Photosynthesis Damage and Protective Pigments in Plants from a Latitudinal Arctic/Alpine Gradient Exposed to Supplemental UV-B Radiation in the Field

Abstract

Arctic and alpine plants grown from seed collected from different locations along a latitudinal gradient were studied to determine if populations inhabiting different solar UV-B radiation environments would show differential photosynthetic inhibition under supplemental UV-B irradiation in the field. In general, plants collected from equatorial, alpine sites where solar UV-B irradiance is high, showed no UV-B induced damage of either light-saturated or light-limited photosynthesis, as measured by intact-leaf gas exchange. Photosynthetic inhibition was detected in some but not all ecotypes or species collected from higher latitude locations where effective UV-B irradiance is lower. When exposed to supplemental UV-B irradiation under a full solar spectrum in the field, significant accumulation of UV-absorbing leaf pigments occurred only in populations from higher latitudes. Most alpine populations were apparently protected from UV-B damage without additional pigment accumulation, whereas increased pigment levels did not necessarily act to complelely protect populations from higher latitudes. Photosynthesis damage in these species was also not related to leaf weight/leaf area ratios. These results provide additional corroborative evidence for the existence of an appreciable latitudinal gradient in UV-B radiation but suggest that the variation in UV-B sensitivity within and between species cannot be attributed solely to differences in the shielding of UV-B radiation by UV-absorbing leaf pigments and/or leaf structure.