Light levels affect carbon utilisation in tropical seagrass under ocean acidification

Ow, Yan X., Uthicke, Sven, and Collier, Catherine J. (2016) Light levels affect carbon utilisation in tropical seagrass under ocean acidification. PLoS ONE, 11 (3). e0150352. pp. 1-18.

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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 (P(max)) 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.

Item ID: 43149
Item Type: Article (Research - C1)
ISSN: 1932-6203
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©2016 Ow et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funders: National Environmental Research Program (NERP), Great Barrier Reef Foundation (GBRF)
Projects and Grants: NERP Tropical Ecosystems Hub Project 5.2. , NERP Tropical Ecosystems Hub Project 5.3. , GBRF Investigating the effects of seagrass productivity on pH at local scales
Date Deposited: 12 Jul 2016 02:19
FoR Codes: 31 BIOLOGICAL SCIENCES > 3108 Plant biology > 310801 Phycology (incl. marine grasses) @ 50%
31 BIOLOGICAL SCIENCES > 3108 Plant biology > 310806 Plant physiology @ 30%
31 BIOLOGICAL SCIENCES > 3199 Other biological sciences > 319902 Global change biology @ 20%
SEO Codes: 96 ENVIRONMENT > 9603 Climate and Climate Change > 960307 Effects of Climate Change and Variability on Australia (excl. Social Impacts) @ 70%
96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960802 Coastal and Estuarine Flora, Fauna and Biodiversity @ 30%
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