The contribution of ammonification to N2O emissions from soils

This project will investigate the significance of a bacterial process called ammonification in the emmission of nitrous oxide (N2O) from soils. N2O is perhaps most commonly known as the anaesthetic 'laughing gas'. However in global terms emissions of N2O is no laughing matter as it is a potent green house gas that can persist in the atmosphere for hundreds of years. The global emmissions of this gas are rising yearly and much of this is from biological sources. This is of great concern due to the involvement of this gas in global warming and the destruction of stratospheric ozone. Thus it is vital to understand the enzymatic processes that underlie N2O release, the regulation of these processes and the nature of the microorganisms responsible for the nitrous oxide release during bacterial ammonification. It will then be possible to propose appropriate management of the soil-plant system to mitigate emissions and to improve existing models. This is important as appropriate mitigation strategies for ammonification are likely to differ from another bacterial process called denitrification that can also lead to N2O emmission. Here we will encompass the whole picture of N2O emission in ammonifiers from the purified enzymes that produce the gas to complex communities that harbour these enzymes in soil. We will use enzyme analysis and stable isotope techniques to determine ammonification rates and N2O production during this process, and will use molecular techniques to investigate ammonifying populations in soil.

N2O is produced during nitrate ammonification, but the contribution of this process to emissions from soils is unknown and denitrification is wrongly often presented as the only soil bacterial nitrate reduction pathway that can produce N2O. Thus little is known about the environmental conditions conducive to this process, the microorganisms responsible or its significance in N2O emissions from soils. This will be addressed in an integrative research programme combining enzymological analysis of N2O production (purified NrfA and in vivo in intact cells), with physiological and molecular techniques to characterise active ammonifier communities in soils (gene expression, real-time PCR) and stable isotope (15N, 18O, natural abundance, enrichment and isotopomer) techniques to determine N2O (and N2) production during ammonification. This will provide invaluable information for finding conditions conducive to the mitigation of N2O production during ammonification, which are likely to differ from those for denitrification, and which are important due to the high global warming potential of this gas and its involvement in the destruction of stratospheric ozone.