Soil chemical and biochemical properties under Populus alba growing: Three years study in trace element contaminated soils

• The presence of root system in soils improves readily soluble C and N.
• Populus alba is an option to remediate trace element contaminated soils.
• Soil remediation can be monitored through specific biomarkers (enzyme test and MBC).
• Poplar growth is an effective option to reduce acidity in soils.

Certain plant species have the ability to grow in trace element-polluted soils without showing any negative symptoms. These species could be considered for phytoremediation techniques and their presence might influence the abundance, activity and composition of soil microbial communities. In this work we investigated the root-induced changes in chemical (pH, soluble trace element concentrations, total organic C, water-soluble C, and nitrogen concentrations) and biochemical (microbial biomass C, β-glucosidase activity and protease activity) properties caused by Populus alba on two contaminated soils (one with neutral pH (AZ) and other with acid pH (DO)) for a period of over 36 months. The results were compared to those obtained with a non-contaminated soil. The experiment was carried out in containers. At the end of the experiment, samples of the soil directly adhered to the root and that located more than 5 cm from the root were also studied. The results showed that, in neutral soils, poplar did not influence soil pH; the greatest effect on pH due to plant growth was found in acid soil. Poplar presence increased C sources, through root exudates, in all soils. In AZ soil, poplar maintained chemical and biochemical properties, whereas an important decrease in soil quality was observed in the same bare soils. The effect of poplar development on soil quality was even more appreciable in acid contaminated soil (DO), in which the tree also produced a strong increment of soil pH, a decrease in trace element concentrations and an improvement of chemical and biochemical properties. We concluded that P. alba is a suitable plant for the phytoremediation of trace element contaminated soils. Moreover, root exudates of this species may be responsible for the improvement of soil quality in trace element contaminated soils.