COMPARATIVE TOLERANCE AND PHYTOSTABILIZATION POTENTIAL OF Conocarpus erectus AND Eucalyptus camaldulensis GROWN IN CADMIUM CONTAMINATED SOIL

Abstract

Phytoremediation is the most promising approach for the remediation of Cd contaminated soils. In the present study, Cd tolerance and phytoremediation potential of Conocarpus erectus and Eucalyptus camaldulensis, was evaluated in a pot experiment for a growth period of 6 months. Two-month-old plants of uniform size were transplanted in Cd-contaminated soil (0, 5, 10 and 15 mg kg-1), and their growth attributes, chlorophyll contents, root and shoot Cd concentration, bioconcentration factor (BCF) and translocation factor (TF) were determined. With increasing soil Cd levels, shoot and root biomass, leaf water and chlorophyll contents (chl a, chl b and total chl) of E. camaldulensis were decreased more than C. erectus. Shoot and root Cd concentrations as well as Cd uptake were more in C. erectus than E. camaldulensis. The TF was less than one for both plant species, while BCF was more than one. It is concluded that due to relatively higher Cd tolerance and greater capacity to retain higher concentration of Cd in roots, C. erectus is a better species than E. camaldulensis for phytostabilization of Cd contaminated soils.

The Change in Growth, Osmolyte Production and Antioxidant Enzymes Activity Explains the Cadmium Tolerance in Four Tree Species at the Saplings Stage

“…Different studies have reported up-regulation in the expression of enzymes synthesizing phenolic compounds (phenylalanine ammonia-lyase), as they act as antioxidant enzymes under stressful environments [60]. Our results are in accordance with the previous studies on P. × canescens and C. camphora species, in which the accumulation of soluble protein and soluble sugar was increased under Cd treatment [52,61,62].…”

“…However, in this study, the reduction in the chl a, b and carotenoid contents was higher in the case of the M. alba and P. deltoides saplings as compared to C. erectus and S. cumini. In the previous studies on Populus nigra, Salix alba, Eucalyptus hybrid, Conocarpus erectus, Eucalyptus camaldulensis and Conocarpus lancifolius, similar decreases have been reported, where the chl a, b and carotenoid contents decreased in plants grown in Cd-contaminated soil [44,[49][50][51][52]. Therefore, based on the lowest reduction in the chl a, b and carotenoid contents observed in C. erectus, it can be assumed that C. erectus showed a higher tolerance against the given Cd treatment.…”

“…The SOD scavenges the production of O 2 − into H 2 O 2 , which is further neutralized to H 2 O by the other antioxidant enzymes such as CAT and POD [58]. CAT is generally present in the single-membrane-bounded structure (peroxisome) and is responsible for scavenging the increased concentration of H 2 O 2 by converting H 2 O 2 to H 2 O in the plant cell [52,59]. The activity of all of the antioxidant enzymes (SOD, POD, CAT and APX) increased significantly in all four tree species under the Cd treatment.…”

“…Several compatible solutes such as proline, soluble sugar, total phenolic contents and soluble protein are regarded as important nonenzymatic antioxidant enzymes that help in protecting the subcellular structure and scavenge the ROS in the plant cell under abiotic and biotic stress conditions [52]. In the present study, the concentration of proline, soluble sugar, total phenolic contents and soluble protein increased significantly in all four tree species under the Cd treatment, with the highest increase evidenced in the C. erectus and S. cumini saplings.…”

“…The results of our experiment suggest that all species adopted an exclusion tactic by retaining the highest content of Cd in the roots and translocating the lower content of Cd towards the stem and leaves. The translocation factor (TF) of heavy metal is another important component for determining the potential of the phytoremediation of heavy metal, as the TF depends upon on the relative accumulation of heavy metal in roots and shoots [17,51,52]. If a species has a translocation factor >1, it shows a high mobility of heavy metal from the roots towards the shoots.…”