Effect of ultraviolet radiation on pigmentation and nitrogen metabolism of antarctic phytoplankton and ice algae

Abstract

Summary Antarctic phytoplankton and ice algae were exposed to UV-A or UV-B radiation under laboratory conditions during the «Polarstern» cruise (ANT XII/2) in Antarctica (23,11,1994 to 5,1,1995). The pattern of pigments varied in dependence on the dose and the UV source used as well as on the nitrogen compound applied. UV-B radiation in conjunction with addition of 15 NH 4 + caused a reduction of the main pigment contents of phytoplankton from the water column: the damaging effect was more pronounced at a relatively high UV-B dose (1.2 or 1.6 Wm −2 ) whereas UV-A radiation led to an increase in the main pigments. A UV-B irradiance of 5 h caused a strong reduction of all the pigment contents from ice algae after addition of 15 N-nitrate (60μmol/L) compared with the effects after 15 N-ammonium (60μmol/L). Uptake rates of 15 N-ammonium and 15 N -nitrate of phytoplankton and ice algae were more affected by UV-B than by UV-A radiation. Nitrate uptake was more reduced by UV than that of ammonium. Patterns of pools and 15 N labelled free amino acids of phytoplankton and ice algae varied in dependence of the UV source applied and inorganic nitrogen compound. 15 N incorporation into all amino acids of phytoplankton was markedly reduced after addition of 15 N-nitrate and 3 h UV radiation. UV-B radiation and addition of 15 N-ammonium led also to a strong reduction of 15 N labelling of all amino acids except for glutamine. However, UV-A irradiance had no significant effect. Patterns of free amino acid pools of phytoplankton samples varied in dependence of the UV source: no effect or an increase in the pools after UV-A exposure. Patterns of free amino acids of ice algae were less affected by UV radiation than those of phytoplankton: pools of main amino acids were enhanced after 3 or 5 h UV radiation. Results are discussed with reference to the UV source applied and the species-dependent response of the Antarctic microalgae under field conditions. The influence of UV radiation on the key enzymes of nitrogen metabolism in conjunction to the pigments was another topic of the discussion.