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  • Plants could clean up toxic soil


Turkish scientists have discovered a plant that can remove boron from soils. They say that it could provide a low-cost way of 'cleaning up' soil contaminated with this naturally occurring trace element that is toxic to most crops at high concentrations.

Scientists from Selçuk University in Konya, Turkey, have found that Gypsophila sphaerocephala — a plant that usually grows on dry slopes and limestone rocks — can survive in boron-contaminated soils and accumulates boron in its tissues. They also suggest that, once it has been harvested, the plant could be transported to sites with very low levels of boron, helping to add the trace element to the soil in regions where it is boron deficient.

High levels of boron have been reported to reduce crop yields in several southern European countries and Mediterranean states, especially in dry regions, including Jordan, Israel and Cyprus. Many crops are quite sensitive to boron, and show severe toxicity symptoms, such as yellowing of the leaf tips and suppressed growth, when soils contain high levels of the element.

"To our knowledge, this is the first report of a plant species possessing the potential for hyperaccumulation [of boron], especially in a region where [boron] toxicity symptoms occur," the researchers write in the Turkish Journal of Botany. They add that the study provides a new plant to explore mechanisms of boron hyperaccumulation, which "may lead to identifying the gene(s) conferring [boron]-resistance".

Conventional methods of removing boron from the soil, such as leaching or increasing pH by liming (adding calcium carbonate to increase soil alkalinity), can be unsuitable for boron-contaminated regions for a variety of reasons, such as low rainfall, a lack of water or the high lime content of the soils.

Furthermore, such techniques are often expensive to apply, requiring chemical additives and regular maintenance. And they can also result in the generation of hazardous by-products, such as chemical sludge, potentially leading to high disposal costs.

The researchers suggest that either developing boron-tolerant crops, or using boron-accumulating plants such as Gypsophila sphaerocephala, may provide a more effective — and cheaper — solution.

Mohamed Hamoud, a plant molecular biotechnologist at Tanta University in Egypt, welcomes the research findings, saying that they could help increase the area in which cereals such as wheat could be successfully cultivated.

Natural hyperaccumulators, such as Gypsophila sphaerocephala, tend to grow slowly, he says. But genetic engineering could be used to create fast-growing plants that carry boron-tolerance genes to improve their ability to tolerate, and accumulate, boron. "It's an approach I call 'cleaning by genes'," he says

The technique could be particularly useful in developing countries, he adds, because the costs of growing plants are minimal compared to those of soil removal and replacement.

Link to research paper in Turkish Journal of Botany 

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