【作者】 袁月；

【导师】 王开运； 李德志；

【作者基本信息】 华东师范大学 ， 生态学， 2014， 博士

【摘要】 崇明东滩湿地是国际重要湿地,为一些珍稀濒危水鸟提供越冬场所。同时,由于其特殊的地理位置和生境状况,容易遭受外来种的入侵。花米草就是入侵崇明东滩湿地的外来植物种之一。互花米草为禾本科米草属植物,原产于大西洋沿岸。最初引种东滩的目的是为了促淤造陆。但后来,在东滩东部与北部,互花米草大面积扩散并不断排挤本地种海三棱藨草,占领了整个低潮位与大部分中潮位。与此同时,人工大面积的围垦活动造成高潮位的部分植被消失,尤其是与互花米草竞争能力相当的本地种芦苇的扩散也受到了人为因素的严重干扰。在这样的背景下,互花米草在短短几十年时间内成为入侵崇明东滩的害草,严重影响了当地生物多样性以及生态系统的平衡,一些水鸟也因此失去了赖以生存的生境。芦苇为崇明东滩湿地的优势种之一,具有很强的无性繁殖能力与竞争能力,适合生长在潮间带滩涂上。有研究表明芦苇与互花米草的竞争能力不相上下,一旦某一个种占领了空白生态位,另一个种就很难再入侵。因此,为了有效控制互花米草的蔓延,利用芦苇生物替代互花米草是比较有效的一种生物治理方法。这种方法既不会造成化学污染,也不会引起天敌入侵,同时节约人力物力。更重要的是,一旦成功将不仅有助于提高生物多样性,还可以优化潮间带植被格局、形成更为稳定的潮间带生态系统。基于上述背景,本论文研究了崇明东滩湿地沿潮位梯度芦苇与互花米草种群间关系格局并探讨了相关影响因素。论文得出的主要结果如下：(1)芦苇与互花米草均为目前崇明东滩湿地的优势植物,二者的重要值总体而言相差不大。具体来说,互花米草在多度上占优势,芦苇在高度上占优势；芦苇在潮位较高的区域处于优势地位,互花米草在潮位较低的区域处于优势地位,在潮间带中部广阔的区域两种植物镶嵌分布。研究区植被大体上有四种斑块：芦苇斑块、互花米草斑块、两种植物混生斑块以及空白斑块(其中有时混有极少量其他植物),沿潮位梯度植物斑块的种类与面积有很大差异。通过计算不同斑块的景观水平格局指数,发现：芦苇种群的斑块密度和边缘密度均显著大于互花米草种群,表明芦苇种群的破碎化程度要比互花米草种群高；芦苇种群斑块、互花米草种群斑块和空白斑块的聚集度都较大,连通度指数接近100；三类斑块在1500m×100m尺度斑块水平上结构较为紧凑、连通性较强。景观形状指数为6.59,表明东滩植被景观水平上的形状并不复杂。从种群地上部分年龄结构来看,芦苇与互花米草均在潮位梯度相对较高的区域为增长型结构,而在潮位梯度相对较低的区域为稳定型的结构,说明低潮位受潮水淹没频繁,不利于幼苗的常年萌发。(2)芦苇与互花米草采取了不同的竞争策略适应潮间带多变的生境。首先,芦苇与互花米草均为克隆植物,在克隆构型上有所差异：芦苇倾向于游击型结构、互花米草则倾向于密集型或混合型结构。克隆构型的差异决定了二者对于土壤水分与营养吸收能力上的差异。其次,本文从表观生长能力、繁殖能力和潜在生长能力三个方面分别比较了芦苇与互花米草的竞争能力。对于表观生长能力来说,互花米草的平均相对生长率远远高于芦苇,然而芦苇在生长末期达到的最大高度比互花米草要高,这说明芦苇具有较大的高度变异能力。芦苇总生物量一般显著高于互花米草,这是因为芦苇地下根茎较粗壮,有利于生物量积累。从芦苇与互花米草的繁殖能力来比较,互花米草的有性繁殖能力较高,芦苇的无性繁殖能力较高。芦苇占据生境的方式主要是通过粗大的根茎进行拓展,而互花米草则主要通过无性繁殖获得更多的植株、提高植株密度以及通过有性繁殖占领新领地而开拓生境。从潜在生长能力上来看,互花米草的净光合速率以及最大光合效率高于芦苇,而芦苇的光化学效率高于互花米草。芦苇可溶性糖含量以及营养元素N、P含量均显著高于互花米草。(3)芦苇与互花米草的竞争能力不同。通过单混生群落调查与野外移除试验研究,我们发现,芦苇与互花米草的种间关系既有促进的一面,又有竞争的一面。单混生群落实验研究的结果表明：对于平均高度和生物量来说,目标种对邻居种存在的反应随着潮位梯度的不同而不同。在相对高、低潮位,邻居种的存在刺激了目标种的生长表现,而在相对中潮位,邻居种的存在抑制了目标种的生长表现。另外,竞争也有利于植物的繁殖,在邻居种存在的样方内,互花米草与芦苇的萌发率均较大。其中,利用平均高度作为响应指标计算两种植物的三种竞争指数,发现两种植物的种间关系为竞争关系。而利用其他参数作为响应指标计算两种植物的竞争指数,发现两种植物的种间关系为互利关系。在野外移除试验研究中,选择相对生长率(RGR)与每天新产生的幼苗数(TNT)两个指标作为测定竞争指数的响应参数。当以RGR为参数时,在相对高潮位与相对中潮位,互花米草的绝对竞争强度(ACI)与相对邻里效应指数(RNE)均为负值,而芦苇的绝对竞争强度(ACI)与相对邻里效应指数(RNE)均为正值。在相对低潮位,芦苇与互花米草的绝对竞争强度(ACI)与相对邻里效应指数(RNE)均为正值,表明二者彼此竞争。随着潮位梯度的下降(从高潮位到低潮位),互花米草的竞争力指数(Ⅰ)值由负变正,芦苇的Ⅰ值均为正且逐渐减小。说明随着潮位梯度的下降,芦苇对互花米草的竞争力逐渐降低。另外,在三个潮位芦苇对互花米草均有拥挤度效应(Dr),其中,在相对中潮位效应值最高。而互花米草对芦苇在相对高、低潮位时具有拥挤度效应,在相对中潮位时不具有拥挤度效应。当以TNT为参数时,在相对高、中潮位,芦苇与互花米草对彼此的竞争效应均为负值,说明二者的种间关系为互利的。在相对低潮位,互花米草对芦苇是有利的,而芦苇对互花米草是竞争的。随着潮位梯度的下降(由高潮位到低潮位),芦苇的Ⅰ值由负变正,说明芦苇对互花米草的竞争力逐渐增强；互花米草的Ⅰ值均为负且绝对值大小在中潮位时最低,说明互花米草对芦苇没有竞争力。在三个潮位,互花米草与芦苇对彼此均具有拥挤度效应,且在相对高、中潮位,芦苇对互花米草的拥挤度效应较高：在相对低潮位,互花米草对芦苇的拥挤度效应较高。总之,芦苇与互花米草的种间关系大多数情况是互利的,而当芦苇与互花米草的种间关系为竞争时,互花米草总的竞争效应高于芦苇。芦苇与互花米草竞争效应指数的方向与竞争力指数的方向一致,拥挤度效应只能影响竞争指数的大小。(4)人为干扰对于芦苇和互花米草的生长具有强烈的影响。本文分析了刈割后两种植物的补偿生长效应。发现：芦苇对于重度刈割后的补偿生长能力不如互花米草。芦苇在被全部刈割与刈割1/2高度后,高度、密度与生物量值均降为0,说明刈割后的三个月,芦苇再没有重新萌发和生长。然而互花米草在全部处理后,都重新萌发和生长。但对于1/2密度刈割干扰下,芦苇的补偿能力强于互花米草,不仅从单株高度、生物量水平上进行恢复,在群体水平(密度)上也得到了补偿。这说明适当的稀疏处理有助于芦苇种群的扩散。然而,在崇明东滩,大面积围垦与冬季牲畜啃食常常给芦苇的生长造成不可恢复的干扰,而这对互花米草的影响却并不大,这也是目前互花米草在崇明东滩大肆蔓延的重要因素之一。(5)芦苇与互花米草共存于崇明东滩,二者共存的原因很多,例如更新生态位的不同,但归根结底是由它们彼此间存在一定程度的互利作用和不同的适应策略来决定的。从芦苇与互花米草的总体特征来看,互花米草的生存策略更倾向于r对策者,芦苇的生存策略更倾向于K对策者。按照Grime的植物生活史策略,在崇明东滩,芦苇倾向于竞争对策,而互花米草倾向于杂草对策。由于在多数情况下,互花米草对于芦苇表现出一定的促进作用,而芦苇对于互花米草具有竞争作用,因此,对于二者在崇明东滩的分布,在完全排除人为干扰因素的情况下,随着潮滩持续淤涨,芦苇的面积可能会出现增大的趋势,而互花米草分布位置则可能从现有位置下移,并且在潮间带中部区域两种植物共存的局面依然会持续。更多还原

【Abstract】 Dongtan wetland of Chongming is one of famous wetlands of the world. It provides a wintering place for some rare and endangered waterfowl. At the same time, it is easy to be invaded by alien species owing to its special location and habitat conditions. Spartina alterniflora Loisel (Smooth cordgrass) is one of the invaders spreading in this area. Smooth cordgrass is native to Atlantic coast, which belongs to Poaceae. It was introduced to Dongtan wetland for siltation and epeirogenic purpose, but then it spread rapidly. Smooth cordgrass continued to outcompete the native specie Scirpus mariqueter and occupied the whole low tidal zone and the majority of middle tidal zone, especially in the north and east parts of Dongtan wetland. At the meantime, reclamation activities resulted in disappearance of large area of vegetation at high tide habitat. In this process, the spreading of Phragmites australis (Cav.) Trin.ex Steud (Common reed) as a native grass with similar competitive ability to smooth cordgrass was seriously disturbed. Therefore, smooth cordgrass invaded Dongtan wetland easily and spread quickly in the decades, which influenced the biodiversity and balance of Dongtan native ecosystems. As a result, some waterfowl also lost their habitats.Common reed is a native dominant species in Dongtan wetland, and it has strong asexual reproductive capability and competitive ability. Common reed is adaptive to grow in the intertidal mudflat. Some results showed the competitive ability between common reed and smooth cordgrass is similar; once one species occupied a habitat, another one can’t intrude again. Thus, it might be an efficient biological method to control smooth cordgrass using common reed replacing smooth cordgrass. This way might have lots of advantages, for example, avoiding chemical pollution, unnecessary introduction of natural enemy and saving manpower and resources. More importantly, it would be helpful for improving biological diversity, optimizing intertidal vegetation pattern and forming stable ecosystem. Based on these backgrounds, this thesis studied the interspecific relationships between common reed and smooth cordgrass along tidal gradient in Dongtan wetland, and discussed some related factors. The main results were as follows:(1) Smooth cordgrass and common reed are both dominant species of Dongtan wetland presently. In general, the important values of the species were similar. Concretely, smooth cordgrass was advantageous in abundance, and common reed was advantageous in height. Common reed dominated in the high tidal zones, and smooth grass dominated in the low tidal zone. In the middle tidal zone, the two species formed a mosaic pattern. In general, there were four patches of vegetation in the study area:Reed patches, Spartina patches, blank patches (sometimes mixing with very few other plants) and two plants mixed patches. The types and areas of patches were different along with tidal gradients. Results showed that:the patch density and edge density of reed population were greater than those of Spartina, suggesting that the degree of fragmentation of reed population was greater than that of Spartina. The aggregation degrees of reed, Spartina and blank patches were larger, connectivity indices were close to100, indicating that the structures of three types of patches at1500×100m2scale were compact, and connectivity was strong. Landscape shape index was only6.59, indicating that the shape of the landscape level was not complicated. The aboveground age structures of common reed and smooth cordgrass showed increasing type in relatively high tidal zones, and a stable type in relatively low tidal zones.(2) Common reed and smooth cordgrass took different competitive strategies to adapt to the different habitats. Common reed and smooth cordgrass are both clonal plants. Clonal architectures of the two species were different:common reed tended to be guerilla type, and smooth cordgrass, the phalanx or mixed type, which determined the difference in acquisition of soil water and nutrient between the two species. This article compared the competitive abilities of smooth cordgrass and common reed from three aspects:the apparent growth capacity, reproductive capacity and the potential growth capacity. The mean relative growth rate of smooth cordgrass was much higher than that of commom reed. However the maximum height reached by common reed at the end of growing period was greater than that of smooth cordgrass, indicating that the height growth variability of common reed was greater than that of smooth cordgrass. The biomass of common reed was generally significantly higher than that of smooth cordgrass, because reed rhizome was coarse, accumulating a large amount of biomass. Comparing the propagation characteristics of common reed and smooth cordgrass, we found that common reed occupied habitats mainly through coarse rhizomes, while smooth cordgrasss mainly through anchoring more ramets by means of asexual reproduction, and increasing plant density and exploring new habitats by means of sexual reproduction. The net photosynthetic rate and the maximum photosynthetic efficiency of smooth cordgrass were higher than those of common reed. However, the photochemical efficiency of common reed was higher than that of smooth cordgrass. The soluble sugar contents or N and P contents of common reed were higher than those of smooth cordgrass.(3) The competitive abilities of common reed and smooth cordgrass were different. Through surveying single-or mix-species community and field removal experiment, we found that the relationship between common reed and smooth cordgrass were facilitative or competitive. Surveying single-or mix-species community showed that:for the average height and biomass, the reaction of the target species to the presence of neighbors differed with tidal gradient. In the high and low tidal zones, the presence of neighbors stimulated the growth of target species, while in the middle tidal zones; the presence of the neighbor species inhibited the growth performance of the target species. Competition was also conducive to the reproduction of plants. Germination rates of common reed and smooth cordgrass were greater in neighbors presence quadrats. In the field removal experiments, we selected relative growth rate (RGR) and the number of seedlings daily produced (TNT) as response parameters to measure the competitive intensity index. In the high and middle tidal zones, the presence of smooth cordgrass facilitated the growth of common reed, but the presence of common reed inhabited the growth of smooth cordgrass when RGR as a parameter, but in the low tidal zone, the absolute competitive intensity (ACI) and relative neighborhood effect index (RNE) of common reed and smooth cordgrass were positive, which represented both competing with each other. Along the tidal gradients (from high to low tidal zone), competitiveness index (Ⅰ) values of smooth cordgrass were from negative to positive; competitiveness index (Ⅰ) values of common reed were positive and decrease with tidal gradient. When taking TNT as a parameter, the existence of smooth cordgrass facilitated the growth of common reed in all three tidal zones, and the presence of common reed inhabited the growth of smooth cordgrass. With tidal gradient decreased (from the high to low tidal zone), I values of common reed were from negative to positive. I values of smooth cordgrass was negative, and the absolute value of I for smooth cordgrass was lowest in the middle tidal zone, In all the three tidal zones, there are crowding effects (Dr) between smooth cordgrass and common reed. In high and middle tidal zone, the crowding effects of common reed on smooth cordgrass were higher than that of smooth cordgrass on common reed. In low tidal zone, the crowding effects of smooth cordgrass on common reed were relatively higher. Overall, interspecific interactions of the two species were mutually beneficial in most cases, and when the relationship is competitive, the total competitive effects of smooth cordgrass were higher than the overall competitive effects of common reed. The direction of the RNE of smooth cordgrass and common reed was consistent with the direction of the I value, the Dr can only affect the size of the RNE.(4) Anthropogenic interference strongly influenced on the growth of common reed and smooth cordgrass. We analyzed the compensatory growth effects of the two species after mowing, and found that:the compensatory growth capacity of common reed afte r severe mowing was not as good as that of smooth cordgrass. While being mowed entirely or at1/2height, the height, density and biomass of common reed reduced to0, indicating that three months after mowing, common reeds did not regerminate and grow. However, in all of the treatments, smooth cordgrass regerminated and grew, but for1/2density-mowing treatment, the compensative ability of common reed was stronger than that of smooth cordgrass, in which it not only recovered from single plant level, but also from population level.(5) Common reed and smooth cordgrass coexisted in Dongtan wetland for many reasons, such as different regeneration niche, but ultimately it is because that they are mutually beneficial to each other to some extent and they played different roles in the habitat with different adaptation strategies. According to the general characteristics of common reed and smooth cordgrass, smooth cordgrass tended to be a r-strategist, and common reed, a K-strategist. According to the Grime classification on the plant life history strategies, in Dongtan wetland, common reed tended to be a competitor, while smooth cordgrass, a weed. In most cases, smooth cordgrass showed the facilitation effects to common reed to some extend, while the latter showed competitive effects to the former. If without the anthropogenic disturbance, along process of the tidal siltation, the area of common reed would gradually increase, while the position of smooth cordgrass would move downward. They would still coexist in the middle intertidal zone.更多还原