OXIDATION OF METHANE IN PEAT - KINETICS OF CH4 AND O-2 REMOVAL AND THE ROLE OF PLANT-ROOTS

Vertical profiles of oxygen uptake potential were measured in peat. Wh en both O-2 and CH4 were in excess, methanotrophy accounted for 85% of the O-2 uptake potential, showing a high capacity for CH4 oxidation i n the peat. In the absence of CH4, maximum O-2 uptake potential was ne ar the peat surface where available labile organic matter was present and decreased with depth as organic matter became more refractory. The oxidation of CH4 followed saturation kinetics with respect to both CH 4 and O-2 when they were at limiting concentrations. For CH4 oxidation in the peat, the k(O2) was 32 mu M O-2 and k(CH4) was 57.9 mu M CH4. The V-max for O-2 was 209 nmol O-2 ml(-1) peat h(-1), which was approx imately double that for CH4, correctly reflecting the stoichiometry of aerobic CH4 oxidation. The CH4 oxidation kinetics were used in a math ematical model to examine the effect of plant roots on increasing the vertical transport rate of CH4 out of and O-2 into the peat, by gas ph ase transport through the roots. In the absence of roots, CH4 oxidatio n was confined to a narrow layer near the peat surface where vertical gradients of O-2 and CH4 overlapped. Little CH4 diffused through this surface layer. With roots present, the model confirmed the possibility of sub-surface peaks of aerobic CH4 oxidation potential below the wat er table in an apparently anoxic peat. These were due to active CH4 ox idation in the oxic rhizosphere maintained by the plant roots in the o therwise anoxic peat. The extrusion of O-2 from the root tips also ten ded to diminish in situ CH4 formation by inhibition of the anaerobic m ethanogenic bacteria. The presence of plant roots increased the Aux of CH4 out of the pear to the atmosphere, by-passing the surface oxic la yer in which active CH4 oxidation mopped up vertically diffusing CH4. (C) 1997 Elsevier Science Ltd.