Grazing is the primary land‐use activity on the Tibetan Plateau and can affect soil microbes and their function through aboveground vegetation removal, animal trampling, and manure deposition. Two distinct grazing systems (i.e., winter grazing [WG] and annual grazing [AG]) dominate on the Tibetan Plateau, but their effects on soil microbes have rarely been assessed. Taking advantage of a 5‐year field experiment that controlled timing and density of grazers via fence exclosures, we examined impacts of different grazing practices on the biomass, diversity, and composition of the soil microbial community in a Tibetan alpine meadow. On the basis of high‐throughput sequencing, we found that grazing had no significant effects on bacterial and fungal α‐diversities but altered their community compositions. Although total soil carbon (TC), total soil nitrogen (TN), and carbon/nitrogen (C/N) were related to both bacterial and fungal community compositions, plant shoot biomass only correlated with bacteria, and soil pH and moisture significantly influenced fungi under grazing. Also, grazing altered plant community composition but did not lead to corresponding changes in bacterial or fungal community composition. Moreover, grazing practices affected the relative abundance of specific bacterial and fungal taxa, reducing Actinobacteria but increasing Basidiomycete fungi in WG. Soil TC and TN were higher, and the soil microbial community was more stable in AG than WG, likely due to more stable litter inputs in AG. Together, these results showed that AG was less disruptive to soil microbes, suggesting that AG may provide a viable option for sustainable utilization and conservation of these fragile alpine systems.

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Background This study focuses on the processes occurring during the acidogenic step of anaerobic digestion, especially resulting from nutritional interactions between dark fermentation (DF) bacteria and lactic acid bacteria (LAB). Previously, we have confirmed that DF microbial communities (MCs) that fed on molasses are able to convert lactate and acetate to butyrate. The aims of the study were to recognize the biodiversity of DF-MCs able and unable to convert lactate and acetate to butyrate and to define the conditions for the transformation. Results MCs sampled from a DF bioreactor were grown anaerobically in mesophilic conditions on different media containing molasses or sucrose and/or lactate and acetate in five independent static batch experiments. The taxonomic composition (based on 16S_rRNA profiling) of each experimental MC was analysed in reference to its metabolites and pH of the digestive liquids. In the samples where the fermented media contained carbohydrates, the two main tendencies were observed: (i) a low pH (pH ≤ 4), lactate and ethanol as the main fermentation products, MCs dominated with Lactobacillus, Bifidobacterium, Leuconostoc and Fructobacillus was characterized by low biodiversity; (ii) pH in the range 5.0–6.0, butyrate dominated among the fermentation products, the MCs composed mainly of Clostridium (especially Clostridium_sensu_stricto_12), Lactobacillus, Bifidobacterium and Prevotella. The biodiversity increased with the ability to convert acetate and lactate to butyrate. The MC processing exclusively lactate and acetate showed the highest biodiversity and was dominated by Clostridium (especially Clostridium_sensu_stricto_12). LAB were reduced; other genera such as Terrisporobacter, Lachnoclostridium, Paraclostridium or Sutterella were found. Butyrate was the main metabolite and pH was 7. Shotgun metagenomic analysis of the selected butyrate-producing MCs independently on the substrate revealed C.tyrobutyricum as the dominant Clostridium species. Functional analysis confirmed the presence of genes encoding key enzymes of the fermentation routes. Conclusions Batch tests revealed the dynamics of metabolic activity and composition of DF-MCs dependent on fermentation conditions. The balance between LAB and the butyrate producers and the pH values were shown to be the most relevant for the process of lactate and acetate conversion to butyrate. To close the knowledge gaps is to find signalling factors responsible for the metabolic shift of the DF-MCs towards lactate fermentation.

1. Global change factors may shift community functional composition by driving species turnover (species occurrence and species relative abundance) and intraspecific trait variability. However, their relative contribution in determining the functional response of community to global change, especially nitrogen enrichment and warming, remains unclear.2. We conducted a fully factorial field experiment in a Tibetan alpine meadow to examine the responses of plant community functional composition to nitrogen enrichment and warming by quantifying seven plant functional traits in each plot. Using the sum of squares decomposition, we further disentangled the relative contribution of intraspecific trait variability and species turnover to changes in community functional composition.3. We found that nitrogen enrichment caused a shift of plant community towards a more resource-acquisitive strategy, while warming resulted in a shift towards a more resource-conservative strategy. Plant intraspecific trait variability controls shifts in community functional composition in response to nitrogen enrichment, whereas species turnover (especially change in species relative abundance) mainly explains warming-induced shifts. Nitrogen enrichment and warming did not show significant interactive effects on plant functional composition.4. These findings suggest that nitrogen enrichment and warming can alter community functional composition of alpine meadow through distinct mechanisms.Plant intraspecific trait variability confers functional resilience of Tibetan alpine meadows under nitrogen enrichment, but warming could induce significant turnover of species that pronouncedly impacts community functioning in this highland ecosystem.