The Response Of Growth Physiological Characteristics And Nutrient Element Absorption To Cadmium Stress On Phoebe Zhennan Sapling And Its Cadmium Accumulation Characteristics

Because cadmium pollution is an irreversible accumulation process,combined with strong biological fluidity,it is easily absorbed by plants and transported to tissues and organs.When the accumulation reaches a certain level,it will not only affect the growth of plants.Development and product quality,and its edible parts are also very vulnerable to human health through the food chain.Phobe Zhennan is a rare and endemic tree species in China.It is mainly distributed in the Sichuan Basin,northern Guizhou and Hubei.It grows in the acidity of humus and acidic to neutral soil.Mostly tall and evergreen trees,long life cycle,fast growth in young age,strong adaptability,especially economic value is particularly prominen.A pot experiment was carried out with 3.5-year-old sapling of P.zhennan to explore the effect of heavy metal cadmium?Cd?stress on the saplings.Six levels of Cd teatments were set?0,10,20,30,40,50 mg/kg?for the test.The effects of Cd on the growth,photosynthetic physiology,resistance physiology and nutrient absorption of the saplings of P.zhennan,and the tolerance and enrichment characteristics of P.zhennan,saplings to cadmium were analysed.The purpose of this study is to provide reference for the site selection of P.zhennan 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,the wilting leaf edge of P.zhennan become wider and the wilting area increased gradually,and the development time of the top buds was delayed.The net growth of plant height,net growth of stem ground diameter,length of buds,length of spring shoots,biomass,root activity showed a downward trend,and the downward trend was more obvious when the Cd addition level exceeded the T2 treatment.?2?With the increase of Cd stress,the total amount of chlorophyll and total content of chlorophyll decreased.Chla/b increased gradually;net photosynthetic rate?Pn?,The stomatal conductance?Gs?and transpiration rate?Tr?decreased significantly with the increase of Cd stress,and the concentration of intercellular carbon dioxide?Ci?increased;the light saturation point?LSP?and the dark respiration rate?Rd?both showed a downward trend,and the light compensation point?LCP?gradually increased;initial fluorescence?Fo?,maximum fluorescence?Fm?,actual photon efficiency??PSII?,electron transport rate?ETR?,photochemical quenching coefficient?qP?showed a downward trend,non-photochemical quenching coefficient?NPQ?gradually increased,the maximum photochemical efficiency?Fv/Fm?,PSII potential activity?Fv/Fo?did not change significantly at T1-T4,and significant increase appeared at T5;indicating that the dissipation of excess light energy by the saplings.The heat dissipation pathway is dominant,but at T3-T5,the dissipation of non-chemical reaction energy?Ex?is increased,and the heat dissipation energy?D?and photochemical reaction energy?P?are reduced.?3?With the increase of Cd content,the content of H2O2 and MDA increased,SOD,POD and CAT activities increased first and then decreased;proline?Pro?and soluble sugar?SS?increased gradually,soluble protein?SP?increased to the maximum when the Cd content was 30 mg/kg,but decreased afterwards.There was no significant change in the content of auxin?IAA?and cytokinin?CTK?in the spring germination of the plants,but the content ratio of IAA/CTK was significantly higher than CK at T5;the content of gibberellin?GA₃?showed a downward trend.?4?At the level of tissues and organs,with the increase of Cd stress,the nitrogen?N?content showed a downward trend in the organs except for the significant changes in the transport roots,while the distribution ratio in the leaves,transport roots and absorbed roots increased.In the branches and trunks,it showed a decreasing trend;The phosphor?P?content was significantly increased in the branches and trunks only at T5 treatment level and decreased in the other organs,while the distribution ratio in leaves and roots increased,in the branches and transport roots;And there was no significant change in the trunk;The kalium?K?content showed a downward trend in all organs,and each treatment was significantly different from CK.The distribution ratio of K in the absorbed root increased,and the changes in other organs were not obvious.?5?The content of Cd in the organs of P.zhennan increased gradually,and each treatment was significantly different from CK.At the same Cd treatment level,the Cd cotent showed the order as:roots>trunk>transport root>leaf>branch.The Cd enrichment coefficient?BC?of absorption root and leaf showed an increasing trend,there was no significant change in trunk.The decreasing trend of BC was showed in transport root and branch.And the Cd transfer coefficient?TF?decreased significantly at T1.And the BC and TF of each organ were lower than 1.In general,Cd stress interfered with the photosynthetic and resistance physiological processes of P.zhennan sapling,and its growth was significantly inhibited.When the amount of Cd was at T2 treament and above,the effect was particularly prominent.The tolerance of P.zhennan to Cd is weaker;and the absorption,transport and distribution of nutrients in P.zhennan sapling are more restricted,the ability to transfer Cd is gradually decreased,and a large amount of Cd is concentrated in the roots of plants,so it is not suitable for the areas with serious Cd pollution to develop P.zhennan plantation.And it is not suitable to use P.zhennan for soil remediation on Cd polluted site.