Effects of defoliation in the developing leaf zone on young Populus Xeuramericana plants. II. Distribution of UC-photosynthate after defoliation

Patterns of UC-photosynthate distribution in growth chamber-grown Populus xeuramericana cv. Negrito de Granada were determined 24 h, 3 weeks, and 5 weeks after defoliation in the developing leaf zone. Translocation patterns were determined by exposing leaves below, within, or above the defoliated zone to UCO2 and determining UC distribution within the plant after 48 h. Translocation patterns were altered within 24 h after defoliation. When leaves below or remaining tissue of leaves within the zone of defoliation were exposed to UCO2, a greater percentage of UC-photosynthate was transported to the expanding shoot and lateral branches and less to the roots in defoliated plants compared to controls. Little difference between defoliated and control plants and UC distribution occurred when new leaves produced subsequent to defoliation were exposed to UCO2. By 5 weeks after defoliation there was little difference in patterns of UC distribution between defoliated and control plants. These results substantiate biomass partitioning data which showed that a single defoliation of young poplar plants did not affect diameter or height growth, whereas leaf growth was stimulated and root growth reduced.