| Biological invasion has been one of the important global environmental problems.As an important part of invasive organisms,exotic plants have caused a major threat to the ecological environment,social economy and human health.The development of global trade and the progress of science and technology have intensified the invasion of exotic plants,which has led to more biological invasion problems.It is necessary to solve the problem of biological invasion by the research on the invasion mechanism and scientific management of invasive species.In order to elucidate the allelopathic effect of an invasive plant Ambrosia artemissifolia,Ambrosia artemissifolia's invasion on the species diversity of neighboring plant communities in the invaded areas and soil microbial function using Biology-Eco plates were investigated.The volatile components of Ambrosia artemissifolia plants were analyzed by gas chromatography-mass spectrometry(GC-MS),and the influences of volatile components on co-occurring native plant and natural enemies were tested.Moreover,the chemical composition of the invaded soil(rhizosphere soil and bulk soil),non-invaded soil(the control),root exudates,and root extracts were also analyzed by GC-MS.The differences of chemical substances in different treatments of soil,root exudates and root extracts were compared to identify the key compounds which may affect the structure of soil microbial community.In addition,the effects of Ambrosia artemissifolia at different growth stages were studied via high-throughput sequencing technology to elucidate the major responsible chemicals affecting the soil microbial community.We attempted to explain the invasion mechanism of Ambrosia artemissifolia from the perspective of allelopathy,including the effects of its released chemicals.Our work will help understand the role of secondary metabolites of exotic plants in the process of invasion,and to testify the Novle Weapon Hypothesis.Our main findings include:(1)Effects of Ambrosia artemissifolia's invasion on plant community and soil microbial functional diversityThrough the investigation of plant community diversity in different habitats of invaded areas,the results showed that the species richness index,Simpson index,Shannon index,and Pielou evenness index of plant communities in the invaded sites decreased significantly by 34.55%,39.66%,41.58%and 46.58%in the mining habitat,by 39.29%,36.84%,45.45%and 24.42%in the wasteland,and by 31.35%,24.00%,30.87%and 10.84%in the farmland,respectively,when compared with the non-invaded sites.By measuring the physical and chemical properties,soil enzyme activities and the culturable microbes of soil,the p H and total salt content of soil were significantly reduced,and the content of organic carbon,total nitrogen,and total phosphorus increased in different habitats of invaded areas.The activities of the urinary enzyme,protease,sucrase and phosphatase of soil increased significantly.Moreover,in different habitats,the carbon source metabolic activity of soil microbial community in invaded soil was higher than that in the non-invaded with time using the Biolog-Eco board test,and the Shannon index of carbon source metabolic diversity of soil microbial communities of in the invaded areas was also increased,when compared with the non-invaded soil.The results showed that Ambrosia artemissifolia's invasion reduced the species diversity and richness of plant communities in the invaded areas,impacted on the growth of native plants,changed the utilization and metabolism mode of soil microorganisms on carbon sources,increased soil nutrients and fertility,improved nutrient cycle,and caused a beneficial soil ecological environment to the growth and development and population expansion of Ambrosia artemissifolia.(2)Effects of the chemicals of Ambrosia artemissifolia on native plants,insects and pathogenBy the bioassay of the volatile components of Ambrosia artemissifolia on the native associated plants Poa annua,Setaria viridis,Amaranthus retroflexus,and Medicago sativa in simulating natural state,the volatiles of the stem,leaf,flower and whole plant of Ambrosia artemissifolia significantly inhibited the growth of Poa annua,Setaria viridis,Amaranthus retroflexus,and Medicago sativa.The results of GC-MS analysis showed that the chemical composition of the volatile oil of Ambrosia artemissifolia included monoterpenes,sesquiterpenes,diterpenes and other non terpenoids,and the main components were germacrene D,limonene?-Pinene?-Pinene and caryophyllene.At 5.00 mg m L-1 concentration,the volatile oil of Ambrosia artemissifolia decreased by 96.22%of the root activity of Medicago sativa,the activities of SOD,POD,and chlorophyll content of the tested plants were significantly reduced,especially,the nuclear aberrations of onion root tip cells were induced,and led to the chromosome abnormalities accounted for 83.45-92.16%of the total aberrations.When the tested insects Aphis gossypii Glover and Tetranychus cinnbarinus were exposed to the volatile oil for 24 hours,the volatile oil completely killed all tested insects at 200?g m L-1concentration.Moreover,the volatile oil completely inhibited the mycelial growth of the pathogen Verticillium dahliae at 5?L/ml contact culture and1.2?L/ml fumigation culture.The results showed that the chemical compounds of Ambrosia artemissifolia had the phytotoxic and cytotoxicity on the native plants,the insecticidal and antibacterial activity on the natural enemies.(3)Effects of the chemicals of Ambrosia artemissifolia on soil microorganismsGC-MS analysis showed that the main chemical substances in the invaded soil were terpenoids,aliphatic aldehydes and ketones,long-chain fatty acids and polyacetynes,phenols,quinones,alcohols,amides,benzoic acid,and derivatives.The compounds(Z)-?-farnesene,(S)-1-methyl-4-(5-methyl-1-methylene-4-hexenyl)cyclohexene,and eicosane were the main chemical substances in the invaded soil.Meanwhile,(Z)-?-Farnesene existed in the invaded soil at flowering stage,while(E)-?-Farnesene appeared in the invaded soil at seedling stage,so it is inferred that the chemical compounds of Ambrosia artemissifolia might undergo configuration transformation at different growth stages.Analysis of the invaded soil microbial community revealed that Proteobacteria,Bacteroidetes,Acidobacteria,Gemmatimonadetes,and Verrucomicrobia were the dominant flora in soil bacteria,Ascomycota,Rozellomycota,Basidiomycota,Chytridiomycota,and Glomeromycota were the dominant fungi in the invaded eares.Compared with non-invasive soil(the control),the diversity index and richness index of the bacterial community were increased in the invaded soil(the rhizosphere soil and bulk soil)at different growth stages,while the diversity index and richness index of the fungal community were decreased.The number of bacterial species in rhizosphere soil and bulk soil were increased by 8.42%and 5.41%at seedling stage,improved by 38.04%and 40.72%in the flowering stage,respectively.The number of fungal species in the rhizosphere and bulk soil were decreased by 14.51%and 19.85%at seedling stage,reduced by 52.19%and 36.18%at flowering stage,respectively.In addition,our results indicated that the chemicals of Ambrosia artemissifolia in soil affected soil microorganisms.Through the correlation analysis between the secondary metabolites of Ambrosia artemissifolia in soil and the soil microbial community,the results showed that the compounds(Z)-?-farnesene,(S)-1-methyl-4-(5-methyl-1-methylene-4-hexenyl)cyclohexene,and eicosane were correlated with soil bacteria and fungi at the phylum level.Specifically,(Z)-?-farnesene had a significant negative correlation with the Nitrospirae phylum,and a positive correlation with the Rozellomycota phylum(correlation coefficient 0.63);(S)-1-methyl-4-(5-methyl-1-methylene-4-hexenyl)cyclohexene had a positive correlation with the Chytridiomycota phylum(correlation coefficient 0.52).The results confirmed that the secondary metabolites of Ambrosia artemissifolia affected the community structure and diversity of soil microbes,and the chemicals of Ambrosia artemissifolia had allelopathic effects on soil microbes.In conclusion,the volatile components of Ambrosia artemissifolia inhibited the growth of the native associated plants,and had insecticidal and antibacterial activities.The chemicals of Ambrosia artemissifolia have strong allelopathic effects on native plants,natural enemies and soil microorganisms;Meanwhile,the chemicals of Ambrosia artemissifolia can regulate soil microbial community,enrich the specific microbial community,so as to enhance the competitiveness and facilitate the successful invasion of Ambrosia artemissifolia.This study provided new evidence for the new weapon hypothesis of invasive plants. |
PDF Full Text Request