Herbivore Dung inputs mainly drive copiotrophic bacterial contributions to soil nutrient pool turnover in alpine grasslands

Abstract

Herbivore dung deposition represents a fundamental ecological disturbance in grassland ecosystems, profoundly modulating biogeochemical processes such as nutrient pool dynamics. While short-term effects on specific nutrient processes is generally established, the long-term consequences of herbivore dung deposition on soil nutrient pool turnover in alpine grassland, particularly the interacting biotic and abiotic regulatory mechanisms, remains incomplete. To bridge this knowledge gap, we established a three-year yak dung decomposition experiment in a permanently grazed alpine pasture on the Qinghai-Tibet Plateau, investigating how dung-induced alterations in bacterial communities and some critical soil parameters (including pH, moisture content, and enzymatic activities) collectively regulate nutrient pool turnover in alpine grassland soils. Results showed that dung deposition substantially accelerates soil nutrient cycling, with peak turnover occurring during the early and middle decomposition phases. Concurrently, dung deposition elevated the soil pH and moisture content and enhanced the enzymatic activities integral to the nutrient turnovers, including β-1,4-glucosidase, β-1,4-xylosidase, L-leucine aminopeptidase, acid phosphatase, and oxidase activities, as well as increased the diversity (Shannon index) and altered the composition of bacterial communities. Bacterial communities, moisture content, enzymatic activities, and pH collectively regulate nutrient pool turnover, with bacterial communities exerting the strongest influence among these factors. Notably, dung deposition significantly enriched bacterial lineages, particularly Pseudomonadota , Bacteroidota , and Bacillota , along with their dominant subgroups (e.g., Alphaproteobacteria ‌, Gammaproteobacteria , Bacteroidia , and Bacilli ), which emerged as the primary copiotrophic microbial drivers of nutrient pool turnover in response to dung inputs. Together, these findings from our full-lifecycle in situ experiment demonstrate that herbivore dung deposition accelerates alpine grassland soil nutrient cycling predominantly by stimulating copiotrophic bacterial activity. This integrated perspective advances our understanding of how escalating herbivore activity may reshape biogeochemical cycling in grazed alpine ecosystems, with implications for sustainable grassland management and carbon sequestration strategies.