Effects Of Copper Stress On Physiology And Growth Of Cassia Occidentalis Linn.and Alleviating Effect Of Fulvic Acid

With the rapid development of industry and agriculture,soil heavy metal copper pollution is becoming more and more serious.Phytoremediation technology is an effective way to control soil heavy metal copper pollution because of its economy and environmental protection.Cassia occidentalis Linn.is an erect,less branched subshrub of Cassia.It has good ornamental value,strong drought resistance,large biomass and so on.It has a certain potential in remediation of copper contaminated soil.In this study,C.occidentalis Linn.seeds were used as experimental materials to study the germination characteristics of seeds treated with different concentrations of Cu²⁺（0,50,100,200,300,500 mg/L）and analyze the copper tolerance of seeds.Pot experiments were conducted to study the physiological and growth responses and Cu²⁺absorption characteristics of roots and leaves under different concentrations of Cu²⁺（0,50,100,150,200,250,300,500 mg/kg）,fulvic acid fertilizer（0,200,400,800,1 000 mg/kg fulvic acid fertilizer）+Cu²⁺（200 mg/kg）.The tolerance of C.occidentalis to copper pollution,the threshold of Cu²⁺content suitable for growth and the effect of fulvic acid on alleviating copper toxicity were discussed.The main results are as follows:1.Effect of copper treatment on Seed Germination of C.occidentalisCu²⁺had no significant inhibitory effect on germination rate,germination potential and germination index of C.occidentalis seeds.Cu²⁺inhibited the growth of seedlings in C.occidentalis.When the concentration of Cu²⁺was 200-500 mg/L,the elongation and fresh weight of seedlings were significantly inhibited.When Cu²⁺concentration>50 mg/L,root growth was significantly inhibited.The root tolerance index decreased with the increase of Cu²⁺concentration.2.Effects of copper treatment on physiology and growth of C.occidentalis（1）The absorption of N and P was not affected by copper stress.When the concentration of Cu²⁺was 150-250 mg/kg,the absorption of K by roots was inhibited.（2）The content of chlorophyll a and total chlorophyll decreased with the increase of stress time and concentration,while the content of chlorophyll b increased first and then decreased.The content of soluble sugar and MDA in leaves reached the highest value at cu²⁺concentration of 250 mg/kg,which was significantly higher than that of the control.The soluble protein content increased gradually with the increase of stress time,and increased first and then decreased with the increase of Cu²⁺concentration.At the later stage of stress,when Cu²⁺concentration was 250-300 mg/kg,the Fv/Fm of C.occidentalis was significantly lower than that of the control,and the electron transfer process was inhibited.（3）The aboveground and underground biomass decreased with the increase of Cu²⁺concentration;when the concentration of Cu²⁺was more than 100 mg/kg,the growth of plant height was inhibited;when the concentration of Cu²⁺was 250 mg/kg,the growth of root length was inhibited.（4）Under Cu treatment,the content of Cu²⁺in roots and leaves increased with the increase of Cu²⁺concentration in soil.The content of Cu²⁺in the root of C.occidentalis was higher than that in the leaf.3.Alleviating effect of fulvic acid on physiology and growth of C.occidentalis under copper stress（1）When the concentration of fulvic acid fertilizer was 800 mg/kg,the content of N in roots and leaves increased significantly.When the concentration of fulvic acid fertilizer was 200 mg/kg,it could promote the absorption of P and K by roots and leaves.（2）The addition of fulvic acid fertilizer could effectively increase the content of total chlorophyll and soluble protein in leaves of C.occidentalis under copper stress.When the concentration of fulvic acid fertilizer was 1 000 mg/kg,it promoted the accumulation of soluble sugar in leaves.When the concentration of fulvic acid fertilizer was 400 mg/kg,the content of MDA in leaves was significantly lower than that of the control.（3）The concentration of fulvic acid fertilizer was 400-800 mg/kg,which could improve ETR value and electron transfer rate of leaves.Under copper stress,400 mg/kg fulvic acid fertilizer could significantly increase the aboveground and underground biomass of C.occidentalis.（4）When the concentration of fulvic acid fertilizer was 200-400 mg/kg,the content of Cu in leaves and roots of C.occidentalis decreased significantly.In conclusion,it is suggested that C.occidentalis should be planted in the soil polluted by copper with Cu²⁺concentration less than 250 mg/kg.Exogenous fulvic acid treatment improved the resistance of C.occidentalis under copper stress,and 400 mg/kg fulvic acid treatment had the best effect.