The Regulation Of The Tolerance Of Poplar And The Secondary Growth Of Nitrogen And Silicon Under Cadmium Stress

Cadmium is one of the heavy metal pollution elements which have great harm to the environment and human health.The treatment of cadmium pollution environment has become an urgent problem to be solved.Phytoremediation is the preferred method for controlling heavy metal pollution due to heavy metal accumulation and no secondary pollution of environment.Poplar is one of the best candidate plants for phytoremediation because of its strong roots,fast growth,large biomass,high accumulation of heavy metals and not entering the food chain.Poplar of secondary growth is the basis of its wood formation,nutrient elements affect plant growth and timber quality,including a lack of nitrogen and phosphorus elements not only affect the photosynthesis of plants,and the biological macromolecules such as protein,nucleic acids and lipids composition elements;Silicon is not only beneficial to the normal growth of plants,but also improves the resistance of plants to adversity.Therefore,it is of theoretical significance to study the growth characteristics of poplar secondary growth and the regulation mechanism of nitrogen and silicon under cadmium stress,and to improve the quality of poplar trees in the soil of cadmium pollution.This research use Populus 97 as the research object sand culture experiment was carried out,based on the related determination of physiological index,physiological response of poplar under cadmium stress tolerance and growth effect was summarized.The main conclusions of the study are as follows:(1)the cadmium treatment reduces the photosynthesis of plants,and the water use efficiency decreases the leaf area and total dry weight,which inhibits the normal growth of the plants.The low nitrogen deficiency treatment also significantly inhibited the growth of plants,especially the effect of low nitrogen treatment on photosynthesis and growth of plants.(2)under low nitrogen treatment,cadmium ions were mainly concentrated in the root system of poplar trees,and the above-ground parts were relatively few.After the normal application of nitrogen,the absorption of cadmium into the ground was increased,and the biological repair efficiency of cadmium pollution was improved.The high concentration of cadmium ions in the leaves and roots of low nitrogen resulted in abnormal structure of leaf and root cells,which had adverse effects on plants.Normal nitrogen supply increases cadmium ion content in cortical cells,which may be the adaptive response of plants to reduce toxicity.No cadmium stress and the lack of nitrogen reduces the length of the rays,the width of the xylem,and the cell lines are loose.Under the treatment of cadmium,applying nitrogen the radiation length,xylem width,xylem cell thickness increased and the cells were closely arranged,indicating that nitrogen had a great influence on the secondary growth of plant.(3)compared with normal for nitrogen,the lower part of the activity of antioxidant enzymes was inhibited under the condition of nitrogen,and reduce the endogenous phytohormones ABA,JA,SA,the content of IAA and decreases the poplar resistance to cadmium stress.(4)the content of cadmium in the root system decreased significantly after silicon treatment,and the tolerance of root system to cadmium stress was improved.Silicon after the cadmium content in leaf organs increased significantly,mainly in the veins,cadmium more focused on stem phloem cells clearance,may be si reduces the cadmium poisoning plant cells,relieve the inhibition of cadmium on plant growth.Under cadmium stress,the xylem became wider,the cell wall thickened,the cells were arranged closely,the mechanical strength of the plant were increased,and the quality of wood was improved.(5)under cadmium stress,the silicon increased parts antioxidant enzyme activity and increased the endogenous hormones(such as ABA,JA,SA,IAA)content,research results show that applying silicon fertilizer enhanced the poplar resistance to cadmium stress.