The Physiological Response Of Populus × Euramericana (Dode) Guineir 'neva'to Cd Stress

The effects of cadmium stress on the leaves photosynthesis, the dry matter allocation and the absorption of Cd,N,P and K in Populus×euramericana(Dode)Guineir'Neva'were studied with pot cultivation. The results showed that in the early phase of cadmium stress, net photosynthetic rate (Pn) of one-year old P.×euramerican decreased with increasing stress with the maximum reduction of 17.1 %, 17.8 %, 23.9 % and 24.7 %, as the recovery speed also slower; but seedlings return to a normal photosynthetic level on the 10 to 20 days. Because the decrease of Pn was mainly related to the decrease of stomatal conductance. In addition, the stems/roots ratios and shoot allocation in dry matter of P.×euramericana increased with stress, while the roots allocation decreased. The change of dry matter allocation under 200 mg·kg^-1 treatment, which leading to the roots/shoot ratios dropped sharply and root growth restricted severely.Under cadmium stress in 10 days, the stem cadmium concentration ( mg·kg^-1) in P.×euramericana is was biggest, and then followed by leaves and roots, which also explains the phenomenon that stems biomass tilt when it was suffered cadmium stress. Under cadmium stress in 40 days, the stem cadmium concentration ( mg·kg^-1) in P.×euramericana is was biggest, and then followed by roots and leaves. Under cadmium stress in 80 days, for 100 mg·kg^-1, the stem cadmium concentration ( mg·kg^-1) in P.×euramericana is was biggest, and then followed by leaves and roots; while for 200 mg·kg^-1, the root cadmium concentration ( mg·kg^-1) in P.×euramericana is was biggest, and then followed by leaves and stem. This research also shows that after a cadmium stress cycle when under cadmium stress 80 d, 100 and 200 mg·kg^-1 treatments can make the cadmium concentration of soil decreased 0.97 and 1.45 mg·kg^-1.With cadmium stresses, the changes of N, P and K concentration of each organs of P.×euramericana were more complex. The whole N concentration of the roots, stems of P.×euramericana after admium stresses was increased, and then reduced in the beginning. But the whole N content of leaves were reduce to their full N concentration level. All P concentration of roots were reduced in its stems with cadmium stresses, and the influence of the P concentration on stems is to promote and after reduce, when the influence on the leaves is to reduce its full P concentration level. For total K concentration, the roots is reduced with cadmium stress; the impact on its stems is increasing their K concentration; and for the influence of theleaves department is to reduce their entire K concentration. In other words, the N and P uptake was suppressed and K uptake was promoted in P.×euramericana by cadmium stresses, and the most significant stress concentration was 200 mg·kg^-1.Overall, P.×euramericana can growth normally in 150 mg·kg^-1 concentration ofcadmium pollution sites, with no significant difference between gas exchange parameters, partitioning and N, P and K absorption.