UC Berkeley

Understanding the relative contribution of environmental and substrate controls on rice paddy methanogenesis is critical for developing mechanistic models of landscape‐scale methane (CH 4 ) flux. A diurnal pattern in observed rice paddy CH 4 flux has been attributed to fluctuations in soil temperature physically driving diffusive CH 4 transport from the soil to atmosphere. Here we make direct landscape‐scale measurements of carbon dioxide and CH 4 fluxes and show that gross ecosystem photosynthesis (GEP) is the dominant cause of the diurnal pattern in CH 4 flux, even after accounting for the effects of soil temperature. The time series of GEP and CH 4 flux show strong spectral coherency throughout the rice growing season at the diurnal timescale, where the peak in GEP leads that of CH 4 flux by 1.3 ± 0.08 hours. By applying the method of conditional Granger causality in the spectral domain, we demonstrated that the diurnal pattern in CH 4 flux is primarily caused by GEP. Key Points Gross ecosystem photosynthesis drives a diurnal pattern in rice methane flux Fluctuations in soil temperature cannot explain the diurnal pattern Close photosynthesis‐methanogenesis coupling presides the entire rice season