Tropical terrestrial and epiphytic ferns have different leaf stoichiometry with ecological implications

Abstract

Terrestrial and epiphytic herbaceous forest species have different ecological qualities and leaf stoichiometry. Ferns represent a great component of herbaceous forest species in tropical regions with different lifeforms and evolutionary histories. However, little is known about the differences in leaf stoichiometry between the lifeforms. We studied the concentrations of leaf elements (N, P, K, Ca and Mg) between lifeforms (16 terrestrial, 4 epiphytic) and evolutionary clades (12 polypods, 8 non-polypods). The leaves were collected from the field, acid-digested and analyzed for nutrient elements. Results show that epiphytic species had a higher concentration of most leaf elements. Epiphytes had a lower N:P ratio compared with terrestrial ones. This suggests that epiphytes were nutrient-limited, relying on stochastic elements supply compared to terrestrial species which have a constant supply. Epiphytes tend to accumulate higher element concentration beyond their immediate metabolic needs, defined as luxury consumption. Epiphytes showed a higher concentration of P and Ca for their necessity of coping with severe habitat conditions and sclerophyll leaves. We found that modern polypod and archaic non-polypod ferns are significant stoichiometry different for K. The results contribute to the context of the poorly studied stoichiometry of tropical Asian fern species and their ecophysiology.