Light Levels Affect Carbon Utilisation in Tropical Seagrass under Ocean Acidification

• Published in: PloS one 2016-03, Vol.11 (3), p.e0150352-e0150352
• Main Authors: Ow, Yan X, Uthicke, Sven, Collier, Catherine J
• Format: Article
• Language: English
• Subjects: Acetazolamide; Acidification; Availability; Bicarbonate; Bicarbonates; Bicarbonates - chemistry; Biology and Life Sciences; Carbon - chemistry; Carbon Cycle; Carbon dioxide; Carbon Dioxide - chemistry; Carbon fixation; Carbonates; Carbonic anhydrase; Carbonic anhydrases; Coral Reefs; Cymodocea serrulata; Dissolved inorganic carbon; Dose-Response Relationship, Radiation; Earth Sciences; Ecology; Ecology and Environmental Sciences; Ecosystem; Enrichment; Extrusion; Grasses; Halodule uninervis; Herbicides; Hydrogen; Inorganic carbon; Light; Light levels; Ocean acidification; Oceans; Oceans and Seas; pH effects; Photosynthesis; Physical Sciences; Physiology; Productivity; Runoff; Seawater; Seaweed - metabolism; Studies; Temperature; Water quality; Zostera marina
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0150352

Under future ocean acidification (OA), increased availability of dissolved inorganic carbon (DIC) in seawater may enhance seagrass productivity. However, the ability to utilise additional DIC could be regulated by light availability, often reduced through land runoff. To test this, two tropical seagrass species, Cymodocea serrulata and Halodule uninervis were exposed to two DIC concentrations (447 μatm and 1077 μatm pCO2), and three light treatments (35, 100, 380 μmol m(-2) s(-1)) for two weeks. DIC uptake mechanisms were separately examined by measuring net photosynthetic rates while subjecting C. serrulata and H. uninervis to changes in light and addition of bicarbonate (HCO3-) use inhibitors (carbonic anhydrase inhibitor, acetazolamide) and TRIS buffer (pH 8.0). We observed a strong dependence on energy driven H+-HCO3- co-transport (TRIS, which disrupts H+ extrusion) in C. serrulata under all light levels, indicating greater CO2 dependence in low light. This was confirmed when, after two weeks exposure, DIC enrichment stimulated maximum photosynthetic rates (Pmax) and efficiency (α) more in C. serrulata grown under lower light levels (36-60% increase) than for those in high light (4% increase). However, C. serrulata growth increased with both DIC enrichment and light levels. Growth, NPP and photosynthetic responses in H. uninervis increased with higher light treatments and were independent of DIC availability. Furthermore, H. uninervis was found to be more flexible in HCO3- uptake pathways. Here, light availability influenced productivity responses to DIC enrichment, via both carbon fixation and acquisition processes, highlighting the role of water quality in future responses to OA.