Trace element partitioning in a poplar phytoextraction stand in relation to stem size

At an Italian field test site the efficiency of phytoextraction of toxic trace elements (TEs) from the soil is determined by uptake capacity, bioavailability of TEs in the soil and biomass yield of the plants involved. Altering the quantity and type of biomass produced, especially among fast-growing trees, may be one method of increasing phytoextraction efficiency. In poplar bark and wood show different TE concentration. Poplar also shows changing proportions of bark and wood with increasing diameter at breast height (DBH). Though it is often thought that the amount of TE accumulated in the biomass increases with the size of the plant, in the current study we show that this is only partially true. In fact while Zn is highly accumulated by the largest (60 mm DBH) poplar plants, Cd, Cu, and Ni were more concentrated in slightly smaller plants (50 mm DBH), and Pb in even smaller (40 mm DBH). These findings could open new strategies for managing a poplar phytoextraction stand in terms of coppicing techniques and planting cycles in order to address specific targeted TEs and enhance the overall performance of this green technology.