【作者】 田耀华；

【导师】 曹坤芳； 冯玉龙；

【作者基本信息】 中国科学院研究生院（西双版纳热带植物园） ， 生态学， 2007， 博士

【摘要】 紫茎泽兰(Ageratina adenophora(Sprengl)R. King & H. Robinson orEupatorium adenophorum Sprengel)是我国危害最严重的外来入侵植物之一,是西南地区热带亚热带草地、农田、次生林、撂荒地等生境中一种常见的多年生入侵杂草。在紫茎泽兰的入侵过程中,其化感物质可能会在入侵地土壤中逐渐积累,土壤微生物群落也可能受到影响,土壤肥力(土壤养分和土壤酶活性)改变。土壤的这种变化可能会影响到紫茎泽兰和其它植物的竞争关系,创造有利于紫茎泽兰自身生长,而不利于其它植物生长的土壤环境,促进紫茎泽兰的入侵,阻碍入侵地的生态恢复。为了研究紫茎泽兰入侵对土壤环境的干扰及其对紫茎泽兰、本地植物和牧草的影响,探讨土壤环境变化与紫茎泽兰入侵性、入侵地生态恢复的关系,本文设计了以下试验:(1)通过比较紫茎泽兰草丛、撂荒地草丛、云南菅(Themeda yunnanensis)草丛和非洲狗尾草(Setaria anceps)草丛群落间土壤养分和土壤酶活性等土壤肥力指标的差异,研究紫茎泽兰对土壤肥力的影响。(2)在实验室内利用多年生紫茎泽兰群落下的土壤作为种子萌发的培养介质,研究紫茎泽兰入侵地土壤中是否有化感物质的积累;通过在野外构建拔毒散(Sida szechuensis)、黄花蒿(Artemisia myriantha)、伏生臂形草(Brachiaria decumbens)和非洲狗尾草的单种人工群落,研究自然条件下多年生紫茎泽兰土壤中残留的化感物质对各植物的生长特性、生物量分配、形态和光合特性等的影响,探讨土壤中残留的化感物质的生态学效应。(3)通过在野外设置不同氮肥供给水平和种植密度下的紫茎泽兰、拔毒散、伏生臂形草和非洲狗尾草的单种和紫茎泽兰与其它3种植物混种的人工群落,比较研究氮肥水平和竞争对4种受试植物的影响,探讨土壤肥力的改变对4种植物的影响,从“地上植被—土壤肥力”相互作用的角度分析紫茎泽兰的入侵机制,为紫茎泽兰入侵地的生态恢复提供基础性的科学依据。主要结果如下:(1)土壤多酚氧化酶、碱性磷酸酶和脲酶活性在不同群落和不同土层间均有明显的差异,并且与土壤养分含量有较显著的相关性,可以作为表征土壤肥力高低的指标。其中,紫茎泽兰草丛下这3种酶的活性均较高,土壤有机质、全氮、全钙、全镁、水解氮、有效磷含量也较高,与本地植物群落云南菅草丛下土壤肥力水平相近,高于撂荒地和狗尾草草丛,表明研究地区草地被干扰破坏后,紫茎泽兰成功入侵并定植多年后土壤肥力水平有所改善。(2)多年生紫茎泽兰群落下的土壤能明显抑制拔毒散、黄花蒿和非洲狗尾草的种子萌发率、苗高和苗干重,表明紫茎泽兰入侵地土壤中有化感物质的残留。但不同植物和不同参数对紫茎泽兰化感物质的敏感程度不同,相同活性碳处理下拔毒散和黄花蒿的种子萌发率、苗长和苗干重低于非洲狗尾草,表明非洲狗尾草的种子萌发尽管受到了土壤中紫茎泽兰残留的化感物质的影响,但与本地植物相比,其所受影响较小。田间试验的2个生长季中,活性碳处理均能使拔毒散、黄花蒿、伏生臂形草和非洲狗尾草的总生物量、株高、分枝数、叶面积、最大净光合速率和氮利用效率升高,使根冠比降低,清除紫茎泽兰后其在土壤中残留的化感物质仍然能对其它植物的生长有持续性的抑制作用。表明化感作用与紫茎泽兰的入侵性有关。不同植物对土壤中残留的化感物质敏感程度不同,4种受试植物中,非洲狗尾草受到的抑制作用最小,因此在适宜环境条件下可以选择其作为替代植物,对紫茎泽兰入侵地进行生态恢复。(3)单种时紫茎泽兰、拔毒散、伏生臂形草和非洲狗尾草均表现了对氮营养的响应,随氮肥水平的升高,4种植物的根冠比和根生物量分数降低;叶生物量分数和叶面积比升高。比较4种植物总生物量增幅发现:非洲狗尾草的氮响应能力>伏生臂形草>紫茎泽兰>拔毒散。通过混种时受试植物与紫茎泽兰的生物量比和株高发现:非洲狗尾草的竞争能力>伏生臂形草>紫茎泽兰>拔毒散,与单种时各植物的氮响应能力相符。中等种植密度下紫茎泽兰对拔毒散的抑制作用最强,低种植密度高氮肥水平下伏生臂形草和非洲狗尾草对紫茎泽兰的抑制作用最强,表明与拔毒散混种的紫茎泽兰以及与紫茎泽兰混种的伏生臂形草和非洲狗尾草的种内竞争随种植密度的增大而增大,导致种间竞争能力下降,在高种植密度下对混种物种的抑制作用减弱。紫茎泽兰入侵导致土壤肥力提高,残留在入侵地土壤中的化感物质抑制其它植物的正常生长,两方面的因素共同形成有利于其自身生长的土壤环境,紫茎泽兰与土壤的正反馈作用是其成功入侵的原因之一。紫茎泽兰在氮响应能力、竞争能力和表型可塑性方面均强于本地种,可能是与其入侵机制有关;牧草的氮响应能力和竞争能力强于紫茎泽兰,其中非洲狗尾草又强于伏生臂形草,可能更适宜于入侵地的生态恢复。试验结果暗示了简单清除紫茎泽兰植株并不能真正实现紫茎泽兰入侵地的生态恢复,应该考虑修复入侵地的土壤环境以及选择适宜的替代植物控制紫茎泽兰。更多还原

【Abstract】 Biological invasion, a present focus of ecological research, severely threatensthe biodiversity of native ecosystems and has caused significant native ecosystemdeterioration and economic loss to the world. Ageratina adenophora, a noxiousperennial forb, has invaded a large area of open habitats and grasslands in tropicaland subtropical areas of southwestern China. A common and important managingpractice is to restore the habitats that have been invaded bythis exotic species usinghigh biodiversity of native species or to cultivate forage grasses with a lowbiodiversitybuthighyieldandeconomicgain.In the present dissertation, the interference of soil environment induced by A.adenophora invasion, including impacts on soil fertility and allelochemicalsremained in soil were examined. Moreover, the effects of these changes on thegrowth, morphological, biomass allocation and photosynthetic trails of this invasivespecies itself, native forbs and grass species were investigated. The experimentdesignsandmainresultsareasfollows:(1) The comparison was made on the activities of six enzymes and 12 physicaland chemical factors in four layers of soil within 0~30 cm depth of four differentcommunities: a grassland invaded by A. adenophora for more than ten years, asecondary grassland that was abandoned from a maize field in November of 2001, aprimary grassland of Themeda yunnanensis, and a two years old artificial grasslandof S. anceps, respectively. The results showed that the activities of polyphenoloxidase, alkaline phosphatase and urase changed significantly among communitiesand soil layers, and were closely related to most of the variables affecting soilfertility, indicatingthat these enzymes can be used as indicator of soil fertility. Theactivities of these three enzymes, content of organic matter, total N, total Ca, totalMg, hydrolyzable N, active P, and pH value were higher in the soil under A.adenophora community compared to the soils under the other communities. These resultsindicatethatlong-termA.adenophorainvasioncanincreasesoilfertility.(2) In the laboratory, seeds of two native forbs (Sida szechuensis and Artemisiamyriantha) and one grass (Setaria anceps) were germinated in the soil that had beeninfested by A. adenophora for more than ten years. Activated carbon (AC) wasmixed into the soil to eliminate allelopathic effects of A. adenophora. The ACtreatment significantly increased the seed germination rate, shoot length and shootdry weight of the seedlings of these species, indicating the allelopathic effectremainedinthesoil.In the grassland that had been infested by A. adenophora for more than tenyears,twonativeforbs (S.szechuensis andA.myriantha)andtwointroducedgrasses(Brachiaria decumbens and S. anceps) were grown separately for two years. As awhole, activated carbon (AC) treatment increased the total biomass, plant height,branch number, total leaf area, maximum net photosynthetic rate and nitrogenutilization efficiency of the four species, and decreased their root / crown ratios.These results revealed that allelochemicals of A. adenophora remained in soil for along time and suppressed other plant species but promoted itself growth. Amongthe tested species, the least allelopathic effects by A. adenophora was found on S.anceps, indicating this grass species is a suitable candidate to be used for theecologicalrestoration.(3) Another field experiment, lasting for two years, was carried out withmonocultures of A. adenophora, S. szechuensis, B. decumbens and S. anceps, andmixed cultures (50/50%) with A. adenophora and other three species in threedifferent nitrogen and densitylevels. The results showed that monocultures of fourspecies exhibited considerable nitrogen-acclimation abilities. With the increase ofnitrogen levels, their root mass fraction and root / crown mass ratio decreased, buttheir leaf mass fraction and leaf area ratio increased. The extent of increase inbiomass growth with the nitrogen level was: S. anceps > B. decumbens > A.adenophora > S. szechuensis. Inmixedcultures,theresultsshowedthesametrend.Under intermediate density level, the greatest adverse effect by A. adenophora wasfound on S. szechuensis, while under low density and high nitrogen level, S. anceps and B. decumbens suppressed A. adenophora. These results revealed that theintraspecificcompetitionofthedominantspecies inthemixedcultureincreasedwithdensity, resulting in decrease of interspecific competition and the decreasedinhibitingeffectsonthemixedspeciesunderhighdensitylevelbyA.adenophora.Insummary,thepresentstudyindicatesthatA.adenophorainhibitedthegrowthof other species via increasing soil fertility and allelochemicals remained in the soilto promote itself. The positive feedback between A. adenophora and soilenvironment is related to its invasiveness, ensuring its competitive dominance incommunity. Therefore, it is difficult to restore a habitat invaded heavily by thisspeciesbysimplycleaningmethod. It isnecessarytorestoresoilenvironmentsandtousethereplacementmethodwithsuitableplantspecies.更多还原