Differences in shoot size and allometry between two evergreen broad-leavedshrubs, Aucuba japonica varieties in two contrasting snowfall habitats

Causes of plant size differences were investigated between two Varieties of Aucuba japonica, an evergreen broad-leaved shrub. Aucuba japonica var. bor ealis is widely distributed in heavy snowfall areas in Japan and is covered , shaded and physically pressured by snow for more than four months of the year. On the other hand, var, japonica is widely distributed in light snowf all areas. The sizes of new shoots and leaves were significantly different between the two varieties with different critical shoot sizes for flowering , The average new shoot dry mass of var. borealis was about one third of th at of var,japonica, Despite the differences in growing conditions and shoot size, no significant differences were observed in the allometry of their s hoot organs between the two varieties. Large new shoots had thicker and lon ger stems per biomass than small shoots because of their larger pith volume . The large shoots showed higher efficiency of stem growth per invested bio mass and had a higher rate of annual height increase than small shoots. Whe n the size of new shoot rapidly increased from year to year, i.e. the plant s are growing well, initiation of flowering was postponed and vegetative gr owth continued. Small new shoots were tolerant of low productivity conditio ns but traded vertical growth for an increase in matter allocation to leave s.