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Plants and microbes cooperate to clean up contaminated soil

Posted May 1, 2013

It is expensive to clean up soil drenched in chemicals, but plants can do part of the work in collaboration with microbes. Microbe-based phytoremediation is gradually making inroads into Finland.

Finland has no shortage of sites that were formerly home to a wood impregnation plant, foundry or landfill. Some of the sites are on record, but others are not identified until they are being zoned for other purposes.

When the soil on site is found to be contaminated to a depth of several metres and construction work needs to get started in a few months’ time, soil replacement is the fastest remedy. However, some of the contaminated areas can be restored by combining modern and age-old methods. This is where plants and their microbial partners may enter the picture in the future.

Plants take on contaminants

It is no new discovery that many plant species can grow in soil contaminated by various pollutants. Some species can even sequester or decompose contaminants. Soil and plant microbes help plants survive in harsh conditions.

This summer, the University of Helsinki and the Finnish Forest Research Institute will jointly launch an experiment in Luumäki, in southeastern Finland, planting aspens on the site of a former wood impregnation plant. The choice of tree fell on aspen because it grows fast and thrives in different types of environments. A deep-rooted tree, it can even change the flow of groundwater. Aspen trees can also cope with stress factors, such as a considerable variety of soil contaminants.

“The problems arising from soil contaminants vary depending on the country,” explains Docent Kim Yrjälä from the Department of Biosciences. “For example, many substances do not decompose at all in hypoxic or cold conditions. Pesticides, on the other hand, do not necessarily remain in the area in which they were originally used.”

On nature’s terms

In the Luumäki project, Yrjälä will be studying the microbes living in the aspen roots and their ability to clean up the soil. Microbes will be introduced into the root system, the goal being for them to cooperate with the plants to gradually reduce the soil contamination.

“People often associate plant biotechnology with genetically modified organisms,” Yrjälä says. “Though we’re working with biotechnology, this does not involve GMO plants or microbes. The trees we will plant were selected from stress-resistant, normally bred aspen clones. In other words, everything is based on nature’s normal processes.”

In Finland, soil restoration often does not appear on the agenda until a site is rezoned. This presents a number of problems for natural methods.

“Plants cannot clean up the soil in a summer or two. They need more time on site, and this conflicts with tight schedules,” Yrjälä admits.

Source: University of Helsinki

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