Adaptation and coordinated evolution of plant hydraulic traits.
Abstract
Hydraulic properties control plant responses to climate and are likely
to be under strong selective pressure, but their macro-evolutionary
history remains poorly characterized. We compiled a global dataset of
hydraulic traits describing xylem efficiency, xylem safety, sapwood
allocation relative to leaf area and drought exposure and matched it
with a newly derived genus-level phylogeny to shed light on woody-plant
hydraulic eco-evolutionary patterns. All hydraulic traits present medium
to high levels of phylogenetic signal, being evolutionarily segregated
into two phylogenetically conserved adaptive modules: the
safety-exposure coordination, whereby lineages exposed to drought
adapted to withstand low water potentials by evolving a xylem with
higher embolism resistance; and the efficiency-allocation coordination,
whereby higher water availability and deeper, water-retentive soils led
to the evolution of hydraulically efficient species with higher leaf
area relative to sapwood area. Moreover, the lack of evolutionary
correlation between xylem safety and efficiency suggest that both
adaptive modules are independent.