Department of Systematic and Evolutionary Botany, University of Zurich, Zurich, Switzerland.
Ann Bot. 2019 Mar 14;123(4):611-623. doi: 10.1093/aob/mcy194.
Heteroblasty is a non-reversible morphological change associated with life stage change and has been linked to predictable environmental variation. It is present in several clades from mediterranean-type climates, such as African Restionaceae (restios). These have heteroblastic shoots: juvenile shoots are thin, branched and sterile (sterile shoots); adult shoots are thicker and less branched, and bear inflorescences (reproductive shoots). Ten per cent of the restios retain juvenile-like, sterile shoots as adults (neoteny). We hypothesize (1) that the two shoot types differ in ecophysiological attributes, and (2) that these shoot types (and the neoteny) are associated with different environments.
We measured shoot mass per surface area (SMA), maximum photosynthetic capacity per biomass (Amass) and chlorenchyma to ground tissue ratio (CGR) of both shoot types in 14 restio species. We also calculated environmental niche overlap between neotenous and non-neotenous species using an improved multidimensional overlap function based on occurrence data, and linked shoot types with environments using a phylogenetic generalized linear model.
Sterile shoots showed higher Amass, lower SMA and higher CGR than reproductive shoots. Neotenous and non-neotenous species overlapped ecologically less than expected by chance: neotenous species favoured more mesic, non-seasonal conditions.
We associate sterile shoot morphology with acquisitive ecophysiological strategies and reproductive shoots with conservative strategies. The heteroblastic switch optimizes carbon efficiency in the juvenile phase (by sterile shoots) in the mesic post-fire conditions. The adult shoots present a compromise between a more conservative strategy favourable under harsher conditions and reproductive success. Heteroblasty in seasonally arid, oligotrophic ecosystems with predictable, fire-driven shifts in water and nutrient availability might play a role in the success of restios and other species-rich lineages in mediterranean-type ecosystems. It may represent a previously unrecognized adaptation in mediterranean clades sharing similar conditions, contributing to their ecological and taxonomic dominance.
异形叶性是一种与生活史变化相关的不可逆形态变化，与可预测的环境变化有关。它存在于几种来自地中海气候类型的类群中，如非洲 Restionaceae（restios）。这些类群具有异形叶性：幼叶纤细、分枝且不育（不育叶）；成叶较厚、分枝较少，且具花序（生殖叶）。10%的 restios 在成体中保留幼叶状、不育的叶（幼态持续）。我们假设：（1）两种叶型在生理生态属性上存在差异；（2）这些叶型（和幼态持续）与不同的环境有关。
我们测量了 14 种 restio 物种中两种叶型的比叶面积（SMA）、每生物量最大光合能力（Amass）和叶绿体与组织比（CGR）。我们还使用基于出现数据的改进多维重叠函数计算了幼态持续和非幼态持续物种之间的生态位重叠，并使用系统发育广义线性模型将叶型与环境联系起来。
不育叶的 Amass 较高，SMA 较低，CGR 较高。幼态持续和非幼态持续物种的生态重叠程度低于随机预期：幼态持续物种偏好更湿润、非季节性条件。
我们将不育叶形态与获取性生理生态策略相关联，将生殖叶与保守性策略相关联。在湿润的火灾后条件下，幼态叶的异形叶性优化了幼叶阶段的碳效率（通过不育叶）。成叶表现出在更恶劣条件下有利于更保守策略和生殖成功之间的妥协。在季节性干旱、贫营养的生态系统中，具有可预测的、由水和养分可用性驱动的水热变化的异形叶性可能在 restios 和其他在地中海型生态系统中丰富多样的类群的成功中发挥作用。它可能代表了在具有相似条件的地中海类群中以前未被认识到的适应，有助于它们的生态和分类优势。
