© 2005 Heron Publishing—Victoria, Canada
Dependency of branch diameter growth in young Acer trees on light availability and shoot elongation
Kosei Sone (1, 2), Ko Noguchi (1) and Ichiro Terashima (1)
1. Department of Biology, Graduate School of Science, Osaka University, 1-1 Machikaneyama-cho, Toyonaka, Osaka 560-0043, Japan / 2. Corresponding author (sonek@bio.sci.osaka-u.ac.jp) / Received May 11, 2004; accepted July 22, 2004; published online November 1, 2004
Summary
Many biomechanical and theoretical studies have been based on the pipe-model theory, according to which a tree is regarded
as an assemblage of pipes, each having the same amount of leaf area or leaf mass. However, the physiological mechanisms underlying
the theory have not been extensively examined, particularly at the branch level. We analyzed how branches and trunks thickened
in nine young Acer mono Maxim. var. marmoratum (Nichols) Hara f. dissectum (Wesmael) Rehder. and A. rufinerve (Siebold & Zucc.) trees. In particular, we examined the roles of light, allocation of photosynthates and shoot heterogeneity.
The cross-sectional area (A) of a branch was proportional to cumulative leaf mass or leaf area of the branch, and cumulative cross-sectional area of
the daughter branches (∑A) above a branching point was equal to the A of the mother branch. These results indicate the validity of the pipe-model theory. However, the theory was invalid for current-year
growth of branch cross-sectional area (ΔA). The ΔA/∑ΔA for a branching point was greatest (nearly equal to 1) at the crown surface, decreased with crown depth, and tended to increase
again at the trunk base, and ΔA strongly depended on light interception and the yearly increment of leaves on the branch. We examined factors that influenced
ΔA with multiple regression analysis. The ratio of ΔA of a branch to branch leaf area depended on both relative irradiance and mean current-year shoot length of the branch, suggesting
that diameter growth of a branch is determined by the balance between supply of photosynthates, which depends on light interception
by the branch, and demand for photosynthates, which is created by the high cambial activity associated with vigorous shoot
elongation.
Keywords:
Acer mono, Acer rufinerve, branch autonomy, current-year shoot growth, growth in cross-sectional area, Leonardo da Vinci’s rule, leaf increment, long
and short shoots, pipe-model theory, sink–source balance, tree architecture, vigor index.
