In this study, we describe the seasonal variation in 13C abundance in the litter of two Sphagnum species and four vascular plant species during 3 years of field decomposition in an Italian alpine bog. Litter bags were periodically retrieved at the end of summer and winter periods, and the δ13C in residual litter was related to mass loss, litter chemistry, and climatic conditions. In Sphagnum litter, higher rates of decomposition during summer months were associated with an increase of δ13C probably due to the incorporation of microbial organic compounds rich in 13C in the residual litter. In the litter of Eriophorum vaginatum, Carex rostrata and Calluna vulgaris, we observed a decrease of δ13C with an increase in the concentration of lignin-like compounds. The residual litter of Potentilla erecta showed a decrease of 13C abundance during the first 2 years, but on proceeding the decomposition, the δ13C increased again probably reflecting the incorporation of microbial organic compounds. © Springer-Verlag 2009.
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