| Cassia corymbosa is a kind of semi-evergreen shrub that belongs to Caesalpiniaceae,which is widely used in landscape garden because of it’s viewing period and landscape effect.In order to apply C.corymbosa better,confirm the tolerance and resistance of C.corymbosa to Pb,Cd and Zn stress,the resistance and physiological response mechanism of C.corymbosa under different concentrations of Pb,Cd and Zn stress was studied.The results are as follows:(1)Under the Pb concentration of 250 mg/kg,the growth of C.corymbosa was not significantly affected after 60 days.The increase of Fo,Fv/Fm,ETR and growth was not significantly less than group CK,the soluble sugar content increased,indicating the light energy transfer and transformation efficiency of C corymbosa were not significantly inhibited and osmotic adjustment ability of plant cells increased.Under the Pb concentration of 350 mg/kg,the growth of C.corymbosa was slightly inhibited and chlorophyll content,photosynthetic rate,MDA content,ETR decreased slightly,soluble sugar content and POD activity increased,indicating that the light energy capture and conversion efficiency of C.corymbosa was slightly inhibited,but C.corymbosa can reduce the toxic effects of Pb by increasing the osmotic potential and producing protective enzymes.Under the Pb concentration of 500mg/kg and 750mg/kg,the growth of C.corymbosa is significantly inhibited,ETR,net photosynthetic rate,respiration rate,soluble sugar content,and growth decreased greatly,the POD activity and MDA content increased greatly,indicating that light energy capture and transmission efficiency of C.corymbosa is obviously inhibited,and energy supplied to life activities of C.corymbosa is reducing.In summary,C.corymbosa has certain resistance under the stress of slight Pb concentration(≤350mg/kg),the growth of C.corymbosa is weaker than group CK,but C.corymbosacan reduce the damage by their regulation and recovery ability.Under the stress of higher Pb concentration(≥500mg/kg),the health of C.corymbosa is significantly inhibited,but it is not fatal.(2)Under the Cd concentration of 25mg/kg,the growth of C.corymbosa was not significantly affected after 60 days,Fo and growth were not significantly different from group CK,and the soluble sugar content increased,indicating that the light energy transmission of C.corymbosa is not significantly inhibited,although the net photosynthetic rate of the plant has decreased in some extent,the increase of osmotic adjustment ability can compensate the energy consumption and metabolic activity caused by Cd.Under the Cd concentration of 50mg/kg,the growth of C.corymbosa was slightly inhibited,showing a slight decrease in chlorophyll content,soluble protein content,plant growth and ETR,indicating light energy capture and transformation efficiency of C.corymbosa is slightly inhibited,but plants can reduce the toxicity by increasing the osmotic potential and generating protective enzymes.Under the Cd concentration of 100mg/kg and 200mg/kg,the growth of C.corymbosa is affected,ETR,net photosynthetic rate,respiration rate,soluble sugar content and plant growth decreased greatly,POD activity and MDA content increased greatly,indicating light capture and transfer efficiency of C.corymbosa significantly suppressed,and energy supplied to the normal life activitiesis reduced.In summary,under low concentration(<25mg/kg)of Cd treatment,C.corymbosa had certain tolerance to Cd stress,the plant growth of C.corymbosa was slightly weaker than group CK,but it was not significantly inhibited.Under high concentration(≥100mg/kg)of Cd stress,the physiological function of C.corymbosa was greatly damaged and plant growth was significantly inhibited,but it was not fatal.(3)Under the Zn concentration of 500mg/kg,the growth of C.corymbosa was promoted after 60 days,the chlorophyll content,net photosynthetic rate,ETR and respiration rate were significantly improved than group CK,increasement in soluble sugar content indicates that low concentrations of Zn promotes the growth of C.corymbosa.Under the Zn concentration of 750mg/kg,the growth of C.corymbosa was slightly inhibited.Chlorophyll content,soluble protein content,plant growth and ETR decreased slightly after 60 days,indicating the light energy capture and transformation efficiency of C.corymbosa is slightly inhibited,but C.corymbosa can reduce the toxic effect by increasing osmotic potential and generating protective enzymes.Under the Zn concentration of 1000mg/kg and 1500mg/kg,the growth of C.corymbosa was significantly inhibited,showing a significant decrease in ETR,photosynthetic rate,respiration rate,soluble sugar content and plant growth and large increase in POD activity and MDA content,indicating the light ability to capture and deliver of C.corymbosa is significantly inhibited,while the energy substances that supply life activities of plants are reduced.In summary,low concentration of Zn(≤500mg/kg)can promote the growth of C.corymbosa.Under the 700～1000mg/k:g concentration of Zn is,the growth of C corymbosa will be inhibited,but the plant can alleviate the toxic effect by its own defense mechanism.When the soil concentration exceeds 1500mg/kg,the growth of C.corymbosa is significantly inhibited,and the plant even can’t survive. |
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