| Magnoliaceae glanca Blume is a Magnoliaceae Magnolia plant,which belongs to one of the precious tree species in China.Because of its straight trunk,beautiful tree posture,gorgeous flowers and fruits,fast-growing and other characteristics,it has great ornamental value and economic value.Aluminum toxicity is the main factor limiting plant growth,crop production and forest degradation in acidic soils.Citric acid can chelate with aluminium to synthesize non-toxic compounds,which can greatly reduce or eliminate aluminium toxicity to plants.Therefore,studying the mitigation effect of citric acid on aluminium toxicity of Magnoliaceae glanca Blume seedlings is conducive to improving the quality of seedlings,protecting germplasm resources of rare tree species and so on.It can provide basic data reference for Magnoliaceae tree in aluminum stress research.In this study,Magnoliaceae glanca Blume seedlings were treated with aluminium sulfate and citric acid.Four gradients of aluminium were 0 mg/L,60 mg/L(Al),120 mg/L(A2),150 mg/L(A3).On the basis of each aluminium treatment,citric acid was added.Four gradients were set to be 0 mmol/L,5 mmol/L(N1),10 mmol/L(N2),15 mmol/L(N3),and treatment without aluminium and citric acid as blank control group(CK).The aim of this study was to analyze the effects of aluminium and citric acid on growth physiology and nutrient distribution of Magnoliaceae glanca Blume,to study the tolerance range of Magnoliaceae glanca Blume to aluminium stress and to explore the detoxification effect of citric acid at different concentrations on Magnoliaceae glanca Blume.The main results are as follows:1.Aluminum and citric acid promoted the growth of Magnoliaceae glanca Blume seedlings at low concentration while inhibited at high concentration.A2N3 treatment was the best for the growth of seedling height;A3N3 treatment was the best for the growth of seedling ground diameter;A1N1 treatment was the best way to increase the leaf area of Magnoliaceae glanca Blume seedlings,and A1N3 treatment was the biggest one in the leaf shape index of Magnoliaceae glanca Blume seedlings.Biomass,root-shoot ratio and water content were all inhibited by low concentration and high concentration under aluminum treatment.The treatment of A3N2 had the greatest effect on root biomass,stem biomass and root-shoot ratio,and the treatment of A1N2 had the greatest effect on leaf biomass of Magnoliaceae glanca Blume seedlings.2.A1N3 treatment was the most beneficial to increase chlorophyll a,chlorophyll b content and total chlorophyll content;A1N2 treatment was the most beneficial to increase net photosynthetic rate(Pn)and stomatal conductance(Gs),and the highest and lowest intercellular carbon dioxide concentration(Ci)were A2N1 and A3N2,respectively.A1N2 treatment was conducive to increase leaf transpiration rate(Tr)of Magnoliaceae glanca Blume seedlings.A3N2 treatment was the best way to improve water use efficiency of Magnoliaceae glanca Blume seedlings.3.A3 treatment could significantly increase the content of malondialdehyde(MDA)in the leaves of Magnoliaceae glanca Blume seedlings;the most significant effects on soluble sugar and soluble protein were A3N3 and A2N3 treatments;The activity of polyphenol oxidase(PPO)in the leaves of Magnoliaceae glanca Blume seedlings is the highest with A1;and the superoxide in the leaves of Magnoliaceae glanca Blume seedlings treated with A3N3 was 129.8%higher than CK control.Dismutase(SOD)activity and peroxidase(POD)activity were the highest.Catalase(CAT)activity in leaves of Magnoliaceae glanca Blume seedlings treated with A1 and A2 was significantly increased,187.3%and 278.7%higher than CK,respectively.Among them,A3N1 treatment had the most promotive effect on catalase(CAT)activity in leaves of Magnoliaceae glanca Blume seedlings.4.A3N3 treatment was beneficial to the absorption of total N by the roots,N3 treatment was beneficial to the increase of total N content in the stems,while N1 treatment was the best for the promotion of total N content in the leaves;N1,N3 and A2N3 treatment were the best for the promotion of total P content in the roots,stems and leaves;A3N3,N3 and A1N1 were the best for the promotion of total K content in the roots,stems and leaves of Magnoliaceae glanca Blume seedlings,respectively.The results showed that A1N2 treatment was beneficial to the absorption of total Ca by the roots,while A2N3 and A2N3 treatment were beneficial to the increase of total Ca content in the stems and leaves of Magnoliaceae glanca Blume seedlings;N2,N1 and A2N3 treatment were the best to promote the total Mg content in the roots,stems and leaves of Magnoliaceae glanca Blume seedlings;A1N3,A1N2 and A1N3 treatment were the best to reduce the A1 content in the roots,stems and leaves of Magnoliaceae glanca Blume seedlings.It was beneficial to the absorption of total zinc by the root of Magnoliaceae glanca Blume seedling,while N3 treatment had the best promotion effect on the total zinc content in the stem and leaf of Magnoliaceae glanca Blume seedling;A2N3 treatment was beneficial to the increase of total Fe content in the root and stem of Magnoliaceae glanca Blume seedling,and N3 treatment had the best promotion effect on the total Fe content in the leaves of Magnoliaceae glanca Blume seedling.5.Net photosynthetic rate(Pn),soluble sugar,soluble protein,total N,total Ca and total Fe were the most favorable factors for the growth of seedling height of Magnoliaceae glanca Blume,and ground diameter increment was positively correlated with soluble sugar,while total A1 was negatively correlated with seedling height and diameter of Magnoliaceae glanca Blume.Total biomass was positively correlated with leaf total N,total chlorophyll content and net photosynthetic rate(Pn),while total A1 content was negatively correlated with biomass.The seedling quality index(QI)of A3N2 treatment was the highest,which indicated that this treatment was most beneficial to balancing the growth of Magnoliaceae glanca Blume seedlings.According to principal component analysis,the optimal concentration of citric acid to alleviate aluminum toxicity was N1 at A1 Al concentration.Adding exogenous citric acid of N2 and N3 concentration at A2 A1 concentration can effectively promote the growth of Magnoliaceae glanca Blume seedlings,improve the synthesis of organic products and improve the utilization of nutrients.N3 concentration of citric acid can effectively alleviate the stress effect of A3 concentration of aluminum. |
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