MATURATION RATE OF TRACHEID LENGTHENING IN SLOW-GROWN YOUNG SUGI (CRYPTOMERIA-JAPONICA) TREES

Maturation rate, the rate of increase in tracheid length in juvenile w ood, was examined in sugi (Cryptomeria japonica D. Don) saplings grown for five years under different shading conditions: 10%, 20% 40% and 1 00 % of relative illumination intensity. The lowest photointensity dra matically suppressed radial growth and slowed tracheid lengthening. Ra dial variation of tracheid length within the stem was associated with distance from the pith, rather than the number of annual rings from th e pith. Furthermore, maturation rate was closely related to the rate o f the radial growth, which changed proportionally with growth rate bel ow a 2-3 mm ring width. A lower maturation rate of tracheid length is associated with a delay in the transition from juvenile to mature wood .