Abstract
The distribution of vessels in broadleaf timber, is directly related to water transport efficiency and safety. Here, I tested the hypothesis that vessel characteristics depend on cambial age (CA) and flow path-length (PL) within the tree rather than solely on CA by measuring vessel hydraulic diameter (VD), vessel frequency (VF), theoretical specific hydraulic conductivity (ks), and theoretical implosion resistance (VIR) in every growth ring of birch (Betula platyphylla Roth.) tree root, trunk, and branch samples. The effects of CA and PL were analyzed using a linear mixed model. Differences in the vessel characteristics are significant between CA, between PL, and between the interaction of CA and PL. VD decreased linearly and VF increased nonlinearly with PL. The PL explained 59.3 and 67.3 % of the longitudinal variation in VD and VF, respectively. ks decreased nonlinearly and VIR increased linearly with PL. The PL explained 25.6 and 43.3 % of the longitudinal variation in ks and VIR, respectively. Radial changes were evident above ground, VD increased, and VF decreased with CA for the first 10–20 years and remained constant thereafter. ks exhibited a logarithmic increase and VIR exhibited logarithmic decrease with CA. Variable radial patterns were observed below ground. The CA explained 30.9–98.8 %, 23.7–96.9 %, 42.9–96.8 %, and 50.9–98.5 % of the radial variation in VD, VF, ks, and VIR, respectively. The results suggest that vessel characteristic changes are determined by CA and PL. While growing, trees adjust their vessels to maximize water transport efficiency and ensure mechanical safety.
Highlights
Conduit size and frequency within a tree are spatially heterogeneous (Gartner 1995; Schulte 2012) and have important functional consequences in long-distance water transport and embolism vulnerability (Tyree and Sperry 1989; Hacke and Sperry 2001; Sperry et al 2006; Jacobsen et al 2007)
The vessel implosion resistance (VIR) was determined for those vessels within the sampled vessels per tree ring that formed pairs from which one or both vessels fell within ±5 μm of the calculated hydraulic diameter in this research
I studied the hydraulically weighted average vessel diameters (VD) and vessel frequency (VF) values in the different tree compartments of B. platyphylla to assess the effect of cambial age (CA) and PL on vessel characteristics
Summary
Conduit size and frequency within a tree are spatially heterogeneous (Gartner 1995; Schulte 2012) and have important functional consequences in long-distance water transport and embolism vulnerability (Tyree and Sperry 1989; Hacke and Sperry 2001; Sperry et al 2006; Jacobsen et al 2007). Vessels are special conduits for water transport in hardwood xylem that vary along the flow path-length (PL) within the tree. The comprehensive radial variation of cells has been extensively studied, and the CA can fully explain the radial variation of xylem structure (HelinskaRaczkowska 1994; Rao et al 2002; Shi et al 2008) Most of these measures were performed at a single stem height, i.e., breast height. The flow PL increased with decreasing CA at a certain position, which caused increased auxin concentration at the position (Lovisolo et al 2002). All these studies showed that vessel properties vary systematically with CA and PL. Theoretical specific conductivity (ks) and vessel implosion resistance (VIR) in different parts were calculated to better understand the effect of vessel characteristics on water transport efficiency and safety
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