Sphagnum moss enzymatic activities indicate nitrogen and phosphorus co-limitation in a pristine boreal bog and poor fen

English Abstract:

Emissions of NO_x associated with Alberta oil sands development are leading to increased atmospheric nitrogen deposition in a pristine region (<1kg N ha^-1 yr^-1). Excess anthropogenic nitrogen deposition has the potential to alter ecosystem function, which can be manifested by changes in plant and microbial enzymatic activities. Since 2011, we experimentally added nitrogen in simulated precipitation to an Alberta bog and poor fen in order to predict future peatland ecosystem responses under high nitrogen deposition scenarios. We assessed the potential alleviation of nitrogen limitation with the addition of up to 25 kg N ha^-1 yr^-1 in a pristine bog and poor fen. After three years of nitrogen addition, phosphorus and nitrogen mineralization enzymatic activities of Sphagnum angustifolium, Sphagnum fuscum, and Sphagnum magellanicum were quantified using methylumbelliferone fluorescent detection. Sphagnum moss enzymatic responses to nitrogen addition were assessed with regards to season, species, and peatland type (poor fen or bog). Phosphatase activities increased from the control to the 25 kg N ha^-1 yr^-1 up to five-folds in all three species and in both peatlands. Chitinase activity also increased with nitrogen addition for Sphagnum magellanicum in the poor fen but not the bog. Increasing enzymatic activities suggest nitrogen and phosphorus co-limitation and nutrient limitations unique to specific Sphagnum species in bogs and poor fens. This sensitivity to increasing nitrogen addition indicates potential consequences for peatland nutrient cycling in the oil sands development area.