Methanogenesis and CO2 exchange in an ombrotrophic peat bog

Methanogenesis was studied in water-saturated pear cores from hollows in Ellergower Moss, New Galloway, Scotland. The concentration of CH4, increased with depth from 0.8 mu M at the surface to reach a plateau of 500 mu M at 14 cm; at this depth CO2 concentrations often reached 10 fold those of CH4. O-2 decreased from near air saturation to less than 10 nM at 6 cm depth. Argon transport from the top of the core downwards occurred more rapidly (D = 0.8-7 x 10(-8) m(2) s(-1), dependent on depth) than could be accounted for by simple diffusion through the peat. Vascular plants (Molinia, Eriophorum and Carex) had well-developed roots and were adapted to water-logged conditions in that they possessed extensive aerenchymatous lacunae throughout their roots, shoots and leaves. As well as facilitating O-2 diffusion downwards to submerged tissues,this system enables rapid diffusion upwards of CH4. This process of gaseous transport in vascular plants is subject to control by stomata. Emission rates of CO2 and CH4 thus show diurnal rhythms at constant temperature. Free-run of CO2 oscillation in the dark at 15 cm depth indicates circadian clock control. The temperature sensitivity of CH4 emission is remarkably high Q(10) = 3.0 between 10 and 20 degrees C in the dark); in cores kept under natural conditions of temperature and daylight the daily rhythms entrain to the peat temperature cycles. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.