Divergent responses of CO2 and CH4 fluxes to changes in the precipitation regime on the Tibetan Plateau: Evidence from soil enzyme activities and microbial communities

Carbon fluxes (CO2 and CH4) are important indicators of the response of alpine meadow ecosystems to global climate change. Alpine meadows on the Qinghai-Tibet Plateau are sensitive to climate change. Although the temporal allocation of precipitation can vary, its intensity is expected to increase, and its frequency is expected to decrease in the future. In this study, a manipulative field experiment was conducted to investigate how carbon fluxes are altered in response to moderate and severe changes in the precipitation regime. Fluctuations in CH4 flux were large under a severely altered precipitation regime (range of -0.048-0.038 mg m-2 h-1). Severe changes in the precipitation regime significantly reduced soil CH4 uptake by approximately 54.3%. This was probably affected by the decrease in the dissolved organic carbon concentration and changes in the microbial community (mainly Gammaproteobacteria), which were induced by variation in soil water conditions under various precipitation regimes. Under moderate changes in the precipitation regime, the average value of CO2 fluxes (ecosystem respiration) was 698.21 ± 35.19 mg m-2 h-1, which was significantly decreased by 20.7% compared with the control. This likely stems from the suppression of enzyme activity (particularly α-1,4-glucosidase and β-1,4-glucosidase) and the alteration of microbial community structure in this treatment, which led to a decrease in organic matter breakdown and a reduction in the release of CO2 to the atmosphere. However, CO2 fluxes were slightly (i.e., not significantly) decreased under the severely altered precipitation regime. Such different responses of CO2 flux are probably driven by differences in microbial strategies. This study not only increases our understanding of the mechanisms underlying the adaptation of alpine meadow ecosystems to global climate change but also provides new insight into the carbon source/sink functions of alpine meadows.