THE HYDRAULIC ARCHITECTURE OF PETIOLES AND LEAVES IN TROPICAL FERN SPECIES UNDER DIFFERENT LEVELS OF CANOPY OPENNESS

Premise of research. Structure-function relationships of xylem in tropical fern species remain poorly explored despite the taxonomic diversity and ecological importance of ferns in tropical environments. The aim of this study is to broaden our understanding of how tropical fern morphology and anatomy are influenced by light availability. Methodology. Nine fern species, including six shade-tolerant species, two sun-exposed species, and one species with representatives in both light conditions, were studied in order to investigate the impact of light exposure on leaf morphology and xylem anatomy. Measured parameters included water potential and micromorphology based on light and electron microscopy. Pivotal results. Canopy openness was significantly correlated with specific leaf area, basic specific gravity, venation density, pit membrane area, pit aperture area, and pit membrane thickness. Intraspecific variation within Pteris quadriaurita showed that leaf morphological features such as petiole length and diameter were unaffected by light exposure, while most anatomical features of the xylem (except for conduit diameter) increased with higher light availability. Pit membrane thickness was correlated with predawn water potential, suggesting that thicker pit membranes provide higher hydraulic safety. The theoretical conduit implosion resistance was found to be surprisingly low compared to xylem of seed plants. Conclusions. Our results illustrate that the hydraulic architecture of ferns shows interesting structure-function relationships that reflect ecological adaptations for optimal growth in relation to light availability. Higher-light regimes increased the need for investment in hydraulic safety characteristics such as pit membrane thickness and diameter, while petiole length was not affected.