Morphological and anatomical traits of leaves and stems in species of Andean Senecio
Description
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.
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Species were sampled in natural stands of montane forest and páramo in the Ecuadorian Andes. Stem segments and leaves were systematically collected from the middle (fully differentiated) part of leaf-bearing shoots and fixed in 2% formaldehyde. Using a hand microtome, sections were prepared for anatomical analyses and histochemical tests. Micrographs were acquired on an Olympus BX51 microscope (Tokyo, Japan) using an Apogee U4000 camera and MicroCCD software (Diffraction Limited, Ottawa, Canada). Quantitative traits were measured from micrographs with the aid of a NIS elements image analyzer (Laboratory Imaging, Prague, Czech Republic). Specific leaf area (SLA) was determined from ten freshly collected leaves per species and 2–4 leaves per plant. Fresh leaves were scanned at 1200 dpi to estimate the leaf area, dried in a herbarium oven at 40–50 °C for several days (at Pontificia Universidad Católica del Ecuador, Quito), and stored in paper bags. Dry biomass was measured using an analytical weight (at Charles University, Prague) after drying the leaves for 24 h at 60 °C.