| In this paper,mangrove Avicennia marina hypocotyls were cultivated in sand with 15‰seawater.Some were treated with Cr(Ⅵ) once planted,and some were treated when growing 180 days.The influence of increasing concentrations of Cr(Ⅵ) (0,1.0,2.5,5.0,7.5,10.0,15.0,20.0 mg·L-1) on hypocotyls germination and growth, photosynethesis metabolism,water metabolism,salt contents and membrance protection system were observed to inquire into the ecophysiological responses of mangrove A.gymnorrhiza to Cr phytotoxicity.The results showed:1.The germination of A.marina seedlings rose first and then dropped during the early germination period.But with the stress time extending and the stress concentrations increasing,the shooting rate and the survival rate were restrained.2.The number of roots was not influenced remarkable by Cr(Ⅵ) whenever stressed 45 days or 150 days,and there were negative effects on the length of roots, the height of stems,the size of leaves and the biomass.3.When hypocotyls were stressed 45,the water content of some parts was not obviously influenced by Cr(Ⅵ) pollution,but when cultivated for 150 days,the water content of some parts increased comparing with it cultivated for 45 days.4.When hypocotyls were stressed 45 days or 150 days,the contents of chlorophyll a,chlorophyll b,and total chlorophyll of leaves were higher than CK,while they rose first and then dropped;Treated 45 days when seedlings growthing 180 days,the contents were below CK remarkably.5.The content of soluble protein in roots and leaves were above CK when hypocotyls treated for 45 days,then dcreased when hypocotyls stressed 150 days; Stressed 45 days when seedlings growthing 180 days,the content of roots climbed with the increasing of Cr(Ⅵ) concentration,but that in leaves declined contrasting on CK..6.When hypocotyls were stressed(45 days or 150 days),the POD activity of roots rose first and then droped,but the POD activity of leaves was restrained with the stress time extending and the stress concentrations increasing;Stressed 45 days when seedlings growthing 180 days,the POD activity of roots and leaves all decreased with t increasing stress concentrations.7.When hypocotyls were stressed 45 days,the SOD activity of roots and leaves all presented rose,when stress time reached 150 days,the SOD activity of leaves was restrained when the concentration of Cr(Ⅵ) was higher then 10.0mg·L-1; Stressed 45 days when seedlings growthing 180 days,SOD activity in roots and leaves all decreased comparing with CK.8.When hypocotyls were stressed 45 days,the CAT activity of roots rose,but with the stress time extending to 150 days,it was opposite.The CAT activity of leaves was decreasing conspicuously when hypocotyls were stressed in a low concentration(≤2.5 mg·L-1) for 45 days,but with the stress time extending to 150 days,it decreased gradually;Stressed 45 days when seedlings growthing 180 days, CAT activity in roots and leaves all rose first and then droped.9.The content of AsA in roots and leaves was rising obviously whenever stressed 45 days or 150 days;Stressed 45 days when seedlings 180 days,the content of AsA in roots and also increased.10.When hypocotyls were stressed(45 days or 150 days),the MDA concentration in the roots inceased when the concentration of Cr(Ⅵ) was higher then 10.0mg·L-1,but the effect of Cr(Ⅵ) on the MDA concentration in theleaves was not abvious;Stressed 45 days when seedlings 180 days,the MDA concentration in roots and leaves all inceased slightly.11.When hypocotyls were stressed(45 days or 150 days),the tendency of Cr absorption in roots and stems of A.marina seedlings rose with the stress time extending and the stress concentrations increasing;Stressed 45 days when seedlings 180 days,the tendency of Cr absorption in roots still increased,but it in stems and leaves first rose and then dropped,and the content of Cr in roots was the highest.13.The rate of excreting salt on leaves was increasing with the Cr(Ⅵ) concentration rising.
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