The importance of xylem constraints in the distribution of conifer species

Abstract

Vulnerability of stem xylem to cavitation was measured in 10 species of conifers using high pressure air to induce xylem embolism. Mean values of air pressure required to induce a 50% loss in hydraulic conductivity (ϕ50) varied enormously between species, ranging from a maximum of 14.2±0.6 MPa (corresponding to a xylem water potential of −14.2 MPa) in the semi‐arid species Actinostrobus acuminatus to a minimum of 2.3±0.2 MPa in the rainforest species Dacrycarpus dacrydioides. Mean ϕ50 was significantly correlated with the mean rainfall of the driest quarter within the distribution of each species. The value of ϕ50 was also compared with leaf drought tolerance data for these species in order to determine whether xylem dysfunction during drought dictated drought response at the leaf level. Previous data describing the maximum depletion of internal CO2 concentration (ci) in the leaves of these species during artificial drought was strongly correlated with ϕ50 suggesting a primary role of xylem in effecting leaf drought response. The possibility of a trade‐off between xylem conductivity and xylem vulnerability was tested in a sub‐sample of four species, but no evidence of an inverse relationship between ϕ50 and either stem‐area specific (Ka) or leaf‐area specific conductivity (K1) was found.

Leaf evolution in Southern Hemisphere conifers tracks the angiosperm ecological radiation

“…In the context of our findings, range effects on speciation and extinction rates could explain contrasting diversities among podocarp lineages (see the electronic supplementary material, figure S3). Podocarps, in general, are strongly limited by drought [6,54] and in the Present, the majority of IL lineages is associated with high rainfall upper montane and alpine conditions, or they grow in high-latitude temperate rainforests as longlived pioneers or riparian species [55]. Such suitable environments are restricted in the Southern Hemisphere, as mesic temperate climates have contracted since the opening of the Southern Ocean from the Oligocene [56].…”

Temperate forest trees and stands under severe drought: a review of ecophysiological responses, adaptation processes and long-term consequences

“…However, the global data-basis used may not take into account local variations in soil water availability. A comparative ecophysiological study indicated that inter-specific variation in drought-induced xylem cavitation is often associated with differences in soil moisture availability [21].…”

Within-crown variation in leaf conductance of Norway spruce: effects of irradiance, vapour pressure deficit, leaf water status and plant hydraulic constraints

“…duration of leaf growth [26]) besides stomatal conductance, net photosynthesis, and primary production. Even geographic distribution of woody species is considered to be associated with xylem hydraulic properties, and with xylem vulnerability to cavitation in particular [3]. At the same time, the relationships between leaf functioning within an individual crown and traits of the plant hydraulic architecture are still poorly understood [10,13].…”