[Growth responses of four northern broadleaved tree species to soil Cd stress]

In this paper, the gradient (0, 10, 50, 100, 200 mg x kg(-1)) of soil Cd concentrations was established by mixing CdCl2 with soil and sand, and the growth responses of four northern broadleaved tree species Acer ginnala Pyrus ussuriensis, Acer mono and Malus baccata to soil Cd contamination were studied by growing their seedlings in pots in greenhouse. The results revealed that the seedling growth of all test species was enhanced under lower soil Cd concentrations (< or = 50 mg x kg(-1)), and Acer ginnala had the strongest response under 10 mg x kg(-1) treatment, with 135.8% and 146.0% increment of collar and height growth, respectively, in comparing with the control. But, the growth of aboveground part decreased with increasing soil Cd, and the collar and height growth of A. ginnala under the highest Cd concentration was only 24.1% and 28.0% of the control, respectively. Under lower Cd concentrations, an increase of foliage and new shoot growth was found in A. ginnala and P. ussuriensis, the biomass of new shoots increased but that of foliage decreased in M. baccata, and both foliage and new shoot decreased in A. mono. Under the highest Cd concentration, A. ginnala had the greatest decrease of foliage and new shoot biomass, being 4.6% and 7.3% of the control, respectively, while P. ussuriensis and M. baccata had a relatively less decrease. The biomass increase of new roots declined with increasing Cd concentration for all tree species except P. ussuriensis, and the least increase was A. ginnala, only 2.3% of the control. The new root biomass of P. ussuriensis was 125.5% and 117.1% of the control at 10 mg and 20 mg x kg(-1), respectively. The total biomass increment of A. ginnala and P. ussuriensis seedlings was greater than that of the control under lower Cd concentrations, while an obvious decrease was found for all tree species under higher Cd concentrations. Under the highest Cd concentration, the total biomass of A. ginnala, M. baccata, A. mono and P. ussuriensis was 13.7%, 27.2%, 36.4 and 40.1% of the control, respectively. Subordinate function analysis suggested that the tolerance of test tree species to soil Cd contamination was in order of M. baccata > A. ginnala > P. ussuriensis > A. mono. Analysis of Cd concentration in plant tissues demonstrated that P. ussuriensis had the highest Cd enrichment coefficient for its root, shoot and foliage, and M. baccata also had a higher Cd enrichment in its root and shoot.