Plant treatment, pollutant load, and soil type effects in rhizosphere ecology of trace element polluted soils

Abstract

Re-vegetation of trace element contaminated soils can alter the pH and chelating capacity in the rhizosphere, increasing the mobility of pollutants, which, in turn, may impact on rhizosphere ecology. In this study a short-term pot experiment was carried out in order to investigate the multi-factorial effects of: buffering capacity (sandy-loam and loam soils); pollutant load (0%, 1.3%, and 4% of pyrite sludge), and the presence/absence of plant (Lolium perenne L. and Medicago sativa L.) on the mobility of trace elements, soil biochemical functionality (hydrolase activities), and biological diversity (bacterial and nematode communities). The experiment was carried out with representative soils from the Guadiamar basin (SW Spain), an area where the Aznalcóllar mining spill affected over 4000ha. Results indicated that the development of rhizospheres in polluted soils (coarse-textured) increases the mobilization of trace elements. In general the presence of roots has stimulatory effects on soil quality indicators such as hydrolase activities and both bacterial and nematode communities. However, the presence of high amount of metals interferes with these beneficial effects. This study provided evidence about the complexity of the impact of growing plants on trace element polluted soils. Trace element mobilization, hydrolase activities and bacterial and nematode communities in the rhizosphere are dependent on plant species, soil type, and pollution dose.