The Influence of Root Pruning on Water Relations, Net Photosynthesis, and Growth of Young ‘Golden Delicious’ Apple Trees

Abstract

Abstract Young ‘Golden Delicious’/M7 trees were root pruned on 2 sides at 2.5, 5.0, and 10.0 cm distances from the stem which removed 10%, 28%, or 59% of their roots. Net photosynthesis (Pn) was reduced 35% and 47% and transpiration (Tr) 29% and 45% one day after root pruning of 28% and 59%, respectively, and recovery began 10 days later. Root pruning reduced leaf water potential significantly for 6 hr; recovery was apparent after one day. Root pruning severity of 10% had no effect on Pn, Tr, or water potential. Shoot growth rates decreased with increasing root pruning severity. The greatest reduction of shoot extension occurred during the 2nd and 3rd week following root pruning, with increasing growth rates observed in the 4th week. Suppression of shoot diameter increase lasted for 2 weeks. Leaves that developed following 28% or 59% root pruning were smaller than leaves of unpruned trees and had increased specific leaf weights (SLW), while previously expanded leaves were not affected. As root pruning severity increased, fresh weight of leaves and current shoots were reduced 45%; older parts of the tree were not influenced. Four weeks after root pruning there was no difference in total fresh weight of roots. The distribution of small roots from root pruned trees was increased in close proximity to the stem and decreased at distances greater than 5 cm from the stem.