Effects Of Arbuscular Mycorrhizal Fungi And Phosphorus Levels On Nutrient Uptake,yield And Quality Of Platycodon Grandiflorum

Platycodon grandiflorum（Jacq.）A.DC.is a perennial herbaceous plant in the Campanulaceae family.There is only one species and one variety in the world.It is one of the traditional Chinese herbal medicines in my country.Because it has the effects of promoting the lung,improving the pharynx,expectorating,and draining pus,it is mostly used for coughing with excessive sputum,poor chest tightness,pulmonary carbuncle,vomiting pus,and sore pus is not ulcerated.Arbuscular Mycorrhizal Fungi（AMF）,as an important part of soil microorganisms,can form a symbiotic relationship with 80%to 90%of vascular plants on land.When AMF and plant roots form a mycorrhizal symbiosis,the extra-root hyphae of AMF will form a huge hyphae network centered on the host plant root system and penetrate deep into the soil that the root system cannot reach to absorb nutrients,thereby increasing the host plant.The absorption and utilization efficiency of nutrient elements improves the nutritional status of plants,promotes plant growth and development,and enhances the ability of plants to resist adversity.Studies have found that soil phosphorus levels will significantly affect AMF infection rate and contribution rate to host plants.In recent years,more and more attention has been paid to the growth-promoting effect of AMF on plants,but there are few studies on the symbiosis effect of AMF and P.grandiflorum,and the symbiosis relationship between AMF and P.grandiflorum under different soil phosphorus levels is still unclear.Therefore,this study used a pot experiment to study the effects of different phosphorus levels and different AM strains on the growth and development,resistance physiology,platycodin biosynthesis and key enzyme gene expression of P.grandiflorum.The results are as follows:1.Three different AMF could form a good symbiotic relationship with P.grandiflorum.Among them,Funneliformis mosseae（FM）was the best,Diversispora eburnea（DE）and Rhizophagus Intraradices（RI）were the second,with the range of 28.3%～57.7%.Soil phosphorus level directly affected the growth and development of AMF and mycorrhizal symbionts.At P₂phosphorus level,the infection rates of three AMF and P.grandiflorum reached their respective maximum,which were 57.7%,41.7%and 38.3%,respectively.2.All the three AMF showed good growth promoting effect,and the plant height,root length,root dry weight and root fresh weight of P.grandiflorum were significantly higher than those of CK.With the increase of phosphorus level,the growth indexes increased first and then decreased,and reached the maximum at P₂ level.At this time,the root fresh weight of FM,de and RI treatment was 2.14,1.62 and 1.90 times higher than that of CK treatment,respectively.Appropriate phosphorus level combined with AMF was beneficial to the biomass accumulation and growth of P.grandiflorum.3.The results showed that the contents of nitrogen,phosphorus and potassium in roots of P.grandiflorum were significantly increased by inoculating three kinds of AMF,and the total nitrogen content of each treatment reached the maximum at P₂ level,which was 1.31,1.35 and1.19 times higher than that of CK treatment,respectively;the total phosphorus content of underground parts was significantly increased except RIP₂ treatment;the total potassium content of underground parts of three kinds of AMF was significantly higher than that of CK treatment.AMF can promote P.grandiflorum to absorb nutrients in the soil,which is conducive to the dry matter accumulation of P.grandiflorum.4.The protective enzymes and osmotic adjustment substances in P.grandiflorum leaves inoculated with three kinds of AMF were increased in varying degrees.With the increase of phosphorus level,all the indexes first increased and then decreased,and reached the maximum at P2 level.Under this phosphorus level,POD activity and soluble sugar content increased by1.25,1.09 and 1.21 times,1.71,1.38 and 1.70 times,respectively.In addition,the content of MDA and proline decreased first and then increased with the increase of phosphorus level,and reached the minimum at P2 level.At this time,the content of MDA in three inoculation treatments decreased by 1.70,1.74 and 1.63 times compared with CK,respectively.This indicated that AMF could activate the protective enzyme system,regulate the metabolism of P.grandiflorum and improve the stress resistance of plants.5.The results showed that AM fungi could increase the content of platycodin,among which Platycodin D,Platycodin D₃,Apigenin D,Apigenin D₃ and total saponins were increased in varying degrees.The content of saponins increased first and then decreased with the increase of phosphorus level,and reached the maximum at P₂ level.Under this phosphorus level,compared with CK,the content of Platycodin D increased by 1.20,1.16 and 1.18 times,and the content of total saponins increased by 1.19,1.11 and 1.07 times.In general,all three AMF could increase the content of platycodin,and the treatment group inoculated with FM was slightly higher than that inoculated with RI and de at the same phosphorus level.In this study,the expression of 10 key enzyme genes（AACT,HMGR,PMK,MVD,IPPI,SS,β-AS,β-28O,UGT1,UGT4）in Platycodin biosynthesis pathway was studied.It was found that the expression of key enzyme genes was more active in plants inoculated with AMF,and Platycodin D content was positively correlated with AACT,MVD,IPPI,β-AS,β-28O,UGT4（p<0.01）.There was a significant positive correlation between the expression of PMK and UGT1（p<0.05）,which indicated that inoculation with AMF could induce the expression of these genes and promote the synthesis of platycodin.6.The main component analysis showed that there was the best combination relationship between AMF and phosphorus level.When P₂ level,the best effect was achieved by inoculating FM fungi and P.grandiflorum.