Contemporary reliance on bicarbonate acquisition predicts increased growth of seagrass Amphibolis antarctica in a high-CO2 world

• Main Authors: Burnell, Owen W., Connell, Sean D., Irving, Andrew D., Watling, Jennifer R., Russell, Bayden D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: USA : Society for Experimental Biology 2014
• Subjects: Pure basic research; 960307 Effects of Climate Change and Variability on Australia (excl. Social Impacts); 960507 Ecosystem Assessment and Management of Marine Environments; 960802 Coastal and Estuarine Flora; Fauna and Biodiversity; 050205 Environmental Management; 050102 Ecosystem Function; 050101 Ecological Impacts of Climate Change; Amphibolis antarctica > Seagrass > Photosynthesis > Carbon dioxide > Climate change; Journal Article. Refereed; Scholarly Journal; Antarc*; Antarctica
• Online Access: http://hdl.cqu.edu.au/10018/1034554

Rising atmospheric CO2 is increasing the availability of dissolved CO2 in the ocean relative to HCO3−. Currently, many marine primary producers use HCO3− for photosynthesis, but this is energetically costly. Increasing passive CO2 uptake relative toHCO3− pathways could provide energy savings, leading to increased productivity and growth of marine plants. Inorganic carbon-uptake mechanisms in the seagrass Amphibolis antarctica were determined using the carbonic anhydrase inhibitor acetazolamide (AZ) and the buffer tris(hydroxymethyl)aminomethane (TRIS). Amphibolis antarctica seedlings were also maintained in current and forecasted CO2 concentrations to measure their physiology and growth. Photosynthesis of A. antarctica was significantly reduced by AZ and TRIS, indicating utilization of HCO3−-uptake mechanisms. When acclimated plants were switched between CO2 treatments, the photosynthetic rate was dependent on measurement conditions but not growth conditions, indicating a dynamic response to changes in dissolved CO2 concentration, rather than lasting effects of acclimation. At forecast CO2 concentrations, seedlings had a greater maximum electron transport rate (1.4-fold), photosynthesis (2.1-fold), below-ground biomass (1.7-fold) and increase in leaf number (2-fold) relative to plants in the current CO2 concentration. The greater increase in photosynthesis (measured as O2 production) compared with the electron transport rate at forecasted CO2 concentration suggests that photosynthetic efficiency increased, possibly due to a decrease in photorespiration. Thus, it appears that the photosynthesis and growth of seagrasses reliant on energetically costly HCO3− acquisition, such as A. antarctica, might increase at forecasted CO2 concentrations. Greater growth might enhance the future prosperity and rehabilitation of these important habitat-forming plants, which have experienced declines of global significance.