Data from: Life cycle matters: DNA barcoding reveals contrasting community structure between fern sporophytes and gametophytes

Ferns are the only major lineage of vascular plants that have nutritionally independent sporophyte (diploid) and gametophyte (haploid) life stages. However, the implications of this unique life cycle for fern community ecology have rarely been considered. To compare patterns of community structure between fern sporophytes and gametophytes, we conducted a survey of the ferns of the islands of Moorea and Tahiti (French Polynesia). We first constructed a DNA barcode library (plastid rbcL and trnH–psbA) for the two island floras including 145 fern species. We then used these DNA barcodes to identify more than 1300 field-collected gametophytes from 25 plots spanning an elevational gradient from 200 to 2000 m. We found that species richness of fern sporophytes conforms to the well-known unimodal (i.e., mid-elevation peak) pattern, reaching a maximum at ca. 1000 – 1200 m. Moreover, we found that fern sporophyte communities become increasingly phylogenetically clustered at high elevations. In contrast, species richness of fern gametophytes was consistent across sites, and gametophytes showed no correlation of phylogenetic community structure with elevation. Turnover of sporophyte and gametophyte communities was closely linked with elevation at shallow phylogenetic levels, but not at deeper nodes in the tree. Finally, we found several species for which gametophytes had broader ranges than sporophytes, including a vittarioid fern with abundant gametophytes but extremely rare sporophytes. Our study highlights the importance of including diverse life history stages in surveys of community structure, and has implications for the possible impacts of climate change on the distribution of fern diversity.

蕨类是唯一一类营养上独立的孢子体（sporophyte，二倍体）与配子体（gametophyte，单倍体）生活史阶段均存在的维管植物主要演化支。然而，这一独特生活周期对蕨类群落生态学的影响却极少被纳入研究范畴。为对比蕨类孢子体与配子体的群落结构模式，我们对法属波利尼西亚莫雷阿岛与塔希提岛的蕨类植物开展了系统性调查。我们首先为这两座岛屿的蕨类区系构建了DNA条形码（DNA barcode）文库，涵盖质体rbcL与trnH–psbA两个基因位点，共收录145种蕨类。随后，我们利用这些DNA条形码对覆盖200至2000米海拔梯度的25个样地中采集得到的1300余份野外配子体样本完成了物种鉴定。研究结果显示，蕨类孢子体的物种丰富度符合学界熟知的单峰格局（即海拔中峰模式），在约1000至1200米处达到峰值。此外，我们观察到蕨类孢子体群落在高海拔区域的系统发育聚集程度逐渐升高。与之形成鲜明对比的是，蕨类配子体的物种丰富度在各样地间保持一致，且其群落系统发育结构与海拔无显著关联。在较浅的系统发育层级上，孢子体与配子体群落的物种更替与海拔紧密相关，但在系统发育树更深的节点处则未观察到此关联。最后，我们发现多个物种的配子体分布范围较孢子体更广，其中包括一种书带蕨亚科（vittarioid）蕨类，其配子体极为常见，但孢子体却极其稀有。本研究强调了在群落结构调查中纳入不同生活史阶段的重要性，同时也为气候变化对蕨类多样性分布的潜在影响提供了重要研究启示。