Predominant role of air warming in regulating litter decomposition in a Tibetan alpine meadow: A multi-factor global change experiment

Alpine ecosystems worldwide are experiencing multi-faceted climate changes, but the interactive effects of these drivers on litter decomposition are poorly understood. Here, we examined the effects of air warming, nitrogen (N) addition and altered precipitation, and their interactions on litter decomposition originating from four species (Elymus nutans, Kobresia capillifolia, Thermopsis lanceolata, Saussurea nigrescens) in a Tibetan alpine meadow. Among the three factors, air warming by open top chambers (OTCs) significantly decreased all litter decomposition except for K. capillifolia with the highest C:N ratio over one-year field decomposition. The reduced litter mass loss in the chambered plots was mainly attributed to OTC-induced decrease in soil temperature, with more negative effects of OTC on litter decomposition in winter and spring than in summer. However, N addition offset the negative effects of OTC on litter mass loss of K. capillifolia, likely by alleviating N limitation to this poor-quality litter decomposition. In addition, simulated precipitation increase promoted decomposition of high quality litter (T. lanceolata and S. nigrescens) in the dry winter, likely by alleviating water stress. Together, our findings highlight the predominant role of climate in controlling litter decomposition in alpine ecosystems.