Species-specific temporal variation in photosynthesis as a moderator of peatland carbon sequestration

Abstract

In boreal bogs plant species are low in number, but they differ greatly in their growth forms and photosynthetic properties. We assessed how ecosystem carbon (C) sink dynamics were affected by seasonal variations in the photosynthetic rate and leaf area of different species. Photosynthetic properties (light response parameters), leaf area development and areal cover (abundance) of the species were used to quantify species-specific net and gross photosynthesis rates (PNand PG, respectively), which were summed to express ecosystem-level PNand PG. The ecosystem-level PGwas compared with a gross primary production (GPP) estimate derived from eddy covariance (EC) measurements. Species areal cover, rather than differences in photosynthetic properties, determined the species with the highest PGof both vascular plants and Sphagna. Species-specific contributions to the ecosystem PGvaried over the growing season, which, in turn, determined the seasonal variation in ecosystem PG. The upscaled growing season PGestimate, 230 g C m-2, agreed well with the GPP estimated by the EC (243 g C m-2). Sphagna were superior to vascular plants in ecosystem-level PGthroughout the growing season but had a lower PN. PNresults indicated that areal cover of the species, together with their differences in photosynthetic parameters, shape the ecosystem-level C balance. Species with low areal cover but high photosynthetic efficiency appear to be potentially important for the ecosystem C sink. Results imply that functional diversity, i.e., the presence of plant groups with different seasonal timing and efficiency of photosynthesis, may increase the stability of C sinks of boreal bogs.