The Influence of Summer Pruning on Photosynthesis, Transpiration, Leaf Abscission, and Dry Weight Accumulation of Young Apple Trees1

Young, container-grown ‘Topred Delicious’/Malling (M) 9 apple trees ( Malus domestica Borkh.) trained to a single shoot out-of-doors were summer pruned to remove 0, 25, 50 or 75% of 78 cm shoots. Net photosynthesis (Pn) and transpiration (Tr) were as much as 36% greater on older, basal leaves of trees with 50 and 75% shoot removal than on unpruned trees. These differences were present for 39 days after pruning. Basal leaves did not abscise in the 11-week period after pruning on trees with 75% shoot removal and remained longer on trees with 50% shoot removal than on unpruned trees. Leaf area removed by pruning was partially compensated by leaves on subsequent regrowth. All summer pruning treatments suppressed the area of individual leaves on regrowth by about 50% of the size of similar aged leaves on unpruned trees. Summer pruning suppressed the dry weight of basal stem sections and roots roughly in proportion to shoot removal amounts, while dry weight of shoot regrowth was less influenced. Eleven weeks after pruning, dry weight of roots on summer pruned trees with 25, 50 and 75% shoot removal was 20, 39 and 50% less, respectively, than root dry weight of unpruned trees.