Growth,Physiological Characteristics And Nutrient Absorption Of Eucalyptus Grandis Response To Cadmium Stress

Soil pollution is becoming more and more serious.In order to study the physiological characteristics of the growth of eucalyptus grandis under Cd stress and the response of nutrient elements to cadmium stress as well as the tolerance and enrichment characteristics of cadmium.To investigate the stress effect of soil cadmium（Cd）on Eucalyptus grandis saplings,which ia a common species in Sichuan Province,a pot experiment of9-month-old E.grandis saplings at five different Cd treatment level（0,12.5,25,50,100mg/kg）was conducted.Moreover,the sapling growth physiological characteristics,the response of the sapling nutrient absorption under cadmium stress,and the tolerance and enrichment characteristics of the sapling to cadmium stress were analyzed.The study objective is to provide a theoretical basis for the site selection of E.grandis plantation,and the restoration of cadmium contaminated soil.The results are as follows:（1）With the increase of Cd treatment concentration,the height,the net growth of the ground diameter,the aboveground biomass and the root activity of the saplings decreased,but the underground biomass increased with the increase of Cd treatment concentration.As a result,the significant change in total biomass was not observed.（2）With the increase of Cd treatment concentration,the photosynthetic pigment content,the total amount of chlorophyll,the net photosynthetic rate（P_n）,the stomatal conductance（G_s）,the transpiration rate（T_r）,the light saturation point（LSP）,the dark respiration rate（R_d）,the initial fluorescence（F₀）,the maximum fluorescence（F_m）,the maximum photochemical efficiency（F_v/F_m）,the PSII potential activity（F_v/F₀）,the actual quantum efficiency（ΦPSII）,the electron transfer rate（ETR）,and the photochemical reaction energy（P）ratio of the saplings decreased.However,the intercellular carbon dioxide concentration（C_i）,the light compensation point（LCP）,the proportion of non chemical reaction energy（Ex）of the leaves,and the heat dissipation energy（D）of the saplings raised with the increase of Cd concentration.The significant changes in the photochemical quenching coefficient（q P）and the non photochemical quenching coefficient（NPQ）were not found.（3）Cd stress has affected the system of the antioxidant protection and the osmotic adjuestment function of E.grandis.With the increase of Cd treatment concentration,the contents of the hydrogen peroxide（H₂O₂）and the malondialdehyde（MDA）,the proline（pro）and the soluble sugar（SS）increased,the activity of the superoxide dismutase（SOD）,the peroxidase（POD）,and the catalase（CAT）and the content of soluble protein（SP）raised at first,then decreased.（4）With the increase of Cd treatment concentration,the content of nutrient elements（N,P,K）decreased.The siginificant changes in the distribution pattern of nutrient elements in each organ were observed,and the distribution proportion of N,K in the root increased significantly.（5）With the increase of Cd treatment concentration,the content of Cd in each organ of the saplings increased.Under the same treatment level,the order of Cd content in each organ was absorption root>transport root>trunk>branch>leaf.The enrichment coefficients（BF）of the absorption root and the transport root increased,and those of trunk,branch and leaf decreased with the increase of Cd treatment concentration.However,the transfer coefficient（TF）decreased significantly with the increase of Cd treatment concentration.The BF and TF of all organs were less than 1.In conclusion,Cd stress significantly affected the growth of the E.grandis aboveground,the processes of photosynthetic,and the processes of resistance physiological of the plant.The underground biomass raised with the increase of Cd treatment concentration,and the siginificant change in total biomass of the plant was not observed,indicating that E.grandis saplings were more tolerant to Cd.Although the absorption and distribution of nutrient elements of E.grandis is greatly limited,the concentration of Cd fixed in stem（trunk and branch）increased with the increase of treatment.Due to the rapid growth and much biomass of E.grandis,planting E.grandis in cadmium polluted areas could be considered to limit the penetration of cadmium into groundwater and repair the polluted soil.