Summer pruning reduces whole-canopy carbon fixation and transpiration in apple trees

Abstract

SummaryCanopy size control is one of the major purposes of summer pruning. However, reducing canopy size might also result in less light interception, consequently decreasing canopy photosynthetic efficiency and carbohydrate production, which might lead to the imbalance of carbohydrate supply and fruit demand. To document the effectiveness of summer pruning on canopy control and the impact on canopy gas exchange, pruning treatments at four levels of intensity (unpruned, light, moderate, and severe) were carried out on mature ‘Empire’/M.9 slender spindle apple trees (Malus domestica Borkh.) on 30 July 1998 and 4 August 1999. Changes in canopy leaf area after summer pruning were estimated. Canopy net carbon exchange rate (NCER) and canopy transpiration before and after summer pruning were monitored. Canopy growth was suppressed by summer pruning and the post-pruning regrowth was insignificant. Canopy NCER was reduced in proportion to the amount of leaf area removed by summer pruning. The result suggests that commercial pruning intensity similar to the moderate to severe treatments in this study could cause a significant reduction in canopy NCER and carbohydrate production. In addition, canopy transpiration was reduced in proportion to pruning intensity. Lower water consumption and improved water status during the growing season after summer pruning might benefit fruit growth and relieve the potential detriment due to carbohydrate shortage.