Asymmetric Diurnal and Monthly Responses of Ecosystem Carbon Fluxes to Experimental Warming

Quantifying the diurnal and monthly responses of ecosystem carbon (C) fluxes is critical to accurately understand the feedback between global climate change and ecosystem C dynamics. However, the diurnal and monthly responses of ecosystem C fluxes to climate warming remain unclear. In this study, a field simulated warming experiment was conducted by using open top chambers to explore the diurnal and monthly responses of ecosystem C fluxes during one growing season (GS) in a Tibetan Plateau grassland. The results showed that ecosystem C fluxes responded unevenly to the simulated warming during one GS. Warming significantly increased C uptake (gross primary production) and sequestration (net ecosystem exchange) during the start (May to June) and peak (July to August) of the GS, but promoted ecosystem respiration (ER) during the peak and end (September to October) of the GS. Warming also had more pronounced positive effects on ER during night than during day. In addition, although warming significantly decreased the temperature sensitivity (Q(10)) of ER over the whole GS, Q(10) also responded positively to warming during the start and end of GS as well as during the night. These results highlight the hypothesis that asymmetrical responses of the diurnal and monthly variations of ecosystem C fluxes and Q(10) should be taken into consideration to project the C-climate feedback, especially under future non-uniform warming scenarios.