Effect of heavy metals (lead, cadmium and chromium) on some root morphological characteristics of Populus alba L. and Populus nigra L. seedlings

Root morphology is one of the significant factors in success of heavy metal remediation of soils using plants where pollutant absorption takes place. In the present study, effect of soil pollution with heavy metals on some root morphological characteristics of two tree species, Populus alba L. and Populus nigra L., were studied. Root length, root diameter, lateral and main root biomass of one-year old seedlings grown in lead-, cadmium- and chromium (VI)-contaminated and uncontaminated soil were compared. The results indicated that increased concentration of three metals in soil led to decrease of all morphological traits of studied species (P<0.01).  Maximum and minimum decreases were related to Cd and lead, respectively. Cadmium pollution at 150 mg kg^-1 led to 25% and 20% decrease in lateral root production in P. nigra and P. alba, respectively in comparison with control treatment. In most studied traits, P.nigra showed more tolerance than P. alba in presence of pollutants. It seems that the strategy used by two species at the increased pollution levels defined by greater focus on main root production rather than lateral root production, could be a fundamental solution for higher tolerance.