蕨上之蕨：探索台灣蕨類附生配子體棲身在台灣桫欏之上

Abstract

Not applicable

Tree ferns have been documented as significant hosts for epiphytes and are often composed of distinct communities that are considerably different from other hosts. Particularly, exclusive growth of epiphytic fern species has been exhibited on tree ferns, however, this fern–on–tree–fern epiphytism has yet to be substantially explored for the gametophyte generation. This study focused on epiphytic fern gametophytes growing on low trunks of a tree fern species, Alsophila spinulosa (Cyatheaceae), and nearby angiosperm hosts. Fern gametophyte surveys were conducted in two seasons, during the months of June and October, in a subtropical forest in Taiwan. These surveys sought to understand what factors make tree ferns optimal habitats for gametophytes, and whether there are notable differences between the composition of fern gametophyte communities on tree ferns compared with other hosts. Gametophytes were identified using an Illumina Miseq approach (Illumina inc., San Diego, CA, USA) which involved sequencing multiplexed trnL–F amplicons derived from tissue–direct PCR. Environmental surveys were conducted for each season, in which we recorded relative humidity (RH) and measured canopy openness and light availability. Overall, October had a higher abundance of individuals in the epiphytic gametophyte community which could be a phenological association. Tree ferns harbored a significantly higher abundance and species richness of gametophytes than angiosperm hosts, and hosted more cordiform gametophytes that were mostly from accidental and facultative fern epiphytes. In comparison, angiosperms had a higher abundance of non–cordiform individuals. In addition, two independent gametophytes were found on the surveyed hosts, Callistopteris apiifolia and a Haplopteris yakushimensis species. Generally, plots with a higher species richness of sporophytes also had a higher richness of gametophytes. Results from the environmental survey showed that the RH for all surveyed hosts was most frequently over 95%, however the angiosperm host spent considerably more time below 95% and 85% RH than tree ferns. The stable RH revealed on the tree fern trunks, which presumably results from the moist root mantle, allowed for a high diversity of fern gametophytes. There was overall no statistical significance for the relationship between canopy openness and gametophyte diversity. Nevertheless, in each season, the plot with the highest total light also had the high species richness and abundance for fern gametophytes. Importantly, this study is among the first insights of epiphytic gametophyte communities on tree ferns.