Environmental rationale

The increasing concentrations of N2O in the atmosphere is due to mankind's interference with the nitrogen cycle.

The ultimate cause is nitrogen enrichment, the proximal N2O sources are nitrogen red/ox reactions by prokaryotes.

We believe that there exist options for reducing N2O emissions, but only if we improve our understanding of the regulatory network at the cellular-, microhabitat-, whole soil-, soil-plant- and ecosystem level.  This a goal for NMBU Nitrogen Group.

We study the regulatory biology and ecology of denitrifcation, dissimilatory reduction of nitrite to ammonium, and ammonium oxidation.

We use model organisms, such as Paracoccus denitrificans;Nitrosomnas europea, Agrobacterium tumefaciens.

.. not because we believe that they are representative for organisms in nature, but because they are "fast tracks" to new insight, novel phenomena, new concepts. 

We are aware that  phenomena discovered in model organisms must be validated by experiments with natural populations; which we do. 


This is best illustrated by an example:

We discovered that the model organism, Paracoccus denitrificans was unable to make functional N2O reductase at pH 6, although it clearly "tried" by transcribing the gene coding for the enzyme.

Through a series of expeiments, we found that the most plausible explanation is that low pH interferes with the assembly of the enzyme in the periplasm, and we hypothesize that Cu-insertion is the critical step.  The enzyme, if successfully assembled at pH 7, was perfactly functional at pH<6! This could of course be a peculiarity for Paracoccus denitrificans, but we have provided ample evidence for the opposite by studying natural populations: in all soils tested, we find that the expression of N2O reductase declines with pH, and experiments with bacteria extracted from soil confirmed the peculiar post translatoric phenomenon described for Paracoccus.   

We would not need the model strain to discover the effect of pH an the N2O/N2 product ratio of denitrification. The phenomenon was observed more than 60 years ago, but never understood, hence forgotten and rediscovered several times since then. But the experiments with the model strain helped us to understand the cause. 

Why is this so intresting? Because the pervasive effect of soil pH on the N2O/N2 product ratio means that we can reduce N2O emissions from soils by liming! Liming increase soil pH, which enhance the expression of N2O reductase, thus lowers the N2O/N2 product ratio of denitrification, hence reduces the N2O emission to the atmosphere! 

Environmental research at its best unravels causations. 

Published 14. May 2008 - 14:00 - Updated 25. January 2019 - 14:29