Denitrification Aligns with N2 Fixation in Red Sea Corals

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Tilstra, Arjen | El-Khaled, Yusuf, C | Roth, Florian | Rädecker, Nils | Pogoreutz, Claudia | Voolstra, Christian, R | Wild, Christian

Edité par CCSD ; Nature Publishing Group -

International audience. Abstract Denitrification may potentially alleviate excess nitrogen (N) availability in coral holobionts to maintain a favourable N to phosphorous ratio in the coral tissue. However, little is known about the abundance and activity of denitrifiers in the coral holobiont. The present study used the nirS marker gene as a proxy for denitrification potential along with measurements of denitrification rates in a comparative coral taxonomic framework from the Red Sea: Acropora hemprichii , Millepora dichotoma , and Pleuractis granulosa . Relative nirS gene copy numbers associated with the tissues of these common corals were assessed and compared with denitrification rates on the holobiont level. In addition, dinitrogen (N 2 ) fixation rates, Symbiodiniaceae cell density, and oxygen evolution were assessed to provide an environmental context for denitrification. We found that relative abundances of the nirS gene were 16- and 17-fold higher in A. hemprichii compared to M. dichotoma and P. granulosa , respectively. In concordance, highest denitrification rates were measured in A. hemprichii , followed by M. dichotoma and P. granulosa . Denitrification rates were positively correlated with N 2 fixation rates and Symbiodiniaceae cell densities. Our results suggest that denitrification may counterbalance the N input from N 2 fixation in the coral holobiont, and we hypothesize that these processes may be limited by photosynthates released by the Symbiodiniaceae.

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