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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.

In this experiment, 4 varieties of Chinese milk vetch (Xinyang, Minzi No. 6, Minzi 8487711, and Shishou) were used as host plants and inoculated with 3 strains of rhizobium (CCBAU 2609, M. h 93, and 7653R). The differences in their morphology, yield, and nodule characteristics at different growth stages were studied and the reasons for these differences were analyzed to explore the exclusivity between different varieties of Chinese milk vetch and strains of rhizobium. Results showed no significant difference in plant height and whole-plant dry weight at seedling stage under different treatments but significant differences in these characteristics at full flowering stage. The results indicated that Minzi 8487711 and Shishou were significantly better than the other varieties. During the whole growth period, the growth indexes and nodule characteristics of the 4 varieties inoculated with strain 7653R were better than those of the varieties inoculated with other strains. At full flowering stage, compared with that of the control group, the biomasses of Xinyang, Minzi No.6, Minzi 8487711, and Shishou had increased by 2.04, 2.84, 1.56, and 2.69-fold, respectively, and nitrogenase activities increased by 3.82, 9.60, 6.21, and 15.18%, respectively. Significant differences in the exclusivity between varieties and strains were observed. Minzi No.6–7653R and Shishou variety–7653R had the strongest exclusivity. The results showed that 7653R was a broad-spectrum and high-efficiency rhizobium strain. 7653R is recommended to be used in combination with Chinese milk vetch varieties, such as Minzi 8487711 and Shishou, to obtain advantages in yield and nitrogen fixation in production.

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.

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.

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.