Shoot development in Betula papyrifera. V. Effect of male inflorescence formation and flowering on long shoot development

One-year-old vegetative and reproductive long shoots of Betula papyrifera Marsh, were collected from 40-year-old trees when leaves were fully expanded. Leaf areas were significantly reduced on shoots bearing developing male inflorescences; late leaves were affected most. Late leaves were thinner than early leaves on vegetative shoots and thinnest on reproductive shoots. The effect of developing male inflorescences was most pronounced on the specific leaf area of early leaves, suggesting that inflorescences are strong sinks for assimilates being exported by early leaves. Two-year-old vegetative and reproductive branches were collected just after bud burst to determine mean bud dry weight. These values were highest for buds on vegetative long shoots, lower for buds on reproductive long shoots, and lowest for buds on reproductive long shoots bearing female short-shoot buds. Formation of male inflorescences reduced the growth potential of buds. Female short-shoot buds on reproductive long shoots and pseudoterminal buds positioned below male inflorescences exhibited reduced growth potentials. Mean total early leaf areas measured 3 weeks after flushing showed similar trends. Thus, development and flowering of male inflorescences lowered the growth potential and vigour of axillary buds and reduced canopy expansion.