Summary of Abstract Submission

Abstract Submission No. IO50-09-0014PresentationOral

NITROGEN LOSS GENES IN THE PHOTIC ZONE

Eric J. Raes*1

1 University of Western Australia, Australia

ABSTRACT :

Nitrogen (N) and oxygen (O) are intimately connected in the ocean and perturbations in the balance between oxygen consumption and the remineralisation of organic matter can have large scale impacts on the N budget of oceanic ecosystems. Bio-available nitrogen losses (as N2O and N2) through denitrification, dissimilatory nitrate reduction to ammonium and anaerobic ammonium oxidation (anammox) are traditionally studied in oxygen minimum zones (OMZ). Yet, little is known about the distribution and potential impacts of the metabolic processes of N loss genes in the photic zone and within oxygenated oceanic waters. Here we show the presence of functional marker genes for denitrification (nosZ) and anammox (hzsA) in oxygenated surface waters (180-250 O2 μmol kg-1) in the eastern Indian Ocean. Clone sequencing from quantitative real-time PCR products revealed that most denitrification genes belonged to Rhodobecteraceae and that the dominant anammox genes belonged to Scalindua, Jettenia and Brocadia. Our data suggested a strong regional temperature sensitivity for both anammox and denitrification reactions. Overall copy numbers indicated that N-loss genes represented a significant proportion of the microbial community, which is unexpected in these oxygenated waters. This work highlights the need to investigate the potential for active N losses outside OMZ¿s, as these could impact the scarce nutrient budgets of the Indian Ocean and those of other similar oligotrophic systems.