Project Title: Biological nitrogen fixation in the Australian marine environment: diversity, distribution and activity of nitrogen fixing microbes
Supervisors: Dr Justin Seymour (UTS), Dr Mark Brown (UNSW) and Dr Martina Doblin (UTS)
Collaborator: Dr Claire Mahaffey (University of Liverpool, UK)
PhD conferred: 2016
In low nutrient marine environments, the availability of nitrogen is considered to be one of the key factors controlling primary production, and consequently the export of organic matter to the deep ocean. Despite the atmospheric input of molecular N2 into surface waters of the oceans, biologically useful forms of nitrogen are scarce over much of the euphotic zone. A diverse yet limited number of microorganisms (diazotrophs) have developed a strategy to overcome this nitrogen limitation, through the reduction of molecular N2 to bioavailable ammonium.
It is becoming increasingly apparent that marine nitrogen fixation is a globally significant process, with diazotrophs believed to supply a source of fixed nitrogen to the euphotic zone to rival that of the vertical supply of nitrate from the deep ocean. Thus, nitrogen fixation is able to support biological productivity in oceanic regions where vertical mixing is inefficient or insignificant. Despite this knowledge, there is a distinct lack of quantitative nitrogen fixation data for the Australian marine environment, and very little is known about the temporal and spatial variability of diazotrophic communities in Australian waters. This purpose of this project is to address this gap in our understanding.
- To characterise the diazotrophic microbial assemblages inhabiting key Australian oceanographic provinces, including tropical, subtropical and temperate regions.
- To quantify the activity of diazotrophs over varying spatial and temporal scales.
- To identify factors affecting the growth, distribution and activity of diazotrophs in Australian waters.