Warming alters photosynthetic rates of sub-boreal peatland vegetation

Abstract: Boreal peatlands are important in the global carbon cycle. Despite coveringonly 3% of the global land area, peatlands store approximately one third of all soilcarbon. Temperature is one of the major drivers in peatland carbon cycling as itaffects both plant production and CO2 fluxes from soils. However, it is relativelyunknown how boreal peatland plant photosynthesis is affected by highertemperatures. Therefore, we measured plant photosynthetic rates under two differentwarming treatments in a poor fen in Northern Michigan. Eighteen plots wereestablished that were divided into three treatments: control, open-top chamber (OTC)warming and infrared (IR) lamp warming. Previous work at this site has shown thatthere was a significant increase in canopy and peat temperature with IR warming (5°Cand 1.4°C respectively), while the OTC’s had mixed overall warming. Plots weredivided equally into lawns and hummocks. We measured mid-day carbon dioxide(CO2) uptake on sedges (Carex utriculata), shrubs (Chamaedaphne calyculata) andSphagnum mosses. Sphagnum moss net primary production (NPP) was also measuredwith cranked wires and compared with CO2 uptake.Our results indicate that there was no significant difference in sedge CO2uptake, while shrub CO2 uptake significantly decreased with warming. A significantincrease occurred in Sphagnum moss gross ecosystem production (GEP), ecosystemrespiration (ER) and net ecosystem exchange (NEE). Contrary to the positive CO2exchange of Sphagnum, overall NPP decreased significantly in hummocks with bothwarming treatments. The results of the study indicate that temperature partly limitsthe photosynthetic capacity of plants in sub-boreal peatlands, but not all speciesrespond similarly to higher temperatures.