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Desiccation tolerance was a key trait that allowed plants to colonize land. However, little is known about the transition from desiccation tolerant non-vascular plants to desiccation sensitive vascular ones. Filmy ferns (Hymenophyllaceae) represent a useful system to investigate how water-stress strategies differ between non-vascular and vascular stages within a single organism because they have vascularized sporophytes and nonvascular gametophytes that are each capable of varying degrees of desiccation tolerance. To explore this, we surveyed sporophytes and gametophytes of 19 species (22 taxa including varieties) of filmy ferns on Moorea (French Polynesia) and used chlorophyll fluorescence to measure desiccation tolerance and light responses. We conducted phylogenetically informed analyses to identify differences in physiology between life stages and growth habits. Gametophytes had similar or less desiccation tolerance (ability to recover from 2 days desiccation at − 86 MPa) and lower photosynthetic optima (maximum electron transport rate of photosystem II and light level at 95% of that rate) than sporophytes. Epiphytes were more tolerant of desiccation than terrestrial species in both life stages. Despite their lack of greater physiological tolerances, gametophytes of several species occurred over a wider elevational range than conspecific sporophytes. Our results demonstrate that filmy fern gametophytes and sporophytes differ in their physiology and niche requirements, and point to the importance of microhabitat in shaping the evolution of water-use strategies in vascular plants. [ABSTRACT FROM AUTHOR]

Tropical ferns are characterized by a high diversity of plant life forms, yet there have been few large-scale studies on the functional ecology of these different forms. We examined epiphytic, hemiepiphytic, and terrestrial ferns, and asked whether there are differences in the mineral nutrition and water relations across different growth forms of a diverse assemblage of species. We measured specific leaf area, leaf nitrogen concentrations, and natural abundance of the stable isotopes δ15N and δ13C of 48 fern species from 36 genera across a wide range of habitats at La Selva Biological Station in Costa Rica. We found that epiphytes were significantly different in all measured variables from hemiepiphytic and terrestrial species, and that terrestrial and soil-rooted hemiepiphytes were indistinguishable in all variables excluding SLW. A multivariate analysis revealed that aspects of N nutrition were the most reliable at separating epiphytic species from other life forms. Our study demonstrates that the natural abundance of both C and N as well as N relations and leaf morphology are useful when segregating different plant life forms, and that the N cycle of epiphytic and terrestrial habitats function independently from each other. [ABSTRACT FROM AUTHOR]