Climate determines vascular traits in the ecologically diverse genus Eucalyptus

Abstract

Current theory presumes that natural selection on vascular traits is controlled by a trade-off between efficiency and safety of hydraulic architecture. Hence, traits linked to efficiency, such as vessel diameter, should show biogeographic patterns; but critical tests of these predictions are rare, largely owing to confounding effects of environment, tree size and phylogeny. Using wood sampled from a phylogenetically constrained set of 28 Eucalyptus species, collected from a wide gradient of aridity across Australia, we show that hydraulic architecture reflects adaptive radiation of this genus in response to variation in climate. With increasing aridity, vessel diameters narrow, their frequency increases with a distribution that becomes gradually positively skewed and sapwood density increases while the theoretical hydraulic conductivity declines. Differences in these hydraulic traits appear largely genotypic in origin rather than environmentally plastic. Data reported here reflect long-term adaptation of hydraulic architecture to water availability. Rapidly changing climates, on the other hand, present significant challenges to the ability of eucalypts to adapt their vasculature.

Wood density and anatomy of three Eucalyptus species: implications for hydraulic conductivity

“…In the present study, when analyzing stem density, anatomy and theoretical Ks, a general trade-off did arise between wood density and Ks, which is in agreement with results reported by Pfautsch et al (2016) for Eucalyptus growing in Australia. However, as in the case of Eucalyptus branches (Barotto et al, 2016), this should not necessarily imply a trade-off between hydraulic efficiency and safety.…”

“…However, studies using different approaches have suggested that Eucalyptus wood structure (anatomy and density of branches) is associated with functional traits involved in stress tolerance or avoidance (e.g. Monteoliva et al, 2015;Barotto et al, 2016), and that it determines the distribution patterns of different species in an aridity stress gradient (Pfautsch et al, 2016). Analysis relating branch anatomy and function in three Eucalyptus species showed that vessel diameter distribution is a key trait correlated not only with measured maximum Ks, but also with the species vulnerability to cavitation (Barotto et al, 2016).…”

Hydraulic Anatomy and Function of Trees—Basics and Critical Developments

“…The influence of pathlength and age occur in tandem and both effects follow power functions, albeit they may not follow universal scaling exponents [63]. In addition, conduit diameters usually also widen with increasing water availability (i.e., environmental effect) as recently demonstrated for herbaceous [64] and woody species [56].…”

“…Besides immediate responses to water availability, trees can adjust their hydraulic system in response to long-term availability of water [20,56]. Selection processes have resulted in specialization of anatomical structures involved in water transport within species and along environmental gradients.…”

“…Ecological wood anatomy can be used to describe the impact of current biotic and abiotic agents on the ecology of woody plants and how they shape xylem and wood development. The literature is rich in reports of relationships between ecology and wood anatomy ranging from species-specific [145][146][147] and genera-and clade-specific [56,148] to more general descriptions [27,28,[149][150][151][152][153]. A clear separation between ecological, functional, and paleontological wood anatomy may not always be possible as demonstrated in the latest book on the topic [154].…”