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

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.

Shrub abundance contributes to shifts in dissolved organic carbon concentration and chemistry in a continental bog exposed to drainage and warming

“…Warmed plot quadrats were positioned between the OTC wall and the plot collar. The biomass was clipped using sharp scissors at the base of capitulum at 1 cm below the moss surface (Granath et al, 2018).…”

Environmental drivers of Sphagnum growth in peatlands across the Holarctic region

“…Sphagnum magellanicum belongs to the subgenus Sphagnum, which is a group of large and stout species with cucullate leaves. Sphagnum magellanicum stands out in its subgenus due to its colour that varies from deep red to almost completely green (Figure 1) collectively in the past, and that they had not been differentiated at the time of data collection, we here follow Granath et al (2018) and treat our study species as S. fuscum coll. and S. magellanicum coll.…”

“…Given that S. beothuk/ S. fuscum and S. medium/S. divinum are sister species and were treated collectively in the past, and that they had not been differentiated at the time of data collection, we here follow Granath et al (2018) and treat our study species as S. fuscum coll. and S. magellanicum coll.…”

Bryophyte species differ widely in their growth and N2-fixation responses to temperature

“…However, earlier research is scarce and does not find a significant relationship between δ 15 N and the quantity of symbiotically fixed N 2 , Hyodo et al 2013, although near zero δ 15 N values indicated high N 2 uptake across six Sphagnum species (Leppänen et al 2015). In a similar manner, bryophyte tissue δ 13 C can provide insight into relative growth rates and photosynthetic activity of bryophytes (Rice 2000), and it is often used as an indicator of environmental factors, such as moisture and temperature conditions (Rice 2000;Bramley-Alves et al 2015;Granath et al 2018). In bryophytes, C uptake is lower at high water content due to low CO 2 diffusion through water (Rice and Giles 1996;Williams and Flanagan 1996).…”