Morphological and anatomical traits of leaves and stems in species of Andean Senecio

Premise of the study: Environmental gradients of mountains are reflected in traits that are common to high-elevation plants worldwide. Closely related species of Senecio from the equatorial Andes grow as broadleaved climbers in montane forests, basal broadleaved rosette herbs in azonal marshy habitats, and ascending, narrow-leaved subshrubs in high-elevation páramo. Habitat variation along the elevation gradient enables testing whether modifications in leaf and stem functional traits among species were driven by contrasting environmental conditions. Methods: We used quantitative analyses to describe changes in morphological and anatomical traits of leaves and stems in ten species from various habitats. We applied univariate (linear regression, hierarchical ANOVA) and multivariate (nMDS ordination, permutational MANOVA) techniques to examine the correlation of traits with the species’ habitats and elevation. Key results: Species from the humid and frost-free montane forest develop xylem optimized for transport efficiency by increasing the conduits’ internal diameter and length. This is in contrast to páramo species, which are optimized towards hydraulic safety by producing narrower conduits, more likely to prevent the risk of frost-induced cavitation. Moreover, species from the high-elevation páramo habitats present a set of water transport-related anatomical traits of leaf lamina allowing for efficient regulation of transpiration losses. Conclusions: Morphological and anatomical traits of leaves and stems in species of Senecio inhabiting montane forests and high-elevation páramo in the equatorial Andes demonstrate a trade-off between hydraulic safety and efficiency of water transport.