The physiological response of marine diatoms to ocean acidification: differential roles of seawater p CO 2 and pH

• Published in: Journal of Phycology
• Main Authors: Shi, Dalin, Hong, Haizheng, Su, Xi, Liao, Lirong, Chang, Siwei, Lin, Wenfang
• Other Authors: Wetherbee, R., National Natural Science Foundation of China
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2019
• Subjects: Ocean acidification
• Online Access: http://dx.doi.org/10.1111/jpy.12855; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fjpy.12855; https://onlinelibrary.wiley.com/doi/pdf/10.1111/jpy.12855; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/jpy.12855

Although increasing the p CO 2 for diatoms will presumably down‐regulate the CO 2 ‐concentrating mechanism ( CCM ) to save energy for growth, different species have been reported to respond differently to ocean acidification ( OA ). To better understand their growth responses to OA , we acclimated the diatoms Thalassiosira pseudonana , Phaeodactylum tricornutum , and Chaetoceros muelleri to ambient ( p CO 2 400 μatm, pH 8.1), carbonated ( p CO 2 800 μatm, pH 8.1), acidified ( p CO 2 400 μatm, pH 7.8), and OA ( p CO 2 800 μatm, pH 7.8) conditions and investigated how seawater p CO 2 and pH affect their CCM s, photosynthesis, and respiration both individually and jointly. In all three diatoms, carbonation down‐regulated the CCM s, while acidification increased both the photosynthetic carbon fixation rate and the fraction of CO 2 as the inorganic carbon source. The positive OA effect on photosynthetic carbon fixation was more pronounced in C. muelleri , which had a relatively lower photosynthetic affinity for CO 2 , than in either T. pseudonana or P. tricornutum . In response to OA , T. pseudonana increased respiration for active disposal of H + to maintain its intracellular pH , whereas P. tricornutum and C. muelleri retained their respiration rate but lowered the intracellular pH to maintain the cross‐membrane electrochemical gradient for H + efflux. As the net result of changes in photosynthesis and respiration, growth enhancement to OA of the three diatoms followed the order of C. muelleri > P. tricornutum > T. pseudonana . This study demonstrates that elucidating the separate and joint impacts of increased p CO 2 and decreased pH aids the mechanistic understanding of OA effects on diatoms in the future, acidified oceans.