Effects Of Lead On Robinia Pseudoacacia And Amorpha Fruticosa Growth And Osmotic Adjustment Substance Under Different Water Supply

In order to research the resistance to Pb of Robinia pseudoacacia and Amorpha fruticosa, common leguminosae woody plants in arid and semi-arid regions in the northwest China, and provide a basis for ecological reconstruction and phytoremediation in arid regions, pot experiments were carried out in the dry shed. One year old R. pseudoacacia and A. fruticosa seedlings were planted under 3 drought treatments (80%, 60%, and 40%) and 6 different lead treatments (0, 300, 500, 1000, 2000 and 3000 mg/kg) with 3 replications. The growth characteristics and Pb distribution in the seedlings, main organic osmolytes contents in the leaves throughout the growing period were measured. The main results are as follows:1. Under Pb stress, stem length of A. fruticosa was significantly lower than CK. With the increasing of lead content, the ground diameter of both seedlings decreased slowly, the growth ratio of stem length and specific leaf area (SLA) was not significantly influenced. The root activity of R. pseudoacacia and A. fruticosa showed declining trend after increasing. In the interaction stress of drought and lead, drought stress played a leading role on inhibiting plant growth. R. pseudoacacia's stem length, ground diameter, SLA, and root activity were higher than A. fruticosa's, but A. fruticosa's Root/Shoot (R/S) was higher than R. pseudoacacia's. The growth ratio of ground diameter of R. pseudoacacia was significantly higher than that of A. fruticosa, in addition, the stem growth ratio and SLA of R. pseudoacacia were almost the same as those of A. fruticosa. Under interaction stress, the R/S of A. fruticosa did not increase with the increasing of stress level. Under drought stress, as the drought stress increased, the growth ratio of stem length and ground diameter and SLA of both types of seedlings decreased, and the root activity of R. pseudoacacia climbed firstly, then declined, while the root activity of A. fruticosa decreased firstly, then showed an upward trend. The ground diameter of R. pseudoacacia was restricted dramatically, the R/S of R. pseudoacacia was increased significantly, either.2. With the increasing of lead stress level, soluble sugar content, proline and soluble protein content in the leaves of R. pseudoacacia and A. fruticosa had no significant changes. In the interaction stress, drought played a dominant role on proline accumulation in the leaves of R. pseudoacacia and A. fruticosa. Under interaction treatment, soluble sugar, proline and soluble protein content were all changed in the leaves of R. pseudoacacia and A. fruticosa, but the proline and soluble protein played a larger role in osmotic adjustment than soluble sugar. With increasing of drought stress, soluble sugar content of R. pseudoacacia increased unobviously, while soluble sugar content of A. fruticosa increased obviously and reached a significant level (P<0.05). Proline content in the leaves of R. pseudoacacia and A. fruticosa increased. Soluble protein content of R. pseudoacacia was significantly reduced, at the same time, soluble protein content of A. fruticosa was soared obviously. With the increasing of stress duration, soluble sugar content in the leaves of R. pseudoacacia and A. fruticosa increased significantly (P<0.05). Proline content in the leaves of both seedlings reached it's maximum at duration of 60 d. Soluble protein content in the leaves of R. pseudoacacia and A. fruticosa changed slightly. Proline accumulation had a bigger contribution to resistance to stress in A. fruticosa than in R. pseudoacacia.3. The Pb content in each part of R. pseudoacacia and A. fruticosa gradually increased with the increasing of soil Pb content. The order of Pb content in each part of R. pseudoacacia and A. fruticosa was root>stem>leaf. The enrichment coefficient of both seedlings varied according to different treatments, the enrichment coefficient of R. pseudoacacia varied from 0.15 to 0.63, while the enrichment coefficient of A. fruticosa varied from 0.16 to 0.84. With the increasing of drought stress, the enrichment coefficient of R. pseudoacacia increased except 3000 mg/kg treatment, which meant that drought played a positive effect on R. pseudoacacia to absorb and accumulate Pb. The enrichment coefficient of A. fruticosa declined after increasing except 2000 mg/kg treatment. And the enrichment coefficient was the highest under 60% water supply. Under Pb stress, the transfer coefficient of R. pseudoacacia decreased with the Pb content increased. Under 80% water supply except 3000 mg/kg Pb treatment, the transfer coefficient of R. pseudoacacia was the highest among all the treatment of R. pseudoacacia. Under interaction stress, the transfer coefficient of R. pseudoacacia showed a decline trend. At the same time, under 40% water regime, the transfer coefficient of A. fruticosa was the biggest, which meant that it was good for transferring Pb under 40% water regime. In addition, with the increasing of drought stress, the transfer coefficient of A. fruticosa increased-drought played a positive effect on A. fruticosa to transfer Pb. Pb transfer coefficient of R. pseudoacacia was higher than that of A. fruticosa.