PHYTOREMEDIATION POTENTIAL OF HEAVY METAL CONTAMINATED SOILS BY THE PERENNIAL ENERGY CROPS MISCANTHUS SPP. AND ARUNDO DONAX L. UNDER LOW IRRIGATION
The increasing demand for biomass for the production of bioenergy is generating land-use conflicts which might be avoided through the establishment of dedicated energy crops on marginal land, e.g. heavy-metal contaminated land. But assessment of bioenergy from marginal land should take into account constraining factors, such as productivity and biomass quality, as well as environmental and social aspects. In this context, this research work aims to study the potentiality of two perennial grasses Miscanthus spp. and Arundo donax. in heavy metal contaminated soils. In a previous study, it was found that giant reed and Miscanthus spp. yields were negatively affected when grown in heavy-metal contaminated soil under full irrigation (950 mm) to overcome water stress. However, both crops can be considered interesting candidates for heavy metals phytoextraction, based on the metal accumulation observed and the high biomass produced. In this work, the yields and the biomass quality of these perennials were tested but under low irrigation (450 mm). Along two years, giant reed was tested on contaminated soils containing 450 and 900 mg Zn kg-1, 300 and 600 mg Cr kg-1 and 450 and 900 mg Pb kg-1, while the Miscanthus genotypes: M. x giganteus, M. sinensis and M. floridulus were tested on 450 and 900 mg Zn kg-1 contaminated soils. Giant reed biomass production was negatively affected by the Cr contamination, but not by the Zn or the Pb contamination. Zn contamination reduced significantly M. x giganteus production but not M. sinensis or M. floridulus yields. Yet, M. x giganteus was the most productive genotype. Biomass obtained in heavy metals contaminated soils presented higher ash content and higher Zn/Cr/Pb content then biomass from non-contaminated soils, thus showing phytoextraction and accumulation capacity. But, lowering the irrigation level reduced significantly the biomass production, causing lower accumulation of metals in the biomass. Even though, both crops still presented favorable potential for phytoextraction and showed to be well suited for phytostabilization of heavy metals contamination as these grasses prevented the leaching of heavy metals and groundwater contamination.