The Effect of Temperature on Key Aspects of the Nitrogen Cycle: Comparisons Across Systems

The nitrogen cycle sustains life by converting inert di-nitrogen gas (N₂) into fixed bio-available forms (e.g. ammonium, nitrate), as well as returning it via gases such as N₂ and nitrous oxide (N₂O) back into the atmosphere. Recently, the effects of long term warming on key components of the carbon cycle, which is tightly coupled to the nitrogen cycle, have been highlighted but how global warming might systematically affect the balance of the nitrogen cycle is still largely unknown.

The effect of long term warming on denitrification and nitrification were investigated using long-term, experimental mesocosm (2006 to present), allowing us to study the effect of warming on natural communities of bacteria involved in these processes. Denitrification activity responded to warming in the short-term in a predictable way, however, long-term moderate warming of 3-5^oC (the predicted global increase by the end of the century) increased the specific activity of the sediment and had a pronounced effect on the ratio of N₂O to N₂. The latter suggesting that with sustained warming, denitrifying bacteria become more efficient at complete denitrification. Molecular analysis of denitrifying communities in our long-term mesocosm experiment also suggested a profound alteration of the communities underlying these differences in process. Similar short-term experiments were carried out on sediments and the water column of the North Eastern Tropical Pacific Oxygen minimum zone (NETP OMZ) including its effect on N₂ fixation and here we contrast the findings from those markedly different settings.

This research has indicated that we may see similar effects on the nitrogen cycle as we have previously determined in the carbon cycle, with the balance of N-species consumed and created becoming out of balance.