Carbon transformations during decomposition of different components of plant leaves in soil

We investigated the effect of lime addition to an upland organic soil on the decomposition of Lolium perenne leaves and isolated fractions of L. perenne leaves in a laboratory experiment lasting 75 d. The L. perenne plants were grown in a (CO2)-C-13-enriched environment and some leaf material was pretreated with ethanol and detergent in order to remove some cell contents and soluble material. The ethanol- and detergent-treated leaves had less alkyl-C, as seen by solid-state C-13 nuclear magnetic spectroscopy (NMR), and a greater proportion of cellulose and hemicellulose than the untreated leaves. Solid-state C-13 NMP spectroscopy and scanning electron microscopy (SEM) were used to follow aspects of the C transformations during decomposition. C mineralization was estimated from total CO2 production. The size and activity of the microbial community was greater in limed than in soils without lime, and microbial respiration was less in both soils amended with ethanol- and detergent-treated leaves compared to soils amended with untreated leaves. In both limed and unlimed soils, amendment with untreated leaves led to additional CO2 production within 7 d of addition. whereas amendment with treated leaves led to a smaller increase in CO2 production. The flush of CO2 production was attributed to decomposition of the more accessible and soluble plant components that, in the ethanol- and detergent-treated leaves, had been removed during the ethanol and detergent treatment. The C-13 NMR spectra recorded for plant material separated from soil 1 d after addition of ethanol- and detergent-treated leaves had larger alkyl-C (30 ppm) signals compared with spectra from untreated leaves. This was interpreted as representing an accumulation of residues from decomposition of plant structural components. (C) 2000 Elsevier Science Ltd. All rights reserved.