ROOT-MEDIATED GAS-TRANSPORT IN PEAT DETERMINED BY ARGON DIFFUSION

Efflux of CH4 from natural wetlands commonly occurs through vascular p lants. These plants also conduct oxygen from the surface to the rhizos phere, permitting CH4 oxidation to occur at depth. It is therefore imp ortant to be able to quantify the extent of plant-mediated gas transpo rt. We treated roots as ubiquitous impermeable hollow tubes open at ea ch end, then incorporated an effective root-ending area density functi on epsilon(r)(z) into a standard transient diffusion equation. We were able to simulate (r(2)=0.98) measured transport of the biologically i nert gas Ar into an intact peat core dominated by bogbean (Menyanthes trifoliata). The best-fit function epsilon(r)(z), itself correlated we ll (r(2)=0.85) with the measured root mass density distribution mu(M)( z), suggesting a means to generate epsilon(r)(z) from root mass data o btained elsewhere. Were such a strategy to have been applied to the co re we examined, the simulated data would have correlated reasonably we ll (r(2)=0.70) with reality. The generality of the proportionality con stant relating root transmissivity [epsilon(r)(z)] and mass [mu(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. pap illosum), diffusion occurs in the liquid phase of the pear only. (C) 1 998 Elsevier Science Ltd. All rights reserved.