By estimating the changes in water table depth, temperature, and precipitation during the twentieth century, we excluded potential effects of these climate parameters on the observed isotopomer responses. Rising CO 2 levels generally suppressed photorespiration relative to photosynthesis but the magnitude of suppression depended on the current water table depth.
Here we investigate the response of the photorespiration to photosynthesis ratio in Sphagnum mosses to recent CO 2 increases by comparing deuterium isotopomers of historical and contemporary Sphagnum tissues collected from 36 peat cores from five continents. Net carbon assimilation is strongly reduced by photorespiration, a process that depends on the CO 2 to O 2 ratio. Atmospheric CO 2 levels have increased dramatically during the twentieth century, from 280 to > 400 ppm, which has affected plant carbon dynamics.
Natural peatlands contribute significantly to global carbon sequestration and storage of biomass, most of which derives from Sphagnum peat mosses.
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