Autochory in ferns, not all spores are blown with the wind

Dispersal is a key process in plant population dynamics. In ferns, two successive vectors are needed: the sporangium catapulting mechanism, and wind or gravity. However, some rock ferns have a growth habit that suggests a kind of autochory by placing spores on the rock surface. Moreover, some ferns show modifications of the sporangial dehiscence. To determine the role of growth habit in spore dispersal, we checked the sporangial opening mechanism and explored the spatial distribution of plants on the walls. The presence of spores of <i>Asplenium celtibericum,</i> a rupicolous fern, in the rock surface was checked. In addition, its sporangial dehiscence, plant size and position in the wall were analysed. Spores and indehiscent sporangia were present on walls at each sampling moment. Their highest number was found close to the plants. There was a positive correlation between crack width and plant size. However, most plants occupy the upper half of the cliffs. The growth habit of <i>A. celtibericum</i> is instrumental to deposit the spores over the neighbouring rock surface, thus enhancing the probability of spores to find suitable crevices for germination. Furthermore, dispersal of indehiscent sporangia might promote intergametophytic mating, and the modified sporangial opening mechanism extends the dispersive period.

孢子扩散是植物种群动态调控中的关键过程。蕨类植物的孢子扩散需要两类依次发挥作用的传播媒介：孢子囊（sporangium）弹射机制，以及风力或重力。然而，部分岩生蕨类的生长习性表明其可通过将孢子直接置于岩石表面的方式实现自动散播（autochory）；此外，部分蕨类还会对孢子囊开裂（sporangial dehiscence）机制进行适应性改造。为明确生长习性在孢子扩散过程中的作用，本研究观测了岩壁上蕨类的孢子囊开启机制，并分析了植株在岩壁上的空间分布格局。本研究以岩生蕨类欧洲铁角蕨（Asplenium celtibericum）为对象，检测了其孢子在岩石表面的存在情况；此外，本研究还对该物种的孢子囊开裂特征、植株体型及其在岩壁上的分布位置进行了分析。每次采样均在岩壁上检测到孢子与未开裂孢子囊的存在，二者的最高丰度均出现在植株邻近区域。岩壁裂隙宽度与植株体型呈显著正相关，但绝大多数植株分布在崖壁的上半区域。欧洲铁角蕨的生长习性有助于将孢子播散至邻近的岩石表面，进而提升孢子找到适宜萌发裂隙的概率。此外，未开裂孢子囊的散播可能促进配子体间交配，而经适应性改造的孢子囊开启机制则延长了孢子的扩散周期。