Relative importance of denitrification within the nitrogen budget of Red Sea coral holobionts
Nitrogen availability is a key limiting factor for primary production on many coral reefs. As such, benthic organisms such as corals adapted and evolved efficient uptake and (re)cycling of the available nitrogen. The microbiome of coral holobionts aids in this cycling of nitrogen by 1) creating de novo bioavailable nitrogen via fixation of atmospheric dinitrogen (N2) performed by so called diazotrophs, and 2) alleviating bioavailable nitrogen through denitrification. While the latter seems counterintuitive at first, the majority of energy for coral holobionts is produced by a symbiotic relationship with photosynthetic dinoflagellates of the family Symbiodiniaceae which need to be in a nitrogen-limited state to translocate their photosynthates to the coral host. As such, denitrification could benefit coral holobiont health by aiding in keeping Symbiodiniaceae in a nitrogen-limited state. Recent research suggests that N2 fixation and denitrification essentially cancel each other out in several Red Sea corals (Tilstra et al., 2019). In contrast, Glaze et al. (2021) recently provided evidence that the significance of denitrification in hard corals from the Great Barrier Reef is negligible relative to other coral holobiont associated N-cycling pathways. However, besides focusing on different reef locations (central Red Sea vs. Eastern Indo-Pacific), both studies utilized different methods for their assessment. While the former used an acetylene based method quantifying holobiont-wide fluxes, the latter used labelled isotopes suitable for targeted quantifications. As such, a comparison between both studies may be confounded. To accurately assess the significance of denitrification relative to other N-cycling pathways (e.g. N2 fixation) associated with Red Sea corals, a comparative analysis using both methods with a range of corals will be conducted.
Biological and Environmental Sciences and Engineering
Center Affiliation -
Red Sea Research Center
Field of Study -
Coral reef microbiology