CONCLUSION
Here we show that S. fuscum’s photorespiration is suppressed,i.e. net photosynthesis increased, in response to the last century’s increase in atmospheric CO2. This response was highly dependent on WT, with water-saturating conditions abolishing the CO2 effect. Although those conditions are not typical for hummocks, they frequently occur for lawns. Lawns did not show any suppression of photorespiration, neither under water-saturation nor under optimal moisture conditions, suggesting a reduced CO2 effect for those microhabitats. Variations in temperature and light intensity did not affect the extent of the CO2-driven suppression of photorespiration. Our study revealed that D isotopomers are a valuable tool for understand metabolic C fluxes in Sphagnum . The results presented in this study will allow validation of D isotopomer analysis of peat archives and provide the basis for modelling global peatland C fluxes.