Understanding Peat Redox and Decomposition Environment with Different Plant Functional Types and a Drier Climate: Considering More Than Just Water Table Position.

The invention of the snorkel illustrates that aerobic heterotrophs need different strategies for surviving beneath a water table, and there is a well-established literature on how different plant functional groups cope with nutrient acquisition and respiration in hydric soils.  Specifically, sedges have aerenchyma cells which can transport O₂ throughout a deep rhizosphere and ericaceous shrubs have unique enzymology for acquiring nutrients within shallow (relatively aerated) peat.  Yet, heuristic understanding of peat decomposition is often restricted to two regions- the variably saturated region below the water table, and the variably unsaturated region above the water table; this simplification is appropriate in a broad sense, but is not sufficient in explaining high rates of respiration often observed beneath the water table in northern peatlands.  Here, we report on changes in oxidation reduction potential, decomposition and the water-soluble products of decomposition, and trace gas production (CO₂ and CH₄) in a full factorial peatland manipulation of water table position and vegetation composition.  Trace gas production was significantly affected by both water table position and vegetation composition; however, plant functional group impacted methane flux differently between water table treatments. Methane flux was greatest with high water tables and did not differ with vegetation composition. Under low water tables, the presence of both sedge and ericoid shrubs resulted in the highest methane flux, while ericoid-only treatments showed lower fluxes. Hence, there are strong interactive effects of plant functional type and water table in determining decomposition in peat.  We suggest new metrics for ascertaining anaerobic mineralization potential, in addition to simply knowing where the water table is.