| Tabebuia chrysantha is a common landscape tree species in South China.Originated in South America,it is now widely cultivated in all corners of tropical and subtropical cities in China,and playing an active role in the construction of urban landscape.Lead is one kind of common heavy metal pollution.Strengthening the research on the Lead Stress for Tabebuia chrysantha is of great significance to explore its suitable growth environment and expanding the introduction scope of lead polluted land.In this experiment,Saplings of Tabebuia chrysantha were used as materials for pot experiment.Four designs of soil exogenous lead concentration(CK,1000 mg·kg-1,3000 mg·kg-1,5000 mg·kg-1)were carried out in the form of controlling soil water content(60%of soil field capacity).The resistance of Tabebuia chrysantha to heavy metal lead was analyzed by measuring its growth,physiological.The results show that:(1)The growth characteristics of Tabebuia chrysanthasaplings were affected by different concentrations of lead in soil.With the increasing concentration of exogenous lead in soil,the plant height,ground diameter relative and biomass of Tabebuia chrysantha saplings showed a trend of first increasing and then decreasing,and the growth trend was the best when 1000mg·kg-1 Pb was applied;the root-shoot ratio and height-diameter ratio basically showed a steady upward trend;Total root length showed a trend of decreasing,increasing and inhibiting with the increasing concentration of exogenous lead in soil.Total root volume and number of root tips were inhibited continuously.(2)The physiological characteristics of Tabebuia chrysanthasaplings were affected by different concentrations of exogenous lead in soil.The chlorophyll content of Tabebuia chrysanthasaplings showed a downward trend with the increasing concentration of exogenous lead in soil,while soluble sugar,soluble protein,superoxide dismutase(SOD)and peroxidase(POD)showed a trend of low concentration for promotion but high for suppression,and reached the maximum when 1000mg.kg-1 Pb was applied.Free proline and Malondialdehyde(MDA)showed a steady upward trend;With the increase of exogenous lead concentration in soil,the intercellular CO2 concentration(Ci)of Tabebuia chrysanthasaplings showed a steady downward trend,while the net photosynthetic rate(Pn),stomatal conductance(Gs)and transpiration rate(Tr)increased first and then decreased:The Fv/FO and Fv/Fm values of Tabebuia chrysanthasaplings also increased with the increase of soil exogenous lead concentration,showing a trend of first increasing and then decreasing.(3)The results of the determination of lead content in Tabebuia chrysanthasaplings showed that the lead content in the underground and upper parts of Tabebuia chrysanthasaplings increased significantly with the increasing concentration of exogenous lead in soil.Basing on the indicators of growth,physiological and photosynthetic characteristics of Tabebuia chrysanthasaplings under different concentrations of lead in soil and using the subordinate function analysis,it can be concluded that the most ideal treatment group is 1000mg·kg-1 Pb,and the least ideal treatment group is 5000mg·kg-1 Pb.The results showed that 1000mg·kg-1 Pb of lead promoted the growth of Suzuki chinensis seedlings,but 5000mg·kg-1 Pb of lead inhibited the growth of Tabebuia chrysantha seedlings. |
