Responses of Sphagnum productivity and net ecosystem exchange of carbon dioxide to modifications of moss moisture content in an ombrotrophic bog

This study investigates the importance of Sphagnum mosses to interannual variability in net ecosystem exchange (NEE) of CO2 at Mer Bleue bog with varying moss moisture conditions. Precipitation exclusion (PE) and water addition (WA) treatments produced varying moss water contents (WC), and Sphagnum, vascular plant, and total ecosystem CO 2 exchange were measured in situ using chambers. Despite a relatively low water table at the site, Sphagnum mosses were able to maintain average WCs in or near the optimal range for Sphagnum net primary productivity (NPP) in all treatments. Consequently, there was no treatment effect on CO2 exchange. However, in measurements associated with below optimal WCs Sphagnum NPP was positive (i.e. net loss) leading to decreased NEE. Water table depth and direct precipitation appear to be equally important controls on Sphagnum WC at the site. Sphagnum was important to CO2 exchange, contributing at least one third of gross ecosystem production (GEP) and ecosystem respiration (ER). Dry moss conditions may affect the balance of these components, thereby influencing Sphagnum NPP and the moss influence on total NEE in drought years.