The effects of elevated pH and total alkalinity (TA ≈ HCO3– + 2CO32–) on marine primary productivity–the cornerstone of marine food webs and trophic dynamics–remains poorly understood. In this study, we investigated the physiological, biochemical and transcriptomic responses of the green microalga Chlorella sp. to elevated pH (pH = 8.30, TA = 2353 μmol kg–1) and elevated TA under high pH conditions (pH = 8.30, TA = 3854 μmol kg–1). Elevated pH reduced the growth rate and cellular carbohydrate contents, and down–regulated transcripts encoding key enzymes involved in photosynthetic carbon fixation (including ribulose–1,5–bisphosphate carboxylase/oxygenase (Rubisco) and carbonic anhydrase), as well as ion transport components (V–type H+ ATPase and Na+ (K+, urea)–H+ transporter). Conversely, elevated TA significantly enhanced the growth rate and increased cellular particulate organic carbon and carbohydrate contents. Furthermore, elevated TA mitigated the inhibitory effect of high pH by up–regulating or stabilizing gene expressions involved in carbon fixation, fatty acid biosynthesis and degradation pathways, V–type H+ ATPase and H+ exporter. Overall, these findings demonstrate that elevated TA effectively relieves high–pH stress and stimulates photosynthetic carbon uptake in Chlorella sp., providing valuable scientific insights in phytoplankton–mediated carbon dioxide removal (CDR) strategies.
Cai J., Shang J., Ke W., Liu D., Chen Y., Zhang H., Han Y., Qian Q., Li Z., Chen T. & Zhang Y., 2026. Physio–biochemical and transcriptomic responses of the marine green microalga Chlorella sp. to elevated pH and total alkalinity. Regional Studies in Marine Science 103: 105529. doi: 10.1016/j.rsma.2026.105529. Article (subscription required).
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