Uv-B radiation effect on chlorophyll a fluorescence parameters of Raphanus sativus under different climates

Abstract

The aim of this research was to investigate the UV-B radiation effect on the radish (Raphanus sativus L.) under elevated concentration of CO2 and temperature. The plants were grown in chambers with controlled environment at three different climate conditions: first 21°C and 400ppm CO2 (CC); second 23°C and 550ppm CO2 (EC1); third 25°C and 800ppm CO2 (EC2). When the radish unfolded 3 true leaves, 6 kJm2d -1 UV-B radiation was started. The UV-B radiation lasted for 10 days. At the end of the experiment chlorophyll a fluorescence parameters were measured. Ultraviolet B radiation decreased growth parameters of radish in all investigated climate conditions. Chlorophyll a fluorescence parameters contributed this tendency also. 6 kJm-2d -1 UV-B radiation decreased efficiency of II photosystem (Fv/Fm) and maximum quantum yield for primary photochemistry (φPo) statistically significant (p<0.05) under both (EC1 and EC2) elevated climates (about 5 %), while under current climate (CC) conditions the effect UV-B was insignificant (about 3 %; p>0.05). UV-B radiation caused reduction of maximum fluorescence under elevated climates, when it decreased by 34.6 (p<0.05) and 27.3 % (p<0.05), compare to reference treatments of EC1 and EC2 respectively. The effect of UV-B on maximum fluorescence under current climate was insignificant (p>0.05). The same tendency was detected for the changes of total complementary area between fluorescence induction curve, i.e. higher negative effect of UV-B was detected under elevated climates. If compare negative effect of 6 kJm-2d -1 UV-B radiation in two elevated climates, the effect of UV-B under EC1 conditions, i.e. 23°C temperature and 550ppm CO2 concentration in air, was the strongest. Our results indicated that elevated climatic conditions have changed the intensity of negative effect of ultraviolet B radiation on photosynthetic parameters of radish.