The effects of ultraviolet radiation (UV) on microalgae will be assessed with a rapid and sensitive method intended for use on natural samples, even in extreme environments such as the Antarctic, where UV effects are of great interest. The method will be developed in a program of research on cultures of marine phytoplankton. The central hypothesis is that short-term tolerance to UV varies within and between species due to the presence of inducible UV-screening pigments. Tolerance may also vary due to the activities of recovery mechanisms. Polar and temperate phytoplankton will be grown under four regimes of UV plus visible radiation. Subsequently, the sensitivity of photosynthesis to UV will be determined by measuring the uptake of C-bicarbonate during or after exposure to a range of UV fluence rates in 6 wavebands between 250 and 400nm. This will yield an action spectrum of the inhibitory effects of UV on photosynthesis. The shapes of action spectra will be compared to spectra of absorption and related to the possible effects of UV-screens. The technique will be modified to assess recovery of photosynthesis from UV-induced inhibition and to measure action spectra of UV effects during exposure to visible light. This new method for measuring the spectral sensitivity of microalgae to UV will be rapid, sensitive and particularly appropriate for comparisons of planktonic and sea-ice microalgae. It should be useful in assessing the effects of UV on polar primary producers and for comparing plankton over latitudinal gradients.
