Are nitrous oxide emissions and nitrogen fixation linked in temperate bogs?

Abstract

A pre-requisite for denitrification and nitrification is the availability of inorganic nitrogen (N). In many natural ecosystems, atmospheric N deposition as well as moss-associated N2 fixation are the main sources of ‘new’ N to the ecosystem N pool and could provide inorganic N to sustain N2O production. While a link between N2 fixation and N2O emissions is plausible, hardly any attempts have been undertaken to test this link in areas with a moss-dominated understory. Here, we report results from a combined field and laboratory study in which we assessed N2 fixation, net N2O emission under different conditions, and potential nitrification and denitrification in three moss species from a Sphagnum-moss dominated, temperate bog. The three moss species were chosen to represent a gradient of N2 fixation activity. Sphagnum mosses emitted less N2O than the other two moss species (Pleurozium schreberi, Hypnum cupressiforme), but at the same time, showed the highest N2 fixation activity. The lack of a link between N2 fixation and net N2O emissions in three abundant and common moss species indicates that N transformation processes may be decoupled within the moss carpet. This raises new questions on N supply for N2O production and the fate of fixed N2 in moss-dominated systems.