In situ impact of solar ultraviolet radiation on photosynthesis and DNA in temperate marine phytoplankton

In situ experiments were conducted at various depths in the water column to determine the impact of solar UV radiation (280 to 400 nm) upon photosynthesis and DNA of natural phytoplankton assemblages from mid-latitudes of Patagonia (Bahia Bustamante, Chubut, Argentina; 45 degreesS, 66.5 degreesW). The effects of UV radiation were significant at the surface; however, the impact decreased rapidly with depth: at 3 m there was no measurable DNA damage accumulation, whereas at 6 m photosynthetic inhibition was almost zero. UV-A radiation (315 to 400 nm) was mostly responsible for photosynthetic inhibition, while UV-B radiation (280 to 315 nm) had a lesser effect on this process. However, UV-B radiation was very effective in damaging the DNA through the formation of cyclobutane pyrimidine dimers (CPDs) in surface waters. The high initial CPD level found in the natural phytoplankton assemblage decreased when samples were incubated at 3 or 6 m, indicating that at these depths repair, dilution or disappearance of damage occurred. Phytoplankton assemblages were dominated by cells less than 2 mum in effective diameter; this cell size category seems to be more resistant to photosynthetic inhibition, but vulnerable to CPD accumulation, as compared with larger eukaryotic phytoplankters (i.e., Phaeodactylum sp.)

Solar UVR-induced DNA damage and inhibition of photosynthesis in phytoplankton from Andean lakes of Argentina.

During January 1999, studies were carried out in temperate lakes of the Andean region of Argentina (41degreesS, 71degreesW) to determine the short-term effects of solar ultraviolet radiation (UVR, 280-400 nm) upon natural phytoplankton assemblages. Organisms from one 'clear' (Lake Moreno) and two 'opaque' lakes (Morenito and El Trebol) were exposed to different radiation regimes to assess photosynthesis inhibition and cyclobutane pyrimidine dimers (CPDs) accumulation/repair. UV-B caused significant DNA damage in organisms from 'opaque' lakes, especially those from Lake Morenito. Organisms from the 'clear' Lake Moreno, on the other hand, presented lower CPDs accumulation rates. UV-B had relatively low effects inhibiting photosynthesis in these opaque lakes (2 and 9.5 %, for lakes Morenito and El Trebol, respectively) and most of the inhibition was due to UV-A (75 and 71 % inhibition for lakes Morenito and El Trebol, respectively). In Lake Moreno, photosynthetic inhibition was 35 and 15 % for UV-A and UV-B, respectively. A number of causes seems to account for the different responses observed among phytoplankton assemblages, being one of the most important underwater radiation fields, and hence for the light acclimation history of cells. In addition, factors such as differences in type and effectiveness of the strategy used by the organisms to cope with solar UVR, as well as differences in the size structure and taxonomic composition of the community, are also important at the time to evaluate the overall impact of solar UVR in these lakes