Root-mediated gas transport in peat determined by argon diffusion

Abstract

Efflux of CH 4 from natural wetlands commonly occurs through vascular plants. These plants also conduct oxygen from the surface to the rhizosphere, permitting CH 4 oxidation to occur at depth. It is therefore important to be able to quantify the extent of plant-mediated gas transport. We treated roots as ubiquitous impermeable hollow tubes open at each end, then incorporated an effective root-ending area density function ε r( z) into a standard transient diffusion equation. We were able to simulate ( r 2=0.98) measured transport of the biologically inert gas Ar into an intact peat core dominated by bogbean ( Menyanthes trifoliata). The best-fit function ε r( z), itself correlated well ( r 2=0.85) with the measured root mass density distribution μ M( z), suggesting a means to generate ε r( z) from root mass data obtained elsewhere. Were such a strategy to have been applied to the core we examined, the simulated data would have correlated reasonably well ( r 2=0.70) with reality. The generality of the proportionality constant relating root transmissivity [ ε r( z)] and mass [ μ M( z)] remains to be established. Where vascular plants are not present (e.g. in a core dominated by the bog mosses Sphagnum cuspidatum and S. papillosum), diffusion occurs in the liquid phase of the peat only.