Influence of time of root pruning on growth, mineral nutrition, net photosynthesis and transpiration of young apple trees

One-year-old greenhouse grown cultivar 'Melrose'/M7A apple trees were root pruned on two sides 5 cm from the stem at 30 days, 55 days, or both times from bud break. A single root pruning, regardless of timing, reduced shoot elongation for 4 weeks and reduced shoot diameter and total dry weight at harvest. Nevertheless double pruning was necessary to reduce shoot length for the entire 11 weeks of the experiment. Net photosynthesis (Pn) and transpiration (Tr) rates were reduced by 3 days after the early root pruning, but recovered by 10 days after treatment. Seven days after the late root pruning, trees pruned for the first time had lower Pn and Tr, but trees which were root pruned at both times had similar Pn and Tr rates to unpruned trees. Similarly, trees root pruned once had severe wilting immediately following the late treatment, while trees pruned for the second time did not have visual water stress symptoms and their Pn and Tr rates were unaffected. A single root pruning at either time had little effect on leaf mineral nutrient levels. Trees root pruned at both times had higher foliar levels of N, P, K, Ca, Mg, Mn, Fe and B than unpruned trees.