Environmental and taxonomic controls of carbon and oxygen stable isotope composition in <i>Sphagnum</i> across broad climatic and geographic ranges
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abstract
Abstract. Rain-fed peatlands are dominated by peat mosses (Sphagnum sp.),
which for their growth depend on nutrients, water and CO2 uptake from
the atmosphere. As the isotopic composition of carbon (12,13C) and
oxygen (16,18O) 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 δ18O tracks the
δ18O 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
δ13C values between species. For S. magellanicum
δ13C decreased with increasing height above the water table
(HWT, R2=17 %) and was positively correlated to productivity
(R2=7 %). Together these two variables explained 46 % of the
between-site variation in δ13C values. For S. fuscum,
productivity was the only significant predictor of δ13C but
had low explanatory power (total R2=6 %). For δ18O
values, approximately 90 % of the variation was found between sites.
Globally modelled annual δ18O values in precipitation
explained 69 % of the between-site variation in tissue
δ18O. S. magellanicum showed lower
δ18O enrichment than S. fuscum (−0.83 ‰
lower). Elevation and climatic variables were weak predictors of tissue
δ18O values after controlling for δ18O values
of the precipitation. To summarize, our study provides evidence for (a) good
predictability of tissue δ18O values from modelled annual
δ18O values in precipitation, and (b) the possibility of
relating tissue δ13C 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.
