采用盆栽试验研究侧柏(Platycladus orientalis)、国槐(Sophora japonica)幼苗在适度供水(田间持水量的80%)条件下对重金属铅(Pb)的阈值反应,计算在适度供水条件下铅对叶绿素含量、生物量、株高生长量、地径生长量等的毒性阈值(ECx,x=10、50).结果发现,低浓度的铅对2个树种所研究指标有促进作用,而高浓度的铅则产生抑制作用.各指标中,侧柏净光合速率EC10为262 mg/kg,即对铅的反应最为敏感;国槐对铅最敏感指标为株高,株高生长量的EC10为667 mg/kg.2个树种叶绿素含量EC50最大,侧柏、国槐分别为11352、10050 mg/kg,说明该指标对铅抗性最强;其余指标对铅耐性大小依次为生物量>株高>地径.多指标综合分析得出的阈值,EC10,国槐为1526.79 mg/kg,EC10,侧柏为1731.62 mg/kg;EC50,国槐为9104.59 mg/kg,EC50,侧柏为6414.73 mg/kg.以上结果表明,在适度供水条件下,国槐幼苗对铅胁迫更为敏感且幼苗抗铅性也强于侧柏幼苗.

This research is aimed at exploring the theory of the changes of antioxidant enzyme system activity and MDA content in one year seedlings of Platycladus orientalis treated by different levels of water(40%,60%,80%,and 100%) and lead(0,300,500,1 000,and 2 000mg·kg-1) and cultivated in pots.The results showed that POD,SOD activities of Platycladus orientalis seedlings increased at first and then decreased under interactive stress,POD,SOD activities of Platycladus orientalis seedlings treated by different levels of water reach maximum in the lead content of 500mg·kg-1,under lead less than 500mg·kg-1,POD,SOD activities of Platycladus orientalis seedlings increased in different water stress conditions,under lead more than 500mg·kg-1,POD,SOD activities of Platycladus orientalis seedlings decreased in different water stress conditions.MDA content of Platycladus orientalis seedlings increased gradually under interactive stress,under lead less than 1000mg·kg-1,MDA content of Platycladus orientalis seedlings showed no obvious change in different water stress conditions,under lead more than 1000mg·kg-1,MDA content of Platycladus orientalis seedlings increased gradually under interactive stress.Platycladus orientalis showed stronger resistance in the interaction stress of drought and lead(500mg·kg-1 lead stress and 60% water stress).

Dynamic changes of the contents of chlorophyll a/b occurring in the 1-year-old seedlings of Platycladus orientalis and Sophora japonica that were under drought(with soil relative water contents of 100%,80%,60%,and 40%,respectively) and lead stress(with the soil lead contents of 0,300,500,1 000,2 000,4 000,6 000,8 000,10 000,and 12 000 mg·kg-1,respectively) were examined.The results demonstrated that in their initial growth stages,the contents of chlorophylls decreased generally in two tree species under lead stress,however,intermediate maximum peaks appeared in the plants that were cultivated in the soils with the lead contents of 4 000 and 1 000 mg·kg-1.Moreover,the decrease amplitude of chlorophylls in S.japonica was greater than P.orientalis.Under water stress,the chlorophyll contents of S.japonica deceased,and slightly increased in P.orientalis.Under double stresses,seedlings of S.japonica died in the soils with the water content of 40% and lead content of 500 mg·kg-1,while the contents of chlorophyll a/b decreased.On the contrary,none of P.orientalis seedlings died,and the contents of chlorophyll a/b were relatively stable.The chlorophyll a/b contents of P.orientalis changed a little with the increase of Pb content,and larger than S.japonica in the soils with the relative water content of 100%,60%,and 40%.It was concluded that a self-compensation mechanism existed in two tree species under drought and lead stresses,manifested as promotion at low levels of stress and inhibition at high levels of stress.In the initial growth stages,S.japonica was more sensitive to lead than P.orientalis.Draught stress had stronger influence than lead.And P.orientalis had a stronger drought tolerance and lead resistance than S.japonica.

The objective of this experiment is to study changes in the antioxidant enzyme activity and the osmotic solute concentration in Sophora japonica L.seedlings grown under drought and heavy metal(Pb) stress.The pot study used four soil water contents(40%,60%,80%,100% of soil water holding capacity) and five Pb concentrations(0,300,500,1 000,2 000 mg·kg-1).The results showed that peroxidase(POD) and superoxide dismutase(SOD) activity initially increased and then decreased under the combined effects of drought and Pb stress.The combination of drought and Pb stress had less effect than only drought or Pb stress on POD and SOD activity in S.japonica seedlings.The combination of drought and Pb stress had either synergistic or antagonistic effects depending on the conditions.Malondialdehyde(MDA) concentrations gradually increased under the combination of drought and Pb stress,however the MDA concentrations in the drought plus Pb stress(2 000 mg·kg-1) treatments were still less than those of S.japonica seedlings grown under drought stress alone.This indicated that the interactive effects of drought and Pb caused more membrane damage to S.japonica seedlings than drought stress alone.Drought stress had little effect on soluble sugar concentrations in S.japonica seedlings;however interaction between drought and Pb stress caused soluble sugar contents to increase and then decrease.The soluble sugar concentration of S.japonica seedlings grown under 500 mg·kg-1 Pb stress and 40% of soil water holding capacity was greater than that of S.japonica seedlings in the control treatment(P0.01).In contrast,the MDA concentration of S.japonica seedlings grown under 500 mg·kg-1 Pb stress and 40% of soil water holding capacity was not significantly different from that of S.japonica seedlings in the control treatment(P0.05).Proline concentrations gradually increased over time in the 500 mg·kg-1 Pb stress plus 40% of soil water holding capacity treatment,indicating that the combination of drought and Pb stress had synergistic effects.In summary,S.japonica was resistant to the combined effects of drought(40% of soil water holding capacity) and Pb(300,500 mg·kg-1) stress.

The objective of this experiment is to study changes in the antioxidant enzyme activity and the osmotic solute concentration in Sophora japonica L.seedlings grown under drought and heavy metal(Pb) stress.The pot study used four soil water contents(40%,60%,80%,100% of soil water holding capacity) and five Pb concentrations(0,300,500,1 000,2 000 mg·kg-1).The results showed that peroxidase(POD) and superoxide dismutase(SOD) activity initially increased and then decreased under the combined effects of drought and Pb stress.The combination of drought and Pb stress had less effect than only drought or Pb stress on POD and SOD activity in S.japonica seedlings.The combination of drought and Pb stress had either synergistic or antagonistic effects depending on the conditions.Malondialdehyde(MDA) concentrations gradually increased under the combination of drought and Pb stress,however the MDA concentrations in the drought plus Pb stress(<2 000 mg·kg-1) treatments were still less than those of S.japonica seedlings grown under drought stress alone.This indicated that the interactive effects of drought and Pb caused more membrane damage to S.japonica seedlings than drought stress alone.Drought stress had little effect on soluble sugar concentrations in S.japonica seedlings;however interaction between drought and Pb stress caused soluble sugar contents to increase and then decrease.The soluble sugar concentration of S.japonica seedlings grown under 500 mg·kg-1 Pb stress and 40% of soil water holding capacity was greater than that of S.japonica seedlings in the control treatment(P<0.01).In contrast,the MDA concentration of S.japonica seedlings grown under 500 mg·kg-1 Pb stress and 40% of soil water holding capacity was not significantly different from that of S.japonica seedlings in the control treatment(P>0.05).Proline concentrations gradually increased over time in the 500 mg·kg-1 Pb stress plus 40% of soil water holding capacity treatment,indicating that the combination of drought and Pb stress had synergistic effects.In summary,S.japonica was resistant to the combined effects of drought(40% of soil water holding capacity) and Pb(300,500 mg·kg-1) stress.

A pot experiment combined with subcellular fractionation and chemical speciation sequential extraction techniques was carried out to study the lead(Pb)distribution and chemical forms in leaves of Platycladus orientalis and Sophora japonica under different Pb concentration(CK 0 mg.kg-1,A 300 mg.kg-1,B 500 mg.kg-1,C 1000 mg.kg-1,D 2000 mg.kg-1).The result showed that the biomass of Platycladus orientalis and Sophora japonica changed significantly under Pb stress.Most of Pb was distributed in the roots of two plants,and which increased with the Pb concentration in soil.A difference was observed in subcellular distribution of Pb and its chemical forms between the two plants leaves under Pb stress.Most of Pb was found to be bound to cell wall in the leaves of Platycladus orientalis and Sophora japonica for all Pb treatments,and the proportion of Pb bound to cell wall was higher in Platycladus orientalis than Sophora japonica.Less Pb was distributed in soluble fractions for both plants.The proportion of cell nucleus raised with Pb concentration increased,whereas the proportion of soluble fractions decreased.For the chemical forms,NaCl,acetic acid and HCl-extractable Pb were predominated in the leaves of the two plants,while the proportion of water and ethanol-extractable Pb were little.Pb supply increased the proportion of NaCl-extractable Pb firstly,and which reduced in leaves of Platycladus orientalis thereafter.On the contrast,the proportion of NaCl-extractable Pb in leaves of Sophora japonica increased gradually with Pb supply increased.Based on these fingings,Platycladus orientalis was likely to possess a higher tolerance to Pb than Sophora japonica did.

【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.

【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'.