The effect of soil acidification on atmospheric methane uptake by a Maine forest soil

Soil from the zone of maximal methanotrophic activity (approximately 5-8 cm depth) in a mixed coniferous-hardwood forest consumed atmospheric methane over a wide pH range (3.5-7.5) with a broad optimum between 4.8 and 6.0. Me thane uptake at native soil pH values (4.4-4.8) was only slightly less rapi d than rates at optimal pH values. Addition of mineral acids to intact soil cores in pulsed applications decreased atmospheric methane consumption. Th e extent of inhibition varied with the type, concentration and volume of ac id added: nitric acid was more inhibitory than sulfuric acid at an equivale nt soil pH, and methane uptake decreased with increasing volumes and concen trations of added acid. Although ammonium chloride at 1 mu mol g fresh weig ht (gfw) soil(-1) inhibited methane uptake, the extent of inhibition did, n ot vary significantly with decreasing soil pH below values of 4.4. (C) 2001 Federation of European Microbiological Societies. Published by Elsevier Sc ience B.V. All rights reserved.