Effects Of Lanthanum And Cerium On The Growth Of Paramichelia Baillonii Seedlings

Paramichelia baillonii is a tall evergreen broad-leaved tree belonging to the genus Paramichelia of Magnoliaceae.It is a rare and endangered plant of the second class in China.The small population base,low self-reproductive ability and relatively long cycle of Paramichelia baillonii are one of the factors restricting the protection and development of Paramichelia baillonii.Therefore,it is of great significance to optimize the seedling-raising technology of Paramichelia baillonii.Adding rare earth elements as supplementary nutrients or beneficial elements is one of the effective ways to improve the quality of seedlings.In this paper,the seedlings of Paramichelia baillonii were used as research materials.Two rare earth elements(Lanthanum and Cerium)were selected in a completely randomized block design.Four different concentrations of Lanthanum and Cerium(LI,C1:10mg/L,L2,C2:20mg/L,L3,C3:40mg/L,L4,C4:80mg/L)were used,of which L and C represent Lanthanum and Cerium respectively.To study the effects of Lanthanum and Cerium on the seedlings growth of Paramichelia baillonii,and to evaluate the effects ofLanthanum and Cerium on the seedlings growth of Paramichelia baillonii,and to provide new ideas and ways for the seedlings cultivation.The main results are as follows:1.Low concentration of Lanthanum and Cerium(0-40 mg/L)was beneficial to increase seedling height and ground diameter,and to promote the biomass accumulation of seedling organs.Among them,the concentration of Lanthanum and Cerium(20 mg/L)was the best,followed by the concentration of 10 mg/L,which had a greater promotion effect on seedling growth.At the same treatment concentration,Lanthanum promoted seedling growth more effectively than Cerium.When the concentration of rare earth Lanthanum and Cerium is too high(>80mg/L),they can inhibit or even poison.The correlation between seedling growth,biomass and IAA content and other endogenous hormones was strong,and there was also a significant correlation with nutrient content.2.Rare earth Lanthanum and Cerium also showed a dose effect of low promotion and high inhibition on root growth of Paramichelia baillonii seedlings.20 mg/L concentration of Lanthanum and Cerium could maximize root length,total root surface area and root activity,and the root system of Paramichelia baillonii seedlings had a stronger response to Lanthanum.Rare earth treatment at 80 mg/L concentration could produce toxic effects on the root growth of Paramichelia baillonii seedlings.3.Low concentration of Lanthanum and Cerium(0-40mg/L)had a positive effect on the physiological indexes of the seedlings,and chlorophyll content,SOD and CAT activities were increased.With the increase of rare earth element concentration,MDA content in seedlings of Paramichelia baillonii decreased first and then increased,and POD activity decreased first,then increased and then decreased.The main peak values of each index appeared in the treatment group of 20 mg/L concentration,and the response order of protective enzyme activity was SOD>CAT>POD.High concentration of Lanthanum and Cerium(40-80 mg/L)could inhibit the physiological indexes of the seedlings.The results of correlation analysis showed that the growth,biomass and physiological indexes of seedlings of Paramichelia baillonii were significantly correlated with Lanthanum and Cerium treatments,and there was a strong positive correlation between plant growth,biomass and chlorophyll a content,SOD activity4.Under low concentration(0-40 mg/L)Lanthanum and Cerium,IAA/ZT,IAA/ABA and(IAA+GA3+ZT)/ABA all showed an upward trend.The increase of endogenous hormone level and the balance between hormones promoted plant growth.The endogenous hormones of seedlings showed negative response at high concentration(40-80 mg/L)5.Low concentration of Lanthanum and Cerium(0-40 mg/L)increased the content of total nitrogen and total phosphorus in the underground part of the seedling,and enhanced the ability of seedling to absorb nitrogen more effectively than that of the aboveground part.Lanthanum and Ce at 20 mg/L concentration were the most suitable treatments for nutrient uptake by seedlings of Paramichelia baillonii,followed by 10 mg/L and 40 mg/L,and 80 mg/L inhibited the ability of seedlings to absorb nitrogen and phosphorus.In conclusion,the morphology,physiology and nutrients of seedlings treated with 0-40 mg/L of Lanthanum and Cerium were better than those of seedlings untreated with rare earth.When the concentration of Lanthanum and Cerium was 20 mg/L,the comprehensive performance of seedlings was the best,followed by 10 mg/L,and the promotion effect of Lanthanum on seedlings was stronger than that of Cerium.