ANTARCTICA鈥橲 native flora is doing better than expected in the face of the
growing ozone hole over the continent. Rather than being killed off by scorching
ultraviolet light, many plants seem able to repair any damage almost
overnight.
Contrary to expectations, the latest evidence suggests that the high levels
of UV light passing through the ozone hole are having little effect on
photosynthesis, researchers told the conference last week. Daniela Lud and her
team at the Netherlands Institute of Ecology in Yerseke found small amounts of
DNA damage in samples of UV-irradiated plants. However, they appeared to be able
to mend any damage within a day.
The plants protect themselves by quickly producing a natural sunscreen,
researchers believe. Kevin Newsham of the British Antarctic Survey found that
within 24 hours of a strong UV blast Antarctic mosses and liverworts increased
production of sunscreen pigments and carotenoids. These substances block out UV
and mop up harmful oxygen radicals produced by the light.
Advertisement
Deneb Karentz, a biologist at the University of San Francisco, says that the
plants are adapted to their new situation. The ozone hole has been developing
for nearly 25 years, she explains. 鈥淎ny organisms that couldn鈥檛 survive the
increase in UV during the first few years are not around now.鈥�
Although the ozone hole presents an extra challenge to Antarctic plants,
Karentz adds, it鈥檚 important to remember that life originally evolved without
the protection of an ozone blanket. 鈥淯V protection and repair processes are very
old mechanisms that came about in times of high UV.鈥�
But life in the ocean seems to be fairing less well. Microbes in the
Antarctic seas are more sensitive to UV than their land-based neighbours, says
Patrick Neale from the Smithsonian Environmental Research Center near Washington
DC. He has found evidence that increased UV light is causing photosynthesis
rates in marine phytoplankton to fall.
Neale believes the difference can be explained by the love-hate relationship
that photosynthetic organisms have with the Sun. Antarctic plants live under
high-intensity light in the summer, so they have developed aggressive UV
defences.
Microbes in the sea have the opposite problem. There is little light in the
ocean depths, so making chlorophyll to harvest the Sun鈥檚 energy is more
important than producing sunscreens. When water movement forces phytoplankton to
the sea surface, they can be damaged by high UV.