Unexpected Parabolic Temperature Dependency of CH4 Emissions from Rice Paddies

Global warming is expected to affect methane(CH4) emissions from rice paddies, one of the largest human-induced sources of this potent greenhouse gas. However, the largevariability in warming impacts on CH4emissions makes it difficultto extrapolate the experimental results over large regions. Here, weshow, through meta-analysis and multi-site warming experimentsusing the free air temperature increase facility, that warmingstimulates CH4emissions most strongly at background airtemperatures during theflooded stage of similar to 26 degrees C, with smallerresponses of CH4emissions to warming at lower and highertemperatures. This pattern can be explained by divergent warmingresponses of plant growth, methanogens, and methanotrophs. Theeffects of warming on rice biomass decreased with the backgroundair temperature. Warming increased the abundance of methanogens more strongly at the medium air temperature site than the lowand high air temperature sites. In contrast, the effects of warming on the abundance of methanotrophs were similar across the threetemperature sites. We estimate that 1 degrees C warming will increase CH4emissions from paddies in China by 12.6%& xe0d5;substantiallyhigher than the estimates obtained from leading ecosystem models. Ourfindings challenge model assumptions and suggest that theestimates of future paddy CH4emissions need to consider both plant and microbial responses to warming.