Structural adaptations in plants from the humid equatorial Andes indicate a trade-off between hydraulic transport efficiency and safety
Abstract
Premise 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 broad-leaved climbers in montane forests, basal broad-leaved rosette herbs in azonal marshy habitats, and ascending, narrow-leaved subshrubs in high-elevation paramo.
Habitat variation along the elevational 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 10 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. Results Species from the humid and frost-free montane forest develop xylem optimized for transport efficiency by increasing the internal diameter and length of the conduits.
In contrast, paramo species are optimized toward hydraulic safety by producing narrower conduits and are more likely to prevent the risk of frost-induced cavitation. Moreover, species from the high-elevation paramo 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 paramo in the equatorial Andes demonstrate a trade-off between hydraulic safety and efficiency of water transport.