Functional Diversity of Boreal Bog Plant Species Decreases Seasonal Variation of Ecosystem Carbon Sink Function

Abstract:

Species diversity has been found to decrease the temporal variance of productivity of a plant community, and diversity in species responses to environmental factors seems to make a plant community more stable in changing conditions. Boreal bogs are nutrient poor peatland ecosystems where the number of plant species is low but the species differ greatly in their growth form. In here we aim to assess the role of the variation in photosynthesis between species for the temporal variation in ecosystem carbon sink function.

To quantify the photosynthetic properties and their seasonal variation for different bog plant species we measured photosynthetic parameters and stress-inducing chlorophyll fluorescence of vascular plant and Sphagnum moss species in a boreal bog over a growing season. We estimated monthly gross photosynthesis (P_G) of the whole study site based on species level light response curves and leaf area development. The estimated P_G was further compared with a gross primary production (GPP) estimate measured by eddy covariance (EC) technique.

The sum of upscaled P_G estimates agreed well with the GPP estimate measured by the EC technique. The contributions of the species and species groups to the ecosystem level P_G changed over the growing season. The sharp mid-summer peak in sedge P_G was balanced by more stable P_G of evergreen shrubs and Sphagna. Species abundance rather than differences in photosynthetic properties between species and growth forms determined the most productive plants on the ecosystem scale. Sphagna had lower photosynthesis and clorophyll fluorescence than vascular plants but were more productive on the ecosystem scale throughout the growing season due to their high areal coverage.

These results show that the diversity of growth forms stabilizes the seasonal variation of the ecosystem level P_G in an ombrotrophic bog ecosystem. This may increase the resilience of the ecosystem to changing environmental conditions.