Coordination and trade‐offs among hydraulic safety, efficiency and drought avoidance traits in Amazonian rainforest canopy tree species

Abstract

Predicting responses of tropical forests to climate change-type drought is challenging because of high species diversity. Detailed characterization of tropical tree hydraulic physiology is necessary to evaluate community drought vulnerability and improve model parameterization. Here, we measured xylem hydraulic conductivity (hydraulic efficiency), xylem vulnerability curves (hydraulic safety), sapwood pressure-volume curves (drought avoidance) and wood density on emergent branches of 14 common species of Eastern Amazonian canopy trees in Paracou, French Guiana across species with the densest and lightest wood in the plot. Our objectives were to evaluate relationships among hydraulic traits to identify strategies and test the ability of easy-to-measure traits as proxies for hard-to-measure hydraulic traits. Xylem efficiency was related to capacitance, sapwood water content and turgor loss point, and other drought avoidance traits, but not to xylem safety (P ). Wood density was correlated (r = -0.57 to -0.97) with sapwood pressure-volume traits, forming an axis of hydraulic strategy variation. In contrast to drier sites where hydraulic safety plays a greater role, tropical trees in this humid tropical site varied along an axis with low wood density, high xylem efficiency and high capacitance at one end of the spectrum, and high wood density and low turgor loss point at the other.

Plant Hydraulic Trait Covariation: A Global Meta-Analysis to Reduce Degrees of Freedom in Trait-Based Hydrologic Models

“…Stepwise multiple regression model for drought tolerance explained along the basis of wood density, rooting depth, and isohydricity (Overall model statistics: RMSE: 0.34, R 2 = 0.63, Adjusted R 2 = 0.52, Prob < F = 0.0154). Similarly to our strong support of our first hypothesis, numerous previous syntheses and database efforts have revealed coordination among vegetation hydraulic traits e.g., [17,32,37,40]. Notably, Chave, et al [3] demonstrated relationships between wood conductivity and conduit diameter, along with relationships between wood density and both growth rate and mortality.…”

“…A more complex mathematical framework revealed coordination between stomatal closure and Ψ 50 to reduce the risk of embolism while maintaining transpiration [67,68]. A number of smaller-scale, biome or growth form specific studies (e.g., [12,40,[69][70][71]) have revealed a number of more specific relationships. For instance, Blackman, et al [71] found that among woody Australian plants, at the leaf level Ψ 50 was significantly related to the ratio of vessel wall thickness to lumen breadth.…”

“…For instance, Blackman, et al [71] found that among woody Australian plants, at the leaf level Ψ 50 was significantly related to the ratio of vessel wall thickness to lumen breadth. The work of Santiago, et al [40] revealed that for several Amazonian canopy species, xylem water-transport efficiency was connected to hydraulic capacitance, leaf turgor loss point and drought tolerance and that wood density was related to xylem cavitation curves.…”

“…Trait correlations have been used to accurately predict physiological processes [7,37,39,40]. In their 2012 study, Choat et al [37] demonstrated relationships between the xylem water potential at which 50% of conductivity is lost (Ψ 50 ), the minimum measured xylem water potential (Ψ min ), mean annual precipitation (MAP) and drought vulnerability.…”

“…Lower safety margins indicate greater risk of hydraulic failure in the event of drought. Santiago, et al [40] found that for several canopy trees in the Amazon, xylem efficiency is significantly related to hydraulic capacitance, sapwood water content, and turgor loss point, and thus propose the use of wood density as an easy-to-measure proxy of hydraulic physiology. Correlations may also be likely between rooting depth and drought tolerance within a biome, where deeply-rooted plants can access water at depth and shallowly-rooted plants are therefore less tolerant to drought conditions.…”