Effect of solar ultraviolet-B radiation during springtime ozone depletion on photosynthesis and biomass production of Antarctic vascular plants

We assessed the influence of springtime solar UV-B radiation that was natur ally enhanced during several days due to ozone depletion on biomass product ion and photosynthesis of vascular plants along the Antarctic Peninsula. Na turally growing plants of Colobanthus quitensis (Kunth) Bartl. and Deschamp sia antarctica Desv, were potted and grown under filters that absorbed or t ransmitted most solar UV-B. Plants exposed to solar UV-B from mid-October t o early January produced 11% to 22% less total, as well as above ground bio mass, and 24% to 31% less total leaf area. These growth reductions did not appear to be associated with reductions in photosynthesis per se: Although rates of photosynthetic O-2 evolution were reduced on a chlorophyll and a d ry-mass basis, on a leaf area basis they were not affected by UV-B exposure . Leaves on plants exposed to W-B were denser, probably thicker, and had hi gher concentrations of photosynthetic and UV-B absorbing pigments. We suspe ct that the development of thicker leaves containing more photosynthetic an d screening pigments allowed these plants to maintain their photosynthetic rates per unit leaf area. Exposure to UV-B led to reductions in quantum yie ld of photosystem II, based on fluorescence measurements of adaxial leaf su rfaces, and we suspect that UV-B impaired photosynthesis in the upper mesop hyll of leaves. Because the ratio of variable to maximal fluorescence, as w ell as the initial slope of the photosynthetic light response, were unaffec ted by UV-B exposure, we suggest that impairments in photosynthesis in the upper mesophyll were associated with light-independent enzymatic, rather th an photosystem II, limitations.