Regulation of denitrification at the cellular level: a clue to the understanding of N2O emissions from soils

摘要

Denitrifying prokaryotes use NO_x as terminal electron acceptors in response to oxygen depletion. The process emits a mixture of NO, N_2O and N_2, depending on the relative activity of the enzymes catalysing the stepwise reduction of NO_3~- to N_2O and finally to N_2. Cultured denitrifying prokaryotes show characteristic transient accumulation of NO_2~-, NO and N_2O during transition from oxic to anoxic respiration, when tested under standardized conditions, but this character appears unrelated to phylogeny. Thus, although the denitrifying community of soils may differ in their propensity to emit N_2O, it may be difficult to predict such characteristics by analysis of the community composition. A common feature of strains tested in our laboratory is that the relative amounts of N_2O produced (N_2O/(N_2tN_2O) product ratio) is correlated with acidity, apparently owing to interference with the assembly of the enzyme N_2O reductase. The same phenomenon was demonstrated for soils and microbial communities extracted from soils. Liming could be a way to reduce N_2O emissions, but needs verification by field experiments. More sophisticated ways to reduce emissions may emerge in the future as we learn more about the regulation of denitrification at the cellular level.