Saturating light and not increased carbon dioxide under ocean acidification drives photosynthesis and growth in Ulva rigida (Chlorophyta)

• Published in: Ecology and Evolution
• Main Authors: Rautenbuerger, R, Fernandez, PA, Strittmatter, M, Heesch, S, Cornwall, CE, Hurd, CL, Roleda, MY
• Format: Article in Journal/Newspaper
• Language: English
• Published: John Wiley & Sons Ltd. 2015
• Subjects: Environmental Sciences; Ecological Applications; Ecological Impacts of Climate Change; Ocean acidification
• Online Access: https://doi.org/10.1002/ece3.1382; http://ecite.utas.edu.au/100168

Carbon physiology of a genetically identified Ulva rigida was investigated under different CO 2(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 CO 2(aq) concentration under ocean acidification (OA) will downregulate CA ext -mediated dehydration and alter the stable carbon isotope ( δ 13 C) signatures toward more CO 2 use to support higher growth rate. At pH T 9.0 where CO 2(aq) is <1 μ mol L −1 , inhibition of the known use mechanisms, that is, direct uptake through the AE port and CA ext -mediated dehydration decreased net photosynthesis (NPS) by only 5683%, leaving the carbon uptake mechanism for the remaining 1744% of the NPS unaccounted. An in silico search for carbon-concentrating mechanism elements in expressed sequence tag libraries of Ulva found putative light-dependent 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 CO 2(aq) suggest preference and substantial use to support photosynthesis and growth. U.rigida is Ci saturated, and growth was primarily controlled by light. Therefore, increased levels of CO 2(aq) predicted for the future will not, in isolation, stimulate Ulva blooms.