Interactions between invasive plants and soil microorganisms play a key role in the invasion process.Exotic plants often produce allelochemicals that inhibit the growth of native plants by inducing changes in the physical and chemical properties of the soil,as well as to the structure of the soil microbial community.Chenopodium ambrosioides,an annual or short-lived perennial herb within the family Chenopodiaceae native to Central and South America,poses a threat to ecosystem structure and function in China.C.ambrosioides is rich in volatile oils,which are released into soils via root exudation and plant decomposition.Previous studies investigating the invasion mechanisms of C.ambrosioides focused primarily on its impacts on the growth of native plants and neglected its potential influences on soil microbial structure.Here,we used the greenhouse flask method to study the effects of volatile oils produced by C.ambrosioides on soil microbial diversity and extracellular enzyme activities.The results indicated that volatile oils deriving from C.ambrosioides inhibited the activity of soil urease,acid phosphatase,invertase and nitrate reductase (P＜0.05),and high doses of these volatile oils significantly enhanced the activity of catalase (P＜0.05).Moreover,the volatile oils had a strong influence on soil enzyme activities during the early stages of treatment,but this effect diminished considerably over time.Bacterial abundance was significantly higher in treatment groups receiving high doses (20 μL and 50 μL) of volatile oils than in the control groups (P＜0.05) after 16 days of treatment,indicating that the volatile oils greatly influenced soil microorganism diversity;for instance,Actinomycetes were abundant when exposed to only low doses of volatile oils,but their populations declined at higher doses.Both Shannon-Wiener and Margalef indices indicated that bacterial and fungal diversity increased with increasing volatile-oil dose and treatment time.In conclusion,volatile oils produced by C.ambrosioides altered the microbial community structure and extracellular enzyme activities in soils,and increased soil microbial diversity.%入侵植物释放的化感物质可改变土壤理化性状和微生物群落结构,通过与土壤微生物的互作抑制本土植物生长.为了进一步诠释土荆芥化感作用机制,采用温室培养瓶法,探讨了其挥发油对土壤胞外酶活性和微生物多样性的影响.结果表明:土荆芥挥发油不同程度降低了脲酶、酸性磷酸酶、蔗糖酶和硝酸还原酶的活性(P＜0.05);较高剂量的挥发油处理组显著促进了过氧化氢酶活性(P＜0.05).处理初期挥发油对土壤胞外酶活性影响较大,但随着处理时间延长,其影响逐渐减弱;处理16 d后,较高剂量(20 μL和50 μL)的挥发油处理组细菌数量显著高于对照(P＜0.05).挥发油对土壤放线菌数量的影响表现为低剂量促进,高剂量抑制的效应;PCR-DGGE分析表明,随着挥发油处理剂量增加和处理时间延长,土壤中细菌和真菌的Shannon-wiener多样性指数和丰富度指数均增大.结论:土荆芥挥发油可改变土壤微生物群落结构和胞外酶活性,增加土壤微生物多样性.
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