The Physiological Mechanism Of Polyglutamic Acid (PGA) In Reducing Fertilizer Dosage And Increasing The Efficiency Of Salvia Miltiorrhiza

As an important bulk medicinal material,Salvia miltiorrhiza has a long history of planting and application in China.In recent years,with the development and utilization of S.miltiorrhiza resources,its market demand has dramatically increased.In order to meet the market demand,people often increase the amount of chemical fertilizer,which further induces ecology destroying.Therefore,it is an urgent problem to explore measures in the production and cultivation to improve the yield and medicinal quality of S.miltiorrhiza under lower dosage of fertilizer.As a new type of fertilizer synergist,polyglutamic acid（PGA）has been widely used in crop production for its excellent physical and chemical properties.However,its application in S.miltiorrhiza planting and production has not been systematically studied.In this study,S.miltiorrhiza was used as the material,we investigated the effects of combined treatment of different concentrations of PGA and different levels of compound fertilizer on growth indexes,chlorophyll index,gas exchange parameters,chlorophyll fluorescence parameters,leaf water physiological indexes,the antioxidant characteristics of leaf and root,the activities of nitrogen and phosphorus metabolic enzymes in leaf and root,biological yield and the contents of main medicinal component by pot experiment.The effects of combined treatment of different concentrations of PGA and different levels of compound fertilizer on the yield and the contents of medicinal component of S.miltiorrhiza were also studied by field experiment.Through above research,we expected to elucidate the physiological mechanism of PGA in reducing fertilizer dosage and increasing the efficiency of S.miltiorrhiza,and further obtained the optimum combination of PGA and compound fertilizer for field production.In addition,our study also can provide theoretical basis for the application of PGA in reducing fertilizer dosage and increasing the efficiency of S.miltiorrhiza.The results of this study are as follows:（1）The effects of PGA on the growth and photosynthetic characteristics of S.miltiorrhiza under normal and lower fertilizer dosage were studied.PGA treatment could improve the plant height,transverse width,longitudinal width,maximum leaf length,maximum width of blade,maximum compound leaf length,basal diameter,root volume,root biomass,chlorophyll SPAD value,net photosynthetic rate（Pn）,transpiration rate（Tr）,intercellular carbon dioxide concentration（Ci）,stomatal conductance（Gs）,water use efficiency（WUE）,PSII actual photochemical efficiency（Y（II））,PSII maximum photochemical quantum yield（Fv/Fm）,PSII effective photochemical quantum yield（Fv’/Fm’）,apparent electron transport rate（ETR）and photochemical quenching coefficient（q P）.PGA treatment at P2 level had the best promotion effect under the 15%weight loss level of compound fertilizer.Under different levels of compound fertilizer,PGA treatment reduced stomatal limitation value（Ls）and non-photochemical quenching coefficient（NPQ）.Among different treatments,PGA treatment at P2 level had also the best effect in reducing these two indexes under the 15%weight loss level of compound fertilizer.（2）The effects of PGA on the water physiological indexes and antioxidant properties of S.miltiorrhiza under normal and lower fertilizer dosage were studied.PGA improved the relative water content and water holding capacity of S.miltiorrhiza leaves,as well as the contents of soluble protein（PR）and soluble sugar（WSS）in leaves and roots.However,PGA reduced water saturation deficit of leaves.Meanwhile,PGA improved the activities of ascorbate peroxidase（APX）,catalase（CAT）,glutathione reductase（GR）,peroxidase（POD）and superoxide dismutase（SOD）,as well as the contents of glutathione（GSH）and vitamin C（Vc）.However,PGA reduced the contents of hydrogen peroxide（H₂O₂）and malondialdehyde（MDA）in leaves and roots.Above results indicated that PGA treatment could significantly improve water balance and antioxidant properties of S.miltiorrhiza.Among different treatments,PGA treatment at P2 level had the best promotion effect under the 15%weight loss level of compound fertilizer.（3）The effects of PGA on the contents of available nitrogen,phosphorus and potassium in potted soil and the activities of nitrogen and phosphorus metabolic enzymes in S.miltiorrhiza were studied under normal and lower fertilizer dosage.PGA treatment could significantly reduce the content of available nitrogen,phosphorus and potassium in potted soil,and improved the activities of glutamate synthase（GOGAT）,glutamate dehydrogenase（GDH）,glutamine synthetase（GS）,alanine aminotransferase（GPT/ALT）,aspartate aminotransferase（GOT/AST）,nitrate reductase（NR）,acid phosphatase（AKP/ALP）and alkaline phosphatase（ACP）in leaves and roots.Among different treatments,PGA treatment at P2 level had the best promotion effect under the 15%weight loss level of compound fertilizer.（4）The effects of PGA on the quality and yield of S.miltiorrhiza under normal and lower fertilizer dosage were studied.The results showed that PGA could increase the aboveground biomass and root biomass of potted S.miltiorrhiza.Among different treatments,PGA treatment at P2 level had the best promotion effect under the 15%weight loss level of compound fertilizer.PGA had also significant effects on the contents of rosmarinic acid,salvianolic acid B,dihydrotanshinone,cryptotanshinone,tanshinone I,tanshinone IIA and tanshinones in potted S.miltiorrhiza.Among different treatments,CF1P2 treatment significantly increased the content of salvianolic acid B,CF1P3 treatment significantly increased the content of tanshinones.Similarly,PGA had also significantly effect on the yield of medicinal components per plant of potted S.miltiorrhiza.Among different treatments,CF1P2 treatment significantly increased the yield of rosmarinic acid and salvianolic acid B per plant,CF1P3 treatment significantly increased the yield of tanshinone I,tanshinone IIA and tanshinone per plant,CF2P3 treatment significantly increased the yield of dihydrotanshinone and cryptotanshinone per plant.Under different levels of compound fertilizer,PGA treatment also significantly increased the yield of S.miltiorrhiza in the field,which is consistent with the results obtained from above pot experiment.However,the effects of PGA on the contents of rosmarinic acid,salvianolic acid B,dihydrotanshinone,cryptotanshinone,tanshinone I,tanshinone IIA and neotanshinone in the field experiment were different from those in the pot experiment.Among different treatments,CF1P1 treatment significantly increased the content of tanshinone IIA,CF2P2 treatment significantly increased the contents of dihydrotanshinone,cryptotanshinone,tanshinone I and neotanshinone,CF2P3 treatment significantly increased the contents of rosmarinic acid and salvianolic acid B.Similarly,PGA treatment can also affect the yield of medicinal components per plant of S.miltiorrhiza in the field,and PGA treatment at P2 level had the best promotion effect under the 15%weight loss level of compound fertilizer.The results of this study showed that all PGA treatments under different levels of compound fertilizer promoted the growth,photosynthetic performance,water balance and antioxidant properties of S.miltiorrhiza plants,which further improved the yield and medicinal quality of S.miltiorrhiza.Among different treatments,PGA treatment at P2 level had the best promotion effect under the level of 15%weight loss of compound fertilize.This study not only analyzed the physiological mechanism of PGA in reducing fertilizer dosage and increasing the efficiency of S.miltiorrhiza,but also provided a theoretical basis for its application in the cultivation technology system used to reduce fertilizer dosage and increase the efficiency of S.miltiorrhiza.