Impacts of UV radiation on photosynthesis and growth of the coccolithophore Emiliania huxleyi (Haptophyceae)

Coccolithophores are exposed to solar UV radiation (UVR, 280–400 nm) in their natural habitats. However, little has been documented on their physiological responses to UVR. We investigated the UV impacts on the photosynthesis, calcification, photochemical efficiency and growth of Emiliania huxleyi while culturing the cells under solar radiation. Presence of UVR significantly decreased the rates of photosynthesis and calcification. Shorter wavelengths of UV-B led to more damages to photosynthetic apparatus than to calcifying machinery, while longer wavelengths of UV-A resulted more harms to the calcification. As the cells were grown during long-term exposures to solar radiation, the ratios of repair to UV-related damage increased, indicating their acclimation to UV. The specific growth rate of the acclimated cells was inhibited by natural levels of UVR by about 25%, and the cells became bigger with more coccoliths, reflecting a slower cell division and enhanced calcification per cell, a trade off to counteract the UV-induced harms. The absorptivity of UV-absorbing compounds (peaked at 280 nm) increased tremendously in response to the exposure of UVR. UV-induced stress led to a protective strategy of E. huxleyi, sacrificing the growth by allocating energy for accumulation of these compounds and calcification.