The Stress Effect Of Cadmium On Quercus Mongolica Seedlings And Its Alleviation By Sulfur

Cadmium(Cd),is one of the sources of heavy metal pollution,has many negative effects on plant growth and development.Quercus mongolica,as landscaping tree,is getting popular.Its Cd tolerance is worth studying under Cd pollution environment.Exogenous S can alleviate the toxic effects of heavy metals on plants by activating the defense mechanism of plants against heavy metals.Therefore,this experiment took Quercus mongolica as the research object,and studied the growth and physiological conditions of Quercus mongolica under different cadmium concentrations and the mitigation effect of different sulfur concentration treatments on Quercus mongolica seedlings under Cd stress.The research results are as follows:1.The damaging effect of increasing Cd concentration on the growth of Quercus mongolica seedlings showed a trend of first decreasing and then increasing.When the Cd treatment concentration is 25 mg/L,the plant height,stem growth,biomass,and water content were all higher than those under normal growth;and its net photosynthetic rate and chlorophyll content also significantly increased;The contents of MDA,osmotic adjustment substances and SOD and POD activities in the seedlings of Quercus mongolica decreased,indicating that low concentrations of Cd could induce the seedlings of Quercus mongolica and stimulate their growth.With the increase of Cd concentration,the plant height,stem growth,biomass,water content and chlorophyll content of Quercus mongolica seedlings under the treatment of 100 mg/L Cd decreased significantly,and the net photosynthetic rate also decreased significantly.The MDA content and cell membrane permeability,soluble sugar,soluble protein,free proline content and protective enzyme activity increased significantly,indicating that Quercus mongolica has a certain resistance to Cd stress lower than 100 mg/L.When the Cd concentration reached 150 mg/L,the edge of the seedling leaves withered and turned yellow.2.Compared to the seedlings of Quercus mongolica under the treatment with Cd alone,the seedlings of Quercus mongolica under the S treatment had different degrees of alleviation.The plant height,stem growth and biomass,water content,net photosynthetic rate,and chlorophyll content of Quercus mongolica seedlings in the treatment groups with exogenous S concentrations of 100 and 200 mg/L increased significantly.The MDA content decreased.The cell membrane permeability,soluble sugar,soluble protein,free proline contents and protective enzyme activity all increased,and reached the maximum under 200 mg/L treatment,indicating that the addition of exogenous S alleviated the physiological damage caused byheavy metal Cd to the seedlings of Quercus mongolica,and 200 mg/L was the best concentration to mitigate Cd stress of Quercus mongolica.When the S concentration increased to 400 mg/L,the seedling height,root collar diameter growth,net photosynthetic rate and chlorophyll content decreased again,but the change was not significantly different from that under 200 mg/L treatment.The MDA content increased.The content of soluble sugar,soluble protein,and free proline all began to decrease,but compared with the seedlings of Quercus mongolica under normal growth conditions,their overall content was higher.