Shoot and root vulnerability to xylem cavitation in four populations of Douglas-fir seedlings

Abstract

The objectives of this study were to assess the range of genotypic variation in the vulnerability of the shoot and root xylem of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings to water-stress-induced cavitation, and to assess the trade-off between vulnerability to cavitation and conductivity per unit of stem cross-sectional area (k(s)), both within a species and within an individual tree. Douglas-fir occupies a broad range of environments and exhibits considerable genetic variation for growth, morphology, and drought hardiness. We chose two populations from each of two varieties (the coastal var. menziesii and the interior var. glauca) to represent environmental extremes of the species. Vulnerability curves were constructed for shoots and roots by plotting the percentage loss in conductivity versus water potential. Vulnerability in shoot and root xylem varied genetically with source climate. Stem xylem differed in vulnerability to cavitation between populations; the most mesic population, coastal wet (CW), was the most susceptible of the four populations. In the roots, the most vulnerable population was again CW; the interior wet (IW) population was moderately susceptible compared with the two dry populations, coastal dry (CD) and interior dry (ID). Root xylem was more susceptible to cavitation than stem xylem and had significantly greater k(s). The trade-off between vulnerability to cavitation and k(s), however, was not evident across populations. The most vulnerable population (CW) had a shoot k(s) of 0.534 +/- 0.067 &mgr;mol m(-2) s(-1) MPa(-1), compared with 0.734 +/- 0.067 &mgr;mol m(-2) s(-1) MPa(-1) for the less vulnerable CD stems. In the roots, IW was more vulnerable than ID, but had the same k(s).

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

“…Seedlings originating from the most mesic population among four populations of Douglas-fir (Pseudotsuga menziesii (Mirb.)) were also the most susceptible to water-stress-induced cavitation [77].…”

Extending sapwood — Leaf area relationships from stems to roots in Coast Douglas-fir

“…Water volume flow rate is directly proportional to sapwood conductivity and changes in this property may also partially explain the decrease in sapwood area from groundline to crown base (Whitehead et al, 1984). The conductivity of root sapwood is typically greater than that of stems in Douglas-fir seedlings (Dunham et al, 2007;Kavanagh et al, 1999) and in small, nonstructural roots (Dunham et al, 2007). There is little information on sapwood conductivity within, or close to, the zone of rapid taper in Douglas-fir roots; however, an inverse relationship between root sapwood CSA and conductivity would be expected under the pipe-model theory.…”

Xylem hydraulic efficiency versus vulnerability in seedlings of four contrasting Mediterranean tree species (Cedrus atlantica, Cupressus sempervirens, Pinus halepensis and Pinus nigra)

“…The presence of latewood in the April stems could have caused the differences in conductivity observed between the two dates of measurement. Lumen diameter is much smaller in latewood making it less efficient for conducting water [9,31]. In addition, in coniferous species membrane pores of latewood have a more rigid structure than earlywood [15].…”