Climate‐related trends in sapwood biophysical properties in two conifers: avoidance of hydraulic dysfunction through coordinated adjustments in xylem efficiency, safety and capacitance

Abstract

In the Pacific north-west, the Cascade Mountain Range blocks much of the precipitation and maritime influence of the Pacific Ocean, resulting in distinct climates east and west of the mountains. The current study aimed to investigate relationships between water storage and transport properties in populations of Douglas-fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa) adapted to both climates. Sapwood thickness, capacitance, vulnerability to embolism, and axial and radial conductivity were measured on samples collected from trunks of mature trees. The sapwood of ponderosa pine was three to four times thicker than Douglas-fir. Radial conductivity was higher in west-side populations of both species, but axial conductivity was higher in the east-side populations and in Douglas-fir. Eastern populations of both species had sapwood that was more vulnerable to embolism than west-side populations. Sapwood capacitance was similar between species, but was about twice as great in east-side populations (580 kg m -3 MPa -1 ) as in west-side populations (274 kg m -3 MPa -1 ). Capacitance was positively correlated with both mean embolism pressure and axial conductivity across species and populations, suggesting that coordinated adjustments in xylem efficiency, safety and water storage capacity may serve to avoid embolism along a gradient of increasing aridity.

Effect of crown class and habitat type on climate–growth relationships of ponderosa pine and Douglas-fir

“…Consequently, greater sensitivity to water availability of Douglas-fir, but not ponderosa pine, in xeric sites most likely reflects known differences in hydraulic architecture and life history strategies of these two species and is consistent with the idea of an adaptive tradeoff between xylem efficiency and hydraulic safety (e.g. Pinol and Sala, 2000;Barnard et al, 2011).…”

“…Ponderosa pine, on the other hand, has developed structural adaptations that allow it to avoid dangerously low water potentials. For example, Barnard et al (2011) found that ponderosa pine had almost twice the sapwood area supplying water to a given leaf area as Douglas-fir, leading to a 50% decrease in the pressure gradient required to conduct a given amount of water. Moreover, ponderosa pine, but not Douglas-fir, is able to significantly modify the ratio of biomass in leaf area relative to sapwood area (A L :A S ) across environmental gradients in response to increasing aridity (Delucia et al, 2000).…”

Influence of region of provenance and climate factors on wood anatomical traits of Pinus nigra Arn. subsp. salzmannii

“…A recent study on Douglas-fir (Pseudotsuga menziesii) and ponderosa pine (Pinus ponderosa) showed that the vulnerability of sapwood to embolism is greater in populations of both species adapted to more arid environments (Barnard et al 2011). However, capacitance was also greater in these populations, suggesting that under conditions of high transpiration, xylem capacitance can play an important role in avoiding levels of tension that would cause excessive embolism.…”

Diverse patterns of stored water use among saplings in seasonally dry tropical forests

“…1e-h). Similarly, Barnard et al (2011) found plasticity in C among conifers in forests that varied in rainfall, yet both species they studied had higher C at lowrainfall sites. Our result that C shifted to be higher or lower in the dry forest is consistent with either greater desiccation avoidance (higher C) or greater desiccation tolerance (lower C) in drier environments (discussed below).…”