Methane production and carbon mineralisation of size and density fractionsof peat soils

For the purpose of characterisation of soil organic matter breakdown, soil organic matter is often divided into different fractions, each with its own decomposition rate. Thus far, no attempts had been made to quantify the me thane production capacity of individual soil fractions. We aimed to improve our understanding of CH4 emissions from peat soils by studying the CH4 pro duction capacity of individual soil fractions in parallel with their carbon mineralisation capacity. Samples from two wet grasslands on peat soil (0-6 0 cm) were fractionated into different size and density fractions (> 2.0 mm ; 0.25-2.0 mm, light; 0.25-2.0 mm, heavy; 150-250 mu m, light; 150-250 IJ-m , heavy; <150 mu m) using sieves and Ludox, an aqueous colloidal dispersion of silica particles. The individual fractions were rather similar with res pect to C mineralisation capacity and C-to-N ratio, but not with respect to CH4 production capacity. C mineralisation capacity ranged from 10 to 100 m u mol CO2-C g(-1) C d(-1) and decreased with depth. CH4 production capacity ranged from 0 to 150 nmol CH4-C g(-1) C d(-1). We found that significant C H4 production only occurred for fractions with a large particle size; the f raction >2.0 mm contributed 90% to total CH4 production capacity. Furthermo re, CH4 production capacity strongly decreased with depth; the layer 0-5 cm contributed 70% to total CH4 production capacity. This indicates that in t he wet peat soils recent plant residues are a major substrate for methanoge ns. (C) 1999 Elsevier Science Ltd. All rights reserved.