Matsuzaki Jun, Masumori Masaya, Tange Takeshi
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.
Ann Bot. 2006 Sep;98(3):573-81. doi: 10.1093/aob/mcl127. Epub 2006 Jun 21.
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.
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.
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.
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.
森林斜坡上树木的主干会不同程度地向下坡倾斜，这是各树种的特征。这种倾斜被解释为对水平不对称光照环境的主动响应，但其生理机制尚不清楚。本研究检验了以下假设：茎的向光性、向重力性或两者的结合决定了森林斜坡上树木主干的倾斜度。
研究了日本柳杉、赤松、小叶栎和枹栎。对每个树种的均匀人工林中成熟树木的主干倾斜度进行了测量，并对盆栽幼苗在光照处理（单侧或顶部）和倾斜处理（人工倾斜或直立）下主干倾斜度的变化进行了测量。根据单侧或顶部光照下人工倾斜引起的主干倾斜度变化，评估了每个树种的向光性和向重力性响应指数。
森林斜坡上的主干倾斜度在不同树种间差异显著：枹栎在下坡方向倾斜度最大，日本柳杉倾斜度最小，赤松和小叶栎居中。各处理下幼苗主干倾斜度的变化在不同树种间差异显著。一年生的枹栎茎和两年生的小叶栎茎向光源弯曲。响应单侧光照的主干倾斜度变化或向光性响应指数的种间差异与森林斜坡上主干倾斜度的差异密切相关。
已完成伸长的木本茎的方向可通过向光性主动控制。树木向光性响应的种间差异可能是森林斜坡上主干倾斜度种间差异的一个重要决定因素。
