Growth of Populus alba and its influence on soil trace element availability

The use of fast growing trees is a common practice for phytoremediation of contaminated soils. Plant roots can change trace element bioavailability in soils. We studied the effect of Populus alba on trace element bioavailability on two contaminated soils (one with neutral pH and other with acid pH) comparing two methods (0.01 M CaCl2-extractable in soil and concentration in soil pore water SPW), trace element accumulation in leaves and plant development over 36 months. Results were compared to those obtained with a non-contaminated soil. The experiment was carried out in containers (95 L of volume and 1 m height). Half of the containers for each soil were planted with P. alba saplings and the others remained without plant. In neutral soils plant growth did not influence soil pH; the greatest effect due to plant growth was found in acid soil. Values of pH obtained by SPW showed a similar trend compared to those obtained after soil KCl extraction. Bioavailability of trace elements determined by both methods followed the same behavior in the three studied soils. Both methods for determining trace element bioavailability in soil were accurate to predict plant uptake. In non-contaminated soil, plants tended to increase micronutrients (Cu, Mn and Zn) availability. However, in case of contaminated soil, the growth of P. alba did not increase trace element availability. Moreover, results on height and diameter of the trunk of the trees, during 36 months, demonstrated that the presence of total trace elements in soil did not affect plant development.