Short-term warming decreased soil DOM content and microbial species in alpine wetlands but increased soil DOM content and hydrolase activity in alpine meadows on the Tibetan Plateau

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As important carbon sinks, alpine wetlands on the Tibetan Plateau are undergoing severe degradation. To reveal warming-induced ecological shifts in alpine environments, this study determined soil nutrient contents, enzyme activities, absorption and fluorescence spectra and quadrupole time-of-flight mass spectra (metabolomes) of dissolved organic matter (DOM) and metagenomes based on short-term incubation (0 °C, 10 °C and 20 °C) of topsoil from alpine wetlands and meadows (degraded wetlands). Compared with meadows, wetlands had higher contents of soil DOM (dissolved organic carbon, dissolved organic nitrogen and dissolved phosphorous) and greater activities of hydrolases (β-glucosidase, cellobiohydrolase, β-N-acetylglucosaminidase and acid phosphatase), with those parameters all being highest at 20 °C in meadows and showing various dynamics in wetlands. Soil DOM in wetlands presented the lowest values of specific ultraviolet absorbances (SUVA254 and SUVA260) at 0 °C and the highest values at 10 °C, whereas the opposite was true in the meadows. Wetland soils had greater diversities of DOM molecular compositions and microbial communities, with warming gradually increasing the number of identified DOM compounds in meadows and decreasing the number of microbial species in both soils. Wetland soils had more Proteobacteria (44.2%) and Acidobacteria (21.1%) and fewer Actinobacteria (18.0%) than meadow soils and contained many temperature-sensitive archaea (which were abundant at 0 °C). Distance-based redundancy analysis and Procrustes analysis indicated the greater complexity of ecological responses in alpine wetlands, which may be attributed to the higher adaptive capacity of soil microbial communities. Our results suggest that both degradation and warming decrease soil DOM content and microbial activities in alpine wetlands, providing important references for alpine wetland conservation under current climate change.