Mechanism Study On The Root Metabolites Of Invasive Plant Solidago Canadensis Regulate Soil Microbial Structure And Drive Its Successful Invasion

Invasive alien plants generally have large underground biomass,which can change the soil microenvironment through root secretion,such as inputting a large number of primary metabolites containing carbon and nitrogen,changing the soil nutrient cycle;also releasing a large number of secondary metabolites(chemical Sensitive substances),which affect the growth of surrounding plants and the structure and function of soil microbial communities.The invasive plant S.canadensis L.is a typical malignant invasive plant in the southern region.There is little attention to the role of its root exudates(allelochemicals)in the actual soil environment and the feedback effect after adjusting the structure and function of the soil microbial community.The researchers of this research group have carried out a lot of chemicals separation work on the root extract(exudates)of S.canadensis L.in the early stage.A large amount of root extract has been separated from the root extract,including caffeic acid,methyl caffeic acid,and caffeic acid.In this study,root metabolite input mediated changes in the structure and function of soil bacterial communities,through seed germination experiments,indoor pot experiments,and soil feedback experiments,comprehensively evaluated the ecological functions of phenolic acid root metabolites of invasive plants.The aim is to reveal the ecological mechanism of the successful invasion of exotic plants from the perspective of the chemical and ecological functions of root phenolic acid metabolites,enrich the theoretical system of invasion ecology,and provide practical theoretical guidance for the prevention and control of invasive plants in practice.The main results of this research work are as follows:1.Through petri dish germination experiments and pot experiments,the direct allelopathy of root metabolite input on seed germination and plant growth of local plants was explored.The results showed that with the increase of the concentration of caffeic acid methyl ester(MC)and caffeic acid ethyl ester(EC),the plant height of P.indica L.showed a decreasing trend.In addition,the leaf width,seed germination rate,seed germination index,and seed germination speed index of P.indica L.treated with a high concentration(1 m M)of phenolic acid metabolites were significantly lower than other treatments.The increase of MC and EC concentration has a significant inhibitory effect on the seed germination of the native plant P.indica L.The above results indicate that phenolic acid metabolites from the roots of invasive plants can inhibit the growth of native P.indica L.and increase its competitiveness.2.Through pot experimentations,the changes of root metabolite input on the structure and function of soil bacterial communities were explored,as well as the feedback effect of the soil after this soil microenvironment change.The experiment was divided into two stages: the first stage,soil conditioning experiment and the second stage,soil feedback experiment.Which explains the feedback effect of phenolic acid metabolite input on the soil bacterial community structure after the change(that is,the indirect effect of phenolic acid metabolite).The results showed that phenolic acid metabolites significantly affected the content of nitrate-nitrogen and ammonium nitrogen in the soil,and CA and MC significantly reduced the content of ammonium nitrogen in the soil.As the concentration of phenolic acid metabolites increases,the content of nitrate nitrogen in the soil gradually decreases.The addition of phenolic acid metabolites at low concentration(0.1 m M)slightly reduced OTU abundance,bacterial abundance,Chao1 index,and Simpson index,but showed no significant difference;Phenol at high concentration(1 m M)and the addition of acid metabolites significantly reduced bacterial OTU abundance,bacterial abundance,Chao1 index,and Simpson index.Phenolic acid metabolites changed the biomass of nitrogen-fixing bacteria such as Nitrospiraa and Nitrospiraceae in the native soil.The phenolic acid metabolites under low concentration conditions have no obvious effect on the growth of Pterocephalus multilobata,but caffeic acid ethyl ester has an obvious inhibitory effect on the growth of P.indica L.,but high/low concentrations of phenolic acid metabolites have no significant difference in the effects of S.canadensis L.growth.The results show that: phenolic acid metabolites have a significant impact on the conversion of available nitrogen in the soil.The data of soil microbial community structure shows that the entry of phenolic acid metabolites can affect the soil nutrient cycle to a certain extent by reducing the types and diversity of soil microorganisms,thereby affecting the invasion process.The feedback test indicators showed that caffeic acid metabolites,as an allelopathy,had a self-toxic effect on itself less than the allelopathy on P.indica L.,thus promoting the invasion of S.canadensis L..3.After the adjustment of S.canadensis L.planting,the changes of root exudates on the soil microenvironment,the structure and function of soil microbial communities and their soil feedback effects were explored.The results show is,compared with CK soil,the effect of plant domestication treatment on TN,TC and TP in the soil was not significant,but significantly increased the content of soil ammonium nitrogen and significantly reduced the content of nitrate-nitrogen.After the domestication of S.canadensis L.,the bacteria and actinomycetes in the soil increased,while the proteobacteria and nitrifying bacteria decreased.Under the conditions of microbial replenishment treatment after sterilization,compared with the undomesticated soil(CK)and the conditioned soil of P.indica L.,the sterilized soil after the conditioning of S.canadensis L.,the replenishment of microbial filtrate increased S.canadensis.L.The plant height in the soil(compared with CK)after conditioning of P.indica L.significantly reduces the plant height,above-ground biomass,and underground biomass of Pteropus multilobate.The dominant bacteria in the soil after the domestication of S.canadensis.L are Anaerolineae,SBR1031,Bacteroidetes,Bacteroidia,and Chitinophagales;the bacteria in the soil of P.indica L.mainly belong to the Chloroflex phylum,and it is more abundant than that of the undomesticated soil(CK control group).The dominant bacteria in the non-domesticated soil(CK)soil are Nitrososphaeria,Thaumarchaeota,Nitrosopumilaceae.The results showed that the invasion process of S.canadensis L.significantly affects the physical and chemical properties of the soil,and also the content of soil ammonium and nitrate.The root exudates of S.canadensis L.significantly changed the community structure of soil bacteria.After the domestication of the invasive plant S.canadensis L.,the bacterial diversity of the soil is more susceptible to changes in the regulation of plant root exudates than the bacterial diversity in P.indica L..Feedback experiments showed that after sterilization,the microbial replenishment treatment had a significant reduction in plant height,aboveground biomass,and underground biomass of P.indica L..It shows that the invasion affects the change of the physical and chemical properties in the soil and thus affects the occurrence of the invasion.The planting of S.canadensis L.can promote its invasion by changing the physical and chemical properties in the soil.The root exudates of invasive plants can directly reduce the growth of local plants,and can also indirectly inhibit the growth of local plants by weakening the symbiotic relationship between local plants and bacteria,shaping a beneficial microbial community,and changing soil physicochemical properties.