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

Abstract

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 (K(S,calc)), theoretical leaf-specific conductivity (K(L,calc)), and vessel diameter and vessel number ratios between distal and proximal locations in the palms. Iriartea 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 ∼1/3 between ranks (root, bole and 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 conduit radii cubed (Σr(3)) 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.

Growth strategies of the arborescent palmIriartea deltoideain a western Amazonian forest

“…). Individuals of I. deltoidea , particularly saplings, have an efficient vascular organization that frees space in the stem for cells to function as storage deposits or mechanical support with minimum redundancy and carbon investment (Renninger et al ., ). These anatomical attributes may account for the growth and survival of I. deltoidea under a closed canopy.…”

“…Attainment of height via cell division of a constantly active apical meristem (Renninger & Phillips, ; Kunert, Barros & Higuchi, ), however, would imply a greater energetic investment relative to that of width, which is attained by cellular expansion and intercellular space formation (Tomlinson, ; Rich, 1987b). Moreover, bole elongation implies greater costs because of the increased risk of mechanical failure (Rich et al ., ) and decreased water conduction efficiency (Renninger et al ., ) as palms get taller. This difference should be borne in mind, particularly when individuals of I. deltoidea show signs of ‘growth dormancy’ (i.e.…”

“…and Socratea H.Karst.). These arborescent palms have a unique stem development and, as a result, have succeeded in competing well with ‘conventional’ woody trees (Renninger, McCulloh & Phillips, ) and continue to represent a significant structural component in many tropical environments (Balslev et al ., ).…”

Palm stem anatomy: phylogenetic or climatic signal?

“…In palms, embolism occurs in petioles rather than in the stem (Sperry, , ; Renninger & Phillips, ; Renninger, McCulloh & Phillips, ). Our results are in accordance with the fact that small vessels are encountered in dry conditions because they are more resistant to cavitation (Hacke et al ., ) and are more easily refilled (Zimmermann, ).…”

Embolism resistance in petioles and leaflets of palms

“…The hydraulic efficiency of the vascular architecture of palms surpasses the theoretical hydraulic conductivity of all tropical and temperate trees (Renninger et al, 2013).…”