Tradeoffs between hydraulic and mechanical stress responses of mature Norway spruce trunk wood
Sabine Rosner (1, 2), Andrea Klein (3), Ulrich Müller (4) and Bo Karlsson (5)
1. Institute of Botany, Department of Integrative Biology, University of Natural Resources and Applied Life Sciences, BOKU Vienna,
Gregor Mendel Strasse 33, A-1180 Vienna, Austria / 2. Corresponding author () / 3. Holzforschung Austria, Franz Grill Strasse 7, A-1030 Vienna, Austria / 4. Competence Centre for Wood Composites and Wood Chemistry, St. Peter Strasse 25, A-4021 Linz, Austria / 5. Forestry Research Institute of Sweden (Skogforsk), Ekebo, S-26890 Svalöv, Sweden / Received December 13, 2007; accepted February 28, 2008; published online June 2, 2008
Summary
We tested the effects of growth characteristics and basic density on hydraulic and mechanical properties of mature Norway
spruce (Picea abies (L.) Karst.) wood from six 24-year-old clones, grown on two sites in southern Sweden differing in water availability. Hydraulic
parameters assessed were specific hydraulic conductivity at full saturation (ks100) and vulnerability to cavitation (Ψ50), mechanical parameters included bending strength (σb), modulus of elasticity (MOE), compression strength (σa) and Young’s modulus (E). Basic density, diameter at breast height, tree height, and hydraulic and mechanical parameters varied considerably among
clones. Clonal means of hydraulic and mechanical properties were strongly related to basic density and to growth parameters
across sites, especially to diameter at breast height. Compared with stem wood of slower growing clones, stem wood of rapidly
growing clones had significantly lower basic density, lower σb, MOE, σa and E, was more vulnerable to cavitation, but had higher ks100. Basic density was negatively correlated to Ψ50 and ks100. We therefore found a tradeoff between Ψ50 and ks100. Clones with high basic density had significantly lower hydraulic vulnerability, but also lower hydraulic conductivity at
full saturation and thus less rapid growth than clones with low basic density. This tradeoff involved a negative relationship
between Ψ50 and σb as well as MOE, and between ks100 and σb, MOE and σa. Basic density and Ψ50 showed no site-specific differences, but tree height, diameter at breast height, ks100 and mechanical strength and stiffness were significantly lower at the drier site. Basic density had no influence on the site-dependent
differences in hydraulic and mechanical properties, but was strongly negatively related to diameter at breast height. Selecting
for growth may thus lead not only to a reduction in mechanical strength and stiffness but also to a reduction in hydraulic
safety.
Keywords:
biomechanics, hydraulic conductivity, Picea abies, vulnerability to cavitation.
