Allometry, root/shoot ratio and root architecture in understory saplings of deciduous dicotyledonous trees in central Japan

Plant allometry that is related to plant architecture and biomass allocation strongly influences a plant's ability to grow in shaded forest understory. Some allometric traits can change with plant size. The present study compared crown and trunk allometries, root/shoot biomass allometry, and root architecture among understory saplings (0.25-5 m height, except for two trees > 5 < 7 m) of seven deciduous dicotyledonous species in central Japan. Associations of the crown and trunk allometries with several plant morphological attributes were analyzed. Branch morphology (plagiotropy vs orthotropy) and life size were correlated with sapling crown and trunk allometries. Both large leaves and orthotropic branches were associated with a narrow small crown and slender trunk. The root/shoot ratio decreased rapidly with increasing plant height for saplings shorter than about 1.5 m. Less shade-tolerant species tended to have smaller root/shoot ratios for saplings taller than 1.5 m. With an increase in plant height, the branch/trunk biomass ratio decreased for saplings with plagiotropic branches but increased for saplings with orthotropic branches. Four subcanopy species (Acer distylum, Carpinus cordata, Fraxinus lanuginosa and Acanthopanax sciadophylloides) had superficial root systems; a common understory species (Sapium japonica) had a deep tap root system; and a canopy species (Magnolia obovata) and a subcanopy species (Acer tenuifolium) had heart root systems of intermediate depth. The root depth was not related to shade tolerance, Among species of the same height, the difference in fine root length can be 30-fold.