Bridging the soil carbon pool to microbial taxa and associated CAZyme profiles in grassland ecosystems

China's grasslands are key to global carbon sequestration but face growing threats amid ecological fragility. Unravelling how grassland microbial communities and their CAZymes predict soil carbon pool stability is pivotal for clarifying carbon cycle mechanisms. We constructed comprehensive bacterial and archaeal MAGs from 570 Chinese grassland metagenomic samples. Actinobacteria had the highest CAZyme abundance, with f__70-9 members accounting for 16% of total CAZymes in o__Solirubrobacterales genomes. Approximately 90% of f__70-9 MAGs have both GH and GT genes,along with abundant Pfam domains and KOs implicated in carbohydrate metabolism, which may uniquely sustain enzyme activity in grassland ecosystems. Additionally, a study across nine Inner Mongolia sites showed TN and pH promoted MAOC accumulation, while biomass carbon inhibited it. Alkaline conditions were found to accelerate POC decomposition via actinomycete carboxylesterase genes (e.g., CE14). It was also found that microbial communities affect the stability of carbon pools by the group-specific regulation of carbon components. Microbial communities affect carbon pool stability via group-specific carbon component regulation; specifically, Actinomycetota promotes stable MAOC formation by secreting glycoside hydrolases (e.g., GH13). Overall, the study uncovers grassland bacteria/archaea diversity and their ecological functions, deepening understanding of microbial communities and their CAZymes in fragile ecosystems' carbon cycles.