Understanding the mechanisms by which the geomorphic structures affect habitat invasibility by mediating various abiotic and biotic factors is essential for predicting whether these geomorphic structures may provide spatial windows of opportunity to facilitate range-expansion of invasive species in salt marshes. Many studies have linked geomorphic landscape features such as tidal channels to invasion by exotic plants, but the role of tidal channel meanders (i.e., convex and concave sides) in regulating the Spartina alterniflora invasion remains unclear. Here, we examined the combined effects of tidal channel meander-mediated hydrodynamic variables, soil abiotic stresses, and propagule pressure on the colonization of Spartina in the Yellow River Delta, China, by conducting field observations and experiments. The results showed that lower hydrodynamic disturbance, bed shear stress, and higher propagule pressure triggered by eddies due to the convex structure of channel meanders facilitated Spartina seedling establishment and growth, whereas the concave side considerably inhibited the Spartina invasion. Lower soil abiotic stresses also significantly promoted the invasibility of the channel meanders by Spartina. Based on these findings, we propose a conceptual framework to illustrate the effects of the meandering geomorphology of tidal channels on the mechanisms that might allow the landward spread of Spartina and related processes. Our results demonstrate that the meandering geomorphic structures of tidal channels could act as stepping-stones to significantly facilitate the landward invasion of Spartina along tidal channels. This implies that geomorphic characteristics of tidal channels should be integrated into invasive species control and salt marsh management strategies.
理解地貌结构通过调节各种非生物和生物因子影响栖息地可入侵性的机制，对于预测这些地貌结构能否为促进入侵物种在盐沼中的范围扩张提供空间“机会窗口”至关重要。许多研究已经将潮沟等地貌景观特征与外来植物入侵联系起来，然而盐沼潮沟的弯曲地貌结构(即凸岸和凹岸)调节互花米草入侵的作用机制仍尚不明确。本文通过开展野外观测和控制实验，探讨了潮沟弯曲地貌结构介导的水动力变量、土壤非生物胁迫和繁殖压力的交互作用对互花米草在中国黄河三角洲定殖扩张的影响。结果表明，潮沟凸侧弯曲地貌结构的涡流引起的低水动力扰动、低底床剪切应力和较高的繁殖压力有利于互花米草幼苗的建立和生长，而凹侧弯曲地貌结构则显著抑制了互花米草入侵。此外，潮沟弯曲结构两侧较低的土壤非生物胁迫(即较低的土壤盐度和较高的土壤含水率)也显著促进了互花米草在盐沼潮沟系统中的入侵。基于上述发现，本研究进一步提出了一个概念框架，以阐明潮沟蜿蜒地貌影响下互花米草沿盐沼潮沟向陆扩张的机制和相关过程。综上，本研究结果表明，蜿蜒的潮沟地貌结构可以作为互花米草入侵的“跳板”，显著促进其沿潮沟不断地从盐沼低潮滩向陆扩张。上述研究结果启示我们应该将潮沟地貌特征进一步整合到外来入侵物种的控制和盐沼的管理策略中。.
Keywords: biological invasion; hydrodynamic disturbance; propagule pressure; salt marsh geomorphology; tidal channel meander; windows of opportunity.
© 2023 The Ecological Society of America.