Effects of water table position and plant functional group on plant community, aboveground production, and peat properties in a peatland mesocosm experiment (PEATcosm)

Abstract

Our objective was to assess the impacts of water table position and plant functional type on peat structure, plant community composition and aboveground plant production. We initiated a full factorial experiment with 2 water table (WT) treatments (high and low) and 3 plant functional groups (PFG: sedge, Ericaceae, sedge and Ericaceae- unmanipulated) in twenty-four 1 m3 intact peatland mesocosms. We measured vegetation cover, aboveground plant production, and peat subsidence to analyze interactive PFG and WT effects. Sphagnum rubellum cover increased under high WT, while Polytrichum cover increased with low WT and in sedge only PFGs. Sphagnum production was greatest with high WT, while vascular plant production was greater in low WT treatments. There was an interactive WT x PFG effect on Ericaceae production. Lowered WT resulted in significant peat surface change and increased subsidence. There were significant PFG and WT effects on net peat accumulation, with the lowest rates of accumulation, high and low WT, in sedge only PFGs. The shift in water balance leading to lowered water table position predicted with changing climate could impact plant community composition and production, and would likely result in the subsidence of peat.