Linear relationship between CH 4 fluxes and atmospheric CO 2 concentration levels controlled by rice biomass and soil methanogenic communities

The contribution of CH 4 emissions from paddy soils to greenhouse gas emissions is key in the evaluation of future climate change scenarios. Most studies in this field have investigated the effects of elevated CO 2 concentrations (e[CO 2 ]s) on CH 4 fluxes and methanogenic communities in paddy soils under constant CO 2 concentrations ([CO 2 ]s). However, atmospheric [CO 2 ] is gradually increasing and the relationship between future climate change and CH 4 emissions from paddy fields is poorly understood. This study explored the responses of CH 4 fluxes and methanogenic communities in paddy soils to different e[CO 2 ]s using open-top chambers. The rice biomass, CH 4 fluxes, methane production potential, and methanogenic characteristics were analyzed under CK (ambient [CO 2 ]), C 1 (e[CO 2 ] by 120 µmol mol –1 ), and C 2 (e[CO 2 ] by 200 µmol mol –1 ) treatments. The results indicated that the C 1 and C 2 treatments insignificantly increased the CH 4 flux in paddy fields. However, the C 1 treatment significantly increased the CH 4 flux/biomass at the elongation stage, while the C 2 treatment significantly increased the CH 4 flux/biomass at all of the growth stages. The C 1 and C 2 treatments had a positive effect on both methane production potential and methanogenic abundance at all of the growth stages, but this effect was not always significant. In addition, the C 1 and C 2 treatments significantly altered the methanogenic community structure at the elongation stage. Notably, there was a significant linear relationship between the CH 4 flux/biomass and [CO 2 ] at all of the growth stages; between the methane production potential and [CO 2 ] at the tillering, elongation, and milk-ripening stages; and between the mcrA g ene abundance and [CO 2 ] at the milk-ripening stage. A linear model based on rice biomass, methane production potential, and soil DOC concentration explained 72.7% of the variation in the CH 4 fluxes. Overall, the linear relationship between CH 4 fluxes and atmospheric [CO 2 ] levels was controlled by the rice biomass, soil carbon substrate, and methanogenic communities.