Elevated CO2 Effects on Peatland Plant Community Carbon Dynamics and DOC Production

Abstract

Northern peatlands are important stores of carbon and reservoirs of biodiversity that are vulnerable to global change. However, the carbon dynamics of individual peatland plant species is poorly understood, despite the potential for rising atmospheric CO2 to affect the vegetation’s contribution to overall ecosystem carbon function. Here, we examined the effects of 3 years exposure to elevated CO2 (eCO2) on (a) peatland plant community composition and biomass, and (b) plant carbon dynamics and the production of dissolved organic carbon (DOC) using a 13CO2 pulse–chase approach. Results showed that under eCO2, Sphagnum spp. cover declined by 39% (P < 0.05) and Juncus effusus L. cover increased by 40% (P < 0.001). There was a concurrent increase in above- and belowground plant biomass of 115% (P < 0.01) and 96% (P < 0.01), respectively. Vascular species assimilated and turned over more 13CO2-derived carbon than Sphagnum spp. (49% greater turnover of assimilated 13C in J. effusus and F. ovina L. leaf tissues compared with Sphagnum, P < 0.01). Elevated CO2 also produced a 66% rise in DOC concentrations (P < 0.001) and an order of magnitude more ‘new’ exudate 13DOC than control samples (24 h after 13CO2 pulse-labelling 2.5 ± 0.5 and 0.2 ± 0.1% in eCO2 and control leachate, respectively, P < 0.05). We attribute the observed increase in DOC concentrations under eCO2 to the switch from predominantly Sphagnum spp. to vascular species (namely J. effusus), leading to enhanced exudation and decomposition (litter and peat). The potential for reduced peatland carbon accretion, increased DOC exports and positive feedback to climate change are discussed.