Search

Highlights The recommended mineral fertilizers plus organic fertilizer treatments increased the soil total carbon (TC) and nitrogen (TN) levels. The application of organic fertilizer markedly reduced the loss of NH3-N compared to the application of mineral nitrogen alone. CO2 and N2O emissions from the application of organic fertilizer were higher than those from the application of mineral nitrogen under long-term fertilization. Abstract. Greenhouse gas (GHG) and ammonia (NH3) emissions from wheat fields have been a serious challenge to agriculture and the environment. The integration of the use of inorganic N fertilizer, organic fertilizer, and crop residues and their environmental effects is needed under conventional tillage. In situ field experiments were established to evaluate the impact of different fertilization practices on soil greenhouse gas and ammonia emissions from a winter wheat field. A fertilizer experiment was performed from 24th October 2019 to 11th June 2020 in a winter wheat (Triticum aestivum L.) field in China with six fertilization treatments: (1) unfertilized control (UC); (2) recommended mineral fertilizer application of 200 kg ha-1 N (RF); (3) RF plus 15 t ha-1 of organic fertilizer (RFLO); (4) RF plus 30 t ha-1 of organic fertilizer (RFMO); (5) RF plus 45 t ha-1 of organic fertilizer (RFHO); and (6) traditional mineral fertilizer application of 300 kg ha-1 N (TF). The results showed that the RF plus organic fertilizer treatments increased the soil organic total carbon (TC) and nitrogen (TN) levels. Under long-term fertilization, the CO2 emissions from the RFLO, RFMO, and RFHO treatments were 18.3, 19.9, and 20.0 t ha-1, respectively, compared with those from the RF and TF treatments (13.2 and 16.0 t ha-1, respectively). In addition, the N2O emissions from the organic-inorganic fertilizer treatment were 7.6 kg ha-1 for the RFLO treatment, 12.4 kg ha-1 for the RFMO treatment, and 8.1 kg ha-1 for the RFHO treatment, which were higher than those from the RF and TF treatments (3.1 and 5.6 kg ha-1, respectively). The NH3 emissions from the RFLO, RFMO, and RFHO treatments (17.3, 26.2, and 22.4 kg ha-1, respectively) were lower than those from the RF (31.2 kg ha-1) and TF (49.7 kg ha-1) treatments under long-term fertilization. The methane emission potential of organic-inorganic fertilizer applications was 27.0% to 98.5% higher than a single application of inorganic fertilizer. Keywords: Ammonia, Carbon dioxide, Fertilization management, Nitrous oxide, Organic fertilizers, Winter wheat.

Belowground plant traits play important roles in plant diversity loss driven by atmospheric nitrogen (N) deposition. However, the way N enrichment shapes plant microhabitats by patterning belowground traits and finally determines aboveground responses is poorly understood. Here, we investigated the rhizosheath trait of 74 plant species in seven N-addition-simulation experiments across multiple grassland ecosystems in China. We found that rhizosheath formation differed among plant functional groups and contributed to changes in plant community composition induced by N enrichment. Compared with forb species, grass and sedge species exhibited more distinct rhizosheaths; moreover, grasses and sedges expanded their rhizosheaths with increasing N-addition rate which allowed them to colonize belowground habitats. Grasses also shaped a different microenvironment around their roots compared with forbs by affecting the physicochemical, biological and stress-avoiding properties of their rhizosphere soil. Rhizosheaths act as a “biofilm-like shield” by accumulating of protective compounds, carboxylic anions and polysaccharides, determined by both plants and microorganisms. This enhanced the tolerance of grasses and sedges to stresses induced by N enrichment. Conversely, forbs lacked the protective rhizosheaths which renders their roots sensitive to stresses induced by N enrichment, thus contributing to their disappearance under N-enriched conditions. This study uncovers the processes by which belowground facilitation and trait matching affects aboveground responses under conditions of N enrichment, which advances our mechanistic understanding of the contribution of competitive exclusion and environmental tolerance to plant diversity loss caused by N deposition.

Major problems in China’s pursuit of sustainable agricultural development include inadequate, low-quality soil and water resources, imbalanced regional allocation and unreasonable utilization of resources. In some regions, overexploitation of soil resources and excessive use of chemicals triggered a web of unforeseen consequences, including insufficient use of agricultural resources, agricultural non-point source pollution and land degradation. In the past decade, China has changed its path of agricultural development from an output-oriented one to a modern, sustainable one with agricultural ecological civilization as its goal. First, the government has formulated and improved its laws and regulations on soil resources and the environment. Second, the government has conducted serious actions to ensure food safety and coordinated management of agricultural resources. Third, the government has planned to establish national agricultural high-tech industry demonstration zones based on regional features to strengthen the connection among the government, agri-businesses, scientific community and the farming community. As the next step, the government should improve the system for ecological and environmental regulation and set up a feasible eco-incentive mechanism. At the same time, the scientific community should strengthen the innovation of bottleneck technologies and the development of whole solutions for sustainable management in ecologically fragile regions. This will enhance the alignment between policy mechanisms and technology modes and effectively promote the sustainable development of agriculture in China.

Since 2015, China has implemented chemical fertilizer reduction, aiming to achieve zero growth in the application rate of chemical fertilizer. Therefore, it is of great significance to explore the effect of chemical fertilizer reduction combined with organic materials in a wheat-maize rotation system from fluvo-aquic soil in North China on soil microbial community. The field experiment included five fertilization treatments, i.e., chemical fertilizer with conventional application rate (F), chemical fertilizer reduction on the basis of conventional fertilization (FR), chemical fertilizer reduction plus straw (FRS), chemical fertilizer reduction combined with organic fertilizer (FRO), and chemical fertilizer reduction combined with organic fertilizer and straw (FROS). The abundance, composition, diversity, and structure of bacterial and fungal communities among treatments were evaluated using qPCR and Illumina high-throughput sequencing technology. The results showed that the concentrations of soil organic matter (SOM) and total nitrogen (TN) in all treatments with addition of organic materials were much higher than those in treatments applied with only chemical fertilizer. The SOM content in the FRS, FRO, and FROS treatments increased by 23.91%, 37.12%, 26.09%, and the TN content increased by 11.96%, 21.08%, 15.22% in comparison with the F treatment, respectively. The lowest contents of available phosphorus (AP) and nitrate nitrogen (NO3−-N) were observed in FR treatment. The AP content in FRO and FROS treatments were 2.44 times and 2.42 times greater than that in FR treatment, respectively. Compared with F treatment, the organic materials input significantly increased bacterial and fungal abundances. More significant effects on the α-diversity with organic fertilizer were observed in the fungal community compared with the bacterial community. The significant increase of Ascomycota and the decline of Mortierellomycota and Glomeromycota were observed in the combined with organic materials treated soils. The nonmetric multidimensional scaling (NMDS) analysis demonstrated that the bacterial community structure in the F treatment was clearly separated from the other treatments, and the other treatments clustered closely, while with respect to fungal community structure, the FRO and FROS treatments grouped together and were separated from the other three treatments. The redundancy analysis (RDA) results showed that the structure of the bacterial community was significantly correlated with SOM and TN, and the fungal community structure was strongly correlated with AP, SOM, and TN. The chemical fertilizer reduction combined with organic fertilizer and straw can effectively improve soil fertility and nutrient availability, altered the community structure of both bacteria and fungi, but only significantly reduced fungal biodiversity. The influence of chemical fertilizer reduction combined with organic materials on fungi was greater than that on bacteria in fluvo-aquic soil of North China.

CO2 fixation by autotrophic microbes has a significant effect on the carbon cycle in temperate grasslands. Nitrogen (N) deposition in soil has been steadily increasing for decades, which has consequences for soil microorganisms. However, the impact of this deposition on the diversity and abundance of CO2-fixing soil microorganisms remains unclear in temperate grasslands. In the present study, the cbbL gene, a key gene in the Calvin–Benson–Bassham cycle that encodes the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase, was used to study CO2-fixing microbes under different rates of N addition (0, 15, 30, 50, 100, and 150 kg N ha–1 yr–1) in a 9-year field experiment in a temperate grassland. The results showed that N addition led to significant reductions in cbbL gene abundance and genetic diversity and altered cbbL gene community composition. High N addition enhanced the relative abundances of Acidiferrobacterales and Rhizobiales but reduced those of Burkholderiales and Rhodobacterales. Structural equation modeling further revealed that N addition primarily reduced cbbL genetic diversity by increasing the soil NO3-N content and decreasing the soil pH. N addition indirectly reduced cbbL gene abundance, possibly by increasing the soil N/phosphorus (P) ratio and decreasing the soil pH. These findings suggest that N addition increases the soil available N and causes soil acidification, which may inhibit growth of CO2-fixing microbes to some extent.

Winter wheat (Triticum aestivum L) is an important crop grown for food in China. Minimizing soil greenhouse gas (GHGs) and ammonia (NH3) emission has significant implications in regional air quality and nitrogen nutrient management from an intensive wheat site. Therefore, information on integrated use of inorganic N fertilizer, organic fertilizer, and crop residue, and their environmental effects is needed under Conventional Tillage. The objective of this work was to evaluate the effect of different fertilization practices on soil greenhouse gas and ammonia emissions from a winter wheat field. The field trial was set up in June 2015. The research was based on six fertilization treatments: 1) unfertilized control (UC); 2) recommended mineral fertilizers application of 200 kg·ha−1 N (RF); 3) RF plus organic fertilizer of 15 t·ha−1 (RFLO); 4) RF plus organic fertilizer 30 t·ha−1 (RFMO); 5) RF plus organic fertilizer of 45 t·ha−1 (RFHO); 6) traditional mineral fertilizers applications of 300 kg·ha−1 N (TF). During growth season from 2019-2020, soil GHGs emission following N fertilization was measured using the closed static chambers method whereas NH3 emissions were by passive adsorption method. The results showed that RF plus organic fertilizer treatments use helps increase soil organic Total carbon (TC) and nitrogen (TN) levels. In the long-term fertilization, the CO2 emission for the RFLO, RFMO, and RFHO treatment were 18.3, 19.9, and 20.0 t·ha-1, respectively, which were higher than for the RF and TF treatment (13.2 and 16.0 t·ha-1, respectively). In addition, under long-term experiments, the nitrous oxide (N2O) emission for the combined applications of organic fertilizer and RF treatment were 7.6 kg·ha-1 for the RFLO, 12.4 kg·ha-1 for the RFMO, and 8.1 kg·ha-1 for the RFHO, respectively, which were higher than for the RF and TF treatment (3.1 and 5.6 kg·ha-1, respectively). The NH3 emission for RFLO, RFMO, and RFHO treatments (17.3, 26.2, and 22.4 kg·ha-1, respectively) were lower than RF (31.2 kg·ha-1) and TF (49.7 kg·ha-1) treatment in the long fertilization treatments. CH4 emissions were ignored in this study. Overall, the application of organic fertilizer can significantly decrease NH3-N loss compared to mineral N application. However, CO2 and N2O emissions due to organic fertilizer application were higher than with the application of mineral N with long-term fertilization.

As one of the typical farmland ecosystems, tea gardens are of vital importance in China. The purpose of this study was to quantify the dynamic of soil properties, soil microbial diversity, and nematodes, as affected by various cover crop patterns in a Tanjiawan tea garden in Hubei Province, China. Four cover crop patterns were established as following: naturally covered of bare land and mixed planting with two species, four species, and eight species. The results revealed that soil organic matter, pH, and total phosphorous content were significantly related to cover crop patterns. The number of nematodes increased with cover crop diversity, and the percentage of plant parasitic nematodes in cover crop treatments was lower than in naturally covered bare land. A higher diversity of cover crops increased the number of bacterivores and fungivores, thereby enhancing the bacterial decomposition pathway of soil organic matter. Both soil nematodes and microbial communities showed significant seasonal changes under different cover crop patterns. The soil food webs were more stable and mature under cover crops with two species and four species. Combined with the results of a structural equation model, we found that soil properties, characterized by the total nitrogen, available phosphorus, NO3--N, and soil organic matter, were significantly correlated with soil nematodes and microbial communities. In addition, acterivores and plant parasites were significantly negatively correlated with omnivores/predators. Our results implied that soil properties and seasonal changes influence the relationships between cover crops, soil nematodes, and microbial communities. These findings provide a theoretical basis for future studies on interactions between soil properties, soil microorganisms, and nematodes in tea gardens.

CO2 fixation by autotrophic microbes has a significant effect on the carbon cycle in temperate grasslands. Nitrogen (N) deposition in soil has been steadily increasing for decades, which has consequences for soil microorganisms. However, the impact of this deposition on the diversity and abundance of CO2-fixing soil microorganisms remains unclear in temperate grasslands. In the present study, the cbbL gene, a key gene in the Calvin–Benson–Bassham cycle that encodes the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase, was used to study CO2-fixing microbes under different rates of N addition (0, 15, 30, 50, 100, and 150 kg N ha–1 yr–1) in a 9-year field experiment in a temperate grassland. The results showed that N addition led to significant reductions in cbbL gene abundance and genetic diversity and altered cbbL gene community composition. High N addition enhanced the relative abundances of Acidiferrobacterales and Rhizobiales but reduced those of Burkholderiales and Rhodobacterales. Structural equation modeling further revealed that N addition primarily reduced cbbL genetic diversity by increasing the soil NO3-N content and decreasing the soil pH. N addition indirectly reduced cbbL gene abundance, possibly by increasing the soil N/phosphorus (P) ratio and decreasing the soil pH. These findings suggest that N addition increases the soil available N and causes soil acidification, which may inhibit growth of CO2-fixing microbes to some extent.

Grassland soil organic carbon (SOC) accounts for 15.5% of the SOC in reservoirs of terrestrial carbon (C) and is a major component of the global C cycle. Current and future reactive N deposited on grassland soils may alter biogeochemical processes and soil microbes. Microorganisms perform most of the decomposition on Earth and shift SOC accumulation. However, how variation in the identity and composition of the bacterial community influences SOC is far from clear. The objective of this study is to investigate the responses of SOC concentration to multiple rates of N addition as well as the roles of bacteria in SOC accumulation. We studied SOC storage and bacterial community composition under N addition treatments (0, 1.5, 3.0, 5.0, 10.0, 15.0, 20.0, and 30.0 g N·m−2 yr−1) in a 6-yr field experiment in a temperate grassland. We determined the soil inorganic nitrogen concentration and pH in a 0–10 cm soil layer. We used high-throughput genetic sequencing to detect bacteria. N addition led to significant increases in the concentrations of SOC. N addition reduced the soil pH but increased the NO3-N and NH4-N levels. The bacterial diversity was highest under low nitrogen addition. N addition increased the relative abundance of Proteobacteria, and Proteobacteria became the second dominant phylum under high N addition. Structural equation modeling further revealed that soil pH and bacterial community structure have an impact on SOC under N deposition. Nitrogen-regulated SOC is associated with Proteobacteria and Planctomycetes. These findings suggest that N deposition may alter the SOC content, highlighting the importance of understanding changes in the bacterial community for soil nutrients under N deposition.

Changes in nitrogen (N) deposition and precipitation can strongly influence grassland ecology. However, the combined effects of N and water addition on soil fungal genetic diversity, and especially the underlying influencing factors, are not well understood. We investigated the response of soil fungal α diversity to experimental N and water addition in a northern Chinese steppe. We found that N addition alone exceeding N100 (100 kg N·ha−1·yr−1) significantly increased soil fungal α diversity. However, when water was added, soil fungal diversity did not significantly change following N enrichment. Structural equation modelling (SEM) results indicated that N addition increased soil fungal α diversity, while N addition combined with irrigation maintains soil fungal diversity that would otherwise be enhanced by N addition. This results from reversing the correlation between soil fungal diversity and plants\\soil physicochemical properties. Our results provide evidence that the effects of N deposition regarding soil fungal diversity might be overestimated if we ignore variations in water availability.

Nitrogen (N) deposition and precipitation change are important phenomena in global climate change and they can strongly influence grassland ecology. Previous studies primarily focused on the impact of N deposition or precipitation on plant community and soil microorganisms separately. They did not account for the relationship between plant and soil microbial communities. To better understand how future climate change may affect the relationship between plant and soil microbial diversity, we simulated N deposition and precipitation change through artificial fertilization (0, 15, 30, 50, 100, 150, 200, 300 kg N ha−1·yr−1) and irrigation (no irrigation and irrigation equivalent to 100 mm extra summer rainfall) at a test area on the Stipa baicalensis steppe. We found that the plant primary productivity increased following N enrichment but the plant diversity declined. The composition, abundance and diversity of soil bacteria changed in the test scenarios. Under normal precipitation, the bacterial OTU richness increased at N100 (100 kg N ha−1·yr−1) and the bacterial diversity increased at N100–N300 (100–300 kg N ha−1·yr−1). When irrigation was applied, the bacterial OTU richness and diversity were improved at low N levels (15–50 kg N ha−1·yr−1) but decreased at high N levels (N100–N300). This is probably due to water addition lead to the dissolution of more nitrates in soil and thus decreased the soil pH. A significant negative relationship was observed between plant diversity and bacterial diversity under normal precipitation. Under irrigation, the correlation was also negative at low N levels (N15–N50), but became significantly positive when the N level exceeded N100, which contributed to decrease in bacterial diversity resulting from significant decrease of soil pH. Our results clearly showed the elevated precipitation modified the relationship between plant and soil bacterial diversity under N deposition. We predict that as the global climate change further intensifies, the interaction between climate change factors may exercise complex impact on ecological properties and lead to unexpected consequences on the feedback in plant-microbe-soil system.

Emergy analysis was performed to evaluate the sustainability of three rice farming systems (rice mono-cropping, rice-fish and rice-duck farming systems) in the Jiangsu province. The results showed that the three systems exhibit unique characteristics on each component. The emergy of rice seeding and the labour input were the most important costs, at 57.18 and 18.20 sej/ha/season, respectively, for the rice mono-cropping system. In the rice-fish and rice-duck systems, the feed input played a more important role, corresponding to values of 63.70 and 79.20 sej/ha/season, respectively. The machinery input was 45.21 sej/ha/season for the rice-fish system due to the construction of fish ponds and ditches. The rice-duck system exhibited lower environmental loading and a higher sustainability index than the rice mono-cropping and rice-fish systems, respectively. The ratios of the economic input to output were 0.41, 0.61 and 0.41 for the rice mono-cropping, rice-fish and rice-duck systems, respectively. The net profit of the rice-duck system was $3264.2 per hectare, which was nearly 40% higher than those of the other systems. Based on the results showing the highest economic efficiency and value on the sustainability index, the rice-duck system may be the optimal rice agriculture system from both ecological and economic perspectives.

Biochars have drawn wide attention as adsorbents, carbon sequesters and soil re-mediators. However, these substances are ambiguous regarding their effects on the motility, phenotypic changes and potential adaptative mechanisms of soil organisms. This study investigated how peanut shell biochar (PBC) affects the C. elegans model via a one-choice selection test and RNA-seq analysis. The results showed that C. elegans were able to select either PBC or a water control, and a clear preference for PBC was observed after 48 h of exposure, with the chemotaxis index (CI) reaching approximately 1.0. The nematode preferences for PBC vs sterile PBC/graphite were not significant, which demonstrated that initial microorganisms and appearances were not the reasons for the worms' selection, but the selection behaviour was instead determined by volatile odours. The treatments also showed that biochar amendment significantly decreased the body length, brood size and superoxide dismutase (SOD) activity of C. elegans to 960.20 ± 15.23 μm, 173.22 ± 4.56, 165.81 ± 3.82 U/mL SOD, respectively. Then, a possible molecular mechanism of PBC-induced developmental and reproductive effects on C. elegans was explored. Differential gene expression analysis was performed, and 1625 genes (1425 up- and 225 downregulated genes) were regulated in response to PBC treatment. The top 20 regulated genes were col genes (col-129; col-81; col-139; col-71), bli-6, perm-4 and his-24, which indicated that cuticle collagen synthesis, eggshell formation and/or heterochromatin in postembryonic growth may be disrupted following exposure to PBC. Therefore, our study suggested that quality standards be used to test nematode preferences and responses to biochar amendment, with the aim of safe application in soils, seedling substrates or fertilizers.

The amount of litter and its type can affect seedling establishment and species richness in plant communities. However, little is known about the species-specific effects of litter, especially in the presence of a competitor. We conducted a common garden test to examine the combined effects of competition and plant litter from conspecific versus heterospecific species on the emergence and early growth of the invasive plant Flaveria bidentis and the co-occurring native plant Amaranthus retroflexus. The litter of native species reduced the rate of seedling emergence of F. bidentis; this effect was stronger in the presence of a competitor. Litter addition reduced the seedling emergence rate of A. retroflexus, but had a neutral to positive effect on its early growth, indicating a clear species-specific pattern. Litter addition, combined with interspecific competition, facilitated growth of A. retroflexus; this species seemed to perform better in changing soil conditions than did F. bidentis. Consequently, a habitat-specific adaptation might be involved in this interspecific plant–soil feedback. Our results contribute our understanding of how to suppress F. bidentis in disturbed sites without herbicide application. Manipulating litter cover could be used to manage this invader; such addition would either affect emergence or the belowground competition for soil resources.

Plants differ in their capacity to use various forms of nitrogen (N). Although previous studies have suggested invasive plants alter N availability, few distinguish their responses to various forms and different concentrations of inorganic N. In order to understand how plant preference for N affects invasions, we tested the growth and physiological response of Flaveria bidentis, an invasive plant across north China, to different forms and concentrations of inorganic N. Seedlings of F. bidentis were cultivated in a mothproof screen house to determine if this invader benefits from increased or altered forms of N. 15N-labeled NH4 + and NO3 − were applied to the soil to gain insight into N partitioning in communities invaded by this species. We determined that plant growth and biomass variables, chlorophyll content, and photosynthesis parameters all varied depending on the form of available N. Specifically, N addition altered the biomass allocation pattern of plants, with F. bidentis tending to maximize its reproductive output under increased N availability. Also, F. bidentis had higher 15N–NH4 + recovery across biomass components than both co-occurring native plants, Amaranthus retroflexus and Eclipta prostrata. F. bidentis demonstrated a strong preference for ammonium (NH4 +) over nitrate (NO3 −) and captured at least twice the 15N–NH4 + as the native plants. By comparison, the two native species showed no preferences for the form of N. The greater above-ground biomass of F. bidentis contributed to its higher 15N recovery. We suggest that the ability of F. bidentis to respond rapidly to changes in the N pool, especially in ammonium, may confer a competitive advantage to this species over native species. Our results provide insight into how species-specific N preferences influence the ability of this species to invade a native community.

During the past two centuries, global changes (i.e., enhanced nitrogen deposition) have exerted profound effects on ecological processes of steppe ecosystems. We used litterbag method and mixed litters of three different plant species tissues (Stipa baicalensis: Sb, Leymus chinensis: Lc and Artemisia frigid: Af), endemic to Stipa baicalensis Steppe, and measured the mass loss of mixtures over 417 days under the N addition treatment. We studied the effect of N addition (N0: no N addition; N15: 1.5 g N/m2·a; N30: 3.0 g N/m2·a; N50: 5.0 g N/m2·a; N100: 10.0 g N/m2·a; N150: 15.0 g N/m2·a) on the rate of mixed litter decomposition and nutrient dynamics change. The decomposition constant (k) of leaf mixtures was higher than that of root mixtures. The k values of leaf mixed combinations were 0.880 (Sb + Lc), 1.231 (Lc + Af), 1.027 (Sb + Lc + Af), respectively. The k value of stem was 0.806 (Lc + Af) and the root mixed combinations were 0.665 (Sb + Lc), 0.979 (Lc + Af) and 1.164 (Sb + Lc + Af), respectively. The results indicated that N addition had significantly effect on the mixed litter decomposition and nutrient releasing. The rate of plant tissues litter decomposition had different response to N addition. In the context of N addition, litter decomposition rate and nutrient dynamics were changed by synthetic effect of decaying time, specie types and N addition dose. Our findings suggested that prairie plants may adapt to environmental change by adjusting litter quality, thus retaining the stability of the steppe ecosystem.

According to its characteristics, biochar originating originating from biomass is accepted as a multifunctional carbon material that supports a wide range of applications. With the successfully used in reducing nitrate and adsorbing ammonium, the mechanism of biochar for nitrogen fixation in long-term brought increasing attention. However, there is a lack of analysis of the NH4+-N adsorption capacity of biochar after aging treatments. In this study, four kinds of acid and oxidation treatments were used to simulate biochar aging conditions to determine the adsorption of NH4+-N by biochar under acidic aging conditions. According to the results, acid-aged biochar demonstrated an enhanced maximum NH4+-N adsorption capacity of peanut shell biochar (PBC) from 24.58 to 123.28 mg&middot, g&minus, 1 after a H2O2 modification. After the characteristic analysis, the acid aging treatments, unlike normal chemical modification methods, did not significantly change the chemical properties of the biochar, and the functional groups and chemical bonds on the biochar surface were quite similar before and after the acid aging process. The increased NH4+-N sorption ability was mainly related to physical property changes, such as increasing surface area and porosity. During the NH4+ sorption process, the N-containing functional groups on the biochar surface changed from pyrrolic nitrogen to pyridinic nitrogen, which showed that the adsorption on the surface of the aged biochar was mainly chemical adsorption due to the combination of &pi, &pi, bonds in the sp2 hybrid orbital and a hydrogen bonding effect. Therefore, this research establishes a theoretical basis for the agricultural use of aged biochar.

A new exotic weed, Flaveria bidentis, is spreading in central China where it forms dense monospecific patches modifying the structure of different native ecosystems and threatening native aboveground biodiversity. However, little is known about the consequences of such an invasion for soil bacterial community, especially its effect pattern at different invasion stages. In this study, soil samples were taken in native ecosystems that were uninvaded, partially invaded (transition), and severely invaded by F. bidentis. The bacterial richness and diversity in F. bidentis in rhizospheres soil was evaluated using denaturing gradient gel electrophoresis (DGGE) analysis. Different stages of F. bidentis invasion can trigger changes in soil physicochemical properties in particularly in available N and P F. bidentis invasion significantly decreased the richness of soil bacterial community, and the decline contents were positively correlated with invasion progress. In the invaded soils, bacterial species in Proteobacteria , Chloroflexi and Actinomycetes decreased with invasion, with the greatest reduction in relative abundance occurring for Proteobacteria, which was the dominant species in the native soils. Invasion of F. bidentis corresponded with an alteration in the structure of soil bacterial community, and soil microbial biomass as well, thus soil environment modification was expected to promote spreading of this exotic weeds in turn. Key words : Biological invasion, Flaveria bidentis, soil nutrients, soil bacteria, polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE).

Invasive Asteraceae are an important group of plants and might have universal impacts on invaded ecosystems. However, research data on the ecological impacts of specific plants are still lacking. Chromolaena odorata, Ageratina adenophora, Flaveria bidentis, and Mikania micrantha are four typical alien Asteraceae in China. The involvement of soil biota, in particular, the community structure of arbuscular mycorrhizal (AM) fungi in their invasion process was tested in present research. It was found that invasion by the four Asteraceae changed, to different extents, the nutrient levels in soils. Invasion by C. odorata, A. adenophora, and F. bidentis followed common patterns: 1) decreasing pH value; 2) increasing the soil AM fungal diversity and species richness. Invasion by all four Asteraceae tested increased nitrogen pools and accelerated nitrogen fluxes with a decrease in the phosphorus pool, especially available phosphorus. It was suggested that mycorrhizal symbiosis might partially promote successful invasion of these Asteraceae by affecting the metabolism of phosphorus in soil. The impacts on soil ecosystems of these Asteraceae tested were also species-specific, and different invasion strategies were exhibited.

Grazing activity can profoundly influence grassland plant community structure and ecosystem functions. However, our understanding of the effects of livestock grazing on ecological stability across different grassland types remains limited. Based on a 5-year investigation along a precipitation gradient (180 mm in desert steppe, 282 mm in typical steppe and 375 mm in meadow steppe) in temperate grasslands of Inner Mongolia, we examined the responses of the temporal stability of plant community aboveground biomass to grazing intensity at three levels (light grazing, moderate grazing and heavy grazing). We found that grazing intensity at all levels reduced biomass temporal stability across all types of grasslands. Heavy grazing intensity reduced community biomass, species richness and species asynchrony. Structural equation modeling further revealed that grazing decreased community stability mainly by decreasing species asynchrony. In addition, community-level stability was driven by grass species stability in the meadow steppe, but it was affected by the stability of forb species in the desert steppe. These findings suggest that grazing practices may alter the stability properties of grassland plant communities, highlighting the importance of understanding changes in different plant functional groups for predicting community dynamics under grazing management.

Grassland desertification seriously threatens sustainable economic and social development. Much attention has been paid to the control of grassland desertification, and even to the restoration and reconstruction of the grassland. Vegetation restoration is considered to be a very effective solution. Soil sustains an immense diversity of microbes, and the characteristics of soil microbial communities are sensitive indicators of soil. It is important to understand the relationship between vegetation and soil microbial diversity during the restoration process. Soil microbial, which is the main index to evaluate soil quality, plays a significant role in ecosystem and soil microbial diversity is the important one of global diversity. Exploring the effects of different vegetation patterns on soil microbial diversity can provide scientific bases and technical support for systemic and impersonal assessment of the best vegetation restoration patterns, as well as the vegetation restoration and reconstruction of Hulunbeier sandy land. Based on PCR–DGGE technology, a case study was carried out to investigate the effects of five different vegetation restoration patterns on soil microbial functional diversity after 4 years in sandy land in Hulunbeier, China. The five vegetation restoration patterns included mono-cultivar planting of Agropyron cristatum (UA), mono-cultivar planting of Hedysarum fruticosum (UH), mono-cultivar planting of Caragana korshinskii (UC), mixed-cultivar planting of Agropyron cristatum and Hedysarum fruticosum (AC) and mixed-cultivar planting of Agropyron cristatum, Hedysarum fruticosum, Caragana korshinskii and Elymus nutans (ACHE). Completely degraded sandy land was used as control. The results indicated that the vegetation restoration increased the genetic diversity of soil bacterial community obviously, and the structure of soil bacterial community was changed. The results of phylogenetic analysis suggested that the bacterial community in Hulunbeier sandy land mainly attributed to Proteobacteria, Bacteroidetes, Firmicutes, Actinobacteria, and Acidobacteria. The dominant groups were Proteobacteria and Bacteroidetes. The effects of different vegetation type on soil bacterial community structures were different.

Grassland desertification seriously threatens economic and social sustainable development. How to control grassland desertification, and even to restore and reconstruct grassland has been paid much attention. Vegetation restoration is considered to be a very effective solution. Soil contains an immense diversity of microbes, and the characteristics of soil microbial communities are sensitive indicators of soil. It is important to understand the relationship between vegetation and soil microbial diversity during the restoration process. Based on Biolog-Eco technology, a case study was carried out to investigate the effects of five different vegetation restoration patterns on soil microbial functional diversity after four years in sandy land in Hulunbeier, China. The five vegetation restoration patterns included mono-cultivar planting of Agropyron cristatum (UA), mono-cultivar planting of Hedysarum fruticosum (UH), mono-cultivar planting of Caragana korshinskii (UC), and mixed-cultivar planting of A. cristatum and H. fruticosum (AC), mixed-cultivar planting of A. cristatum, H. fruticosum, C. korshinskii and Elymus nutans (ACHE). Completely degraded sandy land was used as control. The results indicated that the vegetation restoration significantly increased soil microbial activity. The Average Well Color Development (AWCD), which represents soil microbial metabolic activity, followed the order of UC > UH > UA > ACHE > AC > control. AWCD of five vegetation restoration patterns were all higher than that of control, and the highest soil microbial metabolic activity in mono-cultivar planting of C. korshinskii treatment was found. Five vegetation restoration patterns resulted in significant increase in Shannon index (H), evenness (E) and Simpson’s Dominance (D) of soil microbial community. Greater Shannon index and Simpson’s Dominance was observed in UC treatment than in other four vegetation restoration treatments and control. ACHE treatment had the highest evenness index (E) of soil microbial community. The principal component analysis (PCA) indicated a similar mode in carbon utilization for soil microbial community of UA, AC, ACHE and CK. However, UH and UC treatments had special carbon utilization mode. Treatments of UA, AC, ACHE and CK concentrated in the negative direction of the first principal component. Conversely, treatments of UH and UC concentrated in the positive direction of the first and second principal component respectively. The carbon sources mostly used by soil microbes were carbohydrates, amino acids, metabolic mediates and secondary metabolites. Therefore, vegetation restoration enhanced the metabolic activity and functional diversity of microbial community in sandy soil.

In natural ecosystems, invasive plant litter is often mixed with that of native species, yet few studies have examined the decomposition dynamics of such mixtures, especially across different degrees of invasion. We conducted a 1-year litterbag experiment using leaf litters from the invasive species Flaveria bidentis (L.) and the dominant co-occurring native species, Setaria viridis (L.). Litters were allowed to decompose either separately or together at different ratios in a mothproof screen house. The mass loss of all litter mixtures was non-additive, and the direction and strength of effects varied with species ratio and decomposition stage. During the initial stages of decomposition, all mixtures had a neutral effect on the mass loss; however, at later stages of decomposition, mixtures containing more invasive litter had synergistic effects on mass loss. Importantly, an increase in F. bidentis litter with a lower C:N ratio in mixtures led to greater net release of N over time. These results highlight the importance of trait dissimilarity in determining the decomposition rates of litter mixtures and suggest that F. bidentis could further synchronize N release from litter as an invasion proceeds, potentially creating a positive feedback linked through invasion as the invader outcompetes the natives for nutrients. Our findings also demonstrate the importance of species composition as well as the identity of dominant species when considering how changes in plant community structure influence plant invasion.

Biological nitrogen fixation through prokaryotic microbe is an important source of nitrogen been input into many natural ecosystems. In this study the active diazotrophic community was investigated in the three treatments of mowed, grazed and enclosed Leymus chinensis steppes in Hulunbeier grassland of Inner Mongolia by using approaches of polymerase chain reaction-denaturing gradient gel electrophoresis (PCR–DGGE) and sequence analysis. The community structure and diversity of the bacterial groups from the different samples was further analyzed by using different techniques, such as statistical analysis and diversity index evaluation of the band patterns etc. The results showed that grazing activity significantly reduced the number of species and quantities of nitrogen-fixing microorganisms, as well as the nifH gene diversity. However, enclosed plots had the lowest diversity of nifH gene. While the highest one found in mowing plots. A total of 30 sequences representing 25 different sequence types were recovered from the DGGE gels after phylogenetic constructions. The results also revealed that most sequences were coming from Alphaproteobacteria of Proteobacteria, and characterized by sequences of members of Rhodobacter, Bradyrhizobium, Mesorhizobium, Rhodopseudomonas, Xanthomonas, Azospirillum, Gluconacetobacter, Methylobacterium and Methylocystis. Symbiotic nitrogen-fixers existed in grazing, mowing and enclosed plots accounted for 21.4%, 47.3% and 31.3% respectively in their dominant nitrogen-fixing bacteria. The result of principal components analysis showed that the influence of different land use patterns on nitrogen-fixing microbial communities composition can be ordered as grazing plots > enclosed plots > mowing plots. Nitrogen-fixing microbial communities in L. chinensis steppe were significantly (P

The effects of transgenic plant on ecological and food biosafety have attracted considerable attention recently due to the exploding number of commercialization genetic modified plants. Here, we examined the changes of bacterial and fungal community compositions in the phyllosphere of Cry1Ac Bacillus thuringiensis (Bt) cotton SGK321 by molecular fingerprint method at four major growth stages. The phyllospheric bacteria diversity of SGK321 was decreased at budding stage only, indicated by Shannon index. A slight increase of diversity and abundance of fungal community could be detected at different sampling stage except the seeding stage. Fungal community showed a tendency to be affiliated with the expression of Cry1Ac protein which was detected by enzyme-linked immunosorbent assay (ELISA) method at both the seeding and budding stages. Results suggested that, compared to bacteria, fungi in phyllosphere of transgenic cotton SGK321 might be more susceptible to Cry1Ac protein, which includes Cochliobolus sp., Setosphaeria sp., Blakeslea trispora, Cryptococcus neoformans and Cryptococcus sp. Furthermore, the seasonal and temporal parameters during the growth stages were proved to be the most important factor relating with the shift of phyllospheric microorganism communities.