EFFECT OF SHADE STRESS ON GROWTH, MORPHOLOGY, AND CARBON DYNAMICS OF LOBLOLLY-PINE BRANCHES

Shade treatments were applied to the terminal portions of branches in loblolly pine trees to test whether portions of branches were autonomo us with respect to carbohydrates. The shade treatments reduced light b y 50% and 72% compared with full sun conditions resulting in significa nt reductions in net photosynthesis. Branch growth (branch diameter an d length, branch and needle biomass) decreased significantly within th e shaded portion of the branch. Branch and needle morphology were also affected by shading. Lateral branches subtending terminal shoots were labelled with C-14 times during the growing season. No movement of C- 14 into the terminal portions of the branch was evident during the fir st growth flush. However, during the second flush of growth small but statistically significant amounts of C-14 were imported into the termi nal portion of the shaded branches from subtending laterals. It was co ncluded that loblolly pine shoots were usually autonomous with respect to carbohydrate supply, but that carbohydrate movement into the termi nal shoot from subtending foliage could occur under conditions of very high stress.