Leaf 'sweat glands' to worsen future flooding

18:22 29 August 2007
NewScientist.com news service
Catherine Brahic

Tiny pores on the surface of plant leaves that are sensitive to carbon dioxide may contribute significantly to future flooding as a result of increasing atmospheric pollution, researchers say.

The effect could help researchers predict which regions may be at greatest risk of flooding because of global warming. It may also help them predict which areas will receive some relief from drought.

The tiny pores, known as stomata, are found on the surface of leaves and are each between a tenth and several hundredths of a millimetre across. The underside of black oak leaves can have as many as 60,000 stomata per square centimetre.

The main function of stomata is to regulate the amount of carbon dioxide taken up by the plants during photosynthesis. Crucially, however, they also absorb and release moisture during transpiration. Furthermore, researchers have long known that stomata tend to shrink when CO₂ levels in the atmosphere rise.

Since the late 19th century, atmospheric CO₂ has risen from 280 to 390 parts per million as a result of humans burning fossil fuels and chopping down forests. So it stands to reason that plants should be transpiring less now than they were before the industrial revolution, which triggered a sudden surge in fossil fuel consumption.

The net effect of reduced transpiration is that plants consume less water, meaning more remains in the soil and can run off into rivers.

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