The relationship between chlorophyllous spores and mycorrhizal associations in ferns: Evidence from an evolutionary approach

Approximately 14% of all fern species have physiologically active chlorophyllous spores that are much more short-lived than the usual and dormant achlorophyllous spores. Most chlorophyllous-spored species (70%) are epiphytes, and these account for almost 37% of all epiphytic ferns. Chlorophyllous-spored ferns are also overrepresented among species in habitats with waterlogged soils, of which nearly 60% have chlorophyllous spores. Ferns in these disparate habitat types are also united by a low incidence of mycorrhizal associations. We, therefore, hypothesize that autotrophic chlorophyllous spores represent an adaptation of ferns to habitats with scarce mycorrhizal associations. We evaluated the evolution of chlorophyllous spores and mycorrhizal associations in ferns and their relation to habitat type using phylogenetic comparative methods. We found that chlorophyllous spores and the absence of mycorrhizal associations are strongly associated with epiphytic and waterlogged habitats. Trans...全球所有蕨类物种中约有14%拥有具有生理活性的叶绿素孢子（chlorophyllous spores），这类孢子的存活时长远短于常规的休眠型无叶绿素孢子（achlorophyllous spores）。拥有叶绿素孢子的物种中约70%为附生植物（epiphyte），这类附生蕨类占全球附生蕨类总数的近37%。在渍水土壤（waterlogged soils）生境的蕨类物种中，叶绿素孢子蕨类的占比同样显著偏高，该类生境中近60%的蕨类拥有叶绿素孢子。栖息于上述两类截然不同生境的蕨类，还有一个共同特征：菌根共生关系（mycorrhizal associations）的发生率极低。据此我们提出假说：自养型叶绿素孢子是蕨类适应菌根共生关系匮乏生境的一种适应性演化策略。本研究借助系统发育比较分析法（phylogenetic comparative methods），探究了蕨类叶绿素孢子与菌根共生关系的演化历程，以及二者与生境类型之间的关联。研究结果显示，叶绿素孢子的存在与菌根共生关系的缺失，均与附生生境及渍水土壤生境存在显著关联。后续内容暂未完整展示。