<p>Fine-root decomposition plays a critical role in regulating the carbon (C) cycle in terrestrial ecosystems, however, the underlying microbial-mediated mechanisms under global change remain poorly understood. To address this knowledge gap, we conducted an 18-month field manipulation experiment using the litterbag method in the Tibetan alpine meadow to investigate how warming and nitrogen (N) addition affected fine-root decomposition through changes in litter-associated microbial communities. The results showed that N addition promoted the degradation of cellulose and hemicellulose, but suppressed lignin degradation. In contrast, warming enhanced the decomposition of hemicellulose and lignin. Changes in carbon chemistry composition during fine-root decomposition were significantly correlated with shifts in litter bacterial community composition and enzymatic activities, indicating that litter bacterial communities were more responsive to warming and N addition than fungal communities. Specifically, N addition increased the relative abundance of Proteobacteria and hydrolase activities, but reduced the relative abundance of Actinobacteria, Basidiomycota, as well as oxidase activities during 12–18&#xa0;months period. Warming did not alter bacterial relative abundance at the phylum level (&gt; 1%), but increased both hydrolase and oxidase activities during the late stage. In contrast, warming did not significantly affect fungal relative abundance. Furthermore, warming and N addition showed a significant interactive effect on lignin degradation, whereas they had no interactive effect on overall fine-root mass loss. Overall, our results demonstrate that changes in microbial communities and enzymatic activities are closely linked to fine-root decomposition, and highlight distinct response patterns of decomposition process to global change in alpine meadow ecosystems.</p>