盐度及种间相互作用对海三棱藨草、互花米草萌发及生长的影响

盐度和种间作用是影响湿地植物群落构建的关键因子。然而，已有研究主要集中于植物成体阶段，我们对生活史早期更新阶段的种间相互作用了解十分有限。崇明东滩国家级自然保护区是位于长江口的重要湿地，外来入侵植物互花米草对优势土著物种海三棱藨草的竞争排斥对当地生态系统造成了严重的负面影响。通过受控实验探讨了盐度及种间作用对海三棱藨草和互花米草种子萌发及生长的影响，以深入了解更新过程在盐沼湿地植物群落构建中的作用。结果表明，在培养皿中盐度对海三棱藨草的萌发有显著抑制作用，互花米草的萌发率受盐度影响不显著但萌发进程被延迟。混种处理对两者的萌发存在一定促进效应，且其作用强度受到盐度的调控。海三棱藨草与互花米草种子在萌发阶段的相互促进并非是通过化感作用实现的，可能是由于萌发过程对盐分的吸收减弱了盐胁迫的影响。盆栽条件下，两物种混种时的萌发及生长表现（高度、地上生物量）较单种时有所下降，但差异不显著。种间竞争受环境胁迫程度及生活史阶段的影响，竞争作用在胁迫较弱的淡水环境及生活史后期更强。盐沼湿地植物群落在形成早期受到盐度等环境因子的影响较大，不同植物对盐胁迫的响应是影响种群建成的主导因素，后期种间竞争的重要性不断增加，最终决定了植物群落的整体格局。

Effects of salinity and interspecific interaction on germination and growth of Scirpus mariqueter and Spartina alterniflora

Salinity and interspecific interactions are the main factors affecting community assembly of wetland ecosystems. However, most previous studies focused on the interaction between adult plants, and our understanding of their interspecific interactions at regeneration stage is still limited. Chongming Dongtan National Nature Reserve is a wetland of importance in the Yangtze River Estuary. The invasion of Spartina alterniflora has caused significantly negative impacts on native Scirpus mariqueter and the local ecosystem. This study examined the effects of salinity and interspecific interaction between Spartina alterniflora and Scirpus mariqueter during seed germination and vegetative growth stages by controlled environment experiments, aiming to further understand the influence of regeneration on plant community assembly of salt marshes. The major findings of this study are as follows. (1) In Petri dish germination experiment, germination rate of Spartina alterniflora seeds was not significantly affected by salinity and interspecific interaction, but the germination speed was significantly slowed down under 1% NaCl treatment. Germination rate of Scirpus mariqueter was significantly inhibited by high salinity, and the effects of interspecific interaction were regulated by salinity. Scirpus mariqueter seeds were significantly facilitated by Spartina alterniflora seeds in 1% NaCl solution, but not in fresh water. Germination speed of Scirpus mariqueter seeds was also significantly slowed down under 1% NaCl treatment, but interspecific interaction had no significant effects. (2) In interaction mechanism experiment, germination rate of Spartina alterniflora seeds was significantly promoted by Scirpus mariqueter seeds in mixture, and the germination speed was significantly slowed down in soak solution of competitor seeds. Germination rate of Scirpus mariqueter seeds was significantly promoted by Spartina alterniflora seeds, whereas the germination speed was significantly slowed down. For both species, the salinity of culture solution was significantly lower in mixture than in other treatments. Hence, the interspecific interaction between Scirpus mariqueter and Spartina alterniflora seeds was not mediated by allelopathy. The facilitation may be caused by salt absorption during the germination process. (3) In pot experiment, high salinity also inhibited Scirpus mariqueter more than Spartina alterniflora. Germination and vegetative growth (average shoot height and aboveground biomass) were generally inhibited in mixture compared with those in monoculture, but the difference was not significant. Interspecific competition was affected by stress and life history stage, which became more intense in more stressful environment and late life history stage. In newly formed salt marsh plant communities, environmental factors such as salinity play more important roles, whereas in mature communities, interspecific competition becomes the dominant factor which determines the community pattern.