【作者】 陈慧丽；

【导师】 吴纪华； 李博； 方长明；

【作者基本信息】 复旦大学 ， 生态学， 2008， 博士

【摘要】 生物入侵是全球性的重大生态学和环境问题之一。近年来随着科学家对土壤生态系统重要性认识的深入,评价外来植物入侵对土壤生物多样性及生态系统功能的影响已经成为当前入侵生态学领域的一个研究热点。河口盐沼湿地是联结陆地、河流和海洋三大生态系统的枢纽,拥有独特而不可替代的自然资源,同时也是一个非常脆弱的生态系统,被认为是最易入侵的生态系统之一。在长江口盐沼湿地,外来植物互花米草(Spartina alterniflora)正大面积扩散,并和土著植物芦苇(Phragmites australis)和海三棱麃草(Scirpus mariqueter)形成强烈竞争。线虫是土壤动物中的优势类群,在生态系统物质循环中扮演着重要的角色,且直接受植物群落改变的影响,是评价植物入侵对盐沼湿地生物多样性影响的很好的指示生物。本论文通过野外调查,研究了互花米草入侵长江口盐沼湿地对土壤线虫群落和植物附生线虫群落的影响,并进一步采用凋落盒分解实验和植物移栽实验,分别研究了“凋落物输入”和“根际输入”两种途径在互花米草入侵影响盐沼湿地线虫群落中的作用。主要研究结果如下:1)共发现长江盐沼湿地线虫70属,隶属于2纲7目39科。2)为了解互花米草入侵对土壤线虫群落的影响,以长江口三个潮间带盐沼湿地为研究地点,比较互花米草与两种土著植物(芦苇和海三棱蔗草)典型植物群落中的土壤线虫群落。结果显示互花米草群落中土壤线虫的营养多样性低于两种土著植物群落,表明互花米草入侵降低了长江口盐沼湿地土壤生物的功能多样性,土壤食物网结构趋于简化。互花米草群落中的食细菌线虫比例高于芦苇群落,显示互花米草取代芦苇群落可能改变了凋落物分解速率和途径。互花米草与两种土著植物群落的土壤线虫群落结构均存在显著差异,而互花米草与海三棱麃草间线虫群落结构的差异小于互花米草与芦苇间,可见互花米草入侵不同的土著植物群落所产生的影响会有程度上的区别。互花米草入侵对土壤线虫的密度、属数、多样性等的影响存在地点间的差异,表明植物入侵的生态影响还可能与被入侵生态系统的生境特性相关。3)为了解互花米草入侵对植物附生线虫群落的影响,以崇明东滩盐沼湿地为研究地点,比较互花米草和芦苇典型群落斑块中附生在活秆和枯秆上的附生线虫群落。结果显示在各季节,互花米草与芦苇茎秆上附生线虫的群落结构均存在显著差异,表明互花米草入侵长江口盐沼湿地显著改变了植物附生线虫的群落结构。互花米草活秆和枯秆附生线虫的数量在各季节都高于芦苇,表明互花米草的入侵可能使盐沼湿地中附生生物数量增加。附生在互花米草枯秆上的食细菌线虫数量显著高于芦苇,并主要体现在参与盐沼植物凋落物分解的Diplolaimelloides数量的显著增加,由此我们认为两种植物茎秆分解过程的差异可能是引起枯秆附生线虫数量变化的一个重要原因。4)为了解凋落物输入途径在互花米草入侵改变线虫群落中的作用,采用凋落盒方法,比较了外来种互花米草与土著种芦苇的茎秆分解过程以及线虫群落在这个过程中的集群定居和生态演替。结果显示,与芦苇茎秆相比,互花米草茎秆凋落物具有较高的氮浓度和较低的碳氮比,其降解更为迅速。互花米草凋落盒中的线虫数量最多,其次为芦苇,而对照中线虫数量始终都维持在较低水平,线虫数量的变化主要是由食细菌类群的数量变化决定。与芦苇凋落盒及对照相比,互花米草凋落盒中的食细菌线虫数量显著较高。Diplolaimelloides和Diplolaimella是参与植物凋落物分解的主要线虫类群,分别占凋落物中线虫总数量的53%和28%。参与互花米草茎秆分解的线虫群落成熟指数和结构指数都低于芦苇,表明互花米草入侵可能通过凋落物输入降低土壤线虫群落结构的复杂性。5)为了解根际输入途径在互花米草入侵影响线虫群落中的作用,采用植物移栽实验,比较研究了互花米草与两种土著植物生长过程中根际线虫的群落演替规律。结果表明,互花米草与两种土著植物生长过程中根际线虫的密度、属的丰富度、多样性、营养多样性及群落结构在植物间均没有显著差异,这显示根际输入在互花米草影响土壤线虫群落过程中的作用可能不明显。对线虫食性类群的进一步分析表明,互花米草根际土壤中食细菌线虫数量显著低于芦苇,这与野外调查及凋落物分解实验的结果刚好相反。与土著植物海三棱麃草相比,入侵植物互花米草根际的植物寄生线虫数量显著低于海三棱麃草,显示互花米草抗寄生线虫能力较强。更多还原

【Abstract】 Invasions of exotic species have caused serious environmental problems in the world. As increasing attention has been paid to underground in recent years, the impact of exotic plant invasions on the composition and function of soil communities has emerged as an essential issue in invasion ecology. Coastal and estuarine salt marshes are the critical transition zones between terrestrial and aquatic ecosystems which play major roles in conserving biodiversity. Compared with other ecosystems, the salt marshes have widely been recognized as one of the most heavily invaded ecosystems. In Yangtze River estuarine salt marshes, the ecosystems are now heavily infested with an introduced exotic plant Spartina alterniflora. S. alterniflora spreads to most of the wetlands and is competing with native plant species by forming dense monocultures. This study aims to evaluate the impacts of S. alterniflora invasions on soil biodiversity by using nematodes as indicators and to explore the mechanisms by which S. alterniflora affect the structure and function of soil nematodes. Nematodes are selected as indicators because they are the most abundant soil metazoan taxon, closely linked with plants and mineralization processes, and can provide unique insights into many aspects of ecosystem processes.During the study, a total of 70 nematode genera were found from the salt marsh wetlands of the Yangtze River estuary belonging to 39 families, 7 orders and 2 classes. Photographs of 37 common genera were presented to show their main characteristics.To assess the effect of S. alterniflora invasion on soil nematodes, I compared the nematode communities in marshes respectively dominated by invasive S. alterniflora and native Scirpus mariqueter and Phragmites australis at three local sites in the Yangtze River estuary over two seasons. S. alterniflora stands had generally lower nematode trophic diversity than the stands of the 2 native plants, suggesting that the exotic plant led to a simplified benthic food web. The relative abundance of bacterial-feeding nematodes tended to increase in S. alterniflora marshes compared to P. australis marshes. The increased bacterial-feeding nematodes in S. alterniflora stands are likely to reflect the altered decomposition processes, rates and pathways, which may, in turn, modify belowground nutrient cycling of the estuarine ecosystems. The dissimilarity in nematode community structure between S. alterniflora and S. mariqueter marshes was smaller than that between S. alterniflora and P. australis marshes, suggesting that the detection of the ecological consequences of plant invasions depends on which native plant species is considered. In addition, site effects were generally detected in the comparison of sediment properties and nematodes among 3 plant marshes.To assess the effect of S. alterniflora invasion on epiphytic nematodes, I compared epiphytic nematode communities associated with standing live and dead stems of P. australis and S. alterniflora at Dongtan of Chongming Island across three seasones. In each sampling season, the dissimilarities in epiphytic nematode communities between P. australis and S. alterniflora were significant. S. alterniflora stems supported more abundant epiphytic nematodes comparing to P. australis stems. These results suggest that the invasion of S. alterniflora increase the epiphytic nematode abundance and altered the epiphytic community composition. Greater abundances of epiphytic bacterial nematodes were found on dead stems of S. alterniflora than on those of P. australis, which was mainly due to the decomposing nematode Diplolaimelloides. It indicates that the dissimilarity of stem litter quality between S. alterniflora and P. australis may be important in shaping nematode communities associated with dead stems.To test whether the exotic plant invasions affect soil nematode communities through litter inputs, I compared mass loss and nematode colonization during the stem litter decomposition of invasive S. alterniflora and native P. australis in salt marshes of the Yangtze River estuary. With higher nitrogen content and lower C:N ratio, stem litter of the invasive S. alterniflora decayed faster than the native P. australis. The total nematode abundance was the highest in S. alterniflora litter at each experimental stage, followed by P. australis and control. The total nematode abundance remained low in control containers throughout the experiment. Most changes of nematode abundance were due to the change in bacterivores. Compared to P. australis, the greater nematode abundance in S. alterniflora was mainly due to two dominant genera of bacterial nematodes. Diplolaimelloides and Diplolaimella were dominant genera in both S. alterniflora and P. australis litter, contributing 53% and 28% to the total abundance, respectively. Lower values of maturity index and structure index in S. alterniflora than in P. australis litter indicate that a more degraded food web condition resulted from the invasion of S. alterniflora by producing higher quality of litter than the native P. australis.To test whether the exotic plant invasions affect soil nematode communities through altering root inputs, I conducted a two-year pot experiment grown with S. alterniflora and two native plant monocultures. The plant species identity did not affect the biomass, genus richness and diversity, trophic diversity and community structure of rhizosphere nematodes, which suggests a relatively weak rhizosphere effect. Contrary to the findings from litter decomposition experiment, the abundance of bacterial nematodes in rhizosphere of P. australis significantly increased than that of S. alterniflora. The abundance of plant-feeding nematodes was found significantly decreased in rhizosphere of S. alterniflora compared to S. mariquete, suggesting that the invasive S. alterniflora is less vulnerable than the native S. mariquete.更多还原