Effects Of Phosphorus Deficiency On The Growth And Some Physiological Indexes Of Citrus Grandis

Phosphorus(P)is an essential element for plant growth and development.It has important influence on crop growth,yield,quality,and stress resistance.In the tropical and subtropical regions,due to high temperature and heavy rain,nutrient leaching and fixation effect of iron and aluminum oxides lead to P deficiency,which has became one of limiting factors of crop production.Citrus is a tropical and subtropical evergreen tree.The soil in the main producing areas is acidic or weakly acidic.The citrus is vulnerable to P deficiency.It is of great significance to study how citrus adapt to low P levels in Citrus production in China.In this project,the main rootstocks of Citrus grandis were used as research materials to study the effects of P deficiency on the growth,photosynthesis,carbohydrate metabolism,organic acid metabolism,and reactive oxygen metabolism system of C.grandis seedlings.The main results were summarized as follow:(1)P deficiency inhibited the growth of C.grandis seedlings,significantly reduced root and shoot biomass,increased the contents of iron,manganese,and copper,and decreased the contents of potassium,nitrogen,sulfur,magnesium,P,zinc and boron in C.grandis roots.P deficiency reduced the contents of potassium,nitrogen,sulfur,and P,while increasing the content of iron,manganese,and boron in C.grandis leaves,but had no significant effect on the content of magnesium and zinc.Pi deficiency had a greater effect on the P content in roots than in leaves,but the effect on the sulfur content in leaves was greater than that in roots.(2)P deficiency decreased the chlorophyll content,CO2 assimilation rate,stomatal conductance,and increased intercellular CO2 concentration in C.grandis leaves.Pi deficiency increased the content of starch,fructose and sucrose in C.grandis leaves,while decreased the content of starch,glucose and Fructose content in roots.(3)P deficiency increased the contents of reduced glutathione,superoxide anion and H2O2 in the leaves and roots of sour citron,but only increased the content of reduced ascorbic acid and total ascorbic acid in roots;the deficiency of P increased the content of roots and leaves of C.grandis.P deficiency resulted in membrane lipid peroxidation of C.grandis leaves and roots,revealed as increased malondialdehyde content.Except for GR,Pi deficiency increased the activities of POD,DHAR,APX,MDHAR,GST,CAT,GPX,and SOD in C.grandis roots,while increased the activities of all the enzymes mentioned above in leaves.(4)P deficiency reduced the content of malic acid,isocitric acid and isocitric acid in C.grandis roots,and increased roots citric acid content and leaves malic acid and citric acid contents.In roots,the change of malic acid and citric acid content under different Pi levels were positively correlated with the change of NAD-malate dehydrogenase(NAD-MDH)and phosphoenolpyruvate carboxylase(PEPC),respectively.In leaves,the change of malate and citric acid contents under different Pi levels were negatively correlated with NAD-MDH,NADP-ME and ACO,respectively,while the change of citric acid content was positively correlated with the change of PEPC activity.This suggests that the dynamic change of organic acid content in the root and leaf of C.grandis under different P levels were regulated by the activities of organic acid metabolic enzymes.In conclusion,P deficiency affected the absorption of mineral elements,reduced the outward transport of photosynthetic products and CO2 assimilation rate,affected the metabolism of organic acids and increased oxidative stress and membrane lipid peroxidation of leaves and roots and finally,inhibited the growth of sour pomelo seedlings.