Response of two Antarctic bryophytes to stratospheric ozone depletion
We report a study which measured changes to the radiative environment arising from stratospheric O3 depletion at Rothera Point on the western Antarctic Peninsula (67°S, 68°W) and subsequent associations between these changes and the pigmentation and maximum quantum yield of photochemistry (Fv/Fm) of two Antarctic bryophytes, the liverwort Cephaloziella varians and the moss Sanionia uncinata. We found a strong relationship between O3 column depth and the ratio of UV-B to PAR irradiance (FUV-B/FPAR) recorded at ground level. Weaker, but significant, associations were also found between O3 column depth and noon irradiances and daily doses of unweighted and biologically effective UV-B radiation received at ground level. Regression analyses indicated that FUV-B/FPAR and daily dose of unweighted UV-B were best predictors for concentrations of total carotenoids and UV-B screening pigments extracted from bryophyte tissues. Concentrations of these pigments were loosely but significantly positively associated with O3-dependent irradiance parameters. HPLC analyses of carotenoids also suggested that both species increased the synthesis of neoxanthin during periods of O3 depletion. Violaxanthin, lutein, zeaxanthin and b,bββ-carotene concentrations were also apparently influenced by O3 reduction, but not consistently across both bryophyte species. Concentrations of chlorophylls a and b were apparently unaffected by O3 depletion.No direct associations between Fv/Fm and O3-dependent irradiance parameters were found. However stepwise multiple regression analyses suggested that the production of UV-B screening pigments conferred protection from elevated FUV-B/FPAR on Fv/Fm in both species and that carotenoids conferred protection on Fv/Fm in Sanionia. Our data suggest that changes to the radiative environment associated with stratospheric O3 depletion influence the pigmentation of two Antarctic bryophytes, but that Fv/Fm is unaffected, at least in part because of rapid synthesis of protective pigments.