Sequential reduction of UV-B radiation in the field alters the pigmentation of an Antarctic leafy liverwort

UV-B radiation (280-315 nm) incident on the leafy liverwort Cephaloziella varians growing at Rothera Point on the Western Antarctic Peninsula was manipulated in late austral spring 1998 by screens consisting of a novel combination of plexiglass panes and polyester sheets. The screens transmitted c. 79%, 68%, 48%, 41% and 31% of daily UV-B radiation dose. Plants from under and outside the screens were sampled seven times over 35 d. Correlative analyses indicated that concentrations of an anthocyanin-like pigment located in leaf tips were positively associated with UV-B transmission at the last two samplings, that concentrations of total chlorophylls were negatively associated with UV-B transmission at the final sampling, and that those of UV-B screening pigments were positively correlated with transmission at three intermediate samplings. Chlorophyll a / b ratio did not respond to the applied treatment. Plants exposed to low UV-B transmission levels were visibly greener than those exposed to high transmission levels after approximately 23 d. The closest fits between the treatment and concentrations of UV-B screening pigments were associated with increased ambient biologically-weighted UV-B dose received by plants in the 5.5 h before each sampling, which coincided with the passage of the ozone hole over Rothera Point. As C. varians emerged from melting snow and ice, concentrations of the anthocyanin-like pigment and chlorophyll respectively increased and decreased faster in plants exposed to high transmission levels of UV-B, relative to those exposed to low UV-B transmission levels.