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Plant and Algae Growth

Associate Professor Tony Larkum in the School of Biological Sciences and Drs Paul Walker and Phil Lukins of the School of Physics at the University of Sydney are studying how plant photosynthesis is affected by UV light, thus inhibiting plant growth and productivity.

The impacts of ultraviolet light on vegetation is an area of research that has received little attention to date. There was a spate of work carried out some years ago, during the controversy over supersonic aircraft, when it was thought that nitrous oxide emissions from the aircraft would deplete the ozone layer, but most of that work was on terrestrial (land-based) plants. Now interest is growing again, especially in marine plants, because of the ozone hole over Antarctica. The new emphasis is on marine plants because in Antarctica there are very few terrestrial plants. There are only 2 species of angiosperm there; apart from these flowering plants the only other terrestrial plants are mosses and lichens. It will be mainly organisms and plants in the ocean that will be directly affected in the Antarctic region.

Tony Larkum’s field of study is photosynthesis and benthic algae, phytoplanktonic algae and seagrasses. Benthic algae are the algae which grow on substrate, they are attached to rocks on the sea shore. They are usually macroscopic, so that you can see them, but sometimes they are microscopic. Phytoplankton are a large family of plants that drift in the sea and are generally microscopic. Benthic algae and phytoplankton are both represented in polar waters. Both provide a lot of food for the animals that we associate with those waters - the krill and the things that feed on the krill, seals, whales and penguins.

If the opening up of the ozone hole increases UV radiation in Antarctica and that in turn has an effect on the algae there will also be a flow on effect on the rest of the food chain. This threat of a flow on effect is where Larkum’s interest particularly lies. But he is also interested in the effects that are likely to occur to organisms in Australian waters as a result of increased UV levels,particularly things like the inhibition of photosynthesis.

Photosynthesis is the motor driving plants and since most animals live directly or indirectly on plants the whole ecosystem is driven on the basis of photosynthesis. If photosynthesis is affected then nearly all life is affected. UVB affects a whole lot of other activities as well, in both plants and animals. It effects DNA (genetic coding) and leads to mutations and it also affects the whole protein forming machinery of the cell, as well. But for Larkum photosynthesis is the key part of it because it is the foundation stone of the whole chain of life.

He has found that UVB has a very strong inhibition on photosynthesis and therefore on the growth of plants and, of course, on productivity. “We’ve looked at this from two levels,” he says. “From the basic level we ask, how does the machinery work and how is it affected by UV? And from the ecological level we ask, how does the effect on photosynthesis work out in the system and how do plants adapt to this problem?”