© 2005 Heron Publishing—Victoria, Canada
Hydraulic and anatomical properties of light bands in Norway spruce compression wood
Stefan Mayr (1, 2), Stig Bardage (3) and Jonas Brändström (3)
1. Institut für Botanik, University Innsbruck, Sternwartestr, 15, A-6020 Innsbruck, Austria / 2. Corresponding author (stefan.mayr@uibk.ac.at) / 3. Wood Ultrastructure Research Centre, Department of Wood Science, Swedish University of Agricultural Sciences, P.O. Box 7008,
SE-750 07 Uppsala, Sweden / Received September 20, 2004; accepted May 15, 2005; published online October 3, 2005
Summary
Compression wood (CW), which is formed on the underside of conifer branches, exhibits a lower specific hydraulic conductivity
(ks) compared with normal wood. However, the first-formed tracheids of an annual ring on the underside of a conifer branch often
share several properties with normal tracheids, e.g., thin cell walls and angular cross sections. These first-formed tracheids
appear bright when observed by the naked eye and are therefore called light bands (LB). In this study, hydraulic and related
anatomical properties of LBs were characterized and compared with typical CW and opposite wood (OW). Measurements were made
on branches of Norway spruce (Picea abies (L.) Karst.). Specific hydraulic conductivity was measured with fine cannulas connected to microlitre syringes. Micro- and
ultrastructural analysis were performed on transverse and radial longitudinal sections by light and scanning electron microscopy.
Xylem areas containing both typical CW and LBs had a ks 51.5% that of OW (7.95 ± 0.97 m2 s–1 MPa–1 × 10–4), whereas ks of pure CW was only 26.7% that of OW. The ks of LBs (6.38 ± 0.97 m2 s–1 MPa–1 × 10–4; 80.3% of OW) was estimated from these ks values because the cannulas were too wide to measure the ks of LBs directly. Mean lumen area of first-formed tracheids on the underside of branches was 65.7% that of first-formed tracheids
in OW and about three times that of CW. Light-band tracheids exhibited a bordered pit frequency of 42.7 ± 1.3 pits mm–1, which was three times that in CW and 1.6 times that in OW. Bordered pit apertures in LB tracheids (9.15 ± 0.60 µm2) were 1.7 times wider than those in CW and similar in aperture to those in OW. The high ks of LBs was correlated with their wide tracheid lumina, high pit frequency and wide pit apertures. We therefore suggest that
LBs have a primarily hydraulic function within the mechanically optimized CW region. This might be important for supplying
water to living tissues on the underside of branches, as well as to other distal areas along water transport pathways following
the spiral grain of wood.
Keywords:
conifers, first-formed tracheids, hydraulic conductivity, pit, reaction wood, tracheid, ultrastructure, xylem anatomy.
