镁铁氮磷肥调控芒果幼叶转色的光合及碳氮代谢机制OA

The color transition of young mango leaves from reddish-brown to green is a critical developmental shift from heterotrophic sink organs to autotrophic source organs,which fundamentally determines photosynthetic efficiency and whole-plant nutrient accumulation.Previous studies have mainly focused on the effects of macro-element compound fertilizers on mango fruit yield and quality.In contrast,little is known about the regulatory effects and metabolic mech-anisms of combined magnesium(Mg),iron(Fe),nitrogen(N),and phosphorus(P)fertilization on the leaf color transi-tion process.This study aimed to investigate these regulatory effects and metabolic mechanisms using the mid-season mango cultivar'Palayinda'(Mangifera indica L.)as the experimental material.A combined Mg-Fe-N-P fertilization treatment(T)was established,consisting of foliar application of magnesium sulfate(0.4 g/plant)and EDDHA-Fe(1.67 g/plant),root application of calcium phosphate(7.14 g/plant),and soil application of urea(3.26 g/plant),while the control(CK)received an equal volume of clear water.Leaf color parameters(L*,a*,and b*)and photosynthetic pigment contents(chlorophyll a,chlorophyll b,total chlorophyll,and carotenoids)were measured at five growth stages(August 21,26,31,September 5,and 10,2024).Non-targeted metabolomics analysis was performed on three stages that exhib-ited significant differences between T and CK(August 26,August 31,and September 5).The results showed that ferti-lization significantly increased photosynthetic pigment contents at all stages,with peak values observed on September 5.Compared with CK,the T group exhibited increases of 56.65%in chlorophyll a,88.77%in chlorophyll b,65.76%in total chlorophyll,and 63.58%in carotenoids.Fertilization accelerated the greening process of young leaves,as reflected by significantly lower a* values(redness,P<0.01)and significantly higher b* values(yellowness,P<0.05)and L* values(brightness,P<0.05)in the T group than in the CK group.Metabolomics analysis identified a total of 1704 metabolites,of which 558 were differentially accumulated between T and CK(P≤0.05,VIP>1).These differential metabolites were mainly enriched in pathways related to carbon fixation in photosynthetic organisms,starch and sucrose metabolism,the tricarboxylic acid(TCA)cycle,and amino acid biosynthesis.Among them,carbon metabolites such as sucrose,maltose,and trehalose were significantly up-regulated,whereas pyruvate and malate were significantly down-regulated.Nitrogen metabolites,including glutamate,γ-aminobutyric acid(GABA),arginine,proline,and alanine,were significantly up-regulated.Together,these results indicate that the combined Mg-Fe-N-P fertilization strategy synergistically regu-lates core pathways of carbon and nitrogen metabolism.It enhances photosynthetic carbon fixation efficiency,promotes the accumulation of non-structural carbohydrates(e.g.,sucrose and maltose),and thereby provides energy and carbon skeletons for nitrogen metabolism.It also stimulates nitrogen assimilation and amino acid biosynthesis,increasing the levels of glutamate,arginine,proline,and other amino acids,which supply nitrogenous precursors for chlorophyll syn-thesis and photosynthetic enzyme systems.These processes accelerate the rapid color transition and photosynthetic maturation of young leaves.This study provides a theoretical basis and technical support for precision fertilization dur-ing the young leaf color transition stage in mango production.