DIFFUSION-CONTROLLED TRANSPORT OF METHANE FROM SOIL TO ATMOSPHERE AS MEDIATED BY RICE PLANTS

Methane emission from rice grown in flooded soil was measured in pot e xperiments using headspaces with different gas composition. The emissi on rates varied with the atmospheric composition. Based on the kinetic theory of gases the binary diffusion coefficients for methane in vari ous gases were calculated. The ratios of the measured emissions under a certain atmosphere relative to that in air were similar to the ratio s of the binary diffusion coefficients showing that plant-mediated CH4 transport is driven by diffusion. Small deviations from the theoretic al ratios of emissions support the hypothesis that mass flow of gas to the submerged parts of the rice plant may depress the upward diffusiv e CH4 flux. The results in combination with data from the literature s uggest that the rate limiting step in plant-mediated methane transport is diffusion of CH4 across the root/shoot junction.