Evaluation,Physiological Response And Molecular Mechanism Of Pinus Massoniana Lamb Under Phosphorus And Aluminum Stress

Pinus massoniana Lamb.is a pioneer tree species for afforestation and industrial timber species in southern China.It has the excellent characteristics of wide distribution,fast growth,wide use,large volume and strong tolerance.It can provide a large amount of wood and resin in a short operating period.Pine resin,pine needles,pine pollen,bark and root have a variety of economic values.They are the potential driving force for the development of emerging forest industries and are one of the main industrial timber species in China.The soil in the south is generally low-phosphoric aluminum red soil.With the development and leaching of red soil,as well as the unreasonable fertilization of human beings and the discharge of sulfide in factories,the acidification of soil is deepening,resulting in low phosphorus,acid aluminum and low-phosphoric aluminum stress environment in soil,which is the main reason affecting the growth of Pinus massoniana forest and leading to large-scale decline and yield reduction of Pinus massoniana.Therefore,this paper evaluated the adaptability of Pinus massoniana seedlings to low phosphorus and acid aluminum stress,screened excellent families of Pinus massoniana with low phosphorus and acid aluminum resistance,and then studied the physiological response and molecular mechanism of high resistant and sensitive families in response to low phosphorus,acid aluminum and low aluminum phosphate stress,so as to provide theoretical basis for the cultivation of Pinus massoniana materials resistant to low phosphorus and acid aluminum stress.The main results are as follows :(1)A sand culture experiment was conducted to evaluate the tolerance of 54 families to low aluminum phosphate stress in the second generation seed orchard of Paiyang Mountain of Pinus massoniana.Among them,11 materials such as 17,15 and 12 were highly resistant families,and 12 materials such as 25,26 and 33 were sensitive families.The highly resistant family(PmT)52 and the sensitive family(PmS)26 were selected for subsequent growth,physiological and molecular tests.(2)Phenotypic observation and growth index determination of PmT and PmS families under low phosphorus and acid aluminum stress were carried out by hydroponic experiment.The greater the stress degree of low phosphorus,acid aluminum and low aluminum phosphate on Pinus massoniana,the more serious the red-brown symptoms of old leaves and the worse the growth.Among the three stresses,low aluminum phosphate stress had the greatest impact on the growth of Pinus massoniana.The growth of seedling height,ground diameter and main root length of PmS under severe low aluminum phosphate stress decreased by 57 %,41 % and 20 %,respectively,compared with CK treatment.The growth of seedling height and ground diameter of PmT decreased by 52 %and 47 % respectively compared with CK treatment,while the growth of main root length increased by 13 %.The growth of sensitive families was limited under low phosphorus,acid aluminum and low aluminum phosphate stress.Under low phosphorus and acid aluminum stress,only the ground diameter development of high resistant families was inhibited,and the main root length and root shoot ratio also showed an upward trend under low aluminum phosphate stress,which was more tolerant.In addition,trace amounts of aluminum can promote the growth of Pinus massoniana seedlings.(3)The physiological indexes of roots and leaves of PmT and PmS families changed greatly under low phosphorus,acid aluminum and low aluminum phosphate stress.With the increase of stress degree,MDA content increased,and reached the peak under severe stress.The activities of SOD and CAT and the contents of PRO,SP and SS increased first and then decreased with the deepening of stress.Mild and moderate stress increased the activity of protective enzymes and the content of osmotic regulators,scavenged peroxides,and maintained cell stability to respond to low phosphorus,acid aluminum and low aluminum phosphate stress.Under severe stress,the ability of PmS to remove oxides and maintain cell stability was weaker than that of PmT,and PmT was more tolerant.(4)Under low phosphorus and low aluminum phosphate stress,two stress transcription factors include : WRKY,NAC,MYB,AP2/ERF-ERF,bZIP,C2H2,C3H,bHLH,zn-clus and LOB.The metabolic pathways of Pinus massoniana in response to the two stresses were similar,which may be caused by the inhibition of phosphorus absorption and utilization by Pinus massoniana under acid aluminum stress.The functions of differential genes mainly include : cellular process,genetic information processing,metabolism,biological system and environmental information processing.KEGG enrichment analysis of differently expressed genes showed that the signal transduction in response to stress were : plant hormone signal transduction,MAPK signal pathway,phosphatidylinositol signal system,ABC transporter activation.The specific metabolic pathways are : ribosome,α-linolenic acid metabolism,linoleic acid,phenylpropanoid biosynthesis,glycolysis / gluconeogenesis,fatty acid degradation,isoquinoline alkaloid biosynthesis,pentose and glucuronic acid mutual conversion,flavonoid biosynthesis,betalin biosynthesis,zeatin biosynthesis,nitrogen metabolism,glyoxylate dicarboxylate metabolism,unsaturated fatty acid biosynthesis,etc.(5)The number,pattern and pathway of differentially expressed metabolites in Pinus massoniana under low phosphorus,acid aluminum and low aluminum phosphate stress were similar,with the decrease of phosphoric acid and the increase of organic acids and organophosphorus compounds.The specific metabolic pathways were : metabolic pathway,secondary metabolite pathway,amino acid metabolic pathway,cofactor biosynthetic pathway,heterocyclic compounds,glycerol lipids,terpenoids metabolic pathway,phosphoric acid metabolic pathway,etc.