Abstract: Soil microbes and their mediation of biogeochemical processes play critical roles in soil organic carbon (SOC) formation and persistence and can be significantly affected by water-table changes in peatlands. However, it is still unclear how water-table changes alter microbial attributes associated with microbial-derived carbon (C) pools, particularly in peatlands where soils have very high organic matter and low redox potential. We manipulated water-table declines in an alpine peatland on the Qinghai-Tibetan Plateau, measured soil microbial composition and microbial attributes (e.g. extracellular enzyme activities, and hydrolytic and ligninolytic gene abundances), and quantified living microbial biomass (via microbial biomass carbon) and microbial residues (via amino sugar biomarkers). Declining water tables reduced both living microbial biomass and microbial residues, thereby decreasing microbial-derived C pools, but increased hydrolytic and/or ligninolytic gene abundances and enzyme activities, suggesting enhanced microbial C-acquisition attributes. Water-table decline and the associated reduction in soil water content induced taxonomic shifts in the microbial community with significant phylogenetic signals, indicating that hydrological change acts as an environmental filter favoring aerobic C-decomposing taxa such as Sphingorhabdus and Gemmatimonas. Our findings highlight that these microbial responses, together with shifts in key microbial taxa, influence the effects of water-table changes on microbial-derived C pools in peatlands, and point out the importance of water level management in maintaining peatlands.

Key words: alpine peatlands, key microbial taxa, microbial residue carbon, microbial traits, Qinghai-Tibetan Plateau, soil organic carbon, water-table changes