Root-mediated gas transport in peat determined by argon diffusion

Efflux of CH4 from natural wetlands commonly occurs through vascular plants. These plants also conduct oxygen from the surface to the rhizosphere, permitting CH4 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 εr(z) into a standard transient diffusion equation. We were able to simulate (r2=0.98) measured transport of the biologically inert gas Ar into an intact peat core dominated by bogbean (Menyanthes trifoliata). The best-fit function εr(z), itself correlated well (r2=0.85) with the measured root mass density distribution μM(z), suggesting a means to generate εr(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 (r2=0.70) with reality. The generality of the proportionality constant relating root transmissivity [εr(z)] and mass [μM(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.