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Microbes play key roles in various biogeochemical processes, including carbon (C) and nitrogen (N) cycling. However, changes of microbial community at the functional gene level by livestock grazing, which is a global land-use activity, remain unclear. Here we use a functional gene array, GeoChip 4.0, to examine the effects of free livestock grazing on the microbial community at an experimental site of Tibet, a region known to be very sensitive to anthropogenic perturbation and global warming. Our results showed that grazing changed microbial community functional structure, in addition to aboveground vegetation and soil geochemical properties. Further statistical tests showed that microbial community functional structures were closely correlated with environmental variables, and variations in microbial community functional structures were mainly controlled by aboveground vegetation, soil C/N ratio, and NH4+-N. In-depth examination of N cycling genes showed that abundances of N mineralization and nitrification genes were increased at grazed sites, but denitrification and N-reduction genes were decreased, suggesting that functional potentials of relevant bioprocesses were changed. Meanwhile, abundances of genes involved in methane cycling, C fixation, and degradation were decreased, which might be caused by vegetation removal and hence decrease in litter accumulation at grazed sites. In contrast, abundances of virulence, stress, and antibiotics resistance genes were increased because of the presence of livestock. In conclusion, these results indicated that soil microbial community functional structure was very sensitive to the impact of livestock grazing and revealed microbial functional potentials in regulating soil N and C cycling, supporting the necessity to include microbial components in evaluating the consequence of land-use and/or climate changes. [ABSTRACT FROM AUTHOR]

Abstract Grazing intensity and global warming are expected to increase in the forthcoming decades, with uncertain consequences for their interaction on grassland ecosystems and their functions. We investigated the effects of warming, grazing and their interaction in a factorial warming (+1.2–1.7 °C) and grazing (moderate intensity with ca. 50% vegetation consumption) experiment in a Tibetan alpine meadow on microbial communities by studying functional genes involved in soil carbon and nitrogen cycles, using GeoChip technology. Our results showed that microbial functional gene structure and abundances were largely affected by the interactive effect of grazing and warming, rather than the main effect of warming or grazing. Compared to the control, grazing alone significantly increased the functional gene alpha diversity, changed the overall functional community structure, and increased the abundances of C fixation, C degradation, N mineralization and denitrification genes, likely due to the stimulating impact of urine and dung deposition. Warming alone did not change these microbial properties, possibly related to the unchanged soil nutrient status. Despite an increase in soil NO 3 − concentrations and the deposition of urine and dung, the combined treatment did not change functional gene alpha diversity, community structure, or C/N cycling gene abundances, possibly resulting from the limiting effect of water depletion in the combined treatment. Our study revealed antagonistic interactions between warming and grazing on microbial functional gene structure and abundances, which remained stable under the moderate intensity of grazing in future warming scenario in the Tibetan alpine meadow, raising potentially important implications for predicting future soil carbon and nitrogen processes in these systems. Highlights • Grazing alone significantly increased abundances of some key soil C/N cycling genes. • Warming alone had no significant effects on them. • Functional gene structure and abundances remained stable in the combined treatment. • Antagonistic interaction between warming and grazing may result from water depletion. [ABSTRACT FROM AUTHOR]