Functional traits: Adaption of ferns in forest

Ferns evolved from 400 million years ago show various functional traits and ecological strategies in extant species, and over 80% of them belong to the youngest order Polypodiales. How the functional traits and strategies of ferns have changed during their evolutionary history remains unexplored. Here, we measured functional traits that sensitive to environmental light and water availability of 345 fern species across the fern phylogeny, and reconstructed their evolutionary histories. We found that ferns, mainly Polypodiales, have developed diversified functional traits in response to forest environments. Terrestrial species, especially Thelypteridaceae and Athyriaceae in eupolypods II, showed decreased leaf mass per area (LMA) and area-based leaf nitrogen (N_area) but increased mass-based leaf nitrogen (N_mass) than early-derived polypods since the late Jurassic. Epiphytic species, mainly those in Polypodiaceae, showed reductions in N_mass and individual leaf area (Area) since the late Cretaceous. The adaptation of functional traits of Polypodiales to forest environment may have played a crucial role in fern radiation since the late Jurassic. Integrative analysis of functional traits especially the numerical ones may shed new light on plant evolution.