Effects of uranium on the growth and photosynthesis of two types of Chlorella vulgaris

[Objective] In order to explore the impact of uranium on algae growth and photosynthesis, and to screen new ecological risk assessment indicators for uranium pollution in water bodies based on photosynthesis. [Methods] This experiment used different concentrations of uranium (0, 0.5, 1, 5, 10, 20 mg/ L U6+ ) to treat two types of microalgae, chlorella (Chlorella vulgaris) and Huanglong chlorella, from different environments. The relative growth rate, photosynthetic oxygen release rate, chlorophyll content, and chlorophyll fluorescence kinetic parameters were measured on the 3rd, 5th, 7th, 10th, and 14th days after treatment. [Results] (1) Low concentration uranium (0.5 mg/L) treatment significantly promoted the growth and photosynthetic efficiency of the two types of microalgae, where the relative growth rate, photosynthetic oxygen release rate, maximum photochemical quantum yield (Fv/Fm) of photosystem Ⅱ, actual photochemical quantum yield Y (Ⅱ), and relative electron transfer rate (rETR) of the two microalgae were significantly higher than the control. However, high concentration uranium treatment (5 -20 mg/L) significantly inhibited the growth and photosynthesis of the two types of chlorella. (2) Huanglong chlorella was more sensitive to uranium treatment than chlorella, and its growth and photosynthesis were significantly inhibited at 1mg/L, and it could be used as an bioindicator for monitoring of uranium pollution in water bodies. (3) Regression analysis showed that under different concentrations of uranium treatment, the response speed of chlorophyll fluorescence parameters Y (Ⅱ) and rETR was faster than the changes in relative growth rate, photosynthetic oxygen release rate, chlorophyll content, and Fv/Fm, which could be used as sensitive indicators for ecological risk assessment of uranium pollution in water bodies. [Conclusion] Uranium exhibits a concentration effect on the growth and photosynthesis of chlorella, where low concentrations promote growth while high concentrations inhibit growth. Huanglong chlorella is more sensitive to uranium pollution. Therefore, the combination of Huanglong chlorella and chlorophyll fluorescence kinetic parameters Y (Ⅱ) and rETR can be applied for the ecological risk assessment of uranium pollution in water bodies.