Modeling Rice Plant-Mediated Methane Emission

Late-season methane (CH₄) emissions from flooded ricefields appear to be fueled by root exudation and death and to be transmitted to the atmosphere largely through the plant. We present a general transport-reaction model which accommodates these phenomena, together with a simplified ("cartoon") version intended to reproduce the salient features of most plant-dominated CH₄-emitting systems. Our cartoon model is capable of reproducing measured concentration profiles and fluxes. Sensitivity annalysis suggests that cultivars with high specific root transmissivity may, other things being equal, reduce rather than enhance net emission. Simulations assuming exponential growth of the root system followed by Gaussian die-back resemble measured flux trajectories and also point to great variability in the fraction of CH₄ oxidized before it reaches the atmosphere. Air entry on drainage reduces simulated CH₄ fluxes and the fractions of those fluxes mediated by plants. It also increases the fraction of CH₄ oxidized.