Effects of elevated pCO2 on physiological performance of marine microalgae Dunaliella salina (Chlorophyta, Chlorophyceae
2018
Hu, Shunxin | Wang, You | Wang, Ying | Zhao, Yan | Zhang, Xinxin | Zhang, Yongsheng | Jiang, Ming | Tang, Xuexi
The present study was conducted to determine the effects of elevated pCO₂ on growth, photosynthesis, dark respiration and inorganic carbon acquisition in the marine microalga Dunaliella salina. To accomplish this, D. salina was incubated in semi-continuous cultures under present-day CO₂ levels (390 μatm, pHNBS: 8.10), predicted year 2100 CO₂ levels (1 000 μatm, pHNBS: 7.78) and predicted year 2300 CO₂ levels (2 000 μatm, pHNBS: 7.49). Elevated pCO₂ significantly enhanced photosynthesis (in terms of gross photosynthetic O₂ evolution, effective quantum yield (ΔF/F' ₘ), photosynthetic efficiency (α), maximum relative electron transport rate (rETRₘₐₓ) and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity) and dark respiration of D. salina, but had insignificant effects on growth. The photosynthetic O₂ evolution of D. salina was significantly inhibited by the inhibitors acetazolamide (AZ), ethoxyzolamide (EZ) and 4,4’-diisothiocyanostilbene-2,2′-disulfonate (DIDS), indicating that D. salina is capable of acquiring HCOˉ ₃ via extracellular carbonic anhydrase and anion-exchange proteins. Furthermore, the lower inhibition of the photosynthetic O₂ evolution at high pCO₂ levels by AZ, EZ and DIDS and the decreased carbonic anhydrase showed that carbon concentrating mechanisms were down-regulated at high pCO₂. In conclusion, our results show that photosynthesis, dark respiration and CCMs will be affected by the increased pCO₂/low pH conditions predicted for the future, but that the responses of D. salina to high pCO₂/low pH might be modulated by other environmental factors such as light, nutrients and temperature. Therefore, further studies are needed to determine the interactive effects of pCO₂, temperature, light and nutrients on marine microalgae.
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