In this study, we describe the seasonal variation in N-15 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 delta N-15 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 delta N-15 probably due to the incorporation of microbial organic compounds rich in N-15. The litter of Eriophorum vaginatum and Carex rostrata was characterized by a decrease of delta N-15, so that the final signature was significantly lower than in initial litter. On the other hand, the residual litter of Potentilla erecta and Calluna vulgaris was characterized by a final delta N-15 higher than in initial litter. Our data reported a seasonality of N-15 abundance in the residual litter of Sphagnum species, but not in that of vascular plant species, thus highlighting the role of differences in litter chemistry.
François Maréchal, Jonas Schnidrig, Xiang Li, Raphaël Briguet