Saturating light and not increased carbon dioxide under ocean acidification drives photosynthesis and growth in Ulva rigida (Chlorophyta).
Carbon physiology of a genetically identified Ulva rigida was investigated under different CO2(aq) and light levels. The study was designed to answer whether (1) light or exogenous inorganic carbon (Ci) pool is driving growth; and (2) elevated CO2(aq) concentration under ocean acidification (OA) will downregulate CAext-mediated [Formula: see text] dehydration and alter the stable carbon isotope (δ (13)C) signatures toward more CO2 use to support higher growth rate. At pHT 9.0 where CO2(aq) is <1 μmol L(-1), inhibition of the known [Formula: see text] use mechanisms, that is, direct [Formula: see text] uptake through the AE port and CAext-mediated [Formula: see text] dehydration decreased net photosynthesis (NPS) by only 56-83%, leaving the carbon uptake mechanism for the remaining 17-44% of the NPS unaccounted. An in silico search for carbon-concentrating mechanism elements in expressed sequence tag libraries of Ulva found putative light-dependent [Formula: see text] transporters to which the remaining NPS can be attributed. The shift in δ (13)C signatures from -22‰ toward -10‰ under saturating light but not under elevated CO2(aq) suggest preference and substantial [Formula: see text] use to support photosynthesis and growth. U. rigida is Ci saturated, and growth was primarily controlled by light. Therefore, increased levels of CO2(aq) predicted for the future will not, in isolation, stimulate Ulva blooms.
Department of Botany, University of Otago P.O. Box 56, Dunedin, 9054, New Zealand.
Ralf
R
Rautenberger
Department of Botany, University of Otago P.O. Box 56, Dunedin, 9054, New Zealand.
Pamela A
PA
Fernández
The Scottish Association for Marine Science, Scottish Marine Institute Oban, Argyll, PA37 1QA, Scotland.
Martina
M
Strittmatter
Irish Seaweed Research Group, Ryan Institute for Environmental, Marine and Energy Research, National University of Ireland Galway (NUIG), University Road, Galway, Ireland.
Svenja
S
Heesch
Department of Botany, University of Otago P.O. Box 56, Dunedin, 9054, New Zealand ; Institute for Marine and Antarctic Studies, University of Tasmania Hobart, Tasmania, 7001, Australia.
Christopher E
CE
Cornwall
Department of Botany, University of Otago P.O. Box 56, Dunedin, 9054, New Zealand ; Institute for Marine and Antarctic Studies, University of Tasmania Hobart, Tasmania, 7001, Australia.
Catriona L
CL
Hurd
Department of Botany, University of Otago P.O. Box 56, Dunedin, 9054, New Zealand ; Bioforsk Norwegian Institute for Agricultural and Environmental Research Kudalsveien 6, 8049, Bodø, Norway.
Michael Y
MY
Roleda
Bicarbonate; C:N ratio; Fv/Fm; carbon physiology; carbon-concentrating mechanism; carbonic anhydrase; chlorophyll fluorescence; pigments; seaweed; stable carbon isotope