Aros-Mualin Daniela, Kessler Michael
Department of Systematic and Evolutionary Botany, University of Zurich, Zurich, Switzerland.
Ann Bot. 2024 Dec 31;134(7):1139-1150. doi: 10.1093/aob/mcae167.
Poikilohydry describes the inability of plants to internally regulate their water content (hydroregulation), whereas desiccation tolerance (DT) refers to the ability to restore normal metabolic functions upon rehydration. The failure to clearly separate these two adaptations has impeded a comprehensive understanding of their unique evolutionary and ecological drivers. Unlike bryophytes and angiosperms, these adaptations in ferns are sometimes uncorrelated, offering a unique opportunity to navigate their intricate interplay.
We classified ferns into two syndromes: the Hymenophyllum-type (H-type), encompassing species with filmy leaves lacking stomata that experience extreme poikilohydry and varying degrees of DT, and the Pleopeltis-type (P-type), consisting of resurrection plants with variable hydroregulation but high DT.
The H-type evolved during globally cool Icehouse periods, as an adaptation to low light levels in damp, shady habitats, and currently prevails in wet environments. Conversely, the P-type evolved predominantly under Greenhouse periods as an adaptation to periodic water shortage, with most extant species thriving in warm, seasonally dry habitats.
Out study underscores the fundamental differences between poikilohydry and DT, emphasizing the imperative to meticulously differentiate and qualify the strength of each strategy as well as their interactions, as a basis for understanding the genetic and evolutionary background of these ecologically crucial adaptations.
变水植物描述的是植物无法在内部调节自身含水量（水分调节）的情况，而耐旱性（DT）指的是在重新水化后恢复正常代谢功能的能力。未能清晰区分这两种适应方式阻碍了对其独特进化和生态驱动因素的全面理解。与苔藓植物和被子植物不同，蕨类植物的这些适应方式有时并不相关，这为探究它们复杂的相互作用提供了独特的机会。
我们将蕨类植物分为两种类型：膜蕨型（H型），包括叶片薄且无气孔的物种，这些物种经历极端变水特性和不同程度的耐旱性；以及复叶耳蕨型（P型），由具有可变水分调节但耐旱性高的复苏植物组成。
H型在全球寒冷的冰室期进化而来，是对潮湿、阴暗栖息地低光照水平的一种适应，目前在潮湿环境中占主导地位。相反，P型主要在温室期进化，以适应周期性缺水，大多数现存物种在温暖、季节性干燥的栖息地中繁衍生息。
我们的研究强调了变水特性和耐旱性之间的根本差异，强调必须仔细区分并量化每种策略的强度及其相互作用，以此作为理解这些对生态至关重要的适应方式的遗传和进化背景的基础。
