【作者】 汪承焕；

【导师】 李博； 陈家宽； 方长明；

【作者基本信息】 复旦大学 ， 生态学， 2009， 博士

【摘要】 河口盐沼是一类位于陆地和海洋之间过渡地带的成水湿地,能接受河流、海洋、陆地和大气输入的大量水分、有机质及营养盐等物质,支持捕食食物链和碎屑食物链上丰富的物种,对于生物多样性的维持以及生物地球化学循环过程具有不可替代的作用。长江口盐沼环境梯度明显,物种组成相对比较简单,因而是研究植物群落组织机制的理想系统。只有充分理解了盐沼植物群落的结构、组织及变化动态,才能预测全球变化和人为干扰对这类生态系统的影响,并为生态修复提供理论基础。本论文通过野外观察、操纵实验以及室内受控实验等多种途径,探讨了优势盐沼植物表现与环境因子的关系,揭示了近缘土著种之间以及外来入侵种互花米草与土著种之间的竞争过程,初步阐明了崇明东滩植物群落的组织机制。本研究的主要结论如下:(1)崇明东滩的盐沼植物群落分布格局在大尺度上呈现较为明显的分带,藨草属植物占据滩涂前沿近海区域,互花米草在中潮带占据优势,在高潮带与芦苇共生。从2005年到2007年,植物群落分带发生了很大的变化。互花米草向低潮带扩张的速度大大超过了海三棱藤草,并通过竞争排斥作用使后者的分布面积急剧减少。芦苇分布区也向海扩张了一定距离,与互花米草间的分带变得较为模糊,在高潮带形成了斑块镶嵌分布格局。(2)与潮汐作用相关的土壤理化因子(土壤盐度、容重、含水量、氧化还原电位、pH值等)在盐沼植物群落的组织中起着重要作用。崇明东滩优势物种(藨草、海三棱藨草、芦苇、互花米草)的生长主要受到盐度及淹水状况的影响。藨草的耐盐能力最低,在16ppt盐度下生长受到显著抑制,而有性繁殖受到的影响更大。它对淹水的适应范围广,地下部分受淹水的影响较小。海三棱藨草的耐盐能力比藨草稍强,但对淹水的耐受能力相对较差,总体而言其对盐度和淹水梯度的响应与藨草近似。芦苇对盐度也较为敏感,但在低淹水处理下表现较好。互花米草的耐盐能力最强,且适度淹水对其地上部分的生长有促进作用。在适宜的环境(低盐度、低淹水)下,互花米草与土著植物的生长、繁殖表现差异较小,而在高盐度、高淹水的胁迫生境中,互花米草具有明显优势。较广的生态辐是互花米草成功入侵崇明东滩并快速扩张的重要原因。潮汐的输送、冲刷作用对种子散布、繁殖体建成等生活史早期的过程具有决定性作用,进而影响优势植物的分布范围。移栽实验结果表明,互花米草与芦苇均能在现有分布边界之外存活与生长,在前沿样点,移栽植株的死亡是由潮汐的侵蚀作用而不是土壤因子造成的。一旦定居成功,互花米草能够快速产生形态适应,分株长得十分密集矮小,对地下部分的投入增大。芦苇对潮汐作用和水位急剧变化的适应能力较差,因此其潜在分布下限要高于互花米草。人工移栽显著提高了互花米草向滩涂前沿扩散的速度,大大加快了入侵的进程。(3)形态相近的3种莎草科土著植物(藨草、海三棱藨草、糙叶苔草)间的竞争关系受环境胁迫及干扰的影响而发生改变。藨草对高盐度的耐受能力显著低于海三棱藨草和糙叶苔草,它在淡水条件下具有竞争优势,但当盐度达到16ppt时则成为竞争劣势种。藨草受竞争影响的程度随盐度升高显著增大。海三棱藨草在大多数情况下是竞争优势种,在高盐度下,其受到的竞争影响较小。糙叶苔草相对于藨草属植物是竞争劣势种,但其耐盐能力较强。干扰没有降低群落的整体竞争强度,但改变了不同物种的相对竞争能力。刈割处理(模拟取食)显著降低了所有物种的表现,使地下生物量分配较高的藨草获得了相对优势。淤积处理的总体影响较小,对海三棱藨草的开花率和藨草的密度还有一定促进作用。亲缘关系对土著种间竞争强度的影响不明显,物种对环境胁迫以及不同形式干扰的耐受能力共同决定了竞争结果,进而影响不同生境中植物群落的组成与结构。(4)外来入侵种互花米草对土著种芦苇的竞争效应受到凋落物的强烈影响,且在生长季不同时期会发生变化。生长季早期的竞争对互花米草和芦苇的生长、繁殖表现影响最大,而中期互花米草的存在对芦苇则有一定的促进作用。成熟互花米草和芦苇群落中的凋落物及存活邻株显著降低了冠层下的光照强度,在生长季早期对移栽的其他物种个体具有一定的促进作用,而在中后期则有显著的抑制作用。凋落物对互花米草和芦苇自身种群也有影响:凋落物降低了两者的存活分株密度;在生长季早期对互花米草的高度有促进作用,晚期则变为抑制,而对芦苇的高度始终有促进作用;凋落物对互花米草的地上生物量具有负效应,而对芦苇则只在生长季中期有抑制。(5)互花米草的竞争作用及环境条件对海三棱藨草的表现均有显著影响。互花米草对海三棱藨草具有较强的竞争效应,在所有处理下相对于海三棱藨草均具有显著的竞争优势。作为一个地上竞争优势种,互花米草主要通过冠层的遮荫作用影响海三棱藨草的生长和繁殖。在滩涂前沿,抬升基质减弱了潮汐的冲刷,对海三棱藨草的生长有一定促进作用。营养添加对海三棱藨草则无显著效应,但却提高了互花米草的地上生物量,因而富营养化可能会进一步加剧互花米草入侵海三棱藨草分布区域,造成严重的生态后果。我们只有全面考虑影响植物生长繁殖表现的各种因素,才能正确理解崇明东滩植物群落的结构、组织,并准确预测其变化趋势,为保护区的管理决策提供依据。更多还原

【Abstract】 Salt marshes are wetlands in the transition zones between land and sea.They receive large amounts of water,organic matter and nutrients input,support diverse species of grazing food chain and detrital food chain,and play important roles in biogeochemical cycles.Salt marsh at Chongming Dongtan has sharp environmental gradients and simple species composition,and thus is an ideal system for studying organization of plant communities.Only when fully understanding of the structure, organization and dynamics of salt marsh plant communities has been achieved,can we predict the responses of salt marshes to anthropogenic activities and global change, and guide the conservation and restoration of declining salt marshes.In this study,we used field observation,manipulation and controlled environment experiments to discuss the relationships between performance of dominant plants and physical factors, to reveal the competition processes between invasive species and native species,and to illustrate the organization mechanism of plant communities at Chongming Dongtan. The major findings are summarized as follows:(1)Plant communities at Chongming Dongtan showed distinct zonation pattern at large scale:Scirpus species occupy the seaward area,Spartina alterniflora dominates the middle marsh and coexist with Phragmites australis in the high marsh. From 2005 to 2007,zonation pattern had changed a lot.Spartina alterniflora expanded seaward much more quickly than Scirpus mariqueter did,and greatly reduced its distribution area by competition.Phragmites australis zone had also expanded seaward,and formed mosaic patches with Spartina alterniflora in the high marsh.(2)Tidal effects and the associated edaphic factors(soil salinity,bulk density, water content,ORP and pH)play important roles in organization of salt marsh plant communities.Growth of dominant plants at Chongming Dongtan(Scirpus triqueter, Scirpus mariqueter,Phragmites australis and Spartina alterniflora)were influenced mainly by salinity and inundation.Scirpus triqueter was least salt tolerant,and its growth and reproduction were significantly inhibited at 16 ppt.It was well adapted to inundation and the belowground parts were less affected by submergence.Scirpus mariqueter was more salt tolerant and less tolerant to inundation than Sciprus triqueter.Phragmites australis was also salt sensitive,and performed better in low inundation conditions.Spartina alterniflora was the most salt tolerant species,and moderate inundation could promote its growth.In benign conditions(low salinity,low water level),the differences between invasive Spartina alterniflora and native species were minor,whereas in stressful environment(high salinity,high water level), Spartina alterniflora took more advantages over native species.Wide ecological amplitude was one of the most important reasons that enable the rapid invasion of Spartina alterniflora at Chongming Dongtan.Tidal transportation and scouring are determinants of events in early stage of life history such as seed dispersal and propagule establishment,which will in turn influence the distribution range of dominant plants.Results of trsplantation experiment indicated that both Spartina alterniflora and Phragmites australis could survive out of their current ranges.At the seaward sites,death of transplanted ramets was caused by tidal scouring rather than edaphic factors.Once established,Spartina alterniflora was able to evolve morphological adaption quickly,and formed low but dense ramets with greater allocation to belowground parts.On the contrary, Phragmites australis was not well adapted to the tidal effects and sharp change of water level,so its potential lower border was higher than that of Spartina alterniflora. Transplantation in low marsh had significantly promoted the expansion and invasion of Spartina alterniflora at Chongming Dongtan.(3)Interspecific interactions among three native sedge species with identical morphology were influenced by physical stress and disturbance regimes.Scirpus triqueter was significantly less salt tolerant than Scirpus mariqueter and Carex scabrifolia.It was dominant species in fresh water,but became competitive inferior at 16 ppt.The suppression of Scirpus triqueter by competing species increased significantly with increasing salinity.Scirpus mariqueter was competitive superior in most cases,and it was less affected by competitors at high salinity.Carex scabrifolia was inferior to Scirpus species,but it was most salt tolerant among these species. Disturbance did not reduce the competition intensity within the community,but changed the relative competitive abilities of 3 sedge species.Clipping(simulated grazing)significantly reduced the performances of all species,and favored Scirpus triqueter which had the highest root allocation.Accretion had less effect on the whole, and it enhanced the flowering ratio of Scirpus mariqueter and density of Scirpus triqueter.Phylogenetic distances had minor effects on competition intensity among these native species.It was tolerance to stress and different kind of disturbances that determine the competitive results,and hence the structure and composition of plant communities in different habitats.(4)Competitive effect of invasive Spartina alterniflora on native Phragmites australis was strongly affected by litter,and varied within a growing season. Competition in early growing season had the greatest influence on growth and reproduction of Spartina alterniflora and Phragmites australis,while Spartina alterniflora had facilitative effects on Phragmites australis in mid growing season. Standing litter and vegetation in mature communities of Spartina alterniflora and Phragmites australis significantly reduced the light intensity under the canopy,and promoted the growth of transplants of other species in early growing season,but inhibited them later.Litter also affected the growth of their own populations.Litter reduced the density of living ramets,and promoted the height growth of Spartina alterniflora in early growing season,but inhibited it later.Phragmites australis grew higher during the whole growing season with the presence of litter.Litter also reduced the biomass of Spartina alterniflora,but the negative effects on Phragmites australis only existed in mid growing season.(5)Competitive effects of Spartina alterniflora and physical conditions had significant effects on Scirpus mariqueter.Spartina alterniflora had strong competitive effects on Scirpus mariqueter,and it dominated the mixture in all treatments.As an aboveground competitor,Spartina alterniflora suppressed the growth and reproduction of Scirpus mariqueter mainly by shoot competiton.In the front of intertidal zone,elevated sediment reduced the tidal effects,which would facilitate the growth of Scirpus mariqueter.Nutrient addition had no significant effects on Scirpus mariqueter,but enhanced the biomass of Spartina alterniflora.Therefore, eutrophication might stimulate the invasion of Spartina alterniflora into Scirpus zone, which would cause severe ecological consequences.Only when we have considered all factors affecting growth and reproduction of plants,can we understand the structure and organization of plant communities at Chongming Dongtan and predict the future dynamics,which will provide guidance to management of the nature reserve.更多还原