the bulk soil or soil of the bare saline-alkali field, particularly in the Medicago sativa and Achnatherum splendens fields, which demonstrates that the plants significantly improve functional diversity of the soil microbial community, thus contributing positively to nutrient recycling in the rhizosphere micro-environment in saline-alkali lands.

Abstract:【Objective】Soil microbes, as an active component of the soil, play an essential role in the forest ecosystem. It is, therefore, of great significance to study characteristics of the soil microbial community structures in plantations different in evolution process to evaluation of dynamics of soil quality and maintenance of soil microecological balance in the plantations. 【Method】In this paper, evolution of the soil microbial community structure and soil metabolic function diversity with age (13 a, 25 a, 38 a and 58 a) of Pinus massoniana plantations in subtropical China was explored using the phospholipid fatty acid（PLFA）method and BIOLOG technique. 【Result】Results show that bacteria were the dominant soil microbe, fungi and actinomyces followed in dominance, and protozoa did in the end in the soils of the plantations regardless of age; in terms of soil microbial total PLFAs, fungal population and fungal/bacteria, the plantation 13 a in age ranked first and that 38 a in age in the end, while in terms of soil biomass of bacteria, gram-positive bacteria (G⁺), gram-negative bacteria (G^-) and actinomyces, the plantation 25 a in age ranked first．Hierarchical clustering and principal component analysis (PCA) revealed that stand age did affect soil microbial community structure significantly, and as a result, soil microbial community structure in the plantations 13 a and 25 a old differed sharply from those in the plantations 38 a and 58 a old. Redundancy analysis (RDA) of soil PLFAs and soil nutrients shows that soil organic carbon, total nitrogen and pH were the main factors affecting soil microbial community structure. In the light of average well color development (AWCD) and microbial functional diversity indexes of the soil (Shannon indexes、Simpson indexes and McIntosh indexes) the plantations displayed an order of 25 a > 13 a> 58 a >38 a; the plantations also varied sharply in utilization of carbon sources. Amino acids, carboxylic acids and amines were the main carbon sources in all the soils, and the plantation 25 a old was the highest in utilization rate of these carbon sources. 【Conclusion】 Both the PLFA and BIOLOG demonstrate that when the plantations of Pinus massoniana grow over 25 years, their soil microbial community structures lower in stability and their metabolic function does in activity, too significantly, which in turn exacerbates microecological imbalance in the soils of Pinus massoniana plantations.

Abstract:【Objective】 To study effects of stand density on understory species diversity and soil nutrients in Chinese fir plantations, a field survey was carried out in a Chinese fir plantation, 38 years old, varying in stand density in Dagang Mountain, Jiangxi Province. 【Method】 Five plots of woodlands different in stand density were delineated for investigation of understory species therein, and soil samples were collected from each plot for analysis of soil physical and chemical properties and soil enzyme activities. And One-way ANOVA analysis and correlation analysis and principal component analysis of the obtained data were performed for determination of relationships of understory species diversity and soil properties with stand density. Besides. principal component analysis and factor analysis were conducted to calculate scores of various index factors of the plantation, in an attempt to screen out a suitable density for growth of Chinese fir trees in plantations. 【Result】 Results show that there were 121 species of understory plants found under the Chinese fir trees in the plantation. The shrub layer was dominated by Maesa japonica, while the herb layer was by ferns, such as Diplazium and Dryopteris fuscipes. The two layers both were the highest in diversity in the plot, 5 000 trees hm^-2 in initial density. The variation of soil nutrients did not differ much with soil layer, but did with stand density. All the soil nutrients, except pH, organic carbon and celllase, were the highest in the plots either the highest or the lowest in stand density and obviously varied with stand density. Soil nutrients in the 0~20 cm soil layer were more closely related to herbaceous diversity, while soil nutrients in the 20~40 cm soil layer were more to shrub diversity. The factors of pH, total nitrogen, alkalytic nitrogen, available phosphorus were the most closely related to the species diversity index of the understory. The principal component analysis shows that the plot 6 667 trees hm-2 in initial stand density was the highest in comprehensive score (1.17), and followed by the plots 3 333 trees hm^-2 (0.93), 5 000 trees hm^-2 (0.28), 1 667 trees hm^-2 (0.12) and 10 000 trees hm^-2 (-2.49). obviously the first two were significantly higher than the other three in score. 【Conclusion】The research on plant diversity index and soil physicochemical properties reveals that the initial density of 5 000 trees hm^-2 is good to stability of understory species diversity, but not so to accumulation of soil nutrients. The principal component analysis shows that stand density, either too high or too low, is detrimental to the development of soil physical and chemical properties and plant diversity, especially when the density is too high, its damage to forest land is enormous, exhibiting a "hump model", which indicates the initial densities of 6 667 trees hm^-2 and 3 333 trees hm^-2 are more suitable to the development of soil physical-chemical properties and plant diversity. The "Hump model" shows that taking into comprehensive account, the co-existence of different stand densities in a plantation may better maintain soil properties, increase plant diversity in the ecosystem and improve the ecological environment, thus contributing to multi-purpose cultivation and sustainable development of of Chinese fir plantations.

Abstract:Changes in molecular weight and solubility of humic acid were investigated when hydrochloric acid, formic acid, acetic acid and propionic acid were spiked, by volumetric exclusion chromatography and TOC analysis. To verify the existence of charge-assisted hydrogen bonds (CAHB), formic acid was added into four kinds of model chemicals (i.e. ascorbic acid, benzoic acid, phenol, and catechol), and then excursion of their ultraviolet spectra were detected. Molecular weight of humic acid was reduced by the small molecular organic acids spiked. Additionally, solubility of humic acid significantly increased at pH approaching the p K_a of small molecular organic acids. All the findings demonstrate that CAHB possibly forms between small molecular organic acids and humic acid, which would destroy the supramolecules structure maintained by weak forces, thus leading to reduction of molecular weight and enhancement of solubility of humic acid. Moreover, the smaller the p K_a difference is, the stronger CAHB formed and the greater the molecule structure disturbance is. Small molecular organic acid could interact with some chemicals of humic acid bonded by CAHB when both have similar p K_a, and the energy for transition increases, which were indicated by UV spectrum and synchronous 2D correlation UV spectrum analysis.