The inXuence of life form on carbon and nitrogen relationships in tropical rainforest ferns

Tropical ferns are characterized by a high diversity of plant life forms, yet there have been few largescale studies on the functional ecology of these diVerent forms. We examined epiphytic, hemiepiphytic, and terrestrial ferns, and asked whether there are diVerences in the mineral nutrition and water relations across diVerent growth forms of a diverse assemblage of species. We measured speciWc leaf area, leaf nitrogen concentrations, and natural abundance of the stable isotopes N and C 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 signiWcantly diVerent 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 diVerent plant life forms, and that the N cycle of epiphytic and terrestrial habitats function independently from each other.