Gas exchange responses of two poplar clones (Populus euramericana (Dode) Guinier 561/41 and Populus nigra Linnaeus 63/135) to lead toxicity

Abstract

To evaluate the lead tolerance of Populus euramericana (Dode) Guinier 561/41 and Populus nigra Linnaeus 63/135 clones in relation to photosynthetic efficiency, we measured physiological parameters of the two poplar clones exposed to Pb treatments. The pot experiment was established in a roofed place in a completely randomized design, with 5 Pb treatments (0, 0.5, 1, 1.5 and 2 g Pb.kg-1) per poplar clone. After 3 months, photosynthetic rate (A), transpiration rate (E), stomatal conductance, intercellular CO2 concentration (Ci), leaf water potential were measured and water use efficiency (WUE) and mesophyll conductance (gm) were computed. Results revealed that increasing Pb concentrations in soil reduced all physiological parameters of the two poplar clones, except Ci. At all Pb treatments A and E, and at a concentration of 0.5 g Pb.kg-1 WUE and gm of P. euramericana plants were significantly higher than those of P. nigra plants. On the other hand, while a reduction in most physiological parameters of P. euramericana plants took place at a concentration of 1 g Pb.kg-1 and at higher concentrations, in P. nigra plants these reductions were from a concentration of 0.5 g Pb.kg-1. With respect to physiological parameters, P. euramericana 561/41 clone was more tolerant of Pb than P. nigra 63/135 clone, therefore it can be considered as a suitable species in phytoremediation of lead-contaminated soils.