Photosynthesis and formation of UV-absorbing substances in Antarctic macroalgae under different levels of UV-B radiation

Abstract

Effects of artificial and solar UV-B radiation on five rhodophytes (Curdiea racovitzae, Gigartina skottsbergii, Iridaea obovata, Myriogramme manginii, Palmaria decipiens) from Antarctica have been investigated using PAM fluorescence in laboratory and in the field. Laboratory studies showed that there was significant difference in the UV sensitivity between different species, and that the differences appeared to be correlated with the depth of collection of the specimens. It was apparent from the observations that the samples such as M. manginii, P. decipiens collected from 20∼30 m depths were more sensitive to UV-B radiation compared with those collected from shallower depths. The present study confirmed that acclimation to the surrounding light regime is an important factor to determine the UV-sensitivity of a species or individuals and that PAM measurements are rapid and non-destructive methods to evaluate UV influences. From field studies on M. manginii and P. decipiens it was observed that the plants exhibited diurnal changes in quantum yield with the minimum values at noon followed by recovery in the evening. Photoinhibition occurred in these species could therefore be accounted for by so-called dynamic photoinhibition. It seems likely that this protective mechanism may contribute to survival of the species in shallow water where they may encounter intense solar radiation. The presence or absence of UV-B portion in solar radiation affected the photosynthetic recovery process, and the rate of recovery was much slower in UV-present than in UV-absent conditions. A functional role of UV-B appears to delay the recovery of photosynthesis in the studied macroalgae. Differential sensitivity to UV-B recognised between M. manginii and P. decipiens seemed to correspond well with the amount of UV-absorbing substances (UVAS) contained in the respective species. Higher tolerance to solar radiation by the latter species may be due to the higher amount of UVAS. There were var