The hydraulic architecture of balsam fir (Abies balsamea).

Leaf-specific conductivities (LSCs - hydraulic conductivity per dry weight of supplied leaves). Huber values (transverse sapwood area per dry weight of supplied leaves). specific conductivity (hydraulic conductivity per transverse sapwood area) and tracheid diameters were measured throughout the trunk and crown of 20-year-old trees of Abies balsamea (L. ) Mill. Measured specific conductivity was proportional to the radius to the fourth power of tracheids. LSCs, which indicate the relative water availability to different plant parts, are much higher in the trunk than in first order branches, and lowest in second order branches. The structural basis for this "hydraulic hierarchy" lies both in Huber values and in tracheid diameters. For similar diameter stem segments, there was no statistically significant difference for trunks versus branches in specific conductivity. However, in old parts of the tree, trunks are wider than supported branches and producer wider tracheids resulting in greater specific conductivities than in branches. In vigorous trees with strong apical control. Huber values were 12.0 times greater in the trunk than in similar diameter branch segments. In slow-growing trees with weak apical control, Huber values were 2.2 times greater in the trunk versus similar branch segments. [ABSTRACT FROM AUTHOR]