Microbial network controls on N and N2O cycling in an deoxygenating ocean

The decline in oxygen content (deoxygenation) in the ocean is one of the major features of global change, and affects biological processes and the biogeochemical cycling of key elements such as nitrogen (N). Oxygen minimum zones (OMZs) are intensifying and expanding their distribution, and many coastal waters such as estuaries and enclosed seas are experiencing seasonal anoxia events. OMZs and coastal waters are ecosystems with global relevance for N processing and hot spots for nitrous oxide (N2O) cycling. N2O is a major ozone-depleting substance and a potent greenhouse gas, and its microbial production depends on N and oxygen availability. So far, many studies have addressed the importance of environmental drivers in N and N2O cycling. However they are incomplete predictors of ecosystem functioning. Contrarily, little attention has been paid to biotic community associations, despite they can exert selective pressure on marine microbes and affect ecosystem functioning. NITRODEOX aims to investigate the changes in microbial communities caused by ocean deoxygenation, and to assess how these changes affect N cycling and N2O production. The applicant will develop a novel and interdisciplinary approach combining the quantification of N transformation rates using 15N labeling incubations, with the latest advances in bioinformatics analysis of deep metagenomic sequencing, and network inference methods in order to connect microbial community structure with ecosystem functioning. This project will cover the three major oxygen minimum zones, and two coastal sites (the Chesapeake Bay, and the Mar Menor coastal lagoon), and builds on the advantage of already having an exceptional collection of samples from past cruises. NITRODEOX represents a novel step to identify key taxa and reveal hidden microbial community controls on N and N2O cycling, which is crucial in view of the expansion and intensification of OMZs, and the increasing human impact on coastal waters.