Nitrate uptake by Eriophorum vaginatum controls N2O production in a restored peatland

The clear dependence of N2O production through denitrification on available nitrate (NO3−) in soil has been shown in many studies. Since N availability similarly limits the growth of plants, the resource competition with vegetation limits the activity of denitrifying microbes and may consequently moderate the N2O emissions from peatlands. We used NO3− uptake by Eriophorum vaginatum L. as a vegetation competition factor for microbes. The species was selected for the experiment because it has high nutrient use efficiency in low-nutrient conditions and high nutrient uptake efficiency in luxuriant nutrient conditions. We measured gaseous N flux as N2O (end product of denitrifier activity) in a restored peatland in central Finland with acetylene inhibition technique over a growing season from sample plots with varying NO3− addition levels and E. vaginatum cover. The resource competition effects were analysed with a model that used exponential decay dependence of N2O flux on the leaf area of E. vaginatum, and saturating response of N2O flux to NO3− addition level. The model explained the variation in N2O fluxes well (R2=0.86). The model simulation showed that the increasing nutrient uptake of E. vaginatum decreased the N2O fluxes exponentially. Simultaneously, denitrification appeared to saturate even in conditions with high availability of NO3− and low level of competition by vegetation. Thus, E. vaginatum is an effective competitor for NO3− in sedge-dominated peatlands that controls the availability of NO3− for denitrification, and consequently moderates the N2O emissions from peatlands.