Responses Of Growth And Physiological Characteristics Of Spartina Alterniflora To NaCl,CdCl₂ And Their Interaction Stress

In recent years,the research on the remediation of heavy metal pollution in coastal wetlands has become a hotspot.S.alterniflora has a strong salt tolerance as a salt marsh plant,and its tolerance to heavy metals under salt stress has also been widely concerned.In order to understand the law of S.alterniflora tolerance to different concentrations of salt and heavy metals.In this paper,the seedlings of S.alterniflora in the coastal waters of Mindong were collected,and the experiments of NaCl,CdCl₂ and its interaction stress were carried out for 6 months in pots.The first measurement was made when one of the groups was dead for the first time（4 months later）,the second measure was after 6 months of full stress expires.The growth indexes,osmotic adjustment substances and antioxidant enzymes in leaves and roots were analyzed.The growth and physiological responses of S.alterniflora under the disturbance source（NaCl,CdCl₂）were investigated.The threshold of interaction between NaCl and CdCl₂ was determined.It is helpful to discover the changes of S.alterniflora in different Cd concentrations from the aspects of growth and physiological characteristics,which can provide data support for the anti-salt and anti-heavy metal work of S.alterniflora in coastal wetlands..The results reveal that:（1）Leaves change after 4 months of interaction stress:When CdCl₂ concentration at 0.2-0.8 mmol·L^-1,S.alterniflora salt tolerant threshold is 500 mmol·L^-1.The study found that high salt and high heavy metal stress will accelerate the growth of S.alterniflora,So as to shorten the growth cycle,premature death.According to data statistics:The coefficient of variation of the three major osmotic regulators in the leaves is very small.That is,the degree of dispersion between the data is roughly the same.The results showed that proline,soluble sugar and soluble protein in regulation of cell osmotic pressure was consistent with NaCl,CdCl₂ and its Interactive stress.Leaf soluble protein content under moderate NaCl stress(300-500 mmol·L^-1)will reach the maximum.The highest activity of SOD appeared in the treated group with low concentration of stress(0-100 mmol·L^-1NaCl),Indicating that SOD before the other two enzymes（POD,CAT）appeared in the anti-oxidation process of S.alterniflora.The maximum activity of POD appeared in NaCl concentration at 500-900 mmol·L^-1.CdCl₂ under single factor stress,CAT activity is large,which indicates that the interaction between NaCl and CdCl₂ will inhibit the CAT activity of S.alterniflora leaves.（2）Leaves change after 6 months of interaction stress:With the prolongation of stress time,the difference of stress concentration had less effect on the photosynthesis of S.alterniflora.In the early stage of S.alterniflora（1-4 months）is a greater degree of inhibition of light energy conversion.However,the latter（5-6 months）was changed to inhibit the collection of light energy.After 6 months,the cell membrane extravasation rate and MDA content of S.alterniflora showed a consistent fluctuation trend of NaCl stress gradient in different concentrations of CdCl₂.The coefficient of variation of MDA content in S.alterniflora leaves increased after 6 months of stress.Indicating that the degree of data discrepancy is large.The results showed that the content of MDA in the leaves of S.alterniflora was more intense after the stress（5,6 months later）.The fluctuation of chlorophyll a content was less than that of chlorophyll b after 6 months of stress.Indicating that the stress mainly inhibited the chlorophyll b.The cell extracellular permeability,MDA,proline content and POD activity increased with the increase of NaCl concentration after 6 months of stress.Indicating that the addition of NaCl did not alleviate the stress of CdCl₂ on S.alterniflora and was not related to the stress cycle.（3）Roots change after 6 months of interaction stress:S.alterniflora leaves and root cell membrane extravasation rate are more sensitive to MDA content.Root cell membrane extravasation rate is more intense than leaf,but the leaf MDA content changes more strongly than the root changes.The changes of proline content in leaves and roots of S.alterniflora were consistent with the increase of NaCl concentration gradient.he changes of soluble protein in leaves and roots of S.alterniflora were opposite,showing the difference between leaf and root soluble protein in resistance to stress.Root POD plays a positive role in antioxidant activity,and the POD activity of leaves and roots of S.alterniflora increased with the increase of salt concentration.Indicating that high concentrations of stress do not destroy POD in the formation of antioxidant function in S.alterniflora.0.4 mmol · L^-1CdC12 concentration was the critical concentration of POD activity in the roots of S.alterniflora under CdCl₂ single factor.After this threshold,the POD activity of the roots increased significantly（P<0.01）.The CAT activities of leaf and root of S.alterniflora decreased with the increase of salt stress（P<0.05）,because the high concentration of salt in the late stage of stress can destroy the antioxidant system in the leaves.This is similar to the change of soluble sugar in the leaves after 4 months of stress.（4）The results showed that there was a significant positive correlation between leaf cell extravasation and MDA content after 4 months of stress.The roots of S.alterniflora after 6 months of stress also had the same characteristics,while the leaves after 6 months did not have significant positive correlation.The relationship between leaf cell membrane extravasation rate and MDA content was disturbed by the prolongation of stress.There was no significant correlation between osmotic regulation and antioxidant enzymes in S.alterniflora（P>0.05）.Compared with each leaf measurement index,the correlation between the root measurement index is stronger.There was a significant positive correlation between cell membrane extravasation rate,proline content,soluble sugar content and SOD activity in S.alterniflora roots（P<0.05）.The results showed that with the destruction of cytoplasmic membrane,the content of proline,soluble sugar and SOD activity were significantly increased to resist stress.