Steart, David Charles, Greenwood, David R and Boon, Paul I (2009) The Chemical Constraints Upon Leaf Decay Rates. Taphonomic Implications among Leaf Species in Australian Terrestrial and Aquatic Environments. Review of Palaeobotany and Palynology, 157 (3-4). pp. 358-374. ISSN 0034-6667

Abstract

The decay rate of leaves of five Australian tree species, Acacia melanoxylon R. Br., Atherosperma moschatum Labill., Eucalyptus regnans F.Muell., Lomatia fraseri and Nothofagus cunninghamii (Hook.) Oerst., was quantified to determine whether differences in decay rates influence leaf fossilization potential. Decay rates were determined under 4 sets of conditions that mimicked the main ecological settings where a leaf could come to rest after abscission: the forest floor; buried in terrestrial forest sediments; the sediment–water interface of a stream or lake; and buried in stream sediments. Leaf physiochemisty was characterized to identify the chemical constraints that may affect decay rates, and leaf decay (measured as loss of mass and change in leaf lamella area) was examined to determine whether leaves lost area (a quantity often measured by palaeobotanists) at the same rate as they lost mass (the quantity often measured by limnologists). A. moschatum decayed rapidly regardless of treatment conditions, whilst N. cunninghamii not only decayed more slowly than the other taxa but decayed significantly more slowly when buried than when on the sediment surface. Differences in decay rates across the 5 species were similar when expressed as mass loss or as loss of leaf area, indicating that species that undergo rapid mass loss also undergo rapid area loss and thus become rapidly unrecognizable in the leaf fossil record. An important predictor of decay rates was lignin-tonitrogen ratio; species with high lignin-to-nitrogen ratios had the lowest decay rates and, by implication, the best chances of entering the fossil record. Published leaf-decay rates in the soil ecology and limnological literature thus can be used to indicate which species could be over or under represented in the leaf fossil record using nearest living relative analysis; such an approach may enhance the accuracy of palaeobotanical reconstructions.

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