Grazing exclusion-induced alterations of soil microbial biogeographic pattern and co-occurrence network across a Tibetan elevation gradient

Abstract

Unraveling the shifts of soil microbial community structure in response to grazing practices has recently received considerable attention, but how grazing exclusion affect soil microbial compositions, functions, biogeographic patterns and their interactions remains unclear in alpine grasslands. Using high-throughput DNA amplicon sequencing of soil microbial communities across a 600 m elevation gradient with four different vegetation types in a Tibetan alpine meadow, we examined how the structures and potential functions of soil microbial communities changed due to long-term grazing exclusion and thereafter consequences on their biogeographic pattern and co-occurrence network. Grazing exclusion did not significantly change soil microbial community structure and most of α-diversities except for a significant reduction in bacterial and archaeal richness by 3.9 % and 45.1 % for Shrub and Graminoid meadows, respectively. Meanwhile, the relative abundances of most N-cycling related bacterial genes in Graminoid and Shrub meadows significantly reduced due to grazing exclusion. As a consequence, grazing exclusion enhanced the similarity of soil microbial community structures by 22.2 % on average due to the reduced environmental dissimilarity, and improved the relative importance of stochastic assembly process in structuring microbial communities compared to that under grazing across the elevation gradient. Moreover, grazing exclusion significantly decreased the stability of fungal and bacterial co-occurrence networks and conversely increased the stability of archaeal co-occurrence network. These results suggest that a more random distribution of soil microbial communities across the elevation gradient strengthened by long-term grazing exclusion and a more sensitive response of microbial co-occurrence network attributes than their community compositions to grazing exclusion in the Tibetan alpine meadow even at a narrow elevation scale. Our study highlights long-term grazing exclusion might have a neutral effect on soil microbial diversity, a negative effect on the stability of fungal and bacterial communities and a positive effect on that of archaeal species co-occurrence in the Tibetan alpine meadow.