Departamento de Ecologia, Instituto de Biologia, Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil.
Department of Biology, Duke University, Durham, NC 27708, USA.
Ann Bot. 2022 Jul 18;129(7):839-856. doi: 10.1093/aob/mcac038.
The timing of seed dispersal determines the environmental conditions that plants face during early life stages. In seasonal environments, selection is expected to favour dispersal timing that is matched to environmental conditions suitable for successful recruitment. Our aim here was to test whether the timing of seed dispersal influences seedling establishment success in two populations of Euterpe edulis that are located at contrasting altitudes, have different seed-dispersal phenologies and are subjected to distinct climatic conditions.
We sowed E. edulis seeds in contrasting altitudes on different dates, and monitored seed germination, emergence and seedling establishment at each altitude over 4 years. At the high-altitude site, five seed-dispersal cohorts were established during the natural dispersal period. At the low-altitude site, three seed-dispersal cohorts were established during natural dispersal, and two were established either before or after natural dispersal.
At the high-altitude site, seed-dispersal timing did not affect seed germination, seedling emergence or seedling establishment success. In contrast, at the low-altitude site, late seed dispersal near the end of the wet season resulted in a lower probability of seedling establishment, possibly due to the exposure of seeds, germinants and seedlings to unfavourable drought conditions. In addition, at the low-altitude site, the natural seed-dispersal period was poorly matched to favourable environmental conditions for seedling establishment.
The greater effect of seed-dispersal timing on seedling establishment at the low-altitude site is probably related to a more seasonal and drought-prone environment that favours a restricted period of seed dispersal. The magnitude of the effect of dispersal timing on seedling establishment success was modulated by environmental conditions that vary across altitude. Furthermore, reproductive phenology appears to be subject to more intense selection at the lower limit of the altitudinal range, due to a more restrictive window of opportunity for successful seedling establishment.
种子散布的时间决定了植物在早期生命阶段所面临的环境条件。在季节性环境中，选择应该有利于与适合成功繁殖的环境条件相匹配的散布时间。我们的目的是测试在两个位于不同海拔高度、具有不同种子散布物候学且受到不同气候条件影响的 Euterpe edulis 种群中，种子散布时间是否会影响幼苗建立的成功。
我们在不同日期在不同海拔高度播种 E. edulis 种子，并在 4 年内监测每个海拔高度的种子发芽、出现和幼苗建立情况。在高海拔地点，在自然散布期间建立了五个种子散布群。在低海拔地点，在自然散布期间建立了三个种子散布群，在自然散布前后又建立了两个种子散布群。
在高海拔地点，种子散布时间不会影响种子发芽、幼苗出现或幼苗建立的成功率。相比之下，在低海拔地点，在雨季末期的晚期种子散布导致幼苗建立的可能性降低，可能是由于种子、萌芽和幼苗暴露在不利的干旱条件下。此外，在低海拔地点，自然种子散布期与有利于幼苗建立的环境条件配合不佳。
在低海拔地点，种子散布时间对幼苗建立的影响更大，可能与更具季节性和更易发生干旱的环境有关，该环境有利于种子散布的时间有限。散布时间对幼苗建立成功率的影响程度受到环境条件的调节，这些条件在海拔高度上有所不同。此外，由于成功幼苗建立的机会窗口更窄，繁殖物候学在海拔下限处可能受到更强烈的选择。
