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 (P_N and P_G, respectively), which were summed to express ecosystem-level P_N and P_G. The ecosystem-level P_G was 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 P_G of both vascular plants and Sphagna. Species-specific contributions to the ecosystem P_G varied over the growing season, which, in turn, determined the seasonal variation in ecosystem P_G. The upscaled growing season P_G estimate, 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 P_G throughout the growing season but had a lower P_N. P_N results 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.