Broad- and small-scale environmental gradients drive variation in chemical, but not morphological, leaf traits of vascular epiphytes

Valeria Guzmán-Jacob, Nathaly R. Guerrero-Ramírez, Dylan Craven, Gustavo Brant Paterno, Amanda Taylor, Thorsten Krömer, Wolfgang Wanek, Gerhard Zotz, Holger Kreft

This is a plain language summary of a Functional Ecology research article which is published here.

Vascular epiphytes, such as bromeliads, orchids, and ferns, respond to environmental gradients at different scales. At a broad-scale, i.e. elevational gradient, both temperature and precipitation likely play an important role as drivers of leaf trait variation, but these traits may also respond to small-scale changes in light, temperature, and humidity along the vertical environmental gradient within forest canopies. However, the relative importance of broad- and small-scale environmental gradients as drivers of variation in leaf functional traits of vascular epiphytes is poorly understood. Therefore, we investigated the variation in morphological and chemical leaf traits of 102 vascular epiphyte species along broad- and small-scale environmental gradients in the Cofre de Perote mountain in Mexico. We also assessed whether variation in morphological and chemical leaf traits along these gradients were consistent across photosynthetic pathways, i.e. C₃ (found in the majority of plants) and CAM (found in many succulents of dry habitats).

Humid montane forest at 1500 m above sea level (credit: Valeria Guzmán-Jacob)

We found that broad-scale environmental gradients have less impact on variation in morphological leaf traits than on chemical leaf traits. Contrary to our expectations, environmental gradients explained minimal variation in morphological leaf traits, suggesting that environmental conditions do not constrain morphological leaf trait values of vascular epiphytes. Moreover, our findings suggest that assessing multiple drivers of leaf trait variation among photosynthetic pathways is key for disentangling the mechanisms underlying responses of vascular epiphytes to environmental conditions. In conclusion, vascular epiphytes exhibit a wide range of ecological strategies to acquire resources across environmental gradients that likely shape species distributions.