The Impact Of Element Deficiency And Huanglongbing Stress On Citrus Chlorophyll Fluorescence Characteristic And Physiological Metabolism

Citrus(Citrus reticulata Blanco)elemental deficiency and Citrus Huanglongbing have become important obstacles to the increase in production and income of the entire citrus industry.Zinc,iron,or magnesium deficiency and huanglongbing infection are very similar in the early field symptoms of citrus,it is difficult to distinguish.In plant growth and development processes,zinc,iron,and magnesium are involved in photosynthetic absorption and growth in plants,and they are affecting the function of photosynthesis at different levels.This study treated navel orange(Citrus sinensis Osb.var.brasiliensis Tanaka),Ponkan(Citrus reticulata Blanco cv.Ponkan),and Satsuma(Citrus reticulata’Unshiu’)with zinc deficiency,iron deficiency,magnesium deficiency,and grafting with huanglongbing.Then,continuously treated the annual citrus seedlings with nutrient solution for six months,and recorded the citrus growth data monthly through rapid chlorophyll a fluorescence to monitor citrus growth in real-time.Based on these fluorescence parameters,this study explored the effects of nutritional deficiency on the photosynthetic physiology of citrus leaves,and evaluated metabolic changes and feedback mechanisms caused by nutritional deficiency in combination with metabolomics.(1)Zinc deficiency,iron deficiency,magnesium deficiency,and Huanglongbing alter the morphology,structure,and function of citrus leaves to a certain extent.Both nutritional deficiency and Huanglongbing caused yellowing symptoms in leaves,and significanted changes in leaf size.Especially,zinc deficiency resulted in an average decrease of 20.9%and 22.5%in leaf length and width,respectively.Zinc,iron,magnesium deficiency,and Huanglongbing also affected the development of phloem fiber cells and phloem transport in leaves,greatly affecting the structure and function of citrus leaf veins.(2)Zinc,iron,and magnesium deficiency significantly reduced the light energy utilization efficiency of citrus leaves.Firstly,the deficiencies significantly reduced the chlorophyll content of leaves,and the decrease in total chlorophyll content in citrus leaves,the magnitude of decrease was manifested a zinc deficiency,followed by an iron deficiency,and then a magnesium deficiency.The decrease in chlorophyll content in citrus leaves led to a decrease in chloroplast productivity.Chlorophyll fluorescence was used to evaluate leaf light energy utilization efficiency.The deficiency of zinc,iron,or magnesium led to a decrease in quantum yield by 10%,7%and 6.5%,respectively,and the decline of the light energy absorption capacity of leaves.The decrease in light energy conversion and increase in light energy dissipation in the leaves led to a decrease in the utilization rate of light energy in citrus leaves.(3)As the time of deficiencies treatment increased and the duration of Huanglong infection increased,a monthly downward trend was observed in the fluorescence induced kinetic curve(OJIP)of nutritional deficiency and huanglongbing leaves.The analysis of the curve trend showed that the deficiency of zinc,iron,and magnesium reduced the electron capture rate of the optical system,and reduced the oxidation rate of Q_A-by Q_B and other electron transfer members.Citrus huanglongbing led to a decrease in photochemical efficiency,an increase in non-photochemical dissipation,and a decrease in the number of active reaction centers in Photosystem II(PSII).(4)Through principal component analysis of JIP-test parameters,the JIP-test parameters of each nutritional deficiency and huanglongbing leaves showed good clustering.By Fv/Fm,Phi＿Eo,Phi＿Do,Psi＿o,the photosynthetic characteristics of TRo/RC and Fo,as fluorescent marker parameters,have been successfully used to distinguish between zinc deficiency,iron deficiency,magnesium deficiency,and huanglongbing infected leaves in citrus.(5)Through metabonomics,the metabolic differences of zinc deficiency,iron deficiency,magnesium deficiency,and citrus huanglongbing photosynthetic matter absorption,growth and development were excavated.The results showed that nutritional deficiency led to the decline of photosynthetic efficiency,the decline of citrus sugar metabolism and starch sucrose metabolism,the increase of organic acid and lipid metabolism,and the increase of amino acid metabolism.Citrus huanglongbing caused the accumulation of carbohydrates and an increase in free fat.It indicated that plants jointly resist stress by regulating their metabolic pathway network during the growth process.This study analyzed the effects of nutritional deficiency and huanglongbing on the morphological structure and function of citrus leaves.It used chlorophyll fluorescence technology to comprehensively evaluated the impact of nutritional deficiency and huanglongbing on the photosynthesis of citrus leaves,preliminarily used the fluorescence technology to distinguish and detect nutritional deficiency and huanglongbing in citrus.Finally,combined with the primary metabolomics,it explored the effects of nutritional deficiency and Huanglongbing on the photosynthetic capacity and related metabolic pathways of different varieties of citrus leaves.These provided theoretical guidance for the cultivation and management of citrus industry.