【作者】 何彦龙；

【导师】 李秀珍；

【作者基本信息】 华东师范大学 ， 生态学， 2014， 博士

【摘要】 植物分布格局和共存机制一直以来是生态学关注的核心问题之一。前人研究认为,高程是导致盐沼植物在较大尺度上呈带状分布的综合因素。然而,在中低潮滩高程相近的盐沼,物种之间也存在空间分异格局。因此,研究小尺度上物种空间分布格局的形成过程,不仅有助于进一步理解盐沼植被构建机制,也可为盐沼保护与恢复提供理论依据。本研究以长江口崇明东滩中低潮滩盐沼为研究对象,在大量野外调查和控制实验基础上,结合室内分析,得出以下主要结论：一、在中低潮滩,互花米草和海三棱藨草对水盐环境的不同适应与反馈,是近互花米草一侧海三棱蔗草生境被侵占的重要原因。在崇明东滩中低潮滩高程相近的区域,互花米草植被带的土壤盐度(电导率)为0.41±0.01S/m,显著高于海三棱藨草带的0.35±0.01S/m(P<0.05)。互花米草带土壤含水量约为45%,而海三棱藨草带的土壤含水量约为53%。海三棱藨草带及前沿带淹水频率较高,相对于光滩带,互花米草带的淹水频率较低。互花米草带的氧化还原电位为-21±2mV,海三棱藨草带的氧化还原电位为-27±3mV,光滩带的氧化还原电位为-65±7mV。在中低潮滩,互花米草拓植直接导致了互花米草以及附近区土壤盐度的显著增加。首先互花米草较好的消浪作用显著增加了沉积作用,而斑块内部因水动力较强,相对侵蚀,一定程度上减弱了斑块内上覆水与外界的交换；其次,蒸腾作用将较深土壤中的盐分运输到互花米草叶和茎部并被盐腺泌出体外,另外生长季互花米草植被带土壤温度较其他带高,导致土壤水分加速蒸发,使得表层土壤盐度增加,盐度增加抑制了相邻海三棱藨草向互花米草一侧的扩散和生长；在海三棱藨草分布前沿带淹水频率较高,土壤氧化还原电位较低,抑制了互花米草与海三棱藨草向海一侧的建植。其结果符合群落构建理论提出的环境筛选假说。二、两物种不同的繁殖策略和种间关系的差异,导致中低潮滩互花米草与海三棱藨草生物量分配的差异以及分布模式的不同。两物种的繁殖对策存在差异。互花米草带每个有性繁殖植株大约可产生1-2个地下分蘖,混生带有性繁殖植株大约产生2-3个地下分蘖。海三棱藨草带有性繁殖植株数是营养生长植株数的3-4倍,混生带有性繁殖植株是营养生长植株数的2-3倍,然而在其分布前沿带,营养生长植株数是有性繁殖植株数的8-10倍。二者有性繁殖和克隆生长的生物量投入不同。互花米草百粒重为0.45±0.01g；海三棱藨草带百粒重为0.80±0.01g。互花米草带对地下分蘖的投入大约是种子生产的2-3倍：海三棱藨草对种子生产的投入大约是根状茎投入的10-17倍。表明互花米草主要通过无性繁殖的方式进行种群更新；海三棱藨草在种间竞争压力下,主要采取有性繁殖策略,在环境压力下采取营养增殖策略,其符合贮存效应假说。在4-6月互花米草带相对生长速率约为0.025±0.003g/(g·day);海三棱蔗草带相对生长速率为0.030±0.001g/(g·day);在7-9月份,互花米草相对生长速率达0.034±0.003g/(g·day),显著大于海三棱藨草的同期生长速率(0.012±0.001g/(g·day))(P<0.05)。二者种间、种内竞争能力不同。互花米草种间竞争能力显著强于海三棱藨草(P<0.05)。但当淹水等环境压力增大时,互花米草种内竞争增强,而海三棱藨草种内表现为促进作用。因此,当环境压力对二者产生抑制时,互花米草种内竞争压力的增强,可能会减弱对海三棱藨草的排斥压力；但当环境相对友好或只对海三棱藨草产生抑制时,海三棱蔗草将被互花米草迅速替代。三、植被分异导致了土壤营养库的分异。互花米草带土壤营养库、土壤有机碳、氮积累速率显著高于海三棱藨草带,植被带次表层营养库较表层高,植物生长对营养库贡献显著。不同植被带土壤有机碳、氮含量不同,植被带次表层含量较表层高,光滩带次表层含量较表层低。在0-30cm土壤中,互花米草带土壤有机碳、氮库依次为：1129±76g/m2和145±5g/m2海三棱藨草带土壤有机碳、氮库依次为：640±63g/m2和99±6g/m2。互花米草带土壤有机碳、氮积累速率显著高于海三棱藨草带(P<0.05)。互花米草带有机碳的积累速率为：35.8±8.1g/(m2·yr),氮的积累速率为5.3±0.5g/(m2·yr);海三棱藨草带有机碳、氮积累速率分别为6.6±5.9g/(m2·yr)和1.2±0.4g/(m2·yr)。土壤有机碳、氮库的积累过程与植被之间存在反馈机制。在崇明东滩中低潮滩,发育年限相近的区域,土壤有机碳、氮库与物种生物量之间存在显著的正相关关系(P<0.05)。同时,由于碳氮积累差异,使得土壤中理化性质(盐度、Eh、粒度等)发生改变,从而导致物种分布范围发生改变,并与泥沙沉积过程相结合,影响植被结构。综合而言,在高程相近的中低潮滩,互花米草和海三棱藨草的空间分布格局首先取决于生境内环境因子,尤其是盐度、淹水、氧化还原电位等环境因子与植被的相互作用。同时生态位相近的物种由于生态位重叠发生竞争,导致竞争能力弱的海三棱藨草不断被排斥,因而形成了植被分异结构。本研究提取出来的主导因子,只限于高程相近的中低潮滩,是对更大尺度上潮滩植被分布机制的有益补充。更多还原

【Abstract】 Species distribution and their coexistence mechanism have long been the focus of ecological research. Some previous studies considered elevation as the main factor that resulted in zonal distribution of salt marsh species at large scale. While in the low-middle tidal flat with quite low topographical gradients, zonal differentiation pattern also exists between species. Therefore, study of the mechanism of species spatial distribution will help to understand the colonization process of estuarine salt marsh vegetation and provide theoretical basis for salt marsh wetland management, protection and restoration. We investigated the transects across the tidal flat, Scirpus mariqueter front zone, Scirpus zone, mixed zone of Spartina alterniflora and Scirpus, and Spartina zone, measured biological and environmental factors, and analyzed the data with statistical methods. Based on our results, some main conclusions can be drawn:1. Adaptation and feed backs of Spartina and Scirpus to the soil environmental factors are important factors that hampered the distribution of ScirpusIn the area with similar elevation at eastern Chongming Island, soil salinity expressed as conductivity in the Spartina alterniflora zone was0.41±0.01S/m, which was significantly higher than that in the Scirpus mariqueter zone with the value of0.35±0.01S/m. Soil moisture in the Scirpus zone was53%, which was significantly higher than that in the Spartina zone with the value of45%.The flooding frequency in the Scirpus zone and its frontier was higher than that in the Spartina zone. The Eh (redox potential) in the Spartina zone was-21±2mV, and was-27±3mV in the Scirpus zone. It was-65±7mV in the mudflat, which was significantly lower than that in the two vegetated zones. Therefore, at the area without significant elevation difference, soil salinity and moisture can be significantly different.In the intertidal zone, the invasion of Spartina directly led to the significant increase of soil salinity in their growing zone. One of the important reason was that Spartina secreted salt out through its salinity glands during its respiration. Meanwhile, the temperature in the Spartina zone during its growing period was higher than that in the other zones. As a result, the high temperature increased the water evaporation of sediment’s surface and further increased the surface soil salinity. The increased soil salinity in the Spartina zone inhibited the landward growth of Scirpus. However, at the front of the Scirpus zone, the Eh was extremely low because of the frequent flooding, and it restrained the seaward establishment of Scirpus. This conclusion testified the environmental screening hypothesis in the community establishment theory.2. Different reproduction strategy and growth characteristics result in the better competitiveness of Spartina than ScirpusThe Scirpus and Spartina had different reproductive strategy in different zones, and there were also different responses to environmental factors. The number of vegetative growing individuals was1-2times that of the sexual reproduction growing individuals in the Spartina zone, while it was2-3times in the mixed zone. The number of vegetative growing individuals and sexual reproductive growing individuals of the Scirpus was significantly different among the mixed zone, Scirpus zone and front zone. The number of sexual reproductive growing individuals was3-4times than that vegetative growing individualsin the Scirpus zone,2-3times in the mixed zone, and1:8-1:10at the frontier of the Scirpus zone.The hundred grain weight (HGW) of Spartina was0.45±0.01g, while the HGW of Scirpus was0.80±0.01g. For Spartina, the biomass allocation to the production of rhizomes was2-3times that to the production of seeds. For Scirpus, the biomass investment to the seeds was10-17times compared to that to the rhizomes. The result showed that population regeneration of Spartina depended mainly on the asexual reproduction. For Scirpus, sexual reproduction probably was the main strategy when confronted with the interspecific competition. However, the asexual reproduction will increase with the increase of physical stress.From April to June, the relative growth rate (RGR) of Spartina was0.025±0.003g/g·day, and the RGR of Scirpus was0.030±0.001g/(g·day). From July to September, the RGR of Spartina was up to0.034±0.003g/(g·day), which was much greater than that of Scirpus (0.012±0.001g/(g·day)). The RGR of Scirpus from July to September was also significantly lower than that during the early growth period.Consequently, Spartina took over Scirpus with rapid RGR and shading to Scirpus. Under harsh conditions, the intraspecific competition of Spartina increased. However, facilitation was found among individuals of Scirpus. As a result, when environmental factors restrain the growth of both Spartina and Scirpus, coexistence of Spartina and Scirpus will be promoted; but if environmental factors just restrain the growth of Scirpus, Spartina will take over Scirpus rapidly.3. Vegetation difference result in different nutrient pools in the soil, with N and C storage in the Spartina community much higher than that in the Scirpus communityThe contents of carbon and nitrogen in soil were different among different zones. In vegetation zones, they were higher in the sub-surface layer than that in the surface layer. However, for mudflat, they were lower in subsurface layer than that in the surface layer. Carbon and nitrogen pools were1129±76g/m2and145±5g/m2respectively in the0-30cm layer of Spartina zone. In the Scirpus zone, carbon and nitrogen pools were640±63g/m2and99±6g/m2respectively.The accumulation rates of carbon and nitrogen were significantly greater in the Spartina zone than that in the Scirpus zone (P<0.05), and it was intermediate in the mixed zone compared to that in the Spartina and Scirpus zones. The accumulation rate of carbon (ARC) was35.8±8.1g/(m2·yr), and the accumulation rate of nitrogen (ARN) was5.3±0.5g/(m2·yr) in the Spartina zone. In the Scirpus zone, the ARC was6.6±5.9g/(m2·yr), and the ARN was1.2±0.4g/(m2·yr).Feedback existed between vegetation zonation and the accumulations of carbon and nitrogen. At eastern Chongming Island, the ages of different zones were very close with each other. There was significantly positive linear relationship between nutrient pools and biomass (P<0.05). Consequently, the different vegetation structure affected the accumulation of nutrient pools. The plants with high productivity facilitated nutrient retention in the soil. However, the increase of nutrient pools in soil also affected the vegetation zonation by modifying micro-topography, salinity, redox potential, and particle size, and finally affects vegetation zonation together with feedbacks in the sedimentation process.In conclusion, in the intertidal zone of eastern Chongming Island, the surface elevation was very homogeneous. We believed that the zonation between Spartina and Scirpus probably depended on the stress factors such as salinity, redox potential, and sediment and so on. The overlap of niches will result in competition between them. As a result, physical stress and species competition play interactively during vegetation zonation in the salt marsh. Since determination factors for dominant species are different across scales, the main factors controlling vegetation difference derived from this study at cohort and patch boundary scale are not controdictary with the conclusion that "elevation" is the determination factor of salt marsh vegetation zonation at larger scales.更多还原