Ozone Pollution Link to Drought-stricken Crops
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Ozone pollution stops some plants from protecting themselves when drought strikes, according to a new discovery by plant scientists at Lancaster University and at the Centre for Ecology and Hydrology.
In laboratory experiments on UK upland vegetation, plant physiologists found that when atmospheric ozone levels were artificially increased some plants could no longer close their stomata.
Stomata - microscopic pores in the surface of leaves, through which plants take up carbon dioxide and lose water - usually close when there is not enough water in the soil. Without this essential self-protection tool, plants can lose too much water, putting them in danger of shrivelling and dying.
Researchers have found evidence that ozone causes plants to emit a hormone which interferes with this natural process.
The study, funded by DEFRA and published this month in the scientific journal Plant, Cell and Environment, has far-reaching implications for farmers and growers in the future.
Crop failure - amounting to billions of dollars - and injury to sensitive species from vulnerable communities like forests have been attributed to ozone pollution in the northern hemisphere. However much remains unknown about exactly how ozone damages plants.
When plants detect drying soil a plant hormone called abscisic acid (ABA) is produced, signalling the plant to close its stomata.
This new research shows that ozone causes some plants to emit a gas called ethylene (another hormone) and this in turn can stop the ABA from doing its job properly, so the stomata stay open and the plants lose too much water.
Ozone is an atmospheric pollutant formed by a reaction between sunlight and nitrogen oxides emitted by car engines and industry. There has been some success in reducing peak ozone levels in "smog" episodes in some parts of the world. However, since the beginning of the last century average ground-level ozone concentrations (not to be confused with the ozone layer much higher up in the stratosphere) have steadily increased with industrialisation.
Dr. Sally Wilkinson from the Lancaster Environment Centre said: "We already anticipate that climate change will result in reduced rainfall and higher temperatures which will have a damaging impact upon plants.
"Average ozone levels are also expected to carry on increasing over the coming decades. Our research findings indicate that this rise in ozone could make some plants even less able to cope in our drying world than we previously thought, and this could be very damaging to many plant species including valuable crops.
"Such effects could already be occurring in much of the northern hemisphere when ozone levels reach their peak levels each summer, which is worrying. This has implications for global food security now, and in the coming decades. "
More work is being carried out at a DEFRA-funded ozone field release site in Northumberland. Inset photographs show that ozone causes leaves of buttercup plants to succumb to a drying treatment more quickly than leaves from unpolluted plants.
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