Effective seed dispersal is critical for enabling rapid state shift from a bare tidal flat to a vegetated marsh. While tidal currents are the main dispersal vector in coastal environments, biological characteristics that keep seeds afloat have been shown to influence primary seed dispersal, i.e., seed departure from the parent plant. In contrast, secondary seed dispersal processes that move (germinated) seeds trapped within microsites have been largely neglected. Here, we explore the extent to which the coupling between biotic traits and abiotic factors affects secondary seed dispersal, and whether secondary seed dispersal may explain sudden saltmarsh establishment (i.e., rapid colonization of bare tidal flat by large numbers of seedlings in spring). We used two widely spread pioneer species: Scripus mariqueter and Spartina alterniflora. Combined flume and field results demonstrated that: (1) germination stage, current velocity, and sedimentary regime have a marked effect on the probability of secondary seed dispersal by influencing the threshold lift-off velocity of (germinated) seeds within microsites; (2) density and bud length are critical biotic traits that best predict the potential of secondary-dispersal onset after seed germination; (3) S. alterniflora possess a stronger secondary dispersal ability compared to S. mariqueter; and (4) secondary dispersal of germinated seeds in spring may explain observed sudden marsh establishment on bare tidal flats. Our findings provide novel insight relevant to understanding the drivers of seed dispersal and thereby sudden saltmarsh establishment events, with important implications for understanding the effects of climate change on critical state transitions and enabling human-aided restoration.

中文翻译：

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二次种子传播的开始受发芽特征控制：盐沼突然建立中被忽视的过程

有效的种子传播对于实现从光秃秃的潮滩到植被茂盛的沼泽的快速状态转变至关重要。虽然潮汐流是沿海环境中的主要传播媒介，但已显示使种子漂浮的生物学特性会影响主要种子传播，即种子与亲本植物的分离。相比之下，移动被困在微型站点内的（发芽）种子的二次种子传播过程在很大程度上被忽视了。在这里，我们探讨了生物性状和非生物因素之间的耦合影响二次种子传播的程度，以及二次种子传播是否可以解释盐沼的突然建立（即春季大量幼苗在裸滩快速定植）。我们使用了两种广泛传播的先驱物种：Scripus mariqueter和互花米草。结合水槽和现场结果表明：（1）萌发阶段、流速和沉积方式通过影响微型站点内（萌发）种子的阈值提离速度对种子二次扩散的概率有显着影响；(2) 密度和芽长是最能预测种子萌发后二次传播发生潜力的关键生物性状；(3) S. alterniflora比S. mariqueter具有更强的二次传播能力; (4) 春季发芽种子的二次传播可以解释在裸露的滩涂上观察到的突然沼泽建立。我们的研究结果提供了与理解种子传播的驱动因素相关的新见解，从而理解突然的盐沼建立事件，对于理解气候变化对关键状态转变的影响和实现人工辅助恢复具有重要意义。