Abstract: Aims Diatoms are an important component of marine phytoplankton, and their photosynthetic production reaches more than 40% of the ocean primary productivity. The combined effects of enhanced solar UV radiation and seawater warming will affect the photosynthesis of diatoms, affecting their contribution to the primary production. In this study, we mainly explored the photosynthetic physiological regulation of diatoms in response to UVR radiation by warming, in order to further understand the effects of marine environmental changes on the photosynthesis of diatoms. Methods Thalassiosira weissflogii was cultured at 18oC and 24oC and exposed to high visible light (PAR, 400 to 700nm) and UV radiation (PAR+UVR, 280 to 700nm) to monitor changes in PSII function and other physiological responses. Important findings PAR and PAR+UVR inhibited the maximum photochemical efficiency (Fv/Fm) of PSII in Thalassiosira weissflogii. The photoinactivation rate constant (Kpi) of PSII increased significantly in the presence of UVR. The ratio of repair rate constant to phtotinactivation rate constant of PSII (Krec/Kpi) in UVR was similar to that under low temperature. Analysis of PSII subunit turnover showed that warming under visible light allowed cells to maintain a high PsbD pool, whereas warming under UVR synergistically promoted rapid clearance of damaged PsbA. In addition, the activities of SOD and CAT were higher in the cells under the increased temperature, and low level of NPQ was induced under all treatments. Our results showed that warming can promote the photosynthetic performance of the Thalassiosira weissflogii by adjusting its PSII repair cycle to counteract the inhibitory effect of UVR.

Key words: Diatoms, Photosynthesis, Warming, UV radiation, Thalassiosira weissflogii