【作者】 牛红榜；

【导师】 万方浩；

【作者基本信息】 中国农业科学院 ， 生物安全， 2007， 硕士

【摘要】 入侵植物与入侵地土壤微生物的互作关系是外来入侵植物与入侵地生境互作关系的重要内容，土壤微生物是影响外来植物入侵力和生态系统可入侵性的一个重要因素。外来植物入侵可以引起土壤微生物群落及土壤生态过程发生改变，反过米这种改变可能有利于外来植物的生长及与当地植物的竞争，这是外来植物入侵的一种新机制—土壤微生物学机制。因此，外来入侵植物对入侵地士壤养分循环和土壤微生物群落的影响不仅是入侵效应问题，更与外来植物的入侵机制联系紧密。紫茎泽兰（Ageratina adenophora（Sprengel）R．King & H．Robinson（Synonym：Eupatorium adenophorum））是一种典型的恶性入侵杂草，已对许多国家和地区造成了严重的经济和生态损失。在综述国内外外来植物的入侵机理和紫茎泽兰种群扩张研究的基础上，本研究从紫茎泽兰与土壤微生物的互作关系出发，通过野外取样和温室盆栽实验，分别从紫茎泽兰入侵对土壤生态的影响、紫茎泽兰根际土壤中优势细菌的筛选鉴定及拮抗性能评价、紫茎泽兰浸提液对土壤微生物群落结构的影响和入侵地土壤微生物群落对紫茎泽兰生长、与当地植物竞争的影响等方面研究了紫茎泽兰入侵的土壤微生物学机制。主要结果如下：1．紫茎泽兰入侵对土壤生态的影响通过对紫茎泽兰入侵后不同演替阶段中（重度入侵区、轻度入侵区、未入侵区和当地植物生长区）的土壤微生物群落和土壤理化性质的比较，发现紫茎泽兰入侵显著改变了入侵地的土壤微生物群落结构，在重度入侵区土壤真菌、自生固氮菌、氨氧化细菌数量均较高，分别是轻度入侵区对应菌数量的2.2倍、3.6倍和1.4倍，是未入侵区对应菌数量的5.8倍、8.8倍和3.3倍，是当地植物区对应菌数量的1.7倍、2.6倍和1.9倍。同时提高了土壤中植物可直接吸收的硝态氮、铵态氮、有效磷、速效钾和有机碳含量，其中土壤硝态氮和铵态氮的含量分别为32.5 mg．kg^-1和39.3mg．kg^-1，分别是未入侵区对应含量的3.6倍和2.1倍，是当地植物区对应含量的2.3倍和1.4倍。土壤微生物各生理功能类群的变化与土壤理化性质的变化相关显著，土壤微生物群落的变化可能导致了土壤养分水平的升高。结果表明随着紫茎泽兰的不断入侵扩张，显著改变了土壤微生物群落和土壤养分；重度入侵区丛枝菌根真菌和真菌／细菌比率显著高于其它区，这可能与紫茎泽兰形成菌根真菌共生体有关。2．紫茎泽兰根际土壤中优势细菌的筛选鉴定及拮抗性能评价通过分离、筛选、鉴定紫茎泽兰根际土壤中优势细菌及其拮抗性能测定，发现紫茎泽兰根际土壤中存着丰富的芽孢杆菌和假单胞菌，其中枯草芽孢杆菌和巨大芽孢杆菌数量最多，共占鉴定细菌总数的55.6％；这些优势细菌类群对番茄枯萎病菌和青枯病菌有不同程度的拮抗作用，以枯草芽孢杆菌BS-5和苏云金芽孢杆BT-1对番茄枯萎病菌的拮抗效果最为明显，其代谢产物的抑菌率分别为85.5％和83.8％；优势细菌代谢液比菌体对病原菌的拮抗作用更强。结果表明紫茎泽兰根际丰富的具育强拮抗性能的细菌类群可能是紫茎泽兰不受土传病害侵扰的原因；通过这种根际有益微生物的反馈作用，紫茎泽兰直接或间接的住与当地植物竞争中处于有利地位，从而有利于其排挤当地植物。3．紫茎泽兰浸提液对土壤微生物群落的影响利用紫茎泽兰根系和茎叶浸提液培育入侵地土壤微生物群落，发现紫茎泽兰根系浸提液和茎叶浸提液分别处理轻度入侵土壤2周和3周后，土壤微生物群落发生显著变化，且随着浸提液浓度的增大微生物群落结构向重度入侵靠拢，但茎叶浸提液的作用效果小于根系。试验同时测定了紫茎泽兰根系和茎叶浸提液对已分离鉴定的8株紫茎泽兰根际优势细菌生长的影响，发现根系和茎叶浸提液都显著地促进了细菌的生长，且随着浸提液浓度的增大促进作用增强。结果表明紫茎泽兰可以通过茎叶淋溶物利根系分泌物改变土壤微生物的群落结构，它们间可能存在营养关系或化学通信联系。4．入侵地土壤微生物群落对紫茎泽兰生长、竞争的影响温室盆栽试验测定了被紫茎泽兰改变了的土壤微生物群落对紫茎泽兰生长、与当地植物竞争的影响，发现被紫茎泽兰入侵改变了的土壤微生物群落抑制了当地植物的生长，却增强了紫茎泽兰的竞争能力。重度入侵地土壤微生物群落对当地植物生长的抑制强度极显著地高于紫茎泽兰，灭菌处理使黑麦草生物量提高了23％，佩兰提高了93％，紫花苜蓿提高了73％，而紫茎泽兰仅提高了11％。与此相反，空白地土壤微生物对紫茎泽兰的抑制强度则显著地高于当地植物。当地植物区土壤微生物群落抑制了3种当地植物的生长，却促进了紫茎泽兰的生长。四种不同来源的土壤微生物群落都提高了紫茎泽兰相对优势度，重度入侵地土壤微生物群落提高紫茎泽兰相对优势度最为显著，比未入侵区土壤微生物群落对紫茎泽兰相对优势度的影响平均高出24％。结果表明紫茎泽兰入侵改变了的土壤微生物群落促进了紫茎泽兰生长和竞争。5．总结紫茎泽兰入侵改变了土壤微生物群落，提高土壤自生固氮菌、氨氧化细菌和真菌数量，也提高了土壤的有效磷、速效钾、硝态氮、氨态氮含量；同时其根际存在丰富的具有拮抗性能的细菌类群，可能是紫茎泽兰不受土传病害侵扰的原因；其根系和茎叶浸提液可以改变土壤微生物群落，促进根际细菌的生长；通过这些途径，紫茎泽兰获得了土壤微生物的有益反馈，为自身生长创造有利条件。这是一个自我促进（self-reinforcing）式的入侵机制：紫茎泽兰改变入侵地土壤微生物群落，创造了对自身生长有利的土壤环境。更多还原

【Abstract】 The rapid expansion of invasive plants in agricultural and natural ecosystem is threateningbiodiversity, productivity and ecosystem health throughout the world. Understanding the strategies usedby invasive plant for rapid proliferation is one of the most important problems in ecology, because thesuccessful invasion of particular species is neither mechanistically uniform nor predictable. Positivefeedback of soil biota may facilitate exotic plant invasion which attracts increasing attention recently.Ageratina adenophora （Sprengel） R. King & H. Robinson （Synonym: Eupatorium adenophorum） is anotorious worldwide invasive weed and one of the most unwanted in China. A. adenophora may alterunderground microbial communities, and the feedback of modified soil biota in invaded ranges maypromote its invasivibility. To examine this possible underground invasion mechanism, effects of A.adenophora invasion on soil microbial communities were analyzed, dominant rhizosphere microbes ofA. adenophora and their antibiosis activity were identified and assessed, and plant-soil biota feedbackexperiments were designed to measure the effect of invasion-induced changes of soil biota on A.adenophora growth and competition. The main results are as follows:1. Effects of A. adenophora invasion on native soil biota and soil nutritionSoil biota and soil nutrition were analyzed in the four sites （Heavily invaded, Newly invaded,Non-invaded and Native plant）, and the results showed that soil microbial community structure wasclearly separated in all the four sites, and A. adenophora significantly increased soil fungi, azotobacteria,ammonia oxidizing bacteria and soil VAM （Vesicular-arbuscular mycorrhizal fungi） abundance as wellas the fungi/bacteria ratio. Soil NO₃^--N, NH₄⁺-N, available P and K content were significantly higher inheavily invaded site as compared to the newly invaded site. Soil fungi, azotobacteria and ammoniaoxidizing bacteria were strongly associated with most of the measured soil nutrition characters. Itindicates that A. adenophora changed soil microbial communities, especially the soil nutrition cyclingrelated soil microbe groups and VAM, probably creating favorable soil environment to benefit itself.2. Screening and identification of A. adenophora dominant rhizosphere microbesTotally 25 strains of dominant rhizosphere bacteria of A. adenophora were isolated and identified,of which 8 strains were assessed of their antibiosis activity. The results showed that Bacillus andPseudomonas genus were in high abundance in A. adenophora rhizosphere soil, of which Bacillussubtilis and Bacillus megaterium were the most abundant and consist 55.6% of the total identifiedbacterium. These dominant identified bacteria showed antibiosis activity to Fusarium oxysporum andRalstonia solanacearum at different level and Bacillus subtilis BS-5 and Bacillus thuringiensis BT-1metabolic products had the strongest inhibitory effects to Fusarium oxysporum with antibiosis activity85.5% and 83.8% respectively. The abundant antagonistic bacteria around A. adenophora rhizospheremay help A. adenophora resist harmful soil-borne disease and provide a way to escape natural enemies.3. Effects of A. adenophora leachates on isolated dominant bacterium Soil biota incubation experiments were conducted by using A. adenophora leachates to imitatefield invasion processes. The results indicate that soil microbial community was significantly changedafter A. adenophora root and aerial part leachates treatment in 2 and 3 weeks, respectively. The newlyinvaded soil biota treated by 100% A. adenophora leachates was significantly different from the controland much closer to the heavily invaded soil. Growth of 8 strains dominant rhizosphere bacterium waspromoted by A. adenophora leachates. Effects of A. adenophora leachates on soil biota were in linearwith concentration of leachates and root leachates had stronger effects than aerial part leachates. A.adenophora can change soil microbial community through nutritional and chemical communication.4. Feedback of invasion-induced changes of soil biota to A. adenophora and nativesThe greenbouse experiment indicated that the soil biota in heavily invaded site had more inhibitoryeffects on native plant species than A. adenophora; and the soil biota in native plant site inhibited thegrowth of native plant species, but not of A. adenophora. In pots with soil from heavily invaded site,sterilization improved the biomass of Lolium perenne by 23%, of Eupatorium fortunei by 93%, ofMedicago sativa by 73%, and of A. adenophora by 11%. Soil biota in all of the four sites increased A.adenophora relative dominance as compared to each of the three native plant species, where soil biotain the heavily invaded site had stronger beneficial effects on A. adenophora relative dominance index（24% higher on average） than soil biota in the non-invaded site. Our results suggest that Ageratinaadenophora modified soil microbial communities to facilitate its growth and inhibit natives.5. SummaryA. adenophora is more positively affected by the soil biota in invaded sites than resident natives,and earns its competition superiority directly or indirectly through the beneficial soil biota andantagonistic rhizosphere microbes. Once it establishes in new ranges it further alters the soil communityin a way that favors itself and inhibits natives helping promote invasion. Soil biota alteration followingA. adenophora establishment may be an important part of its invasion process, which is used as anunderground self-reinforcing invasion mechanism to strengthen its invasiveness.更多还原