Nitrogen fixation, nitrification and denitrification in ombrotrophic bog

Abstract

Nitrogen fixing activity estimated in peat cores in NE Russia did not exceed 0.014-0.022 mg N kg-1 h-1 in the most active 10-20 cm depth layer, but all examined samples possessed a high nitrogen fixing potential determined in glucose-amended samples in optimum conditions. Numerically the leading groups of diazotrophs are methylotrophic bacteria (aerobic) and enterobacteria (anaerobic). The nitrification rate was 0.05 mg N-NO3- kg-1 day-1 only in samples from upper the 0-10 cm layer amended by ammonium. It was negligible in all other samples. Nitrosomonas and Nitrobacter were present in aerobic ammonium oxidizing enrichment cultures from the top layer. Denitrification rates were estimated in anaerobic acetylene inhibited intact flooded peat cores upon fertilization with nitrate. Addition of 10 mg glucose g-1 to the peat samples led to an increased N2O production from 5.3 to 14.7 mg N kg-1 day-1 in 10-20 cm layer and from 2.7 to 4.7 in the 20-30 cm layer.