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Smog spells invisible damage for crops
Ground-level ozone pollution, also known as smog, is eating away at agriculture all over the world. Worse yet, new research in Europe reveals the damage to crops isn't always visible.
Crop yields of winter oilseed rape, a common crop in the UK, fell by as much as 14 percent when plots were exposed to high levels of ozone. Similar field trials on winter wheat, another major UK crop, produced a 13 percent loss in yields.
Previous research based solely on laboratory experiments indicated crop yields were unlikely to be affected by ozone because plants in the study showed no visible signs of foliage damage.
"Effects on productivity occurred in the absence of visible leaf injury, so would not have been noticed without a controlled experiment," said Tom Lyons, a researcher in the air pollution lab in the Department of Agricultural and Environmental Science at the University of Newcastle upon Tyne, where some of the research was conducted. "For rape, the quality of the seed was detrimentally effected by ozone, again inferring the pollutant may be having 'invisible' effects on agricultural production."
Ground-level ozone is created when nitrogen oxide emissions, primarily from automobiles and power plants, react with oxygen in the air. Although controls exist in the UK for emissions of ozone precursor gases such as nitrogen oxide from vehicles and industrial plants, pollutants still manage to travel far and wide, damaging crops and impacting human health in rural areas.
Ground-level ozone interferes with a plant's ability to produce and store food, so that growth, reproduction and overall health are compromised. Plants exposed to ozone are more susceptible to disease, pests and environmental stresses.
In the United States, smog has been shown to reduce agricultural yields for vital crops such as soybeans, kidney beans, wheat and cotton.
There are options to help lessen ozone's insidious effects, according to Lyons. They include resistant crop varieties, chemicals specially developed to protect crops from ozone, conventional breeding programs and transgenic technology to develop more ozone resistant plants.
In the study, crops grown in field plots on University of Newcastle land were exposed to controlled doses of ozone. While there was no visible damage to the crops, researcher John Ollerenshaw found that in oilseed rape, for example, the number of flowering branches produced by individual plants fell by 38 percent. The plants compensated in part by producing more and larger seeds per pod.
Nevertheless, in the most sensitive variety of oilseed rape, Eurol, seed yield fell by 14 percent, a loss equivalent to $26.31 per ton. The oil content of the seeds fell by 5 percent, a loss equivalent to another $13.07 per ton.
In winter wheat, the number of grains per ear declined while the number of infertile florets increased, resulting in a 13 percent yield reduction.
Research was also conducted on crops in Spain and other Mediterranean countries where crop damage is more severe than in the UK. Crop damage is visible in some areas of these countries; older leaves become discolored and eventually die.
In eastern Spain, watermelons grown in open-top chambers showed a 19 percent drop in yields. In this study, ozone levels were double the guidelines set by the United Nations Economic Commission for Europe. In the second year of the study, ozone levels were five times the guideline, resulting in a 39 percent loss in yields.
The findings will help UK officials review and possibly revise their policy on atmospheric pollution. Based on their research, the scientists have also advised the United Nations to re-examine its intervention policies.
"These findings draw attention to the need for exposure-response relationships to be examined in a wider range of crops grown over a broader range of climatic conditions, particularly those prevalent in the Mediterranean region," said Barnes. "Until the results of such studies are available, critical levels aimed at the protection of crop yield in Europe will remain valid only for a defined range of climatic conditions."
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