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

Abstract

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 5 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 5 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 5 0.002), (b) increasing modelled midday UVB/PAR ratio (Po0.001), and (c) decreasing ozone concentration (Po0.001). 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.

Dominating the Antarctic Environment: Bryophytes in a Time of Change

“…Increasing UVAC in response to increasing UV-B radiation have been found in the liverwort, Cephaloziella varians and the mosses; Sanionia uncinata (Newsham et al, 2002), Andreaea regularis (Newsham, 2003), B. pseudotriqetrum (Dunn and Robinson, 2006) and Bryum argenteum (Ryan et al, 2009). In contrast two other Antarctic bryophyte species (C. purpureus and S. antarctici) have been shown to contain UVAC that are not particularly responsive to changes in UV-B radiation (Lovelock and Robinson, 2002;Dunn and Robinson, 2006).…”

“…Both these mosses have since been shown to accumulate UVAC in their cell walls and it remains to be seen if these cell wall UVAC are responsive to changing UV-B radiation or produced constitutively (Clarke, 2008;Robinson and Waterman, 2012). Given that UV-B radiation dose has only been measured around Antarctica for the last 30 years, bryophytes and bryophyte spores that contain UVAC that respond to UV-B radiation could be used to determine historic levels of UV-B radiation (Lomax et al, 2008;Ryan et al, 2009). …”

Flora and vegetation of Cape Hallett and vicinity, northern Victoria Land, Antarctica

“…The ASPA also contains photographic sites established by ED Rudolph in 1962, and this has provided the longest period for lichenometric growth measurements in continental Antarctica (0.07 mm radial per year for B. frigida, Brabyn et al 2005). Another example of the use of historical data has been the estimation of historical ozone levels from the flavonoid content of moss samples collected at various times at Cape Hallett (Ryan et al 2009). …”

Retrospective analysis of heavy metal contamination in Rhode Island based on old and new herbarium specimens

“…A more recent review of the use of herbarium specimens (Lavoie, 2013) documented their use in studies focused on biogeographical patterns, collection biases, plant diseases, and climate change–induced impacts on plant distribution. Herbarium specimens have also been part of studies investigating changes to atmospheric ozone concentrations (Ryan et al, 2009) and are critical components of studies examining changing patterns of chronological events (Primack et al, 2004; Calinger et al, 2013; Everill et al, 2014; Hart et al, 2014; Park and Schwartz, 2015; Davis et al, 2015). All these studies indicate a growing interest in using herbarium collections for environmental and ecological research.…”