In order to understand the responses of Robinia pseudoacacia,a common Leguminosae woody plant in arid and semi-arid regions to lead stress,pot experiments were carried out in the dry shed.One-year-old R.pseudoacacia seedlings were planted and imposed double stresses of drought and lead.The main osmotic substances in the leaves were measured throughout the growing period.The results showed that the content of soluble sugar(SS) in the leaves under double stresses changed slightly and the differences were not significant,however,it was significantly affected by the duration of the stresses.Drought stress played a dominant role on proline(Pro) content and soluble protein(SP),in which the effect of severe drought stress(40% of the field water content) on Pro reached a significant level.Mild and severe drought stress on SP also reached a significant level.The effect of lead on SP content in the 300 mg·kg-1 treatment was significant.It was concluded that under the stress of drought and lead,the contents of SS,Pro and SP in the leaves of R.pseudoacacia were all changed in various degrees,but significant changes were observed in the contents of Pro and SP,indicating that they played more important roles in osmotic adjustment than soluble sugar.

【Objective】 The research was done in order to study the effect of soil water,Pb and interaction between the two on leaf water potential,cell membrane permeability and leaf relative water saturation deficit of Robinia pseudoacacia.【Method】 With one-year-old seedlings of R.pseudoacacia as material,a potted experiment was conducted respectively in simulating different water conditions（the soil relative water content with 40%,60%,80% and 100%） to measure the change of water and Pb stress（Pb content with 0,300,500,1 000,2 000 and 3 000 mg/kg） on leaf water potential,cell membrane permeability and leaf relative water saturation deficit of R.pseudoacacia seedlings.【Result】 The results showed that water situation had significant influence on every physiological characteristic,in which the leaf had the minimum water potential when the soil relative water content was 40%.When Pb content was 300-3 000 mg/kg,cell membrane permeability was first increased and then decreased again increased with the increase of the soil water content;leaf relative water saturation deficit was first decreased and then increased with the increase of the soil water content.Under the same soil water conditon,Pb stress exerted no significant effect on leaf water potential and leaf relative water saturation deficit of R.pseudoacacia（P〉0.05）,only cell membrane permeability was decreased and then increased again decreased with the increase of Pb concentration.Although,in different soil water conditions,Pb content in leaf of R.pseudoacacia showed different trends with the increase of Pb content in soil,but overall it was increased.【Conclusion】 The water situation had influence on every physiological characteristic of R.pseudoacacia,but Pb stress had apparent influence only on cell membrane permeability,no influence on other physiological characteristics.R.pseudoacacia had a certain absorption of lead in soil.Experimental results show that R.pseudoacacia have a strong adaptive ability.

The effects of heavy metal Pb and drought stresses on the antioxidant enzyme activities and malondialdehyde concentration of Robinia pseudoacacia and Amorpha fruticosa in one-year old seedlings were studied with pot experiments for the selection of tree species with strong resistance.The results showed that lead stress at higher concentration(1 000~3 000 mg·kg-1) and at lower(300~500 mg·kg-1) could improve activity,could improve SOD and POD activities,respectively.Both water and lead stresses could improve antioxidant enzyme activities of the leaves.Based on a comprehensive analysis,the resistance of A.fruticosa was better than R.pseudoacacia.Antistress abilities to Pb were in the order of A.fruticosa seedlingA.fruticosa cuttingR.pseudoacacia seedling.

【Objective】 The study was conducted with the purpose of comparing the tolerance of lead to two common drought-enduring trees in northwest China,Robinia pseudoacacia and Amorpha fruticosa,and provided a basis for phytoremediation of soil contaminated by lead in arid and semi-arid regions.【Method】 One-year old seedlings were planted in containers under 6 different lead treatments(soil Pb content 0,300,500,1 000,2 000,3 000 mg/kg,respectively) and 4 water treatments(relative soil water content 100%,80%,60%,40%,respectively).The contents of organic osmotic adjustment substances in the leaves were determined under water,Pb stress and water and Pb interaction stress.【Result】 With the increase of stress level,the changes of Pro,soluble sugar(SS) and soluble protein(SP) content of the two types of trees were complicated.The Pro content in the leaves of R.pseudoacaciawere under water stress was larger than under Pb stress,and when the relative soil water content was 40%,at the same soil Pb content level,the Pro contents in the leaves of R.pseudoacacia were significantly higher than under other relative soil water contents.Under Pb or water stress or interaction,at the same soil Pb content(except for 3 000 mg/kg),the SS contents in the leaves of R.pseudoacacia under different water stress treatments had no significant difference(P0.05).Under water or Pb stress,as the stress level increased,the SP contents in the leaves of R.pseudoacacia did not decrease,so did A.fruticosa.【Conclusion】 The contribution of Pro to raise the resistance to water was stronger than to Pb.R.pseudoacacia's accumulation ability of Pro to raise the resistance to water and Pb stress was stronger than A.fruticosa',vice vercer.A.fruticosa's production of SS and SP to raise the resistance to water and Pb stress was stronger than R.pseudoacacia'.