Zweng RC, Koch MS, Bowes G. The role of irradiance and C-use strategies in tropical macroalgae photosynthetic response to ocean acidification.
Sci Rep 2018;
8:9479. [PMID:
29930306 PMCID:
PMC6013460 DOI:
10.1038/s41598-018-27333-0]
[Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2018] [Accepted: 05/27/2018] [Indexed: 12/02/2022] Open
Abstract
Fleshy macroalgae may increase photosynthesis with greater CO2 availability under ocean acidification (OA) and outcompete calcifying macroalgae important for tropical reef accretion. Macroalgae use energy-dependent carbon concentrating mechanisms (CCMs) to take up HCO3-, the dominant inorganic carbon for marine photosynthesis, but carbon-use strategies may depend on the pCO2, pH and irradiance. We examined photosynthesis in eight tropical macroalgae across a range of irradiances (0-1200 μmol photon m-2 s-1), pH levels (7.5-8.5) and CO2 concentrations (3-43 μmol kg-1). Species-specific CCM strategies were assessed using inhibitors and δ13C isotope signatures. Our results indicate that the log of irradiance is a predictor of the photosynthetic response to elevated pCO2 (R2 > 0.95). All species utilized HCO3-, exhibited diverse C-use pathways and demonstrated facultative HCO3- use. All fleshy species had positive photosynthetic responses to OA, in contrast to a split amongst calcifiers. We suggest that shifts in photosynthetically-driven tropical macroalgal changes due to OA will most likely occur in moderate to high-irradiance environments when CCMs are ineffective at meeting the C-demands of photosynthesis. Further, facultative use of HCO3- allows greater access to CO2 for photosynthesis under OA conditions, particularly amongst fleshy macroalgae, which could contribute to enhance fleshy species dominance over calcifiers.
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