The Response Of Growth Physiological Characteristics And Nutrient Element To Cadmium Stress On Alnus Cremastogyne Sapling

A pot experiment was carried out with 1.5-year-old sapling of Alnus cremastogyne to explore the effect of heavy metal cadmium（Cd）stress on the saplings.Five levels(0,12.5,25,50,100 mg·kg^-1,expressed as CK,T1,T2,T3,T4,respectively)of Cd teatments were set for the test.The effects of Cd on the growth,photosynthetic physiology,resistance physiology and nutrient absorption of the saplings,and the tolerance and enrichment characteristics of saplings to cadmium were analysed.The purpose of this study is to provide reference for the site selection of A.cremastogyne plantation and find the theoretical basis for the the restoration of cadmium-contaminated.The results of the study are as follows:（1）With the aggravation of Cd stress,net growth of height,ground diameter and root activity of saplings were all decreased,and the ratio of root-crown increased.（2）With the aggravation of Cd stress,the content of hydrogen peroxide（H₂O₂）and malondialdehyde（MDA）in the leaves of saplings increased,and the activities of superoxide dismutase（SOD）,peroxidase（POD）and catalase（CAT）all increased first and then decreased.Proline（Pro）and soluble sugar（SS）contents increased gradually,while soluble protein（SP）contents increased to the maximum at T2 treatment and then decreased gradually.（3）With the aggravation of the stress degree of Cd,the content of photosynthetic pigment and the total amount of chlorophyll all showed a decreasing trend,and there was no significant change in Chla/b.Net photosynthetic rate（P_n）,stomatal conductance（G_s）and transpiration rate（T_r）decreased significantly,while intercellular carbon dioxide concentration（C_i）increased.Light saturation point（LSP）and dark respiration rate（R_d）gradually decreased,while light compensation point（LCP）gradually increased.Potential activity of PSII（F_v/F₀）and the maximal photochemical efficiency（F_v/F_m）and effective photochemical efficiency（F_v’/F_m’）,the actual light quantum efficiency（ΦPSⅡ）,electron transport rate（ETR）,coefficient of photochemical quenching（q P）were descend,while the coefficient of photochemical quenching（NPQ）gradually increased;（4）With the aggravation of Cd stress,the content of N and P in all organs of the plant（absorption root,transport root,trunk,branch and leaf）showed a decreasing trend.The content of N in trunk decreased significantly in T1 treatment,the content of N in absorbed root and leaf decreased significantly in T4 treatment,and the distribution ratio of N in the leaf increased,while that in the trunk decreased.The content of P in trunk decreased significantly in T1 treatment,while the content of P in absorption root,transport root and leaf decreased significantly in T3 treatment.The content of K in the absorption root increased first and then decreased,and the content of K in the branch had no significant change under the treatment of T2,while the content of K in the other organs showed a decreasing trend,and the distribution ratio of K in the leaf decreased,while the distribution ratio of K in the absorption root increased.（5）With the aggravation of Cd stress,the content of Cd in each organ of saplings increased gradually,and there was a significant difference between each treatment and CK.At the same level of Cd treatment,the content of Cd in absorption root and transport root was significantly higher than that in other organs.The absorption root enrichment coefficient（BC）increased first and then decreased,and it peaked at T1（1.0353）.There was no significant change in the transport root BC,and the BC of other organs all showed a decreasing trend.The transfer coefficient（TF）of ground part BC and ground part（TF）decreased significantly in T1 treatment,and the values were all less than 1.Cd stress had significant effects on the growth,photosynthetic physiology,resistance physiology,nutrient absorption and distribution of A.cremastogyne saplings,and had significant effects on T2 treatment and above.At the same time,the Cd enrichment and transfer ability of the saplings was low,and it was mainly concentrated in the root system.This indicates that the tolerance of A.cremastogyne saplings to Cd is limited,so it is not suitable to plant A.cremastogyne in the area with serious Cd pollution.But alder grows fast,has a large biomass,and can grow normally under low concentration Cd stress,so it can be used in light Cd contaminated soil remediation.