Moderate grazing optimizes the allocation and microbial fate of recently assimilated carbon in an alpine grassland

作者：Mingxue Xiang, Jun Wu, Lha Duo, Ben Niu, Ying Pan, Xi Zhang, Zhaoqi Wang, X Zhao, Yakov Kuzyakov · 发表于：Journal of Plant Ecology · 年份：2026 · DOI：10.1093/jpe/rtag165 · 研究领域：Soil Carbon and Nitrogen Dynamics、Microbial Community Ecology and Physiology、Biocrusts and Microbial Ecology

Abstract Alpine grasslands are crucial carbon (C) reservoirs, facing strong disruptions from intensified grazing. However, how grazing intensity regulates the allocation of recently assimilated C belowground and its utilization by soil microorganisms remains uncertain. Using in-situ 13CO2 pulse labeling in an alpine steppe, we compared the effects of non-grazing (NG), moderate grazing (MG), and heavy grazing (HG) on the allocation and cycling of recently assimilated C in shoots, roots, soil, and soil microorganisms. The initially assimilated 13C in shoots were highest under MG (245 mg C m–2). Root δ13C peaks were also highest under MG (28.5 mg C m–2), yet their mean residence time (MRT) was shortest (3.1 days), indicating rapid uptake and downward transport of newly fixed C through roots under MG. In contrast, HG delayed shoot δ13C peaks (to day 14) and produced the only pronounced soil δ13C peak (4‰), followed by a rapid decline, suggesting accelerated but short-lived belowground C allocation after severe defoliation. Despite phospholipid fatty acid (PLFA) profiles remaining stable, the share of 13C-PLFA held by Gram-positive bacteria increased from 30% to 40% under HG, indicating they became the dominant consumers of rhizodeposits. Besides, increasing grazing intensity exponentially shortened MRT across plant, soil, and microbial C pools. These results demonstrate that MG optimizes C allocation belowground and the microbial fate of plant-derived C, but HG accelerates plant–...