EFFECTS OF UV-B RADIATION ON FRESHWATER
AUTOTROPHIC AND HETEROTROPHIC
R. Bertoni and C. Callieri
The study of the detrimental effect of UV-B radiation on aquatic organisms has mostly
focused on Antarctica but the increase of UV-B radiation in northern latitudes (20% at
310nm, at 55°N) has generated concern about its impact on temperate aquatic ecosystem of
the Alpine region. The present study has been carried out in the frame of the EU project
MICOR (MIcrobial COmmunity response to UV-B stress in European waters) with the purpose of
evaluating the effect of UV-B radiation on natural picoplanktonic populations (size range
0.2-2 µm), both autotrophic (APP) and heterotrophic (HPP). We have used quartz and
Mylar D screened quartz tubes to measure APP photosynthetic activity and HPP
production under natural and artificially increased UV-B radiation.
This research was addressed to the
- how strong is the UV-B underwater radiation in latitude
around 45°N and how deep does it penetrate ?
- are freshwater pico size populations affected by UV-B under
ambient UV-B climate?
- under stressing UV-B conditions are APP more susceptible to
photoinhibition than HPP?
The few data available on the effects of UV-B to
picocyanobacteria cells show that, as for other algal groups, UV-B inhibits the PSII
reaction centre activity, altering the structure of D1/D2 polypeptides and the
light-harvesting complex (Rajagopal and Murthy, 1996). Bergeron and Vincent (1997) have
found a significant decrease of APP and not of HPP cells in the presence of UV-B, but no
data on the activity of these two pico fractions were presented. Contrasting data have
demonstrated that ambient UV-B can inhibit bacterial activities as much as 40% (Herndl et