Disentangling plant establishment in sandy coastal systems: biotic and abiotic factors that determine Allagoptera arenaria (Arecaceae) germination

ABSTRACT Germination rate and establishment success of plants in harsh environments depend on the ability of seeds to withstand unfavorable environmental conditions and avoid predators. Brazilian coastal plains, known as restinga, are subject to environmental factors that seriously limit plant establishment and survival (e.g. salinity, desiccation, oligotrophy, flooding, high temperature and radiation levels). We tested, both in field and laboratory experiments, conditions for germination and establishment of Allagoptera arenaria, a palm tree often found in restinga ecosystems of southeastern Brazil, and which have a principal role in plant community dynamics. Our results showed that the absence of mesocarp, high radiation exposure, and temperature were the main drivers of seed germination. In the field, the highest germination rate was linked to nude seeds buried in open areas. High temperatures and/or predation damaged seeds that remained on the soil surface, especially if they were close to the mother plant and alongside dung piles made by dispersers. Under controlled conditions, seeds exhibited optimum germination at 35 ºC. Therefore, the germination and establishment of A. arenaria depend as much on environmental conditions as on a network of interactions including vertebrates and invertebrates, which allow this species to colonize harsh, open areas in restinga ecosystems.

摘要：严酷环境下植物的发芽率与定植成功率，取决于种子耐受不良环境条件以及躲避天敌的能力。被称为滨海沙生植被（restinga）的巴西滨海平原，存在诸多严重限制植物定植与存活的环境因子，包括盐胁迫、干旱、寡营养、积水、高温与强辐射。我们通过野外与实验室实验，针对巴西东南部滨海沙生植被（restinga）生态系统中常见的棕榈科植物银叶椰子（Allagoptera arenaria）开展了发芽与定植条件的测试——该物种在植物群落动态中发挥核心作用。结果表明，中果皮（mesocarp）的缺失、强辐射与温度是影响种子发芽的主要驱动因素。野外实验中，去除中果皮的种子埋置于开阔区域时发芽率最高；留存于土壤表面的种子，尤其是紧邻母株且位于传播者粪便堆旁的个体，易因高温和/或捕食行为受损。在可控环境条件下，种子的最适发芽温度为35℃。综上，银叶椰子（Allagoptera arenaria）的发芽与定植，既依赖环境条件，也依赖包括脊椎动物与无脊椎动物在内的交互网络，这一网络使其能够在滨海沙生植被生态系统的严酷开阔区域成功定植。