A comparison of the hydraulic efficiency of a palm species (Iriartea deltoidea) with other wood types

This is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by Oxford University Press and can be found at: http://treephys.oxfordjournals.org/.Palms are an important component of tropical ecosystems, living alongside dicotyledonous trees, even though they have a very different growth pattern and vascular system. As monocots, vessels in palms are located within vascular bundles and, without a vascular cambium that many dicotyledonous trees possess, palms cannot add additional vessels to their vascular system as they get older and taller. This means that hydraulic architecture in palms is more predetermined, which may require a highly efficient hydraulic system. This preset nature, along with the decoupling of hydraulic and mechanical functioning to different cell types, may allow palms to have a more efficient hydraulic system than dicotyledonous trees. Therefore, this study seeks to determine the efficiency of the hydraulic system in the palm Iriartea deltoidea (Ruiz & Pav.) and compare this efficiency with other tree forms. We measured cross-sectional areas of roots, stems and fronds as well as leaf areas of I. deltoidea saplings. Likewise, cross-sections were made and vessel diameters and frequencies measured. This allowed for the calculation of theoretical specific-conductivity (KS, calc), theoretical leaf-specific conductivity (KL, calc), and vessel diameter and vessel number ratios between distal and proximal locations in the palms. I. deltoidea palms were found to have the largest, least frequent vessels that diverged most from the square packing limit (maximum number of vessels that fit into a given area) compared with other major tree forms, and they therefore invested the least space and carbon into water transport structures. Likewise, conduits tapered by approximately one third between ranks (root, bole, petiole), which represents an efficient ratio with regard to the trade-offs between safety and efficiency of the conducting system. Conduits also exhibited a high conservation of the sum of the\ud conduit radii cubed (Σr³) across ranks, thereby approximating Murray’s Law patterning. Therefore, our results indicate that the palm, I. deltoidea, has a very efficient hydraulic system in terms of maintaining a large conducting capacity with a minimal vascular investment. This efficiency may allow palms to compete well with dicotyledonous trees in tropical and subtropical climates but other developmental factors largely restrict palms from regions that experience prolonged freezing temperatures