An additive effect of elevated atmospheric CO2 and rising temperature on methane emissions related to methanogenic community in rice paddies

Abstract Both elevated atmospheric carbon dioxide (CO 2 ) and rising temperature can alter soil methane (CH 4 ) fluxes, leading to a feedback to climate change. However, predicting this feedback needs to understand the microbial mechanisms involved in CH 4 emissions driven by climate change. A 3-year field measurement of CH 4 fluxes from rice paddies was taken in 2012–2014 to examine their responses to elevated CO 2 (enriched up to 500 μmol mol −1 ) and rising canopy air temperature (above ambient 1.5–2.0 °C) using a free-air CO 2 enrichment (FACE) system. Using real-time PCR and Illumina MiSeq sequencing of 16S rRNA genes, we measured the abundance and composition of methanogenic community in rhizosphere soil of rice paddies in 2014. Elevated CO 2 and rising temperature showed additive effects on CH 4 fluxes and methanogen abundances, where CH 4 fluxes were correlated with methanogen abundances. Elevated CO 2 , rising temperature and their combination increased seasonal CH 4 emissions by 28–120%, 38–74% and 82–143%, respectively. Either elevated CO 2 or rising temperature did not significantly alter the diversity of methanogenic community, and methanogenic genera Methanosaeta , Methanosarcina , Methanobacterium , Methanocella and Methanoregula dominated in rhizosphere soils for all treatments. However, elevated CO 2 induced a shift from acetoclastic to hydrogenotrophic methanogens in their relative abundances. Rising temperature stimulated CH 4 emissions by increasing CH 4 production per individual predominant methanogen genus. Besides the enhancement of soil C substrates and rhizosphere methanogen abundances as previously reported, an additive effect of elevated CO 2 and canopy warming on CH 4 emissions is also associated with elevated CO 2 -induced changes in the composition of methanogenic archaea and warming-stimulated the activity of methanogenic archaea in rice paddies.