Investigating biological uptake of nitrous oxide in soils

Climate change is one of the greatest challenges we face as a society. Excessive emissions of greenhouse gases (GHGs), so-called because they trap the sun’s energy in the atmosphere, are driving uncontrolled planetary heating. This is already causing devastating consequences for our climate and to avoid the worst consequences of climate change, we mustn’t let global heating exceed 1.5°C. This project concerns nitrous oxide (N2O), a GHG 265 times as powerful as CO2. N2O persists in the atmosphere for 120 years, meaning today’s N2O emissions will still be affecting the climate in five generations’ time. Given the ongoing trajectory of global GHG emissions, we already require negative emissions technology to limit global heating to 1.5ºC The largest source of N2O is agriculture, where N2O is emitted when soils receive nitrogen fertiliser. The simplest way to reduce N2O emissions, would be to reduce use of these fertilisers, but due to the need to feed a growing population, the use of nitrogen fertiliser is not likely to decline any time soon. Current understanding is that the only process which consumes N2O in soils, is under extremely wet conditions, a small proportion of N2O produced is converted to nitrogen gas and returned to the atmosphere. New technologies, however, have provided data which suggest that there may be a previously unknown biological process which consumes N2O in soils, under dry aerated conditions. If this is proven, it has the potential to be a powerful tool in trying to achieve Net Zero. My initial experiments indicate that there are microorganisms in the soil that, instead of producing N2O, use N2O as a source of nitrogen and incorporate it into their biomass. This project will address the key questions of how N2O uptake occurs in soils; who is responsible; why these organisms take up N2O; where within the soil N2O uptake occurs; when it occurs and under what conditions and; how much N2O is drawn down. I will identify soils which have this capacity by screening a large range of soils in the laboratory, using a state of the art laser N2O analyser. I will then conduct a series of manipulations to understand what the controlling drivers of this process are. I will ‘feed’ soils which have been shown to take up N2O with a stable isotopic tracer (15N2O) and use DNA sequencing to identify the organisms responsible. I will use this tracer to image soils to show where in the soil environment these organisms live, and I will also use another innovative technique (15N2O pool dilution) to ascertain whether N2O uptake occurs in all soils. Once I have identified the microorganisms responsible, I will work with microbiologists to culture them and attempt to induce N2O uptake in other soils. The final objective is to work with computer modellers to use my experimental data to calculate how much N2O is consumed by soils globally by this process.