UV-B effects on physiological parameters of three species of Rumex with natural distribution at different altitudes

Abstract

Three species of the genus Rumex (Polygonaceae) with a natural distribution in lowland, montane and alpine regions within Europe were analysed with regard to their UV-B tolerance. The plants were cultivated in natural sunlight and then transferred to a chamber with artificial light sources for a total of three weeks, one «adaptation week« and two «irradiation weeks«. For a period of three successive years the plants were subjected to varying UV-B irradiances. Gas exchange parameters, chlorophyll fluorescence as well as the chlorophyll content were measured. The lowland ( R. maritimus ) and the montane ( R. crispus ) species revealed a high UV-B tolerance (indicated by their photosynthetic CO 2 fixation), even without a preceding adaptation to UV-B irradiance. Only the highest UV-B irradiance applied (6.47 kJ·m −2 ·d −1 ) resulted in a diminished photosynthetic capacity (CO 2 fixation) of the lowland species while the other UV-B levels (4.71 kJ·m −2 ·d −1 and 5.59 kJ·m −2 ·d −1 ) increased photosynthetic CO 2 fixation. By contrast, the alpine species ( R. alpinus ) required an adaptation to a threshold UV-B irradiance to prevent UV-B caused inhibition of photosynthetic CO 2 fixation. The reduced photosynthetic CO 2 fixation of the non-adapted R. alpinus seems to be due to the effect of the UV-B radiation on stomatal conductance. There was no correlation between the UV-B effects on components of the photosynthetic electron transport chain and the UV-B effects on photosynthetic CO 2 fixation in any of the species studied. The chlorophyll content of all three species was not affected by the applied UV-B levels.