PATTERN OF DEFOLIATION AND ITS EFFECT ON PHOTOSYNTHETIC CAPACITY IN OENOTHERA-BIENNIS

1 Five different patterns of tissue removal were used to mimic natural herbivore damage in Oenothera biennis. The effects of defoliation by: (1) half edge (tissue removed from one side of the leaf, parallel to and exclusive of the midrib); (2) double edge (tissue removed from leaf perimeter); (3) perforation (roughly circular portions removed, leaf edges and midrib intact); (4) tip (apex of leaf removed); and (5) entire leaf defoliation on photosynthesis were examined. 2 Plants were subjected to removal of tissue from either a single leaf or throughout the plant. Photosynthesis, stomatal conductance, nitrogen content and water potential of the remaining portion of the youngest fully emerged leaf at the time of defoliation was examined over a one to two week period. 3 Tip defoliation at both the single leaf and whole plant level enhanced photosynthesis relative to undefoliated controls. Half edge and entire leaf defoliation at the whole plant level also enhanced photosynthesis relative to controls, but not to the same extent as tip defoliation. Double edge and perforation defoliation at the single leaf level depressed photosynthesis relative to controls and tip defoliation. 4 Differences among defoliation treatments can best be explained by intraleaf variation in photosynthetic capacity and nitrogen content and by the extent of wounding to residual tissue. Results from this study illustrate that the way in which tissue is removed can have a dramatic effect upon photosynthetic capacity of the remaining tissue.