Study On The Effects Of Heavy Metal Stress On The Young Trees Of Three Wood Plants

The thesis studied the effects of heavy metal stress on the physiological and biochemical indicators of young trees of three wood plants including Ligustrum lucidum ^ Ginkgo biloba > Pittosporum tobira by the means of pot culture.The comprehensive heavy metal resistance ability of these young trees was also appraised.The main results were described as follows:1.The investigation showed that leaves appeared the symptom of losing green, but the symptom gradually weakened in the growing period.With the increasing of heavy metal concentrations and the prolongation of the time of heavy metal stress, the height growth and diameter growth was restrained.2. With the increasing of heavy metal concentrations and the prolongation of the time of heavy metal stress, chlorophyll a, b and chlorophyll contents all decreased, but relative conductivity rates and free proline contents all increased. The ratios of chlorophyll a to b increased with the increasing of heavy metal concentrations and the ratios in the final time were larger than that in the middle time.3. With the increasing of heavy metal concentrations, the activity of catalase gradually decreased. With the prolongation of the time of heavy metal stress, the activity of catalase of Ligustrum lucidum decreased, while the activity of catalase of Ginkgo biloba and Pittosporum tobira increased.4. With the increasing of heavy metal concentrations, the contents of kalium and calcium of roots > stems and leaves all decreased.5.The accumulation to cadmium and/or lead of two-year-old young trees exceeded that of contrast in a growing period.The accumulation to cadmium and/or lead in roots increased with the increasing of the contents in the soil.And stems and leaves reflected the similar laws. The accumulation to cadmium and lead in joint pollution was larger by comparison with the single pollution.The absorption to cadmium through roots of Ligustrum lucidum and Ginkgo biloba mainly accumulated in roots, while Pittosporum tobira could transfer fifty percent or so to stems and leaves. The absorption to lead through roots of three species mainly accumulated in roots, hardly transferred to stems and leaves.6.The accumulation ratios to cadmium of roots, stems and leaves were clearly larger than that to lead, and the accumulative ability of roots was bigger than that of stems and leaves. Comparing with the accumulative ability of stems, Pittosporum tobira was strongest .7.The absorption to cadmium and/or lead of three wood plants in a growing period was not similar. Ginkgo biloba and Pittosporum tobira were similar in the absorption to cadmium, while the absorption to cadmium of Ligustrum lucidum was close to saturation in the middle time. The absorption to lead of Ginkgo biloba was close to saturation in the middle time, whlie Ligustrum lucidum and Pittosporum tobira were similar in the absorption to lead.8.The comprehensive heavy metal resistance ability of young trees was analyzed by both subordinate function method and coordinate comprehensive appraisal method.The results from two methods showed the rank of heavy metal resistance ability of young trees of three wood plants were: Pittosporum tobira > Ginkgo biloba > Ligustrum lucidum.