Rockcress, Arabidopsis halleri, can grow on contaminated brown field sites sucking up heavy metal ions from the soil and storing the harmful elements in its leaves at high concentration. This discovery by a German team points to a bioremediation approach based on cultivation of this plant.[Stein et al., New Phytol. (2016) DOI: 10.1111/nph.14219]
Researchers from Ruhr-Universität Bochum, Germany, and their colleagues have analyzed some 2000 specimens of rockcress from 165 locations across Europe and not only have they revealed the diversity of this species group but have demonstrated how it might be exploited technologically for materials bioremediation and metal extraction and reclamation.
"In plants, the natural processes of evolution have produced contrasting extremes of biological performances, as well as overwhelming biological diversity," explains Bochum's Ute Krämer. "However, these phenomena have been described only incompletely, and explained to an even lesser degree."
Krämer's team has collaborated with Stephan Clemens of Universität Bayreuth to analyze specimens for cadmium, copper, lead, and zinc and found that soil composition varied from location to location across almost five orders of magnitude in terms of concentrations of these metals. This reinforces the finding that rockcress can tolerate a wide range of soil compositions; leaf concentration of zinc was as high as 5.4% and 0.3% cadmium based on dry biomass.
"Some plants had the sponge-like capacity of sucking out the heavy metals cadmium and zinc from mere trace amounts in the soil," Krämer says, adding that this is perhaps evidence of an unusual defense mechanism against predators or competitors. The team also showed that plants growing along the border between Germany and the Czech Republic could concentrate cadmium more efficiently than plants growing in northern Italy. The team suspects that this is a result of on-going evolution with diverse adaptations of plants to specific local ecological conditions.
The next step will be to carry out genetic studies in order to determine what causes those differences and how they originate in a plant, Krämer adds. This would then allow specific species to be bred or engineered for particular sites requiring remediation or two optimize the extraction of a particular metal of economic interest from contaminated soil for "phytomining"
"Such biological phenomena are highly relevant for us, because they help us gain universal insights into evolutionary processes and the way they are interlinked with a highly changeable environment that is often hostile to life," Krämer explains.
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".