Tolerance And Accumulation Characteristics Of Two Species Of Eucalyptus Under Lanthanum And Cerium

Fast-growing plants for phytoremediation can improve the efficiency of remediation of rare earth contaminated soil. In order to choose suitable plant materials, this study chooses Guanglin 9 (Eucalyptus grandis×Eucalyptus urophlla, Gn9) and Eucalyptus grandis 5 (Eg5) as test materials, investigate the growth, physiological and biochemical response, and Lanthanum (La) or cerium (Ce) accumulation of Guanglin 9 and Eucalyptus grandis 5 in both pot and plot experiments. The major results showed as follows:(1) In pot experiments, two species of Eucalyptus in soil culture showed great tolerance characteristics of La or Ce. The plant heights, root length, dry biomass of Gn9 and Eg5 increases at the beginning and then decreases with increasing soil La or Ce concentrations. Compared with the control, plant heights and root length of the two species of Eucalyptus were obviously lower than those of the control at soil added La or Ce of 500 mg kg-1 (P< 0.05) except root length of Eg5 under La stress. Shoots biomass of the two species were close to or higher than those of the controls at soil added La and Ce below 350 mg kg-1. However, they significantly were lower than those of the control at soil added La and Ce of 500 mg kg’1 (P< 0.05).The net photosynthetic rate (Pn), stomatal conductance (Cond) and transpiration rate (7>) of Gn9 and Eg5 increased with increasing soil La or Ce concentrations up to some levels and then decreased. The intercellular CO2 concentration (Ci) of the two species were slightly decreased first and increased afterwards.On a whole, with increasing soil La and Ce concentrations, the activities of peroxidase (POD) and catalase (CAT) of Gn9 and Eg5 rose at first and lowered later. The emzyme activity of leaves was higher than that of roots. And the glutathione and soluble protein concentrations presented similar change tendency to the emzyme activity. Moreover, the soluble protein concentrations of the two species were higher than those of the control except soluble protein concentrations in roots of Eg5. They were lower than those of the control at soil added La and Ce below 200 mg kg-1,but not significant (P>0.05).In pot experiments, two species of Eucalyptus in soil culture showed great accumulation characteristics of La or Ce. The La or Ce concentrations in roots, stems, leaves and shoots display quadratic increment or linear increase with increasing soil La or Ce concentrations. Under La stress, La concentrations in shoots of Gn9 and Eg5 reached their maximum of 144.91 and 178.63 mg kg-1, respectively, at soil added La of 500 mg kg-1; La accumulations in shoots of the two species reached their maximum of 5.78 and 10.11 mg pot-1, respectively, at soil added La of 350 mg kg-1; BCF and TF values of the two species were 0.32 to 0.85,0.25 to 1.46 and 0.34 to 0.75,0.58 to 1.18, respectively. Under Ce stress, Ce concentrations in shoots of Gn9 and Eg5 reached their maximum of 112.32 and 173.66 mg kg-1, respectively, at soil added La of 500 mg kg-1; Ce accumulations in shoots of the two species reached their maximum of 3.54 and 4.88 mg pot-1, respectively, at soil added Ce of 350 mg kg-1; BCF and TF values of the two species were 0.35 to 0.74,0.42 to 0.86 and 0.39 to 0.61,0.55 to 1.00, respectively.(2) In plot experiments, Gn9 and Eg5 had great tolerance of La stress because they grown vigorously and showed no visible symptoms of La or Ce toxicity in the plot. Average of shoot biomass were between 211.51 to 250.12 g plant-1. La and Ce accumulation per unit area were 34.76 and 43.40 mg m-2 for Gn9, and 25.24 and 31.80 mg m-2 for Eg5.