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AOBPreview published online on June 21, 2006
Annals of Botany, doi:10.1093/aob/mcl127
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© The Author 2006. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Received February 20, 2006
Revised April 12, 2006
Accepted May 2, 2006

Article

Stem Phototropism of Trees: A Possible Significant Factor in Determining Stem Inclination on Forest Slopes

JUN MATSUZAKI 1 *, MASAYA MASUMORI 1, and TAKESHI TANGE 1

1 Department of Forest Science, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan

* To whom correspondence should be addressed.
JUN MATSUZAKI, E-mail: jm{at}fr.a.u-tokyo.ac.jp


  Abstract

• Background and Aims The main stems of trees on forest slopes incline down the slope to various extents that are characteristic of the species. The inclination has been explained as an active response to a horizontally asymmetrical light environment, but the contributing physiological mechanisms are unknown. The present study tested the hypothesis that stem phototropism, gravitropism, or a combination of the two determines the inclination of tree stems on forest slopes.

• Methods Cryptomeria japonica, Pinus densiflora, Quercus myrsinaefolia and Q. serrata were studied. Measurements were made of stem inclination of mature trees on forest slopes in uniform plantations of each species, and changes in stem inclination of potted seedlings in response to illumination treatments (unilateral or overhead) and inclination treatments (artificially inclined or erect). Indices of phototropic and gravitropic responsiveness were evaluated for each species, calculated from the change in stem inclination in response to artificial inclination with unilateral or overhead illumination.

• Key Results Stem inclination on forest slopes varied significantly among species: Q. serrata inclined most in the down-slope direction, C. japonica inclined the least, and P. densiflora and Q. myrsinaefolia were intermediate. The change in stem inclination of seedlings in each treatment varied significantly among species. One-year-old stems of Q. serrata and 2-year-old stems of Q. myrsinaefolia bent toward the light source. Interspecific variation in the change in stem inclination in response to the unilateral illumination or that in the index of phototropic responsiveness was strongly correlated with the variation in stem inclination on forest slopes.

• Conclusions The orientation of woody stems that have finished elongation can be actively controlled by phototropism. Interspecific variation in phototropic responsiveness of trees is a possible significant determinant of interspecific variation in stem inclination on forest slopes.

Keywords: Phototropism, gravitropism, tree, woody stem, reorientation, stem inclination, forest slope, Cryptomeria japonica, Pinus densiflora, Quercus myrsinaefolia, Quercus serrata.
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