Xiang, Nan, Meyer, Achim ORCID: https://orcid.org/0000-0002-4345-274X, Pogoreutz, Claudia, Rädecker, Nils, Voolstra, Christian R., Wild, Christian and Gärdes, Astrid (2023) Excess labile carbon promotes diazotroph abundance in heat-stressed octocorals. Royal Society Open Science, 10 (3). DOI https://doi.org/10.1098/rsos.221268.

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Abstract

Nitrogen limitation is the foundation of stable coral-algal symbioses. Diazotrophs, prokaryotes capable of fixing N2 into ammonia, support the productivity of corals in oligotrophic waters, but could contribute to the destabilization of holobiont functioning when overstimulated. Recent studies on reef-building corals have shown that labile dissolved organic carbon (DOC) enrichment or heat stress increases diazotroph abundance and activity, thereby increasing nitrogen availability and destabilizing the coral-algal symbiosis. However, the (a)biotic drivers of diazotrophs in octocorals are still poorly understood. We investigated diazotroph abundance (via relative quantification of nifH gene copy numbers) in two symbiotic octocorals, the more mixotrophic soft coral Xenia umbellata and the more autotrophic gorgonian Pinnigorgia flava, under (i) labile DOC enrichment for 21 days, followed by (ii) combined labile DOC enrichment and heat stress for 24 days. Without heat stress, relative diazotroph abundances in X. umbellata and P. flava were unaffected by DOC enrichment. During heat stress, DOC enrichment (20 and 40 mg glucose l−1) increased the relative abundances of diazotrophs by sixfold in X. umbellata and fourfold in P. flava, compared with their counterparts without excess DOC. Our data suggest that labile DOC enrichment and concomitant heat stress could disrupt the nitrogen limitation in octocorals by stimulating diazotroph proliferation. Ultimately, the disruption of nitrogen cycling may further compromise octocoral fitness by destabilizing symbiotic nutrient cycling. Therefore, improving local wastewater facilities to reduce labile DOC input into vulnerable coastal ecosystems may help octocorals cope with ocean warming.

Document Type:	Article
Programme Area:	PA1
Research affiliation:	Science Management > ZMT Academy Biogeochemistry and Geology > Tropical Marine Microbiology Biogeochemistry and Geology
Refereed:	Yes
Open Access Journal?:	Yes
DOI:	https://doi.org/10.1098/rsos.221268
ISSN:	2054-5703
Date Deposited:	01 Mar 2024 10:12
Last Modified:	26 Mar 2024 13:31
URI:	http://cris.leibniz-zmt.de/id/eprint/5323

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