Reactivation of vessel expansion in relation to budbreak in sycamore (Acerpseudoplatanus) trees

Abstract

The origin and progress of production of the first vessels of the new growth ring has been followed within trees of sycamore (Acerpseudoplatanus L.) and compared with stages of bud and shoot development within the crown and with variation in temperature at bud level. Reactivation of vessel expansion originated at the bud base when the bud had elongated 50% over dormant length; this stage of budbreak was delayed by 2 days for each metre up the crown. Vessel expansion did not appear to progress actively down branches until the leaf tips began to emerge. Changes in carbon partitioning may suggest that this lag period is associated with the importing phase of bud growth, progress beginning when the leaves become self-sufficient in assimilates. After the lag period, progress of vessel expansion down the branches was estimated to be about 3 cm day−1. Expanding vessels reached the trunk first in upper or middle crown, while the predetermined leaves of the lower and middle crown buds were expanding. Vessel expansion progressed more rapidly down the trunk than down branches; the predetermined leaves of the lower to middle crown had fully expanded by the time vessel expansion reached the base of the trunk.