Abstract:Black soils in Northeast China, reclaimed in recent 60~200 years, is one of the most productive soils in the world, and plays a vital role in guaranteeing national food security. Based on the summarized general situation of black soils in Northeast China including definition, distribution, soil types and reclamation span, this review presents a research footprint for black soils in the recent 70 years and raises future research orientations. Black soils including mollisol, chernozem, meadow soil, albic soil, dark brown soil, and brown soil are dominantly distributed in Liaohe plain, Songnen plain, and Sanjiang plain. The soil fertility under virgin land is relatively high but underwent great changed under the combined role of ecological system change and human activity. Also, the soil organic matter (SOM) sharply decreased during the early period (0-30 a) of black soils reclamation, then the decrease rate of SOM tended to reach stability after 50 years of reclamation. Black soil layer loss observed in eroded regions resulted from water erosion and wind erosion. The organic amendment, rotation, and contouring cropping were extensively adopted to enhance soil fertility and control soil erosion. The black soil layer is the landmark layer in black soils and is the core of soil fertility. Given black soil layer protection, the following suggestions can play a key role in the protection and utilization of black soil:(1) reveal the change processes of thickness and color in black soil layer and the driving mechanism and explore approaches that maintain and increase black soil layer thickness in current agronomic practices; (2) integrate building patterns of protection and utilization of black soil according to the local conditions. Consider conditions such as the core of fertile cultivated layer, barriers layer subduction and conservation of water and soil based on the dominant factor limiting black soils' productivity, and deeply mining the adaptation, effect and mechanism of the patterns; (3) establish monitoring sites on the long slopes in the slope cropland and focus on new technologies research related to controlling soil erosion.

Abstract:Ralstonia solanacearum is a kind of soil-borne bacteria destructive to agricultural crops. As it is extensively distributed in the tropical, subtropical and temperate zones, it seriously threatens food safety of the world. In the world, a large number of scientists have devoted their efforts to studying bacterial wilt and R. solanacearum, but few have done a systematic research because there are so many factors contributing to the survival of R. solanacearum and most of the researches focus on a single factor only. Therefore, it is essential to identify what are the key factors that influence R. solanacearum survival in the soil to gain some valuable insights into management and control of the soil-borne diseases. Nevertheless, the factors are multifarious and their dynamics in soil systems together with their effects on R. solanacearum remain poorly explored. Herein, this paper aimed to primarily collate the effects and traits of R. solanacearum, as well as soil biotic and abiotic factors on the survival of R. solanacearum in soil. To achieve this goal, this paper first reviewed researches on impacts of individual and population characteristics of R. solanacearum, and then those on interactions of soil biotic and abiotic factors on R. solanacearum, especially reports on their roles in controlling soil-borne plant diseases. In the next section, this paper put forth an outlook for control of plant pathogenic R. solanacearum in future in light of the problems existing currently in this aspect. The traits of R. solanacearum include gene, behavior, and metabolite; soil biotic factors, such as populations and community structures of soil nematode, protozoan, bacteria, fungi, and specialized phage; and soil abiotic factors, such as root exudate, soil nutrients (i.e. N, P, and K), and soil physiochemical properties (i.e. pH, density, and temperature). Similarly, R. solanacearum survival in soil has three aspects:survival in the non-rhizospheric soil adjacent to the host plant, survival in the rhizosphere of the host plant, and survival on the root surface of the host plant. Hence, it is suggested that future researches be oriented towards investigation of R. solanacearum survival in soil and exploration of measures and practices of preventing soil-borne diseases. Therefore, future efforts should be accordingly devoted firstly to investigations of influences of soil microorganism, soil fungal communities, and general phage on R. solanacearum survival in soil. Soil microorganisms, such as earthworm and mite are important components of the soil food web, which can significantly change the above-mentioned biotic factors of R. solanacearum in soil together with soil structure. Secondly, it is essential to clarify how R. solanacearum dynamic in soil responds to climate change. Climate change, such as warming and drought can directly influence R. solanacearum survival by regulating soil temperature and moisture, and indirectly by affecting growth of the host plants. Thirdly, mathematical models should be constructed as soon as possible for predicting survival rate of R. solanacearum in soil. This is essential due to the multifarious nature and complexity of the factors influencing R. solanacearum survival in soils. Hence, mathematical models might be the only tools to clearly assess these elements with designed objects and parameters. The models can even assess relative contribution of each factor to R. solanacearum survival separately under certain conditions and further distinguish key influencing factors. And fourthly, it is important to comprehensively investigate influencing factors while controlling the soil-borne disease in the field. This is a result of manipulating the factors influencing R. solanacearum survival in soil. At the end, more, attention should be paid to irrigation schemes. Irrigation may significantly affect effectiveness of the measures or practices of preventing the bacterial wilt due to its substantial R. solanacearum introduction to the field.

Abstract:Soil microbes play an important role in a number of processes of the terrestrial ecosystem. Rapid urbanization brings about drastic changes in land use in urban and rural areas, thus forming a heterogenous environmental gradient, and directly and/or indirectly affecting compositions and functions of soil microbial communities and further on their ecosystem services. In the present review, composition characteristics of the soil microbial community varying with the landscape unit in the complex ecosystem and their main affecting factors, and functional variation of the soil microbial community along an urbanization gradient were summarized. An environmental gradient from urban to rural areas was found as a result of rapid urbanization causing variation of composition and functions of the soil microbial community. Land use, soil pollutants, vegetation cover, soil properties and some others were the main environmental factors jointly affecting soil microbial communities. However, the leading factors affecting soil microbial communities vary with the landscape. Then ecological service functions of soil microbes were discussed and their variation with the landscape analyzed. It is, therefore, essential to analyze further in detail effects of the social-economic-natural complex ecosystem, varying in characteristic and pattern, on soil microbial communities, to explore mechanisms of the generation and maintenance of ecological services that soil microbes in different functional zones of urban-rural complex ecosystem render to the soil, and to specify mechanism of soil microbes maintaining soil security and human health in a varying environment, so as to improve ecological service functions of the soil and maintain urban and rural soil security and health of the living environment.

Abstract:Soil organic carbon is the foundation and core of farmland fertility, which is of great significance for crop yield, agricultural environment and the earth's carbon cycling. Crop straw is one of the important external sources for soil organic carbon replenishment in cropping soils. The processes of returning straw to soil exert a significant effect on the turnover of soil organic carbon and hence carbon pool balance. Soil carbon priming is a common phenomenon, which can be defined as an distinct shift of native organic carbon mineralization due to fresh organic matter inputs into the soils. There is an increased attention to the straw-induced priming effect in the recent years, due mainly to the fact that straw incorporation not only involves high-effective resource utilization of crop straw residue, but also directly relates to the balance of soil carbon pool and its functionality. Despite a tremendous advance in the theoretical study on soil organic carbon priming following the external organic matter inputs, we are currently facing other big challenges. For instance, that how to combine this latest theoretical knowledge into the practical application of straw residue management aiming to promote soil carbon sequestration and reduce carbon emissions. To tackle these difficulties, the characteristics and potential mechanisms of the organic carbon priming due to straw return to soils should be clarified, and its specific drivers (i.e., edaphic, climatic and anthropogenic factors) should also be fully identified fully. This paper first systematically summarized the potential theoretical basis of organic carbon priming such as co-metabolism theory, N-mining theory, stoichiometric decomposition and microbial, and necromass reuse. Secondly, we combined existing research data and theoretical hypotheses to elaborate a series of implicit factors that govern the direction and magnitude of soil carbon priming, including the straw type and quantity, return method, water and fertilizer management, soil properties, and climatic agency, et al. Finally, taking into the consideration the high-effective utilization of straw residue, the sustainable build-up of soil carbon pool, and environmentally friendly farming practices, the potential research directions on straw-induced soil carbon priming we proposed, and the adaptative straw management methods designed to promote soil carbon sequestration were also outlined.

Abstract:Sugar alcohols which are products of photosynthesis of many plant species have a variety of biological effects and participate in plant life activities through different ways. Sugar alcohols-chelated fertilizers synthesized with sugar alcohol as a chelating ligand promote the migration of calcium, boron, and other nutrients in plants. Although related studies have shown that sugar alcohol chelating agent can effectively improve crop yield and quality, its development in China is still in the initial stage. One reason for this slow adoption is that researchers pay more attention to the efficiency of sugar alcohol chelated fertilizers than they do for the response mechanism of crops under different conditions. Thus, scientific research on sugar alcohol chelated fertilizers lags far behind its practical application, which has resulted in the lack of in-depth understanding of the ecological effects. Importantly, previous studies have often neglected the role of sugar alcohols in organisms, and sugar alcohol chelated fertilizers are mostly mixtures, so it was difficult to distinguish whether sugar alcohols or sugar alcohol complexes played a key role in promoting crop growth. Besides, due to the unclear chelating mechanism of sugar alcohol complexes, it was difficult to use available methods to perform qualitative and quantitative analysis. This hindered the promotion and application of sugar alcohol chelated fertilizers in China's agriculture. Based on the above reasons, this paper briefly describes (i) sugar alcohol chelating technology, (ii) the advantages of sugar alcohol chelated fertilizers, (iii) the biological effects of sugar alcohols in plants, and (iv) the shortcomings in the research of sugar alcohol chelated fertilizers through the current application status. Thus, this review aims to provide a technical basis and development direction for the research, development, and popularization of sugar alcohol chelated fertilizers.

Abstract:[Objective] This paper is oriented to reveal changes in climate, monsoon and sandstorm activity in Holocene in Xi'an area, to explore impacts of cold dry climate and warm wet climate on loess erosion and to define erosion period of the loess strata.[Method] Field surveys were carried out to investigate how loess and paleosol eroded in Holocene. Of the loess and paleosol, chemical compositions were determined with an X-ray fluorescence analysis instrument, CaCO₃ content with the gas volume method, and magnetic susceptibility with a magnetic susceptibility instrument.[Results] Through the field investigation of 13 sample sites points at Bailuyuan of Xian, it is found that the mid-Holocene paleosol, rarely discovered in the loess plateau in the past, can be divided into three layers, including one layers of loess and two layers of paleosol. The loess and paleosol in the entire Holocene profile can be divided into five layers. The Holocene profile in Milucun displayed apparent changes in chemical composition and magnetic susceptibility and its loess and paleosol can also be divided into five layers, of which two paleosol layers are high and three loess layers low in SiO₂, Fe₂O₃, Al₂O and K₂O, and the five layers exhibit reverse trends in soil CaO. In the early mid-Holocene S₀₂ paleosol layer, Fe₂O₃ content varied in the range of 56.8~62.4 g·kg^-1, and in the lower part of the paleosol it has been enriched up to 8.0 g·kg^-1and Al₂O₃up to 15.0 g·kg^-1. The two paleosol layers are high in Rb, Ba, Ni, Sr and V (five trace elements) and the three loess layers are just the opposite, except in Sr. In the Holocene loess profile, CaCO₃ varies similarly to CaO in content. The S₀₂ paleosol layer is very low in CaCO₃, demonstrating the feature of leaching soil being low in CaCO₃. The two paleosol layers are high in low frequency magnetic susceptibility, while the three loess layers are low.[Conclusion] Various environmental indices indicate that in Beiluyuan the Holocene climate change and sandstorm activity can be divided into five stages. In the mid-Holocene, the period between 8 500-6 000 aB.P and 5 000-3 100 aB.P when paleosol was developing witnessed stronger summer monsoon activity, higher precipitation, more humid climate, and weaker sandstorm activity than the period from 10 000-8 500aB.P to 6 000-5 000 aB.P when paleosol was developing in Bailuyuan. During the five climatic stages of Holocene, the five soil layers display an order of paleosol S₀₂> paleosol S₀₁> loess Lx > loess L₀ > loess L_t in terms of thermohumidity and a reverse order in terms of intensity of sandstorm activity. The mid-Holocene S₀₂ paleosol developed during 8 500-6 000 aB.P experienced moderate and moderate on the strong side chemical weathering, and enriched Fe₂O₃ and Al₂O₃ to some extent, hence the soil could be sorted into a type of soil similar to subtropical yellow brown forest soil, which indicates that the average annual precipitation at that time is about 150 mm more than it is today. Although the interglacial period with weak sandstorm activity is the theoretical erosion period of loess strata, in fact, the soil erosion in the interglacial period was very weak. The Holocene loess erosion happened mainly during the period under a cold dry climate instead of under a thermohumid climate. Between the period of 6 000-5 000 aB.P in the mid-Holocene when the thin-layered loess was developing, the climate became dry and cold, thus leading to degradation of the vegetation and intensification of loess erosion. The loess in most areas of Xi'an got lost through erosion more than it accumulated during this period, and so was the case in most areas of the Loess Plateau, too, which is the main reason for the absence of thin-layered loess in the Holocene from 6 000 to 5 000 years in most areas of Loess Plateau.

Abstract:[Objective] Soil erosion is a major contributor to the loss of land resources, and hinders development of the agricultural production and construction of the ecological civilization. The purpose of this study is to explore impacts of slope gradient on amount and distance of splash erosion.[Method] Using splash collectors that can be adjusted towards eight directions separately, five troughs (packed with lou soil and set at a slope gradient of 0°, 5°, 10°, 15° and 20°, separately and a new model of needle spinkling device driven by a linear vibration motor, simulated rain-splash erosion experiments were carried out to explore relationships between slope gradient with amount and distance of splash erosion.[Results] (1) the amount of splash erosion on the slope of 0°, 5°, 10°, 15° and 20° was measured to be 0.486 g, 0.871 g, 1.235 g, 1.757 g and 3.570 g, respectively. It can be seen that a linear relationship between slope and amount of downward splash erosion was observed with y=0.1411x + 0.173 and R²=0.9983in the range of 0°~20°. The amount of downward splash erosion on the slope of 0°, 5°, 10°, 15° and 20° reached 0.632 g, 0.629 g, 0.621 g, 0.557 g and 0.588 g respectively. (2) The total amount of splash erosion on the slope of 0°, 5°, 10°, 15° and 20° was 3.815g, 3.902g, 4.106g, 4.889 g and 6.657 g, respectively, from which a binary function relationship was observed with y=0.0156 x²-0.21 x + 4.5815 and R²=0.9983 between total amount of dispersed splash erosion and slope. (3) the net sediment transportation volume of splash erosion on the slope of 0°, 5°, 10°, 15° and 20° was -0.148 g, 0.242 g, 0.614 g, 1.200g and 2.982 g, respectively. (4) the percentage of the splash erosion of first round on 0°, 5°, 10°, 15° and 20° slope was 46%, 34%, 33%, 30% and 29%, respectively, while the percentage of the splash erosion of the third round was 10%, 5%, 13%, 17% and 23%, respectively.[Conclusion] On the slope varying in the range of 0~20°, with rising slope gradient, the total amount of dispersed splash erosion, the net sediment carrying amount of splash erosion and the amount of downward splash erosion on the slope increases, while the amount of splash erosion decreases first and then increases. There is no significant relationship between splash erosion and slope gradient.

Abstract:[Objective] How to arrange rationally land preparation measures on terraced slopes affects runoff generation, rainfall infiltration, and water conservation capacity, thereon. It's of great significance to understand the spatio-temporal heterogeneity of soil moisture in terraced orchards different in land preparation measure and its mechanism, for promoting development of the forest and fruit industry.[Method] For this paper, the navel orange orchard development demonstration area in the small watershed of Xiaoyang in a low hilly red soil region in South China is selected as the research area. Three slopes, typical of the area, but different in land use structure (optimally prepared terraced slope, extensively prepared terraced slope, and unprepared waste grassland slope) and four types of land use (orchard on optimally prepared terraced slope, orchard on extensively prepared terraced slope, waste grassland, and cropland) were selected as the research objects for the study on spatio-temporal distribution of soil water relative to land preparation and land use. Soil water content in five soil layers (0~20, 20~40, 40~60, 60~80 and 80~100 cm) at five slope positions (top slope, upper slope, middle slope, lower slope, and toe slope) on all the four slopes was monitored in both seasons (rainy and dry season). And redundant analysis was performed to determine the main terrain factors (including slope position, slope, land use type and altitude) that affect spatio-temporal distribution of soil water content in different seasons and soil layers.[Result] Results show:1) soil water content during the rainy season varied with land use of a slope, exhibiting an order of slope of cropland (0.4088 m³·m^-3) > orchard on extensively prepared terraced slope (0.3227 m³·m^-3) > orchard on optimally prepared terraced slope (0.3078 m³·m^-3) > slope of waste grassland (0.2739 m³·m^-3). Apparently, the two orchards did not differ much, but did significantly from the other two. During the dry season, soil water content decreased much faster in the slope of waste grassland and the orchard on extensively prepared terraced slope than in the two. On the slope of farmland, the impact of slope position on soil water content was the least. In terms of soil water content during the dry season, the four slopes followed a decreasing order of slope of cropland (0.3524 m³·m^-3) > orchard on optimally prepared terraced slope (0.1980 m³·m^-3) > orchard extensively prepared terraced slope (0.1475 m³·m^-3) > slope of waste grassland (0.1380 m³·m^-3). Obviously the last two were much lower than the first two. 2) Soil water content gradually increased along the slope from the top to the toe, during both the rainy and dry seasons, but differed slightly between the upper, middle and lower parts of the three slopes, however, spatial heterogeneity intensified significantly after land preparation of the slopes. 3) The main topographic factors affecting the distribution of soil water content during the rainy season were slope position (P=0.002) and land use (P=0.048), and during the dry season were land use (P=0.008), slope position (P=0.024) and altitude (P=0.024), however, slope gradient was an insignificant one.[Conclusion] In general, land preparation of the slopes significantly increased rain water infiltration capacity and hence soil water content of the surface (0~20 cm) soil layer during the rainy season, especially in the orchard on the optimally prepared terraced slope, where the water storage and retention capacity was significantly improved during the dry season. All the findings in this study may serve as a scientific basis for rational arrangement of land resources in the region, optimization of the spatial layout of soil and water conservation measures, and comprehensive soil erosion control.

Abstract:[Objective] Effects of the implementation of the "Grain for Green" policy, relative to history, on oasis vegetation composition, soil physical, chemical and microbial properties, and soil enzyme activities were analyzed.[Method] To that end, plots of lands different in "Grain for Green" history (1, 2, 4, 8, 13, 20, 30 and 40 a) and a plot of farmland as CK in the Minqin Oasis were cited for exploration of effects of the practice on vegetation restoration and soil properties, using the spatial-temporal substitution method.[Result] Results show that in the 9 plots (including CK), representing natural succession of vegetation during a period of 40 years, a total of 43 species of plants were observed, and the vegetation evolved gradually from a community of annual herbaceous plants to that of shrubs only, showing strong continuity and progressiveness. With the increase in age, soil moisture content declined first, then rose and declined again, appearing like an inverted "N" in variation trend, and was higher in the upper soil layer than in the lower layer in the plots over 20 years in age; soil bulk density decreased gradually on the whole; soil particle size composition did not show any regular trend in variation, and was dominated with fine sands rather than clay; soil total nitrogen, soil available potassium, soil organic matter and soil microbial biomass carbon all rose first and then declined in content, while soil available phosphorus did not change much in content, but did in margin; soil bacteria and actinomycetes decreased to a different degree in population; with bacteria being in dominancy and reaching up to 611.46×10⁵Cfu.g^-1; and soil enzyme activities fluctuated, but on a generally declining trend. Moreover, with increasing soil depth, soil bulk density, soil nutrient contents and soil microorganisms generally decreased, and the phenomena of surface accumulation was quite obvious.[Conclusion] The cluster pedigree chart of the plots demonstrates that the 4^th years after the "Grain for Green" practice was implemented are critical for the land to have vegetation recovered in the Minqin Oasis. All the findings in the experiment may serve as a practical and theoretical basis for conservation and restoration of ecosystems in arid oases.

Abstract:The Sichuan Basin is an area the most representative of purplish sandstones and shales distribution in China, with the Shaximiao formation (J₂s) being the most widely distributed strata.[Objective] The purpose of this article is to improve soil taxonomy in Sichuan Province, and to discuss rationality of the requirement for hue in classification of "L.C. of Purplish Sandstones and Shales" in line with the Chinese Soil Taxonomy.[Method] A total of 19 soil profiles typical of the Shaximiao formation in Sichuan were selected for analysis of soil-forming environment, morphological features and physico-chemical properties. In line with the criteria set in the Keys to the Chinese Soil Taxonomy (3rd edition), diagnostic horizons and characteristics of the soil profiles were determined and attributions of the profiles specified in the Chinese Soil Taxonomy.[Result] The 19 soil profiles could be sorted into 3 orders, 3 suborders, 7 groups and 12 subgroups, and only 7 of them were found in conformity with the requirement for hue of "L.C. of Purplish Sandstones and Shales", accounting for only 43.75% of the purplish soil, which indicates that most of the purplish soil individuals did not meet this hue requirement.[Conclusion] The purplish soils matched 10 subgroups in the soil taxonomy. Compared with the system of soil genesis classification, the soil taxonomy pays more attention to properties of the purplish soil per se in classification. Taking into account the color characteristics of the purplish soil in this study, it is suggested that the hue range of "2.5YR~5YR, dry value of 4~6 and dry chroma of 3~4" be augmented in addition to the original hue requirements of "L.C. of Purplish Sandstones and Shales", then the purplish soil individuals that match this diagnostic feature in visual colorimetry may reach 64.71% in proportion and increase from 0 to 3 in number in the instrumental colorimetry. Since visual colorimetry is more likely to have errors than instrumental colorimetry it is suggested that the Chinese Soil Taxonomy should stipulate the use of a modern, more objective and more accurate color measuring instrument, and on such a basis the color ranges of some diagnostic features need to be redrafted.

Abstract:[Objective] Plot tests were designed to study the effects of coal gangues and caliche nodules on the characteristics of plant growth and soil water content on the Loess Plateau. This study was important for accurate quantification of soil water content and scientifically formulating vegetation restoration strategies.[Method] Caragana (Caragana korshinskii Kom.) and Alfalfa (Medicago sativa.) were planted in 2 m³ experimental plots underground, containing reconstituted soil, made up of the fine earth and either coal gangues or caliche nodules (300 g·kg^-1) under natural climate conditions. The water content and plant growth were regularly observed.[Result] The results showed that coal gangues negatively affected plant development and quality, while caliche nodules had no significant effect. The accumulative aboveground biomass of Caragana and alfalfa in the soil containing coal gangues was 47% and 21% lower than that in the fine earth, respectively. Also, the accumulative aboveground biomass of Caragana and alfalfa in the soil containing coal gangues was 45% and 24% lower than that in the soil containing caliche nodules, respectively. Therefore, the adaptability of alfalfa to the soil containing coal gangues was better than that of Caragana. Plant species had weak effects on soil water content when compared to the media types. The water content of the soil with coal gangues was significantly higher than that of the other two media. The differences in the water content between medium types were the largest at a depth of 30 to 50 cm. When Caragana was planted, the differences of evapotranspiration between soils containing coal gangues and caliche nodules, and between soils containing coal gangues and the fine earth accounted for about 12% and 23% of the average water storage of the fine earth, respectively. Also, when alfalfa was planted, the differences of evapotranspiration between soils containing coal gangues and caliche nodules, and between soils containing coal gangues and fine earth accounted for -11% and 11% of the average water storage of the fine earth, respectively. Importantly, the inhibiting effects of coal gangue and caliche nodules on soil water loss were different and varied with plant species.[Conclusion] In conclusion, we observed that the importance of coal gangues and caliche nodules cannot be ignored when predicting soil water content, especially under vegetation coverage.

Abstract:[Objective] A shallow karst fissure(SKF) is a significant habitat in rocky desertification areas that provides growing space, water, and nutrients for plant growth. To explore the differences in the stability of aggregates, the primary mechanism of aggregate decomposition in different soil horizons in SKF, and the vertical variation characteristics of nutrient contents in aggregates, an experiment was performed in the karst region of southwest China.[Method] Two typical forms of SKF (rectangle-type SKF and funnel-type SKF) was selected for this study and the particle size distribution and stability characteristics of soil aggregates in different soil horizons (0-20 cm, 30-50 cm, 50-70 cm, 70-90 cm, and 90-110 cm) were explored by the dry and wet sieving method. Also, the mechanisms of soil aggregate decomposition were analyzed by the Le Bissonnais method. Furthermore, the contents of soil organic matter (SOM), alkali-hydrolyzable nitrogen (AHN), and available phosphorous (AP) were determined in aggregates with different particle sizes, and the relationship between these nutrients and the stability of soil aggregates was analyzed.[Result] The aggregate fractal dimensions (D) under dry and wet sieving ranged from 1.57 to 2.18 and from 1.55 to 2.15, respectively. The stability and erosion resistance of SKF soil aggregates decreased with the depth of soil horizons, and the rectangle-type SKF soil aggregate was more stable than funnel-type SKF. The major mechanism observed for SKF soil aggregate decomposition was slaking generated by fast wetting. According to the indicators of percentage of aggregate disruption (PAD); the fractal dimension D and mean weight diameter (MWD), SKF soil aggregates have good water stability and permeability. In the 0-20 cm soil horizon, the variation of SOM, AHN, and AP contents in aggregates of different particle sizes were 38.34±6.53-90.91±10.02 g·kg^-1, 208.09±24.10-373.93±38.27 mg·kg^-1, and 1.98±0.96-8.13±6.45 mg·kg^-1, respectively. In soil 30 cm below the surface, the contents of SOM, AHN, and AP declined sharply compared to those in 0-20 cm soil horizon, which were 13.27±0.94-37.53±3.47 g·kg^-1, 71.58±3.27-198.54±22.63 mg·kg^-1, and 0.15±0.03-0.38±0.10 mg·kg^-1, respectively; with a very low AP content. Importantly, the particle size of aggregates was not an important factor governing the nutrient content of the aggregates. Additionally, SKF morphology had different effects on the variations in SOM, AHN, and AP contents with soil depth. SOM content below surface 30 cm horizons in rectangle-type SKF was significantly decreased with increasing depth of SKF, while no significant difference was observed in funnel-type SKF. The variation trends of AP content with increasing SKF depth were consistent in rectangular and funnel-type SKF profiles, while there was no significant correlation between the variation trends of AHN content and SKF morphology. According to the correlation analysis, higher SOM, AHN, and AP contents indicated stronger water stability of the SKF soil aggregates.[Conclusion] The water stability of SKF soil aggregates is an important factor for these soils and decreases as the soil horizons deepen, with the major mechanism of soil aggregate decomposition being slaking generated by fast wetting. Also, the morphology of SKF showed varied effects on the variations of SOM, AHN, and AP content at different soil depth.

Abstract:[Objective] Greenhouse soil is a typical commercial upland soil in suburban areas of China. With heavy metals, especially cadmium, accumulating year by year the greenhouse soil gradually loses its productivity, while degrading in ecological environment and agricultural product quality. Application of organic manure is one of the main measures to improve soil fertility and soil microbial activity in greenhouse agriculture, however, the manure often carries a certain amount of heavy metals. Consequently, long-term application of organic manure will increase the input of heavy metals in soil. In order to rationalize application organic manure for better soil properties and less heavy metal pollution in greenhouse soil, it is essential to study effects of long-term application of organic manure on the contents of total and available cadmium (Cd) and physicochemical properties of the greenhouse soil, as well as their correlations.[Method] Soil samples were collected from 0-10 cm, 10-20 cm and 20-40 cm soil layers of greenhouses different in fertilization, that is, application organic manure at a conventional rate (M1), application of organic manure at less than the conventional rate (M2), application of organic manure at less than the conventional rate plus chemical fertilizer at a certain rate (M3) and no fertilizer or manure (the control, CK), at the Zhuanghang Experimental Station of the Shanghai Academy of Agricultural Science, China for analysis of soil physicochemical properties, total Cd and available Cd, and further relationships between soil (total and available) Cd contents and physicochemical properties.[Result] As compared to the control, the greenhouse applied with organic manure significantly decreased the content of total Cd in the surface (0-20 cm) soil layer, and the reduction was more significant with less manure application. However, the effect was not observed in the subsurface (20-40 cm) soil layer, and how to apply organic manure did not have any effect either. The content of available Cd in the surface soil layer was higher than that in the subsurface soil layer. Long-term application of organic manure did increase the content of available Cd content in the surface soil layer, especially the 0-10 cm soil layer, where the content of available Cd was significantly higher than that in the control. Compared with Treatment M1, Treatment M2 and Treatment M3 was significantly or 17.56% and 14.04% lower than Treatment M1, respectively, in available Cd content in the 0-10 cm soil layer. Treatment M3 was significantly higher than CK in contents of soil organic matter, soil total nitrogen, and surface soil available phosphorous, and than Treatment M1 in pH. Correlation analysis shows that the contents of organic matter and available phosphorus were significantly and positively related to the contents of total and available Cd, and so was the content of total nitrogen to the content of available Cd, however pH ultra-significantly and negatively related to the content of available Cd.[Conclusion] All the above findings show that application of organic manure at a properly reduced rate, while applying appropriate amount of chemical fertilizer, can further improve greenhouse soil properties, and reduce accumulation and availability of Cd in the surface soil of the greenhouses.

Abstract:[Objective] China nowadays has approximately 100 million people suffering from zinc (Zn) deficiency, mainly because they live on cereal crops as their staple food and hence fail to take in adequate Zn, especially in the rural areas. As one of the major wheat-producing areas, the Huanghuai Plain contributes to about 70% of the wheat (Triticum aestivum L.) grain yield of China. So it is of great significance to understand causes of the variation of Zn concentration in wheat grains to guarantee high-yield and high-quality wheat production in the region, so as to ensure food security and human health.[Method] Combined with a two-year in situ farm survey, samples of wheat shoot (the aboveground part) and soil in the 0~100 cm layer were collected from 276 randomly selected farmers' fields during the wheat harvesting season in the Huanghuai wheat production region for analysis of Zn concentration. Comparison was made between wheat grains produced in Zn-deficient (DTPA-Zn<1.0 mg·kg^-1) and non-Zn-deficient (DTPA-Zn ≥ 1.0 mg·kg^-1) soils in grain Zn concentration and correlation analysis performed of grain Zn concentration with grain yield, yield components, fertilization rates, soil nutrients in the 0-100 cm layer, and Zn uptake and utilization of the crop, separately.[Result] Results show that 42% and 58% of the wheat fields in the region were of Zn-deficient (DTPA-Zn<1.0 mg·kg^-1) and non-Zn-deficient (DTPA-Zn ≥ 1.0 mg·kg^-1) soils, and produced grains with Zn concentration ranging from 16 to 52 mg·kg^-1 and from 17 to 58 mg·kg^-1, respectively. About 7% and 9% of the grain samples from the two types of wheat fields met the recommended criterion (≥ 40 mg·kg^-1) for grain Zn concentration. Generally, the farmers in the region prefer to grow local specific elite cultivars of wheat, however, it was difficult to identify high-Zn or potentially high-Zn traits of the cultivars due to the limited sample size at a regional scale. In this survey, the selected wheat fields did not receive any Zn fertilizer or other Zn-containing fertilizers, and only 10% and 18% of the fields of Zn-deficient soil and non-Zn-deficient soil were applied with organic manure. In the fields of Zn-deficient soils, grain Zn concentration had nothing to do with nitrogen (N) and potassium (K) fertilization rates, but did negatively, with phosphorus (P) fertilization rate (r=-0.273, P < 0.01) and available P in the 0-20 cm soil layer (r=-0.283, P < 0.01). In the two groups of wheat fields, high and low in grain Zn concentration, with soil available P being 13 and 20 mg·kg^-1, and available Zn being 0.8 and 0.7 mg·kg^-1 in 0-20 cm soil, P₂O₅ fertilizer was applied at 65.8 and 68.4 kg·hm^-2to achieve targeted grain yield. Also, the grain yield and shoot Zn uptake were observed to be lower in the fields of Zn-deficient soils(7 204 kg·hm^-2 and 279 g·hm^-2) than in the fields of non-Zn-deficient soils (7 857 kg·hm^-2 and 318 g·hm^-2). In the fields of non-Zn-deficient soils, grain Zn concentration had nothing to do with N and K fertilization rates, either, but was negatively related to P fertilization rate (r=-0.181, P < 0.05) and positively to soil available Zn in the 0-20 cm (r=0.236, P < 0.01) and 20-40 cm (r=0.183, P < 0.05) soil layers. In the two groups of wheat fields of Zn-deficient and non-Zn-deficient soils, with available P being 29 and 30 mg·kg^-1, and available Zn being 3.3 and 2.2 mg·kg^-1 in the 0-20 cm soil layer, P fertilizer was applied at a rate of 112 and 145 kg P₂O₅·hm^-2, respectively, and P₂O₅ requirement for targeted average grain yield reached 69.2 and 70.8 kg·hm^-2, respectively.[Conclusion] Therefore, it could be considered that it is advisable to address the problem of lack of available soil Zn firstly, by increasing the content of soil available Zn up to the critical values of 1.0 and 3.0 mg·kg^-1 in the fields of Zn-deficient and non-Zn-deficient soils, respectively, and then to reduce P fertilizer application rate and hence available soil P content, so as to alleviate the negative effect of excessive P on crop Zn uptake and accumulation, for the purpose of maintaining high grain yield and improving grain Zn nutrition simultaneously in winter wheat grown in the Huanghuai wheat production region of China.

Abstract:[Objective] Effects of straw returning coupled with application of the mixture of controlled-release urea(CRU) and common urea on maize yield and soil fertility were investigated, in an attempt to provide a scientific basis for rationalizing the application.[Method] A long-term field experiment from 2014 to 2018 was conducted to investigate effects of application of the mixture fertilizer consisting of sulfur and polymer-coated urea, polymer coated urea, and normal urea at a ratio of 3.5:3.5:3 in terms of N to summer maize (Zea mays L., Zhengdan 958) on yield. The experiment was designed to have six treatments:1) No nitrogen applied or straw returning (CK1); 2) No nitrogen applied in addition to straw returning (CK2); 3) Common urea applied only (BBF1); 4) Common urea applied in addition to straw returning(BBF2); 5) Application of the mixture only (CRF1); and 6) Mixture applied in addition to straw returning (CRF2). At the mature stage, soil samples were collected from the 0-20 cm soil layer of each plot for analysis, and LAI, SPAD, yield and yield composition of the maize were measured.[Result] Results show that:1) Treatment BBF2 was 5.9% and 13.3% higher than Treatment BBF1 in 5-year mean of grain yield and accumulative N use efficiency (ANUE), respectively, and Treatment CRF2 and CRF1 was 12.0% and 4.2% higher in maize yield, and 57.3% and 42.4% higher in accumulative N use efficiency, respectively, than Treatment BBF2; 2) The soil samples collected from Treatments CRF2、BBF2、CRF1 and BBF1 at the maize harvest stage in 2018 were 33.5%, 25.9%, 19.5% and 11.4%, respectively, higher in soil organic matter content, 26.6%, 18.6%, 9.9% and 7.0%, respectively, higher in soil total nitrogen content than their respective samples collected in 2013; 3) Treatment CRF2 and BBF2 was 11.8% and 13.0% higher in soil organic matter content, 15.2% and 10.9%, higher in total nitrogen content, respectively, than Treatment CRF1 and BBF1; 4) Treatment CRF1 was 52.0%, 18.6%, 19.5% and 24.7% higher in soil NO₃^--N, NH₄⁺-N, available phosphorus and available potassium content, respectively, than Treatment BBF1, indicating that straw returning further increased soil nutrient content. Treatment CRF2 was 66.3%, 25.2%, 47.5% and 30.4%, higher, respectively, in soil NO₃^--N, NH₄⁺-N, available phosphorus and available potassium content than Treatment BBF1.[Conclusion] All the findings demonstrate that long-term application of the mixture of urea fertilizers coupled with straw returning can significantly improve maize yield, ANUE, net income and soil fertility due to their synergistic interactions.

Abstract:[Objective] In calcareous soils, recent studies have found that soil-derived CO₂not only comes from the decomposition of soil organic carbon (SOC) but also from dissolution of soil inorganic carbon (SIC). Under straw addition, CO₂emission in calcareous soils comes from at least three sources, i.e., straw-C, endogenous SOC and SIC. Owing to technical limitations in source partitioning of CO₂, the effects of straw addition on SOC and SIC release are still not fully understood in calcareous soils. Therefore, this uncertainty needs urgent attention.[Method] We conducted a 32-week laboratory incubation experiment with ¹³C labeled maize straw under different straw rates in calcareous soils collected from farmlands of North China Plain. The effects of straw addition on CO₂ emission from SOC decomposition and SIC dissolution were investigated. The approach was based on using three-source mixing model(IsoSource) to differentiate three sources of CO₂(straw-C, SOC and SIC). Four treatments were set up, including no straw addition (CK), low rates of straw addition(S1, 9.6 t·hm^-2of maize straw amendment), medium rates of straw addition (S2, 28.8 t·hm^-2of maize straw amendment) and high rates of straw addition (S3, 48.0 t·hm^-2of maize straw amendment).[Result] As the incubation time progressed, the contribution of straw decomposition to soil CO₂ emission decreased. The contribution of straw decomposition to soil CO₂ emission increased with the increase of straw addition rates. For S1, S2 and S3 treatments, the soil CO₂ emission derived from straw, SOC and SIC was about 3:3:4, 5:2:3 and 6:2:2, respectively. S1 treatment decreased SOC decomposition by 9%, while S2 and S3 treatments increased SOC decomposition by 22% and 57%, respectively. The mineralization of straw and SOC increased SIC dissolution, and the degree of promotion increased with the amount added. The degrees of promotion for S1, S2 and S3 treatments were 368%, 561% and 652%, respectively.[Conclusion] Straw addition not only affected the release of SOC-derived CO₂, but also the release of SIC-derived CO₂. In calcareous soils, if the contribution of SIC dissolution to soil CO₂ emission is unaccounted for, it may lead to overestimation of SOC decomposition and affect the accuracy of priming effects evaluation.

Abstract:[Objective] The paddy soil in South China rich in iron oxides has soil organic carbon (OC) stored for a long time in association with iron oxides. As the iron oxide and organic carbon in the soil exist mainly in adsorbed-, bonded, and encapsulated forms, the carbon-goethite association vary in stability with the form. Although a large volume of studies have analyzed how OC and iron oxides associate in the soil and what form they exist in. However, so far little is known about mechanism of the association, relative to type, between iron oxides and OC affecting mineralization of OC and its priming effects (PE) in paddy soil.[Method] Glucose was used as the typical low molecular weight exogenous C, and prepared into goethite-adsorbed glucose (Goe-G) and goethite-encapsulated glucose (Goe*G), which were then incubated in the experiment to explore characteristics of the mineralization of the two iron oxides-glucose associations and their PE in paddy soil.[Result] Results show that compared with the pots amended with glucose alone, the pots amended with the two types of carbon-goethite association, separately, had CO₂ and ¹³CO₂ emission increased by 0.39-0.53 times and 0.87-1.07 times, respectively, and CH₄ and ¹³CH₄ emission decreased by 0.44-0.59 fold and 0.25-0.44 fold, respectively. Relative to amendment of goethite-adsorbed glucose, amendment of goethite-encapsulated glucose significantly inhibited CH₄ release. What is more, amendment of carbon-goethite association, regardless of type, promoted the mineralization of SOC into CO₂ but inhibited the release of native SOC-derived CH₄. The inhibitory effect of goethite-encapsulated glucose on the release of native SOC-derived CH₄ was significantly greater than that of goethite adsorbed glucose. The fast pool of goethite-encapsulated glucose was higher than that of goethite adsorbed glucose, and its half-life (T_1/2) was 10.85 times longer than that of goethite adsorbed glucose, and the turnover rate of the fast pool (k₁) and slow pool (k₂) was 10.74 and 19 times smaller than that of the goethite adsorbed glucose, respectively. Secondly, the goethite encapsulated glucose-induced a weak positive PE for CO₂ emission (6.44 mg·kg^-1), but a negative PE for CH₄ emission (-15.49 mg·kg^-1). The findings suggest that the amendment of goethite-encapsulated glucose inhibits mineralization of native SOC(-9.05 mg·kg^-1) and enhances the potential of C assimilation in the paddy soil. Though the addition of either carbon-goethite association has the effect inhibiting mineralization of native SOC, the amendment of goethite-encapsulated OC is more beneficial than that of goethite-adsorbed OC to soil C stabilization and sequestration.[Conclusion] The findings in the experiment suggest that iron-oxides-bonded low molecular weight OC is higher in biological stability than soluble OC, but relatively low in mineralization rate, thus inhibiting mineralization of native SOC and inducing negative priming effect. Therefore, amendment of OC bonded with iron oxides is beneficial to long-term C sequestration effect in paddy soils.

Abstract:[Objective] Nitrous oxide (N₂O) and nitrogen (N₂) are important gaseous products of denitrification in soil profile of flooded rice field, which may be discharged directly into the atmosphere through soil-water interface, or leached into groundwater and eventually into the atmosphere. Application of biochar can alter denitrification process in the paddy field by changing physicochemical and microbiological properties of the paddy soil and then affect the generation and emission of N₂ and N₂O in the field.[Method] In this study, based on a long-term (since 2010) rice-wheat rotation field experiment on biochar amendment. Soil solutions (0-1 m depth) were collected through specially designed piezometers imbedded in the paddy soil. And concentrations of dissolved N₂O and exN₂(N₂ produced by denitrification) in soil solution were determined by gas chromatography and membrane inlet mass spectronmeter. The experiment was designed to have 4 treatments (CK:each season 0 t·hm^-2; 1BC:each season 2.25 t·hm^-2; 5BC:each season 11.3 t·hm^-2; 10BC:each season 22.5 t·hm^-2) for the two rice seasons in 2018 and 2019, and aimed to investigate spatial and temporal variations of N₂O and exN₂ concentrations in soil solution as affected by biochar application rate. The effects of long-term application of biochar on denitrification in paddy soil profile and the exN₂, which was the main gaseous nitrogen product, was washed away by water were evaluated.[Result] The concentration of N₂O is higher in the soil 60 cm in depth in CK and exN₂ concentration decreased with soil depth. N₂O and exN₂ concentrations in profile decreased with rising biochar application rate, thus being the lowest in treatment 10BC. Among them N₂O concentration decreased the most significantly in the soil 60 cm in depth and exN₂concentration decreased with increasing soil depth. Biochar amendments had no obvious effect on inorganic nitrogen (NO₃^- +NH₄⁺) in the soil profile, but increased the concentrations of soluble organic carbon (DOC), dissolved oxygen(DO) and redox potential (Eh) in 5BC and 10BC. The variations of N₂O and exN₂ was related to DOC, NO₃^- and DO in CK, and to DO and Eh in the biochar treatments. The leaching amount of exN₂(calculated by 1 m depth) is 2.3-5.5 kg·hm^-2 in CK, which was equivalent to 32%~34% of the leaching amount of inorganic nitrogen and organic nitrogen (DON), while it was reduced to 1.7-3.7 kg·hm^-2 and 1.1-1.9 kg·hm^-2 in 5BC and 10BC.[Conclusion] All the findings show that the leaching amount of N₂ produced by denitrification with water can not be ignored, the amendment of biochar can improve aeration of the soil profile and increase DO and Eh, thus inhibiting denitrification and reducing the risk of leaching loss of its main gaseous products, exN₂.

Abstract:[Objective] Allylthiourea (ATU) is a promising nitrification inhibitor. However, its effects on soil nitrification and greenhouse gas (GHG) mitigation are still unclear.[Method] In this study, a 21-day microcosm incubation was established with the application of nitrogen (N) and different doses of ATU (1%, 5%, 10%, 15% and 20% of N applied) to a yellow-brown upland soil. Also, dicyandiamide (DCD, 10% of N applied) was applied to compare the inhibition efficiency on nitrification and GHG emission with ATU. The dynamics of inorganic nitrogen and N₂O/CO₂ emission during the incubation were detected, and changes in the different microbial population were analyzed by real-time PCR and 16S rRNA gene-based high through-put sequencing.[Result] N application greatly stimulated soil nitrification activity and promoted N₂O emission. DCD had a strong inhibitory effect on soil nitrification (68.6%) and N₂O emission (93.3%). ATU did not influence soil nitrification at low doses (<5%), but inhibited the nitrate accumulation at high doses (>10%) with the highest inhibition efficiency of 14.7%. All treatments with ATU decreased N₂O emission by 60.3%~68.2% but was still much higher than when DCD was applied. In general, the global warming potential (GWP) of N₂O and CO₂ were the highest in N treatment and seconded by ATU+N treatment. There were no significant differences in GWP between DCD+N and CK treatment, or among different doses of ATU with N treatments. The quantitative real-time PCR of amoA genes suggested that ammonia-oxidizing bacteria (AOB) rather than ammonia-oxidizing archaea (AOA) and complete ammonia-oxidizing bacteria (Comammox), had a positive relationship with soil nitrate accumulation and N₂O emission，but a negative correlation with pH. Microbial community analysis by high through-put sequencing revealed Nitrosovibrio tenuis-like AOB dominated in soil nitrification process which was greatly stimulated by nitrogen. Besides, ATU and DCD significantly increased the relative abundance of cupriavidus but reduced the relative abundance of Patulibacter, Aeromicrobium, Actinomycetospora, Defluviicoccus and Acidipila.[Conclusion] This study reveals the exact mechanisms of ATU on soil microbial guilds and GHG emission and plays an important role in the future implementation of agricultural management strategies and the evaluation of global climate change.

Abstract:[Objective] Soil aggregates, subjected to the joint impact of soil biological and non-biological factors, play a crucial role in determining soil functions and ecosystem services. Soil microorganisms are one of the most active biological factors that affect the formation of soil aggregates. This study is aimed to explore long-term effects of biochar application on stability of paddy soil aggregates in paddy soil at two locations from abiotic and biological perspectives.[Method] From two long-term field experiments under the wheat-rice rotation system, located in Jurong and Nanjing, separately, 3 and 5 years old in history, and consisting of two treatments each, i.e. CK (Conventional fertilization) and AB (Conventional fertilization + biochar), soil samples were collected after harvesting wheat in the annual rice-wheat rotations for particle size fractionation of soil aggregates using the wet sieve method, and for analysis of contents of organic carbon, total nitrogen and total phosphorus as well as abundance of soil microorganisms (bacteria, fungi, arbuscular mycorrhizal fungi, archaea and actinobacteria) in each fraction of soil aggregates using the quantitative PCR technique.[Result] Treatments AB in the two field experiments were significantly higher in macro aggregate ratio (R_>0.25) and field soil water holding capacity after biochar getting aged in situ, and exhibited increase trends in both mean weight diameter and geometric mean diameter (P>0.05). Soil nutrient contents (SOC, total phosphorus) and soil microbial abundance in soil aggregates changed significantly, too. Compared with Treatment CK, Treatment AB was 93.0% and 61.5% higher in content of macro aggregates, respectively, in the Jurong and Nanjing experiments, but exhibited a decreasing trend in both the 0.002-0.053 mm and <0.002 mm fractions of soil aggregates; besides, Treatment AB was significantly or 26.3% and 26.9% higher in SOC content of the bulk soil, 72.4% and 52.3% higher in SOC content of the macro aggregates, and 20.8% and 30.0% higher in SOC content of the micro aggregates, respectively, in the Jurong and Nanjing experiments, significantly higher in fungi abundance of the bulk soil in both experiments, significantly or 25.4% higher in total phosphorus in the Nanjing experiment; and also exhibited an increasing trend in abundance of the arbuscular mycorrhizal fungi and archaea(P>0.05). Correlation analysis showed that the soil aggregate mean weight diameter was very significantly and positively related to macro aggregate ratio, SOC content, abundance of fungi and arbuscular mycorrhizal fungi(P<0.01). The total phosphorus content and archaea abundance were significantly and positively correlated, with correlation coefficient being 0.641 and 0.646, respectively.[Conclusion] Aging biochar improves soil pH, field water holding capacity, other physical and chemical properties, increases the proportion of 0.25-2 mm macro aggregates, SOC and total phosphorus content, and stabilizes soil aggregates. Moreover, it increases abundance of the soil microbes in the rice fields in Jurong and Nanjing to a varying degree. Aging biochar is beneficial to the growth of soil microorganisms, increases the abundance of fungi and arbuscular mycorrhizal fungi, promotes the formation of soil aggregates, and indirectly improves the stability of soil aggregates. To sum up, biochar demonstrates sustained effects of increasing macro aggregate ratio, carbon and phosphorus contents, and fungal, arbuscular mycorrhizal fungal and archaeal abundances, and improving soil aggregate stability during the wheat season of the rice-wheat rotation system.

Abstract:[Objective] For this paper a pot experiment was conducted to evaluate effects of water management varying in pattern on composition of soil selenium, bacterial community diversity in rhizosphere soil and Se accumulation in grains of rice, and further to explore mechanism of water management affecting the absorption and accumulation of selenium in rice, so as to provide considerable theoretical and practical support to effective regulation of selenium transfer from rice field to agricultural products, to meet the demand of human for selenium nutrient and health.[Method] The experiment was designed to have three treatments in water management treatments, that is, (I) flooded irrigation(F); (II) aerobic irrigation(A); and (III) alternation of flooded and aerobic irrigation (AFA), and three replicates for each treatment. Starting from D20 (20 days after rice transplanting), soil pH and Eh were measured every 12 days. The selenium in the rhizosphere soil was fractionated at the tillering stage, heading stage and maturity stage of the crop. Content of selenium in rice roots, stems, leaves and grains as well as yield of the crop were measured at maturity. Before rice harvest, the fresh soil in the rhizosphere bag was retrieved and placed in a bag, which was then sealed and stored at low temperature (-80℃) for high-throughput sequencing analysis.[Result] Results show that at all the rice growth stages, Treatments A and AFA were higher than Treatment F in soil pH and Eh to a certain extent and in content of soluble and exchangeable selenium as well, thereby in availability of soil selenium. In terms of selenium content, the organs of a rice plant exhibited an order of root (1.38-2.22 mg·kg^-1) > leaf (0.55-0.85 mg·kg^-1) > stem (0.53-0.61 mg·kg^-1) > grain (0.15-0.53 mg·kg^-1). Treatment AFA was the highest in selenium content in rice grains, while Treatment F was the lowest. The difference between the two was obvious. Treatment AFA was significantly or 7.83% higher than Treatment F and 13.51% higher than Treatment A in grain yield. The dominant species of bacteria in the rhizosphere soil of rice were Proteobacteria, Chloroflexi, Bacteroidetes, Acidobacteria, Patescibacteria and Gemmatimonadetes, with Proteobacteria being the most abundant one in rice rhizosphere soil in all the treatments. Obviously water management had a significant impact on richness of the bacteria. Treatments AFA and A were significantly higher than Treatment F in richness of Proteobacteria. On the level of class, abundance of Gammaproteobacteria was positively related to content of available Se in the soil, so the increase in the former may be deemed as an important reason for higher bioavailability of selenium in the soil.[Conclusion] Comprehensive analysis shows that alternation of flooded and aerobic irrigation can not only improve yield and selenium content of rice grains, but also save water for irrigation as compared to normal flooding irrigation. Therefore it can be recommended as preferential water management method in rice production.

Abstract:[Objective] Biological soil crusts can be effective in wind-preventing and sand-fixing. This is of great significance to ecological restoration in desert areas. Nevertheless, there is no literature showing a comparative analysis between the biological soil crusts and the bare sand surface layer with the same thickness or for soils beneath them.[Method] The abundance of 16S rRNA gene and the structure of bacterial communities of the moss crust layer, bare sand surface layer, and soil layers beneath them in Mu Us sandy land was analyzed by fluorescent quantitative PCR and high-throughput sequencing. Based on the data of soil physical and chemical factors, the effect of moss crust on the diversity of bacterial community in sandy land was analyzed. Also, the moss crust layer and soil layer beneath it, and the corresponding surface and underlying layers of bare sand were collected and the effects of biological crusts on soil bacterial communities and their living environments was analyzed more accurately through a comprehensive analysis.[Result] Compared with bare sand surface layer, moss crust significantly increased the contents of soil available nutrients, total nitrogen, and organic matter. Also, the contents of available nutrients, total phosphorus, and organic matter in the soil beneath moss crust were higher than those in the soil beneath bare sand surface layer. The contents of coarse silt and silt in moss crust and its underlying soil were significantly higher than those in bare sand surface layer and its underlying soil. The results showed that moss crust significantly improved the physical and chemical properties of sandy soils. Additionally, the available phosphorus, potassium, nitrogen, clay, silt, and coarse sand were important factors affecting bacterial community composition of sandy soil. The moss crust layer had the highest 16S rRNA gene copies and the bacterial abundance of moss crust and its underlying soil was significantly higher than that of bare sand surface layer and its underlying soil. The results of diversity analysis showed that the soil beneath moss crust had the highest bacterial diversity. Futhermore, the relative abundances of unclassifiled_f__Micromonosporaceae, norank_c__Cyanobacteria, and Pseudonocardia in moss crust were significantly higher than those in the bare sand surface layer. Also, the relative abundances of norank_c__Acidobacteria and Rubrobacter in the soil beneath moss crust were significantly higher than those in the soil beneath bare sand surface layer. These genera with significant differences play an important role in stabilizing the soil structure of sandy land.[Conclusion] The formation of moss crust has a significant effect on the bacterial community of the original surface and underlying soils in sandy land. This is beneficial for biological sand-fixation. This study provides an important theoretical basis for sandstorm control and desert ecological restoration in Microbiology.

Abstract:[Objective] Tomato is one of the fruit and vegetable crops cultivated with the highest economic benefits in open fields and greenhouses. It is of great necessity to explore salt tolerance of germinating tomato seeds and its mechanism, especially changes in polyamine metabolism in the seeds.[Method] In this study, Impacts of NaCl stress on seed germination percentage (SGP) and development of radical and hypocotyl, seed water content (SWC), seed vigor index (SVI), Malondialdehyde (MDA) content, protective enzyme activity, solute accumulation and contents of various forms of polyamine of/in the seeds of tomato, "Hezuo 903" in variety were studied.[Result] When the soil was treated with 25 or 50 mmol·L^-1 NaCl for seven days, germination of tomato seeds was slightly delayed, but SGP was not affected, however, SVI of the tomato decreased significantly. With rising salt concentration in the treatment, both the SGP and SVI decreased significantly. With SGP and SVI cited as dependent variables, and NaCl concentration in the treatment as independent variable, salt tolerance threshold for seed germination and seedling establishment was 106.1 mmol·L^-1 NaCl (0.62%) and 43.38 mmol·L^-1NaCl (0.25%), respectively. With rising NaCl concentration, MDA content, soluble protein (SP) content and the activities of enzymes like SOD, POD and CAT in germinating seeds were increased significantly, also, the contents of fPut, fSpd, fSpm, (fSpd+fSpm)/fPut, bPut, bSpd, and bSpm in the germinating tomato seeds all increased significantly, but (bSpd+bSpm)/bPut did not change much. Compared with the seeds in CK, the seeds treated with 50 mmol L^-1 NaCl did not change much in conjugated Put (cPut), but increased significantly in the contents of cSpd, and cSpm and the ratio of (cSpd+cSpm)/cPut. With increasing NaCl concentration, the seeds declined gradually in cPut, cSpd, cSpm and (cSpd+cSpm)/cPut. It was also found that salt stress significantly reduced the content of total polyamines (TPAs) and free total polyamines (fPAs) in germinating tomato seeds, but increased the content of free total polyamines with rising NaCl concentration.[Conclusion] Salinity delays and even inhibits germination of tomato seeds, and has a much stronger inhibitory effect on establishment of the seedlings after germination. Tomato seeds per se have certain salt tolerance during their germination phase mainly due to the drastic increase in (fSpd+fSpm)/fPut, cSpd, cSpm, and significant accumulation of all the forms of bound polyamines, SS and SP in the seeds under salt stress, thus raising the seeds' antioxdation and osmotic adjustment capacities. However, when salt reaches as high as 150 mmol·L^-1NaCl, the effects of salt stress raising cSpd and cSpm weaken, while the effects raising bound polyamine of all forms, fSpd and fSpm, and regulating SS and SP accumulation are still intensify.