【作者】 肖德荣；

【导师】 张利权；

【作者基本信息】 华东师范大学 ， 生态学， 2010， 博士

【摘要】 互花米草(Spartina alterniflora)作为生态工程种引种长江河口湿地,由于其极强的适应性和繁殖能力,目前已在长江口湿地大面积分布并对该区域的生物多样性与生态安全产生威胁。研究互花米草扩散方式及其入侵机理,对深入了解和掌握该物种入侵生态学过程,实施有效控制管理以维护湿地生态系统结构与功能、保护湿地生物多样性具有重要的理论意义和实践价值。本研究选择长江河口盐沼湿地崇明东滩为主要研究区域,自大堤向海方向、依据高程从高到低将互花米草划分为高、中、低三个潮间带分布区,分别研究不同潮间带互花米草种子产量和活性以及其种子萌发特性,种子在土壤库中的萌发与存活动态,土壤种子库时空动态及类型,互花米草在互花米草-光滩(S-M)和互花米草-海三棱藤草-光滩(S-S-M)前沿的扩散格局,治理控制区内互花米草二次入侵等,分析互花米草在崇明东滩湿地扩散的生态学过程及快速入侵机制,主要研究结果如下：1.种子产量、活性、萌发特性和种子漂浮力互花米草种子产量与活性随分布潮间带的不同而异,其中,中潮带分布的互花米草种子产量(83,638±11,852粒/m2)和活性(59.7％±3.5%)最高,高潮带种子产量(54,489±20,433粒/m2)与低潮带种子产量(41,955±8,999粒/m2)无显著差异,但高潮带种子活性(51.3%±2.9%)显著高于低潮带种子活性(28.0％±3.0%)。互花米草种子成熟后在冬季低温环境条件下不萌发,低温春化能显著提高互花米草种子萌发速度和萌发率。高潮带互花米草种子在水体中平均漂浮时间(14天)与中潮带种子漂浮时间(12天)无显著差异,两者均显著高于低潮带互花米草种子在水体中的漂浮时间(6天)。2.种子在土壤库中的萌发与存活及土壤种子库时空动态种子野外埋藏试验表明：互花米草种子2月份开始萌发,>80%的萌发率集中在3和4月份,至6月种子在土壤库中的萌发结束。种子在土壤中萌发率与其自身活性及其埋藏深度有关,而与埋藏的潮间带无关,高活性、浅埋藏的互花米草种子在土壤库中的萌发率最高,而低活性、深埋藏互花米草种子在土壤库中的萌发率最低。互花米草种子在土壤库中的存活率与种子自身活性和埋藏深度有关,高活性、深埋藏种子在土壤库中存活率相对较高、存活时间较长,而低活性、浅埋藏种子存活率低、持续时间较短。种子在土壤库中的存活率和持续时间与埋藏的潮间带无关,相同潮间带种子在不同潮间带埋藏的存活率间无显著差异。互花米草种子在土壤库中存活的时间不超过9个月。互花米草在不同潮间带所形成的土壤种子库大小与持续时间不同,中潮带互花米草土壤种子库规模最大、种子活性最高、持续时间最长,其次是高潮带,低潮带互花米草种子库规模最小、种子活性最低、持续时间最短,三个潮间带互花米草土壤种子库持续时间均不超过9个月,为短期土壤种子库类型。3.互花米草入侵前沿的扩散格局互花米草在崇明东滩的入侵前沿主要包括互花米草-光滩(S-M)前沿和互花米草-海三棱藨草-光滩(S-S-M)前沿。互花米草主要通过实生苗扩散与定居,以及从连续植物群落边缘通过分蘖和根状茎生长向前沿扩散。5月份,互花米草实生苗随着潮水作用向前沿传播并定居,而连续群落边缘通过无性繁殖向前沿的扩散主要集中在5-8月份,但两种扩散方式在不同前沿的作用不同。在S-M前沿,互花米草主要通过实生苗的传播在前沿光滩定居,其定居密度随着连续植物群落边缘向海距离的增加而逐渐降低(8.2±0.7株/m2→0.2±0.4株/m2),定居距离>50m。实生苗在光滩上定居后,其存活率较高(80.6%—86.7%),并通过快速分蘖(30±4—40±5/株)和根状茎生长形成斑块。经过一个生长季,在实生苗定居密度较高的区域,其分蘖和根状茎生长所形成的斑块不断连接而逐渐形成连续植物群落,向光滩扩散距离达23.4±3.2 m,而从原有连续植物群落边缘通过无性繁殖向光滩扩散的距离仅为2.0±0.4 m。在S-S-M前沿,由于本地种海三棱藨草的竞争作用,互花米草实生苗在海三棱藨草群落中定居的密度较低,其定居主要集中在海三棱藨草边缘的光滩,并随着向海距离的增加降低,实生苗定居密度(1.5±1.7株/m2→0.1±0.3株/m2)和距离(45m)较S-M前沿低,定居后的实生苗存活率在80.0%—84.0%之间。经过一个生长季,互花米草实生苗在S-S-M前沿扩散所形成的斑块不能连接形成连续植物群落,从连续植物群落边缘通过无性繁殖向前沿扩散的距离为2.7±0.5 m,为整个S-S-M前沿扩散距离,显著低于S-M前沿扩散的距离；S-M前沿是崇明东滩互花米草快速扩散的主要区域,整体呈现为连续锋面状的扩散模式,实生苗的传播与定居是互花米草在前沿实现种群快速入侵的基础。4.治理控制区内的互花米草二次入侵实生苗在治理控制区内的扩散与定居是互花米草实现快速二次入侵的基础。5月份,在破堤恢复水文的互花米草治理控制区内,相邻互花米草群落中种子与实生苗通过潮水作用带到治理控制区内,大量实生苗定居后、通过快速分蘖和根状茎生长形成种群斑块,并不断扩大连接而形成连续分布的群落。通过两年的二次入侵,互花米草再次占据所有已治理控制区内的裸地,并形成连续群落,实现整个控制区域的二次入侵。二次入侵两年后,互花米草群落结构和以及种子产量有关的繁殖参数与对照群落无显著差异,而通过无性繁殖从相邻连续植物群落边缘向治理控制区扩散的距离<1m,在种群二次入侵过程中贡献较小。互花米草二次入侵主要是依靠实生苗和种子的扩散实现空间拓植,实生苗的分蘖和根状茎生长实现其新种群的建立。防止互花米草二次入侵的关键是控制互花米草实生苗和种子向治理控制区内传播。更多还原

【Abstract】 Spartina alterniflora was introduced to the Yangtze Estuary for the purpose of land reclamation and has expanded rapidly thereafter. The rapid expansion of this exotic plant has threatened the native species richness and ecological security. Both the sexual reproduction by seeds and asexual propagation by tillering and rhizoming are the two main approaches by which Spartina aterniflora can keep fast rate of geographic spread. Therefore, studies on the spreading patterns and its role played on invasion of Spartina alterniflora will help understand their invasive ecological procession and mechanism, provide a scientific basis and guideline at a strategic control of this species to maintain the wetland ecological structure and function as well as the wetland biodiversity.In this study, the high, middle and low intertidal zones were divided from 1998 dyke to mudflat seaward according to their elevations, respectively. Using field investigation and laboratory test, the spreading patterns of exotic Spartina alterniflora at Chongming Dongtan Nature Reserve were studied, which included in seed production, viability and germination characteristic, seed floatation, spatial-temporal dynamic and type of soil seed bank, seed fate respecting to seed germination and survivor in soil after across intertidal dispersal, the range expansion patterns by sexual and asexual propagation at the advancing fronts and the reinvasion at controlled area. The ecological process and mechanism of Spartina alterniflora invasion by sexual and asexual reproduction were also discussed. The main results were as follows:1. Seed production, viability, germination characteristics and seed floatationSeed production and viability of Spartina aterniflora varied along an intertidal gradient, the middle intertidal zone (MIT) had the largest seed production (83638±11852 no./m2) and highest viability (59.7%±3.5%), the seed production and viability of high intertidal zones (HIT) were 54489±20433 no./m2 and 51.3%±2.9%,41955±8999 no./m2 and 28.0%±3.0% for low intertidal intertidal zones (LIT). The seed germination did not occurred at low temperature, the chilling treatment (at low temperature and in moist conditions) could significantly enhance the germinability of Spartina alterniflora seeds and shorten the time of onset seed germination. The seeds from the site MIT had much higher germinability than the sites of LIT and HIT. Spartina alterniflora seeds have capacity to remain afloat in water, the floating time differed among seeds from different intertidal zones, which were 14 d,12 d and 6 d for the site of HIT, MIT and LIT, respectively. There were no significant differences in floating time between the HIT and MIT, but both were significantly higher than that of LIT, which has very important role for good quality seed to survive in winter and increase the validity of seed dispersal on spring tides.2. Seasonal changes in seed germination and persistence in soil and spatial-temporal dynamics of soil seed bankSeed germination in soil started in February and ended in June whatever their burial depths (5cm,10cm and 20cm), over 80% germination occurred in March and April. The germinations significantly correlated with seed quality and burial depth, the MIT seeds buried at depth of 5 cm have the largest values, and the seed germination percentages decreased with increased burial depth, while the seed germination of LIT with 20cm burial depth was the lowest one. The germination was independent on the intertidal zones where they were buried, no significant differences in germination among the same burial depths across intertidal burial. Before the spring flush of germination, seed survival correlated with seed quality and was independent on the intertidal zones and burial depths. The seed survival decreased quickly at 5 cm burial with the flush germination in field, which were much lower than that of 10 cm and 20 cm burial. However, seeds of Spartina alterniflora did not survive 9 months even buried at 20 cm burial depth and no germinable seed were recorded after July.The size of soil seed bank of Spartina alterniflora depends on the seed production, viability and elevation of zones. The highest density and seed viability of soil seed bank was recorded at the site of MIT, where had the highest seed production, then the HIT, the smallest soil seed bank was at the site of LIT. By July, before there was any replenishment with fresh seeds from the current year, the soil seed bank was completely exhausted and the persistent time of soil seed bank for Spartina alterniflora was less than 9 months, which is in agreement with that of the transient seed bank.3. Range expansion patterns of Spartina alterniflora at advancing frontsTwo types of advancing fronts of Spartina alterniflora, i.e. Spartina alterniflora-mudflat (S-M front) and Spartina alterniflora-Scirpus mariqueter-mudflat (S-S-M front) could be found at the Chongming Dongtan nature reserve. Both sexual reproduction by seeds and asexual propagation by tillering and rhizoming were the two main means by which Spartina aterniflora maintained a fast rate of geographic spread at their advancing fronts, the roles which sexual reproduction and asexual propagation might play in the range expansion were probably dependent on their location and the type of habitat as well as local abiotic and biotic factors. Initial recruitment of seedlings did not occur until May, when seeds transported by the tidal water germinated in front of the continuous edge of dense Spartina alterniflora meadow. Comparing the seedling recruitment occurred at these two fronts, the mean number of seedling recruitment was much higher at the S-M (8.2±0.7 no./m2→0.2±0.1 no./m2) front than the S-S-M front (1.5±1.7 no./m2→0.1±0.3 no./m2). Once established, the seedling survivorship was high and there were no significant differences in seedling survivorship between the S-M (80.6%±86.7%) and S-S-M fronts (80.0%—84.0%). Once the seedlings established at the front of the continuous Spartina alterniflora meadows in May, they quickly formed tussocks by vegetative tillering and rhizoming and finally merged into dense meadows at S-M front. The mean distance of range expansion of Spartina alterniflora after one growing season at the S-M front was 25.4±3.1 m/year, while 2.7±0.5 m/year at the S-S-M front. The range expansion rate at the S-S-M front was much slower than the S-M front. These two patterns of range expansion of Spartina alterniflora on an expansion front scale revealed from this study confirmed the pattern on a large scale of range expansion of Spartina alterniflora at the salt marshes in the Yangtze Estuary. The colonization behaviors of Spartina alterniflora at the expansion fronts differed as a reaction to various external and internal factors.4. The reinvasion by Spartina alterniflora in the controlled areaSeeds and seedlings in the neighbouring Spartina alterniflora community were the basis for fast reinvasion of Spartina alterniflora in controlled area. Seeds and seedlings were transported by tidal water to occupy empty niches and quickly formed tussocks through vegetative propagation, and finally merge into dense continuous meadows. After two years’reinvasion by Spartina alterniflora, there were no significant differences in culm density, vegetation height, above biomass and sexual parameters between new formed continuous meadow and the former continuous meadow. However, the spreading distance by vegetative propagation from neighbouring continuous meadow edges were less than 1 m for two years, which contributed little to reinvasion. Since Spartina alterniflora mainly achieved reinvasion by seed and seedling dispersal, the most effective measures of controlling the reinvasion of Spartina alterniflora should be taken by preventing the dispersal of seeds and seedlings by tidal water.更多还原