The Soil Environment Behivor Of Astragalin,A Secondary Metabolite Of Flaveria Bidentis

An exotic weed native to South America,Flaveria bidentis?L.?Kuntze,is spreading in northern China where it forms dense monospecific patches threatening native aboveground biodiversity and agricultural production from 2001.F.bidentis contains high amounts of astragalin,one flavonoid metabolite,which has been knows allelochemical of some plants,the movement,degradation,adsorption-desorption and accumulation of astragalin in the soil,remain unclear after being released into the soil.The regular of the environment behavior of astragalin in five soils was studied.The bacteria diversity and mechanism of degradation astragalin was evaluated with soil enzyme activity and the high-throughput sequencing method.These results provided an important evidence for the analysis of the invasive mechanism of F.bidentis.The results were as follows:?1?The effects of F.bidentis on the plant communities and rhizosphere soils bacterial diversity were revealed.The results showed that F.bidentis was the most abundant species in the habitats of riverbank and wasteland with its 100%frequency.The seed density of F.bidentis was 12527 ind.·m^-2and13947 ind.·m^-2in riverbank and wasteland,respectively.The seeds of F.bidentis were decreased with the increasing of soil depth,seed density in the 0-2 cm soil layer was the highes.Using high-throughput sequencing technology,it was found that the invasion of F.bidentis decreased the relative abundance of Actinobacteria,Firmicutes,increased the relative abundance of the Proteobacteria,Bacteroidetesand Gemmatimonadetes which may be related to the large number of flavonoid metabolites in the plant.At the phylum level,the relative abundance of Actinobacteria decreased but Proteobacteria increased significantly,after the soil treated with astragalin.Astragalin may play an important role in the invasion of F.bidentis as a signal molecule for changing the relative abundance of Actinobacteria,Proteobacteria and Firmicutes.?2?A method for the determination of astragalin in soil was established based on the solid phase extraction and high performance liquid chromatography?SPE-HPLC?.The samples were extracted by 2%EDTA/methanol?v:v?=1:1 and the average recoveries of astragalin were 72.1%-80.4%with the standard deviation of 0.37%-3.42%.The method was simpleand suitable for the large amount of rapid extraction and detection of astragalin.?3?The migration,degradation,adsorption–desorption of astragalin in the soils were elucidated.The R_fof astragalin was 0.14-0.51 from weak to moderate-mobility in five soils,which was affected by the soil mechanical composition,metal ion content and CEC.The degradation of astragalin was fitted well with a first-order kinetic equation,with astragalin concentrations decreasing rapidly and then maintaining relatively constant thereafter.The half-lives(t_1/2)of astragalin in the non-sterilized soils were 2.68 h-18.55 h,and 111.8 h in the sterilized fluvo-aquic soil.The activities of soil dehydrogenase,polyphenol oxidase and?-glycosidase were all increased after adding astragalin.Soil microbes,organic matter content,total nitrogen,total potassium and soil enzymes affected the degradation of astragalin.The adsorption-desorption kinetics and isothermal adsorption-desorption behavior of astragalin in five soils were studied by batch balance method.The result showed that,the adsorption of astraglin in five soils was divided into two groups:instantaneous rapid adsorption and slow adsorption.The order of adsorption rates was red soil?83.3%?>fluvo-aquic soil?63.8%?>sandy soil?38.9%?>alkaline soil?33%?>purple soil?28.5%?.Adsorption-desorption isotherm results showed that adsorption isotherms were described by Freundlich isothermal equation.The adsorption coefficient(K_d^ads)were red soil?3.4977?>fluvo-aquic soil?1.6047?>alkaline soil?1.4034?>wind sand soil?1.2278?>purple soil?0.4418?.The desorption difficulties were red soil>fluvo-aquic soil>alkaline soil>sandy soil>purple soil.The adsorption-desorption of astragalin was negatively correlated with organic matter and pH,and positively correlated with Fe,Mn content and CEC.?4?The accumulation effect of astragalin on F.bidentis and soil was clarified.The change of astragalin content in natural growth of F.bidentis was similar to that in the soil with increasing from the seedling stage to the maximum at the flowering stage,and then decreasing,and the roots and seeds of F.bidentis contained a certain amount of astragalin.In the greenhouse,and the content of the astragalin in the rhizosphere soils in the second growing season was significantly higher than that in the first growing season,but the astragalin content in plants was not obvious in different growth seasons.After the stress treated by PEG-6000 and UV-B,the content of astragalin and kaempferol in the leaves of F.bidentis had different degrees of accumulation,and the expression of FLS was also increased.After the stress was removed,the accumulation affect also decreased to the level of CK.The redundancy analysis?RDA?was performed by using the half-lives(t_1/2),the migration value?R_f-L,R_f-H?,adsorption-desorption constants(K_d^des?K_d^ads)of astragalin and soil physical and chemical properties,the results showed that organic matter and pH were the main factors influencing the accumulation of astragalin in the soilswith the secondary factors with soil mechanical composition and metal ion content.