Environmental and taxonomic controls of carbon and oxygen stable isotope composition in iSphagnum/i across broad climatic and geographic ranges

摘要

Rain-fed peatlands are dominated by peat mosses (Sphagnum sp.), which for their growth depend on nutrients, water and COsub2/sub uptake from the atmosphere. As the isotopic composition of carbon ( sup12,13/supC ) and oxygen ( sup16,18/supO ) of these Sphagnum mosses are affected by environmental conditions, Sphagnum tissue accumulated in peat constitutes a potential long-term archive that can be used for climate reconstruction. However, there is inadequate understanding of how isotope values are influenced by environmental conditions, which restricts their current use as environmental and palaeoenvironmental indicators. Here we tested (i)?to what extent C and O isotopic variation in living tissue of Sphagnum is species-specific and associated with local hydrological gradients, climatic gradients (evapotranspiration, temperature, precipitation) and elevation; (ii)?whether the C isotopic signature can be a proxy for net primary productivity (NPP) of Sphagnum; and (iii)?to what extent Sphagnum tissue δsup18/supO tracks the δsup18/supO isotope signature of precipitation. In total, we analysed 337 samples from 93?sites across North America and Eurasia using two important peat-forming Sphagnum species (S. magellanicum, S. fuscum) common to the Holarctic realm. There were differences in δsup13/supC values between species. For S. magellanicum δsup13/supC decreased with increasing height above the water table (HWT, Rsup2/sup=17 %) and was positively correlated to productivity ( Rsup2/sup=7 %). Together these two variables explained 46?% of the between-site variation in δsup13/supC values. For S. fuscum, productivity was the only significant predictor of δsup13/supC but had low explanatory power (total Rsup2/sup=6 %). For δsup18/supO values, approximately 90?% of the variation was found between sites. Globally modelled annual δsup18/supO values in precipitation explained 69?% of the between-site variation in tissue δsup18/supO . S. magellanicum showed lower δsup18/supO enrichment than S. fuscum ( ? 0.83?‰ lower). Elevation and climatic variables were weak predictors of tissue δsup18/supO values after controlling for δsup18/supO values of the precipitation. To summarize, our study provides evidence for (a)?good predictability of tissue δsup18/supO values from modelled annual δsup18/supO values in precipitation, and (b)?the possibility of relating tissue δsup13/supC values to HWT and NPP, but this appears to be species-dependent. These results suggest that isotope composition can be used on a large scale for climatic reconstructions but that such models should be species-specific.