Early degradation of plant alkanes in soils: A litterbag experiment using 13C-labelled leaves

We monitored the carbon isotope composition of bulk leaves and specific long-chain alkanes during a four-year litterbag experiment using 13C-labelled leaves and unlabelled reference leaves of the European beech tree (Fagus sylvatica L.). Whereas the isotope composition of alkanes from 13C-enriched leaves exhibited a marked decrease in 13C-content, the isotope composition of unlabelled reference leaves remained nearly constant. We interpreted this difference as evidence for a microbial contribution to the long-chain alkane pool of the decomposing leaves and related it to the progressive invasion of leaves by soil organisms which was revealed upon microscopic examination. These results suggest that long-chain alkanes may not provide an unaltered record of organic carbon isotope composition in soils and sediments.

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► Specific isotope composition of long-chain alkanes was modified during leaf decay.
► Isotope modification during leaf decay probably reflects a microbial contribution to leaf alkanes.
► Long-chain alkanes may not be used as an unaltered record of plant isotope composition.