Study On The Mechanism Of Green Control Of Ambrosia Artemisiifolia And Ambrosia Trifida Based On Reproduction Blocking

Common ragweed（Ambrosia artemisiifolia）and giant ragweed（Ambrosia trifida）are two annual invasive plant species that are difficult to control worldwide.In 2010,they were discovered in the Yili Valley of Xinjiang,China,and quickly spread,becoming the most serious invasive species in the region,causing significant harm to local agricultural production and ecological environment.Traditional chemical control has a significant impact on indigenous plants,making it urgent to develop green and efficient control technologies.Based on the high-density clustering population distribution characteristics of both common ragweed and giant ragweed,which are both annual plants,we propose a control strategy that inhibits seed production and prevents population clusters to reduce invasiveness and block population reproduction.Therefore,we selected the populations of common ragweed and giant ragweed that have invaded the Yili Valley as the research objects,and studied the mechanisms of population formation,maintenance,and growth to population clusters from genetic variation,pollination and mating patterns,plasticity regulation of reproductive traits within and among populations,and characteristics of soil seed banks.We developed control technologies by using reproductive blocking methods and selecting chemical agents to reduce or inhibit seed production of the two species and break population clusters.We evaluated the control effects by comparing the effects of chemical agents on common ragweed and giant ragweed and their impact on indigenous plants.We conducted research in the following five aspects:Sample collection and genetic information analysis using Simple Sequence Repeat（SSR）and Methylation-Sensitive Amplified Polymorphism（MSAP）techniques in the primary distribution areas of both species were conducted to analyze intra-and inter-populations genetic variation;The reproductive trait changes of the two species from establishment to invasive stages were studied to determine if the two species maximized their reproductive output at the population level;The invasion time series was combined with soil seed bank characteristics to determine the source of seeds for the above-ground plants of the two species;Efficient and green control technology was developed by selecting suitable chemicals for"reproduction（seed）blocking",identifying the sensitive period of the chemical action,and determining the minimum effective dose to suppress seed production;The impact of"reproduction blocking"technology on the above-ground population coverage and underground seed bank density of both species,as well as the impact on native plant communities,was evaluated.The main research results are as follows:1.The genetic differentiation degree between populations of common ragweed or giant ragweed was low,and gene flow occurred frequently among populations.Genetic variation mainly occurred within populations.Through SSR and MSAP analysis,it was found that the genetic differentiation degree between different populations was low,with mean genetic differentiation indices Fst of 0.089 and 0.152,and mean gene flow indices Nm of 2.55 and 1.38,respectively.Genetic variation mainly occurred within populations,accounting for 92%and 84%,respectively.Both species had rich DNA methylation sites,with over 90%of tested sites showing methylation.Therefore,the two invasive species in the Yili Valley had similar genetic backgrounds between populations,and gene flow could occur among populations,but there was a high level of variation within populations,and rich epigenetic bases that provided genetic foundations for alleviating intraspecific competition caused by high-density clustering.2.The reproduction of common ragweed and giant ragweed was based on highly outcrossed populations.Regardless of population establishment,population growth,or high-density clustering,both species could ensure the maximum seed production at the population level by adjusting branching,canopy width,and reproductive investment allocation.Both species had the highest fruit set rates when cross-pollinated,which were 9-10 times higher than self-fertilization rates,and their Fis values were 0.0461and 0.3075,respectively.After entering a new habitat,both species invested more biomass in reproduction to produce more seeds and rapidly increased population size through concentrated sprouting advantages.As the population grew,both species reduced their biomass investment in branching,narrowed their canopy width,increased the number of plants per unit area,ensuring a competitive advantage at the population level,and ensuring maximum reproductive output at the population level.3.Common ragweed and giant ragweed could form a high-density soil seed bank,with a large number of seeds and dense plants simultaneously germinating from seeds produced by the previous year’s plants,which provided important support for the application of reproduction blocking technology.Using a space-for-time substitution method,common ragweed and giant ragweed populations invading for 1-8years in the same habitat were selected to analyze the changes in above-and below-ground features during the invasion process.The results showed that with the increase in invasion duration,the relative seed bank density of both species increased significantly year by year underground.After 8 years of invasion,common ragweed and giant ragweed accounted for about 94%and 74%of the community seed bank,respectively.The relative coverage and plant density of the two species on the ground also increased significantly,and the number of seeds that could simultaneously germinate increased.In contrast,the seed bank density of the native plant community decreased significantly year by year,with a decline of 93%and83%caused by common ragweed and giant ragweed,respectively,after 8 years of invasion.Therefore,the large amount of seeds produced by the two species of plants in the previous year and the seed bank formed mainly supplied the consumption during the next year’s concentrated germination to establish and maintain a high-density population on the ground.4.Based on the"reproduction blocking"control method,common ragweed and giant ragweed could effectively inhibit seed production.In the main distribution habitats of the two species,plant growth hormone,synthesis enzyme inhibitors,oxidative enzyme inhibitors,and photosynthesis inhibitors were screened,and Aminopyralid,a growth hormone-like drug,was finally identified as the most effective for the control of the two species.At a rate of 110g ai ha^-1,the mortality rates of common ragweed and giant ragweed were 90%±6%and 100%±0%,respectively,and their seed yields were reduced by 98%±1%and100%±0%,respectively.When the drug was applied during the fast-growing and nutrient-growing period of the stems of the two species,the seed yield of both species could be reduced by over 90%at a rate of33g ai ha^-1.The control ability mainly manifested in inhibiting the increase in plant height,reducing the number of plants entering reproductive growth,and reducing or even not producing pollen,thereby eliminating the harm of pollen to human health.5.The reproductive blocking control technology had no side effects on the native plant community,and the cover of the native plant community could quickly recover after the drug treatment ended.After two years of continuous control,the control effect was consistent for both species.The relative cover of common ragweed and giant ragweed decreased by 93.89%and 96.25%respectively,and the soil seed bank density decreased by 99.38%and 99.89%respectively.Correspondingly,the cover and seed bank density of native plants significantly increased.Especially in the grassland habitat invaded by giant ragweed,the seed bank density of native plants increased significantly every year,and by the third year,the seed bank density was already similar to that of the uninvaded area.These results demonstrated that the"reproduction blocking"control technology,when applied for two consecutive years,not only effectively inhibited seed production of aboveground plants,but also consumed the soil seed bank.Within three years,it could achieve efficient and environmentally friendly control effect.In summary,common ragweed and giant ragweed were outcrossing plants that reproduced on a population scale,and the seeds produced in a given year formed a seed bank that mainly supplied the concentrated germination in the following year.We innovatively proposed the concept of"reproduction blocking"for control,using low-dose herbicides to suppress plant fertility,achieving efficient and environmentally friendly control.This provides an important method for solving the world’s problem of controlling common ragweed and giant ragweed,and offers a theoretical and applied basis for controlling similar annual invasive plants that reproduce by seed.