Temperature-dependent photosynthesis and antioxidant system in the marine diatom Phaeodactylum tricornutum

Ocean warming is expected to alter the productivity and composition of marine phytoplankton communities, thus impacting global biogeochemical cycles. However, the physiological mechanisms and antioxidant systems in response to temperature in Phaeodactylum tricornutum remain poorly understood. In this study, we examined the effects of temperature variation on growth, photosynthesis, inorganic carbon utilization, and antioxidant enzyme activity in P. tricornutum. Our results showed that the specific growth rate and pigment contents significantly increased between 13 °C and 22 °C, and followed by a decline at 25 °C. The maximum photochemical efficiency (F_v/F_m) and actual photochemical efficiency (Yield) were maximized at the optimal temperature. Photosynthetic efficiency (ɑ) remained a higher levels at elevated temperatures, while the relative electron transport rate (rETR_m) decreased. Low activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), peroxidase (POD), catalase (CAT) were observed at the optimal temperature. Glutathione (GSH) and malondialdehyde (MDA) content also exhibited similar trends with antioxidant enzyme activity. Carbonic anhydrase activity initially rose and then dropped with rising temperatures, whereas Rubisco activity increased significantly with temperature. Our study highlights the temperature-dependent growth and physiological plasticity of P. tricornutum, suggesting that phytoplankton may adapt to ocean warming in the future by modulating light use efficiency, CO₂-concentrating mechanism (CCM), and antioxidant systems.