空心莲子草响应南方菟丝子寄生的生长-防御权衡

为探讨全寄生植物南方菟丝子(Cuscuta australis)防治入侵植物空心莲子草(Alternanthera philoxeroides)的可行性,以二者野外天然生长的种群为研究对象,分析南方菟丝子寄生对空心莲子草生长及防御的影响,阐明空心莲子草在受到寄生胁迫时如何权衡自身生长与防御的关系,进而发展出一套应对南方菟丝子寄生的生长-防御策略。结果显示:(1)南方菟丝子寄生显著改变空心莲子草茎的形态,茎直径和平均节间长均增加,茎直径变化极显著(P0.01);(2)南方菟丝子寄生显著减少空心莲子草叶片数,但同时显著增加后者茎的分枝数,而茎上的节是潜在的无性繁殖体,故有利于空心莲子草的克隆繁殖;此外,南方菟丝子寄生显著降低了空心莲子草的根、茎、叶生物量和总生物量,抑制空心莲子草的生长;(3)南方菟丝子寄生显著增加空心莲子草茎的单宁、总酚、三萜皂苷含量,增强其防御能力;(4)南方菟丝子寄生的空心莲子草的生物量与茎部木质素、三萜皂苷、单宁和总酚含量均呈现显著负相关性(P0.01),对照组则不存在相关性;且寄生组较对照组相比,生物量的相对百分比显著低于对照组(P0.01),而用于防御的次生代谢产物总含量的相对百分比显著高于对照组(P0.01)。以上结果表明,受到南方菟丝子寄生胁迫后,空心莲子草改变自身的生长-防御策略,减少营养生长投入而将更多的资源投向克隆繁殖,同时增强对"防御"物质的投入,增强其防御能力,以利于后代生存和繁衍。     

水陆生境和氮沉降对香菇草(Hydrocotyle vulgaris)入侵湿地植物群落的影响

大气氮沉降对湿地外来植物入侵的影响已成为生态学研究的热点之一。选用梭鱼草(Pontederia cordata)、水菖蒲(Acorus calamus)、黄花鸢尾(Iris wilsonii)和粉绿狐尾藻(Myriophyllum aquaticum)模拟湿地植物群落,设置有无香菇草入侵、水生和陆生生境(水位分别为15 cm和0 cm)及有无氮沉降处理(15 g N m~(-2)a(-1)和0)交叉组成的8种处理组合,进行为期70d的温室控制实验,以分析水陆生境及氮沉降对香菇草入侵湿地植物群落的影响。结果表明:(1)水生生境下,香菇草的总生物量、叶生物量、叶片数和节点数与陆生生境相比显著降低;水生生境下氮沉降处理对香菇草各指标无显著影响,陆生生境下氮沉降处理的香菇草叶片数、节点数显著多于无氮沉降处理。(2)实验周期内氮沉降和香菇草入侵没有对群落的多样性指数及群落内4种湿地植物的生物量产生显著影响;水生生境下植物群落的总生物量及梭鱼草和粉绿狐尾藻的生物量与陆生生境相比显著提高。(3)水生生境下香菇草的相对优势度相比陆生生境下显著下降;氮沉降只在陆生生境下显著提高了香菇草的相对优势度。因此,香菇草向水生生境扩散和入侵的能力不强,其入侵在短时间内对湿地植物群落影响较小。研究结果可以为入侵植物生态学研究提供案例借鉴。     

飞机草入侵种群和原产地种群生长和数量型化学防御物质含量差异的比较研究

增强竞争能力的进化假说认为,在入侵地外来植物逃离了原产地天敌的控制,把原来用于防御的资源分配到生长、生殖等,从而提高竞争力。为探讨进化在恶性外来入侵植物飞机草（Chromolaena odorata）入侵中的作用,在同质种植园中的两个养分条件下比较研究了飞机草原产地和入侵地各8个种群叶片单宁含量,茎和叶片总酚、半纤维素和纤维素含量以及总生物量的差异。结果表明,在两个养分条件下,飞机草入侵种群和原产地种群总生物量差异均不显著,入侵种群茎和叶片半纤维素含量均低于原产地种群;在高养分条件下,飞机草入侵种群叶片纤维素含量低于原产地种群;在低养分条件下,入侵种群茎和叶片总酚含量高于原产地种群。由此,我们得出结论：在入侵地,飞机草未发生加快生长的进化,但数量型化学防御物质发生了遗传变化;降低的半纤维素和纤维素含量可能是对入侵地专性天敌缺乏做出进化响应的结果,提高的总酚含量有利于飞机草防御入侵地的广谱天敌。     

不同生境下喜旱莲子草营养器官中抗氧化物质含量的比较

以水陆两种生境下生长的喜旱莲子草为实验材料 ,分别测定并比较了根、茎、叶可溶性蛋白及SOD、POD、Vc、GSH及绿原酸和类黄酮等抗氧化物质活性和含量 ,结果表明可溶性蛋白在叶中含量最高 ,并且水生环境中叶的含量高于陆生环境。除Vc外生态环境对各抗氧化物质含量影响具有一致性。水生环境下喜旱莲子草营养器官的抗氧化物质含量高于陆生环境下喜旱莲子草相应营养器官的含量。这是植物体内一种生理生化的生态适应     

酸雨和采食模拟胁迫下克隆整合对空心莲子草生长的影响

研究表明克隆整合可以显著提升异质环境中克隆植物的生长,然而当克隆植物遭受均质环境压力时,整合对植物生长影响的研究相对较少。本文以典型入侵克隆植物空心莲子草（Alternanthera philoxeroides）为例,研究均质环境压力酸雨和采食模拟胁迫对空心莲子草生长的影响,以及克隆整合在空心莲子草适应不利环境过程中所起的作用。酸雨设3种浓度梯度：pH值3.5 、pH值4.5和 pH值6.5（对照）;采食设3种水平：不去叶、去叶50%和去叶90%;整合水平：匍匐茎切断和连接。结果表明：无论保持或切断匍匐茎的连接,酸雨处理都不影响空心莲子草生物量。当保持匍匐茎连接时,pH值4.5酸雨处理增加了空心莲子草匍匐茎长度和分株数目,因此,低度酸雨可能对空心莲子草生长有一定的促进作用。同样,无论匍匐茎是否被切断,采食处理都显著降低了空心莲子草克隆片段生物量,而显著增加了叶片数目。当切断匍匐茎连接时,采食处理使空心莲子草分株数目显著增加。本文得出的结论是：空心莲子草能较好地适应酸雨和采食的环境压力,当空心莲子草全部克隆分株遭受均质环境胁迫时,克隆整合并不能显著改善它的生长。     

光照和氮素对喜旱莲子草形态特征和生物量分配的影响

研究了两个光照梯度和3个土壤氮素水平交互作用对喜旱莲子草(Alternan thera philoxeroides(Mart.)Griseb.)形态特征和生物量分配的影响。结果表明,全光照促进喜旱莲子草总生物量的积累,但在遮荫条件下,喜旱莲子草可以通过增加株高、光合叶面积和改变生物量分配来适应弱光生境。土壤中氮素含量对喜旱莲子草生长有明显影响,总生物量、株高、叶面积、茎生物量比和叶生物量比等随土壤氮素水平增加而增加。光照和氮素的交互作用对总生物量、根生物量比、茎生物量比和叶生物量比也有显著影响。随着氮素水平的增高,遮荫和高光照处理下喜旱莲子草的叶面积、总生物量和叶生物量比之间的差异减小,而株高和根生物量比之间的差异增大。此外,光照强度对茎生物量比的影响具有明显的氮素浓度依赖性,低氮条件下,茎生物量比在高光照处理下显著高于遮荫处理,而在中氮条件下,遮荫处理却显著高于高光照处理,且在高氮处理下其差异进一步加大。这些结果表明喜旱莲子草在高氮素环境下能够通过形态可塑性和生物量分配模式的改变来适应弱光环境所带来的不利影响。研究结果不但可为研究喜旱莲子草对异质生境的入侵机制提供资料,也可为进一步研究喜旱莲子草的入侵和扩散与农业等生态系统中土壤氮素残留的关系提供参考。       

喷施茉莉酮酸甲酯及感染内生真菌对羽茅生长的影响

以天然禾草羽茅为试验材料,外源喷施茉莉酮酸甲酯(MJ)模拟食草昆虫的采食,研究感染内生真菌(染菌)和不染菌羽茅生长及生理等方面的差异.结果表明:MJ处理显著降低了羽茅地上部分生长,显著提高了其防御物质总酚和木质素的含量,并降低了蚜虫种群数量.染菌能显著增加羽茅的分蘖数及地上总酚和木质素的含量,但地上生物量和地下总酚含量受到MJ处理的影响,在不喷施MJ的对照中,染菌与否对羽茅的地上部生物量及地下总酚含量无显著影响,而MJ处理下,染菌植株的地上生物量显著低于不染菌植株,而地下总酚含量显著高于不染菌植株.染菌能显著降低羽茅上蚜虫的种群数量,而且这一影响被MJ处理所促进,当受到3次MJ喷施处理后,染菌羽茅上不再有蚜虫.表明内生真菌感染能够改变宿主植物在生长和防御之间的物质分配,MJ处理则进一步促进染菌植株以牺牲生长为代价而提高其防御能力.     

Effects of elevated temperature on chemistry of an invasive plant,its native congener and their herbivores

增温对莲子草属入侵植物与本地同属植物化学物质组成和天敌昆虫的影响 气候变暖影响植物生长和生理活动,然而气候变暖如何改变入侵植物化学物质组成并间接影响其与植食性昆虫互作还少有报道。本研究以入侵植物空心莲子草(Alternanthera philoxeroides)及其本地同属 植物莲子草(A. sessilis)为对象,探究增温对其叶片化学物质组成的影响并进一步检验这些变化如何影响两 种植食性昆虫虾钳菜披龟甲(Cassida piperata)和斜纹夜蛾(Spodoptera litura)的生长发育。通过模拟增温实验,探究增温对空心莲子草和莲子草13个叶片化学物质的影响,并用其饲养两种植食性昆虫,测量它们的生长和发育时间。研究结果显示,增温显著改变了空心莲子草和莲子草叶化学物质组成;增温降低了空心莲子草叶片氮浓度,增加了莲子草叶片总黄酮和总酚浓度;增温对其它营养物质(果糖、蔗糖、总可溶性糖和淀粉)随物种和具体物质发生改变;采用增温处理的莲子草饲养的虾钳菜披龟甲蛹重和斜纹夜蛾幼虫重量,以及增温处理的空心莲子草饲养的斜纹夜蛾幼虫重量,显著低于对照不增温处理;此外,采用增温处理的莲子草饲养的斜纹夜蛾幼虫发育时间显著延长。这些结果表明,增温对植物化学物质组成的影响随物种发生变化,增温对入侵植物和本地植物化学物质组成的影响间接改变了其与植食性昆虫的互作关系。     

喜旱莲子草入侵群落土壤对植物生长的影响

分别以受喜旱莲子草(Alternanthera philoxeroides)入侵和未受喜旱莲子草入侵的当地植物群落土壤为生长基质,比较不同基质上入侵植物喜旱莲子草和同属的土著植物莲子草(A.sessilis)的生长指标,探讨喜旱莲子草入侵群落土壤对喜旱莲子草及莲子草生长的影响机制。结果表明,喜旱莲子草入侵群落土壤抑制了莲子草的生长,显著降低了根生物量、茎生物量和总生物;改变了形态特征,显著降低了分枝数量、茎长度、根长、根体积;减少了对根的生物量分配,显著抑制了根质量比与根冠比。喜旱莲子草入侵群落土壤对入侵植物喜旱莲子草的生物量、分枝数量、茎长度、根长、根体积没有显著的抑制作用,而显著增加了其叶片数量和叶质量比。这种效应将有利于喜旱莲子草在入侵地形成单优群落,表明土壤在喜旱莲子草成功入侵中起了重要作用。     

草海自然保护区空心莲子草群落植物组成及多样性分析

湿地生态系统极易受外来入侵植物侵害, 为调查草海湿地生态系统空心莲子草不同入侵程度的群落物种组成及多样性的变化, 在夏季对草海自然保护区水陆生境的空心莲子草群落进行调查, 按空心莲子草盖度分为水Ⅰ(0-20%)、水Ⅱ(20%-50%)、水Ⅲ(50%-100%)、陆Ⅰ(0-20%)、陆Ⅲ(50%-100%)五种群落类型。结果表明: 在调查的25 个样方中, 水生生境共有10 科22 种植物, 陆生生境共有13 科29 种植物, 随空心莲子草入侵程度的增加, 禾本科植物在两种生境中比例均上升; 地面芽植物种类减少; 根茎型植物种类增加; 水中丛生型植物种类增加, 陆地分枝型植物种类减少; 水中物种丰富度增加, 陆地物种丰富度降低; 两生境多样性和均匀度均呈一致的下降。     

Effects of simulated herbivory and resource availability on the invasive plant, Alternanthera philoxeroides in different habitats

In biological control programs, the insect natural enemy’s ability to suppress the plant invader may be affected by abiotic factors, such as resource availability, that can influence plant growth and reproduction. Understanding plant tolerance to herbivory under different environmental conditions will help to improve biocontrol efficacy. The invasive alligator weed (Alternanthera philoxeroides) has been successfully controlled by natural enemies in many aquatic habitats but not in terrestrial environments worldwide. This study examined the effects of different levels of simulated leaf herbivory on the growth of alligator weed at two levels of fertilization and three levels of soil moisture (aquatic, semi-aquatic, and terrestrial habitats). Increasing levels of simulated (manual) defoliation generally caused decreases in total biomass in all habitats. However, the plant appeared to respond differently to high levels of herbivory in the three habitats. Terrestrial plants showed the highest below–above ground mass ratio (R/S), indicating the plant is more tolerant to herbivory in terrestrial habitats than in aquatic habitats. The unfertilized treatment exhibited greater tolerance than the fertilized treatment in the terrestrial habitat at the first stage of this experiment (day 15), but fertilizer appears not to have influenced tolerance at the middle and last stages of the experiment. No such difference was found in semi-aquatic and aquatic habitats. These findings suggest that plant tolerance is affected by habitats and soil nutrients and this relationship could influence the biological control outcome. Plant compensatory response to herbivory under different environmental conditions should, therefore, be carefully considered when planning to use biological control in management programs against invasive plants.     

Multi-generational effects of simulated herbivory and habitat types on the invasive weed Alternanthera philoxeroides: implications for biological control

Long-term pre-release evaluations of how invasive plants respond to herbivory in introduced ranges can help identify the most effective biological control agents. However, most evaluations have been conducted within only one generation of introduced invasive species. This study tested effects across seven generations of simulated herbivory (i.e., defoliation) and habitat types on the invasive weed Alternanthera philoxeroides. We found total biomass of A. philoxeroides was decreased by defoliation during the first three generations when grown in a simulated aquatic habitat, but was decreased by defoliation only in the first generation when grown in a simulated terrestrial habitat. Defoliation significantly decreased stem diameter and collenchyma thickness and increased cortex thickness and total phenol production in A. philoxeroides grown in a simulated terrestrial or aquatic habitat during the first generation, but showed little effect during the following six successive generations. The associations between stem anatomical structural parameters and biomass significantly differed between non-defoliation and defoliation treatments in the simulated aquatic habitat, but not in the simulated terrestrial habitat. Our results suggest simulated herbivory exerted successful biological control on A. philoxeroides during the first generation in a simulated terrestrial habitat and the first three generations in a simulated aquatic habitat, but failed to restrain the vegetative offspring of A. philoxeroides. This failure of long-term biological control on A. philoxeroides might be caused by changes in the stem anatomical structure and compensatory growth. Our study highlights the need for long-term pre-release evaluation when testing the efficiency of biological control agents.

     

The Invasive Plant Alternanthera philoxeroides Was Suppressed More Intensively than Its Native Congener by a Native Generalist: Implications for the Biotic Resistance Hypothesis

Prior studies on preferences of native herbivores for native or exotic plants have tested both the enemy release hypothesis and the biotic resistance hypothesis and have reported inconsistent results. The different levels of resistance of native and exotic plants to native herbivores could resolve this controversy, but little attention has been paid to this issue. In this study, we investigated population performance, photosynthesis, leaf nitrogen concentration, and the constitutive and induced resistances of the successful invasive plant, Alternanthera philoxeroides, and its native congener, Alternanthera sessilis, in the presence of three population densities of the grasshopper, Atractomorpha sinensis. When the grasshopper was absent, leaf biomass, total biomass, photosynthesis, and leaf nitrogen concentration of A. philoxeroides were higher than those of A. sessilis. However, the morphological and physiological performances of A. philoxeroides were all decreased more intensively than A. sessilis after herbivory by grasshoppers. Especially as the concentrations of constitutive lignin and cellulose in leaf of A. philoxeroides were higher than A. sessilis, A. philoxeroides exhibited increased leaf lignin concentration to reduce its palatability only at severe herbivore load, whereas, leaf lignin, cellulose, and polyphenolic concentrations of A. sessilis all increased with increasing herbivory pressure, and cellulose and polyphenolic concentrations were higher in A. sessilis than in A. philoxeroides after herbivory. Our study indicated that the capability of the invasive plant to respond to native insect damage was lower than the native plant, and the invasive plant was suppressed more intensively than its native congener by the native insect. Our results support the biotic resistance hypothesis and suggest that native herbivores can constrain the abundance and reduce the adverse effects of invasive species.     

入侵植物水花生解剖学和组织化学染色研究

水花生(Alternanthera philoxeroides)因其表型可塑性、高生长速率和快速无性繁殖能适应水、陆生境。该文利用光学显微镜和荧光显微镜对水、陆生境的水花生不定根、茎解剖结构、组织化学特征及质外体通透性进行了研究。结果表明:(1)水生境下,其不定根皮层中具较大裂生型通气组织,无次生生长,内皮层具凯氏带且栓质化,皮层和皮下层明显木质化。(2)在陆生环境下,其不定根有次生生长,胞间具通气组织,内皮层具凯氏带且栓质化,皮层和皮下层略木质化;此外,不定根还具额外形成层,产生次生维管束、薄壁组织和不定芽;多年生不定根中具直接分裂的薄壁组织,周皮具凯氏带,且栓质化和木质化。(3)水、陆生境下,其匍匐茎具髓和中空髓腔,发生次生生长,具裂-溶生型通气组织、单层内皮层、厚角组织和木质化且栓质化的角质层,陆生匍匐茎周皮栓质化且木质化。(4)水花生质外体屏障结构组成复杂,黄连素无法穿透质外体屏障结构。水花生的上述解剖学特征,是水花生适应水、陆生境的有力证据。     

喜旱莲子草对喀斯特三种不同生境的可塑性反应

喜旱莲子草自入侵以来在我国各地广为传播蔓延,对人们生产生活产生了重要影响。该研究通过野外采样和室内理化指标分析,探讨喀斯特不同生境中喜旱莲子草的可塑性。结果表明:(1)在三种生境中喜旱莲子草的节间长度、叶面积、单株重和叶干重差异显著。(2)在岩石环境中其无性繁殖器官——茎的投入比例占其生物量的比例最大,其次是行道生境和湘江河道。(3)节间距随环境因子从岩石环境、绿化行道和水生生境的变化,依次增加,叶质比(叶面积/质量)也随水分环境的增加而增加;(4)在岩石环境中,喜旱莲子草通过缩短节间距并增加无性繁殖器官——茎的质量来增加其在水分匮乏生境的繁殖能力。该研究结果为喜旱莲子草今后的防治对策提供了科学依据。     

Differences in physiological traits and resistances of <Emphasis Type="Italic">Alternanthera philoxeroides</Emphasis> after herbivory by generalists and specialists

Many researchers have surveyed damages caused by natural enemies of invasive plants in both native and introduced ranges to test the enemy release hypothesis. In this study, we report our findings on the physiological and morphological impacts of a co-evolved specialist insect (Agasicles hygrophila) and two generalist insects (Atractomorpha sinensis and Hymenia recurvalis) in introduced ranges on an invasive plant, Alternanthera philoxeroides, in both field trials and controlled environments. The resistance of A. philoxeroides against the generalists and the specialist was also studied. We obtained consistent results in both the field trials and the controlled treatments: both the generalists and the specialist decreased leaf biomass, photosynthesis, leaf nitrogen content, and total leaf non-structural carbohydrate content in A. philoxeroides. However, the specialist decreased leaf mass, photosynthesis, and leaf nitrogen content more acutely than the generalists. Moreover, A. philoxeroides increased both leaf lignin and cellulose concentrations upon the generalists’ attack but only increased cellulose concentration in response to the specialist. Our results showed that even under the same population density, the co-evolved specialists from original ranges caused more severe morphological and physiological damage to A. philoxeroides than the generalists in introduced ranges. This revealed that invasive plants released some herbivory stress before their co-evolved specialists were introduced, which may contribute to the superior performance of invasive plants in introduced regions.     

Effects of a nematode Meloidogyne incognita and its interaction with above‐ground herbivory on an invasive wetland plant,alligator weed (Alternanthera philoxeroides)

Invasive plants may be attacked both above ground and below ground. Few studies have, however, investigated the simultaneous effects of above‐ground and below‐ground herbivory. In the present study, we report the effects of beetle herbivory and nematode infection on alligator weed, Alternanthera philoxeroides, an invasive plant in China. We found that the root‐knot nematode Meloidogyne incognita widely occurred on the plant in south China. To examine its effect on the plant in conjunction with above‐ground herbivory, we conducted a field common garden experiment with a local insect defoliator, Cassida piperata. We also included the native congener Alternanthera sessilis in our experiments for a comparison of the response of invasive and native species. We found no significant effects on plant biomass of the nematode infection in conjunction with the above‐ground herbivory. Further chemical analysis, however, showed that the water‐soluble carbohydrate content in roots of A. philoxeroides was significantly increased in plants attacked by both the nematode and the herbivore compared with the water‐soluble carbohydrate content in plants attacked by only the nematode or herbivore alone. We found no such change in the native congener A. sessilis. Together these results may suggest that A. philoxeroides tolerates joint above‐ground and below‐ground damage by allocating more resources to below‐ground material.     

The interspecific competition between Humulus scandens and Alternanthera philoxeroides

Bioinvasion has become a serious environmental problem in the world in general and is considered the second biggest threat to biodiversity. Alternanthera philoxeroides is widely distributed and causes the most serious threat to biodiversity in China. The traditional physical or biological control methods are not effective in controlling the invasion and extension of A. philoxeroides. In the present paper, some physiological characteristics of Humulus scandens and A. philoxeroides were investigated in the field and laboratory. The results showed that H. scandens is more competitive than A. philoxeroides, the competitive rate (CR) of H. scandens against A. philoxeroides was 9.834. Additionally, the leaf, stem, and root biomass of A. philoxeroides decreased significantly when the two species co-occurred. Thus, the invasive abilities of these two invasive plants are different and H. scandens strongly inhibited the growth of A. philoxeroides. Moreover, as an annual herb, H. scandens can be easily eliminated by harvesting before its seeds mature. The result suggests that sowing seeds of H. scandens in the habitats invaded by A. philoxeroides could be an ideal biological control method.     

Phenotypic plasticity rather than locally adapted ecotypes allows the invasive alligator weed to colonize a wide range of habitats

Both phenotypic plasticity and locally adapted ecotypes may contribute to the success of invasive species in a wide range of habitats. Here, we conducted common garden experiments and molecular marker analysis to test the two alternative hypotheses in invasive alligator weed (Alternanthera philoxeroides), which colonizes both aquatic and terrestrial habitats. Ninety individuals from three pairs of aquatic versus terrestrial populations across southern China were analyzed, using inter simple sequence repeat (ISSR) marker, to examine population differentiation in neutral loci. Two common gardens simulating aquatic and terrestrial habitats were set up to examine population differentiation in quantitative traits. We found no evidence of population differentiation in both neutral loci and quantitative traits. Most individuals shared the same ISSR genotype. Meanwhile, plants from different habitats showed similar reaction norms across the two common gardens. In particular, plants allocated much more biomass to the belowground roots in the terrestrial environment, where alligator weed may lose part or all of the aboveground shoots because of periodical or accidental disturbances, than those in the aquatic environment. The combined evidence from molecular marker analysis and common garden experiments support the plasticity hypothesis rather than the ecotype hypothesis in explaining the adaptation of alligator weed in a wide range of habitats.