Nitrogen Fixation and the Nitrogen Balance in Peatland Ecosystems

Abstract

A survey of heterotrophic nitrogen fixation was carried out using the acetylene reduction assay on peat from mires in Canada, England, Scotland, Ireland, Norway, Germany, Italy, and Malaysia. A detailed study of the relationship between nitrogen fixation and peatland ecology was carried out on the German sites. Nitrogenase activity was detected in all 16 fen sites examined, with the highest rates of activity being >100 nmol C 2 H 4 °mL peat — 1 °d — 1 . Lower rates were found in both extreme rich fen and poor fen sites, with the lower rates found in bogs. A multiple regression analysis indicated pH and K to be positively correlated with nitrogenase activity whilst the correlation with Ca was negative. These results suggest that the systems as a whole may be in balance with regard to nitrogen. The rate of nitrogenase in peat from lower latitudes is greater than in peat from higher latitudes when temperatures are allowed for. The concentration of soluble nitrogen was higher, and the rate of nitrogenase activity lower in peat from beneath fen woodland than in peat from the early unwooded phase of succession. The estimated amount of nitrogen fixed annually by heterotrophic bacteria in peat from the south German mires is as follows (mg N/m 2 ): fen, 2100; poor fen, 530; and bog, 70.