Hydraulic properties of fronds from palms of varying height and habitat

Abstract

Because palms grow in highly varying climates and reach considerable heights, they present a unique opportunity to evaluate how environment and plant size impact hydraulic function. We studied hydraulic properties of petioles from palms of varying height from three species: Iriartea deltoidea, a tropical rainforest species; Mauritia flexuosa, a tropical rainforest, swamp species; and Washingtonia robusta, a subtropical species. We measured leaf areas, petiole cross-sectional areas, specific conductivity (K(S)), petiole anatomical properties, vulnerability to embolism and leaf water potentials and calculated petiole Huber values and leaf-specific conductivities (K(L)). Leaf and petiole cross-sectional areas varied widely with height. However, hydraulic properties including Huber values, K(S) and K(L), remained constant. The two palmate species, M. flexuosa and W. robusta, had larger Huber values than I. deltoidea, a pinnately-compound species which exhibited the highest K(S). Metaxylem vessel diameters and vascular bundle densities varied with height in opposing patterns to maintain petiole conductivities. I. deltoidea and W. robusta petioles had similar P(50) values (the point at which 50% of hydraulic conductivity is lost) averaged over all crown heights, but W. robusta exhibited more negative P(50) values in taller palms. Comparison of P (50) values with transpiring midday leaf water potentials, as well as a double-dye staining experiment in a 1-m-tall palm, suggested that a fairly significant amount of embolisms were occurring and refilled on a diurnal basis. Therefore, across palms differing widely in height and growing environments, we found convergence in water transport per unit leaf area (K(L)) with individuals exhibiting differing strategies for achieving this.

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

“…With vessels in their trunks around 240 m in diameter, I. deltoidea also has some of the largest mean trunk vessel diameters when compared with several reported mature tropical species and growth forms (Ewers et al 1990, McCulloh et al 2011. Vessel sizes in the petioles were also found to increase (from 80 to 120 m in diameter) in larger, taller I. deltoidea palms (Renninger and Phillips 2011) and are among the largest of the measured vessel diameters in the branches of early-and late-successional trees (McCulloh et al 2011).…”

Branching morphology of decapitated arborescent monocotyledons with secondary growth

“…On the other hand, recent studies (Renninger and Phillips, 2011) have shown that parts of the vasculature of the Washingtonia robusta palm are not functional (i.e., water conducting) at all times. As this may well be the case for other arborescent monocotyledons such as the studied Dracaena species, the complex network and interconnection of the vascular bundles within the ramification may compensate for this deficiency and allow for the adequate distribution of water and nutrients within the branch.…”

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, ).…”

“…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, ). Accordingly, Renninger & Phillips () specified (p. 933) that, ‘a monocot species with little ability for secondary growth would be especially resistant to embolisms in order to preserve its conductive tissue’, and concluded (p. 934) that, ‘opposing patterns were seen between metaxylem vessel diameter and vascular bundle densities in the tropical rainforest Iriartea deltoidea and the subtropical Washingtonia robusta . In I. deltoidea , taller palms had larger but less frequent vessels, while in W. robusta , taller palms had smaller but more frequent vessels in petioles’.…”