The separate roles of vascular plants and Sphagnum mosses in regulating the net CO2 exchange in a boreal peatland

Boreal peatlands are an important sink for carbon. Carbon uptake and emission are controlled by abiotic factors as well as vegetation composition and plant phenology. Plant functional types (PFT) have distinct phenological trajectories and respond differently to environmental controls which results in seasonal variations in their relative contribution to peatland net CO₂ ecosystem exchange (NEE). However, detailed knowledge on the separate responses of PFT-specific production and respiration fluxes to abiotic factors on daily to sub-seasonal scales are currently missing. In this study, we used high resolution flux data from an automated chamber system established across experimental vegetation removal plots to separate the production and respiration fluxes of vascular plants and Sphagnum mosses over three growing seasons at the oligotrophic minerogenic mire Degerö Stormyr in northern Sweden. We found that Sphagnum mosses dominate ecosystem gross primary production (GPP) during green-up and senescence, whereas vascular plants primarily regulate GPP during the peak growing season. Further, we observed shifts in the relative importance of environmental variables in controlling autotrophic respiration of Sphagnum mosses and vascular plants across different phenophases. A better understanding of how vascular plants and Sphagnum mosses contribute to regulating NEE under varying environmental conditions is essential to improve predictions of the seasonal dynamics in process-based models, and to give insight on the potential climate change feedbacks on the carbon cycle of boreal peatlands.