Fangyue Zhang, Quan Quan, Fangfang Ma, Dashuan Tian, Qingping Zhou, Shuli Niu
Increases or reductions in rainfall will substantially impact the net exchange of CO2 (NEE) between the atmosphere and land, which is determined by gross primary productivity and ecosystem respiration, while the latter includes plant and microbial respiration. Although NEE will decrease under drought, it remains unclear whether the different components of NEE respond in the same way to changes in rainfall. In order to explore the response of different components of NEE, we conducted a manipulative field experiment with six rainfall treatments in an alpine meadow. We achieved varying levels of rainfall amount using combinations of water catchments and rainout shelters operating the whole year round. Over three years (2015-2017), all carbon fluxes increased nonlinearly with the increasing of rainfall amount, except for plant root respiration, which indicates that the reduction of carbon fluxes under future drought will not equal to the increase under increased rainfall. The most extreme drought treatment caused strong reductions in plant respiration, but did not change microbial or plant root respiration. This suggests plant respiration was more sensitive to changes in rainfall than microbial respiration, and aboveground plant respiration was more susceptible than root respiration. These responses of carbon flux to changes in rainfall were primarily due to changes in soil moisture and aboveground net primary productivity. These findings indicate that the different components of carbon fluxes respond differently to changes in rainfall in an alpine meadow. Future changes in rainfall, particularly extreme drought, will decrease ecosystem carbon fluxes to varying degrees, leading to a consequent reduction of NEE.