Gross ecosystem photosynthesis causes a diurnal pattern in methane emission from rice

Abstract

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.