Historical ozone concentrations and flavonoid levels in herbarium specimens of the Antarctic moss Bryum argenteum

Depletion of stratospheric ozone since the mid 1970s has led to significant increases in ultraviolet B (UVB) irradiation over Antarctica. The detrimental effects of UVB on plants are many, but plants produce photoprotective flavonoids that reduce cellular damage. We used herbarium samples of the moss Bryum argenteum collected in Antarctica to compare the levels of flavone aglycones in plants collected before and after the formation of the ozone hole. The interpretation of historical data is difficult, because environmental conditions immediately before sample collection are unknown. Factors such as cloud cover can have a significant influence on UVB dose at ground level, modifying the flavonoid content of the specimen and adding considerable variability to the results. Nevertheless, our results revealed significant relationships between total flavone concentration and pooled year classes (P = 0.001). Furthermore, regression analysis showed a significant negative relationship of total flavone concentration and the level of ozone immediately before the time of collection (P = 0.016). In addition, the ratio of luteolin (an ortho-dihydroxylated flavone) to apigenin (a monohydroxylated flavone) increased significantly with several environmental parameters. These included (a) increasing modelled midday UVB radiation (P = 0.002), (b) increasing modelled midday UVB/PAR ratio (P < 0.001), and (c) decreasing ozone concentration (P < 0.001). We emphasise the utility of this ratio in interpreting the historical ozone trends rather than relying on changes in total flavone concentrations alone. These results illustrate that herbarium specimens may reveal historical levels of UVB radiation.