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 e(r)(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 e(r)(z), itself correlated well (r²=0.85) with the measured root mass density distribution µ(M)(z), suggesting a means to generate e(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 (r² = 0.70) with reality. The generality of the proportionality constant relating root transmissivity [e(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.