Increased annual methane uptake driven by warmer winters in an alpine meadow
Peiyan Wang, Jinsong Wang, Bo Elberling, Yang Lu, Weinan Chen, Lei Song, Yingjie Yan, Song Wang, Junxiao Pan, Yunlong He, Shuli Niu
Abstract
Abstract Pronounced nongrowing season warming and changes in soil freeze–thaw (F–T) cycles can dramatically alter net methane (CH 4 ) exchange rates between soils and the atmosphere. However, the magnitudes and drivers of warming impacts on CH 4 uptake in different stages of the F–T cycle are poorly understood in cold alpine ecosystems, which have been found to be a net sink of atmospheric CH 4 . Here, we reported a year‐round ecosystem daily CH 4 uptake in an alpine meadow on the Qinghai‐Tibetan Plateau after a 5‐year warming experiment that included a control, a low‐level warming treatment (+2.4℃ at 5 cm soil depth), and a high‐level warming treatment (+4.5℃ at 5 cm soil depth). We found that warming shortened the F–T cycle under the low‐level warming and soils did not freeze under the high‐level warming. Although both warming treatments increased the mean CH 4 uptake rate, only the high‐level warming significantly increased annual CH 4 uptake compared to the control. The warming‐induced stimulation of CH 4 uptake mainly occurred in the cold season, which was mostly during spring thaw under low‐level warming and during the frozen winter under high‐level warming due to a longer period with thawed soil. We also found that warming significantly stimulated daily CH 4 uptake mainly by reducing near‐surface soil water content in the warm season, whereas both soil water content and temperature controlled daily CH 4 uptake in different ways during the autumn freeze, frozen winter, and spring thaw periods of the control. Our study revealed a strong warming effect on CH 4 uptake during the entire F–T cycle in the alpine meadow, especially the unfrozen winter. Our results also suggested the important roles of soil pH, available phosphorus, and methanotroph abundance in regulating annual CH 4 uptake in response to warming, which should be incorporated into biogeochemical models for accurately forecasting CH 4 fluxes under future climate scenarios.