Effect of root pruning and irrigation regimes on leaf water relations and xylem ABA and ionic concentrations in pear trees

Root pruning is an effective approach for controlling vegetative growth of pear trees (Pyrus communis L.), yet the underlying mechanisms for such effect remain largely elusive. A two-year field experiment was conducted to investigate the effect of root pruning and irrigation regimes on leaf water relation characteristics, stomatal conductance and xylem sap abscisic acid (ABA) and ionic concentrations. Results showed that leaf water potential, leaf turgor and stomatal conductance of root pruning (RP) treatment was significantly lower than those of non-root pruning (NP) treatment indicating that root pruning caused water deficit stress in pear trees. Further RP trees had significantly lower concentrations of total cations and anions and the sum of cations and anions than the NP trees implying root pruning decreased acquisition of nutrients from the soil. In the root pruned trees, the leaf water potential, leaf turgor and stomatal conductance were highest for full irrigation (FI), followed by the deficit irrigation (DI) and non-irrigation (NI) treatments. Osmotic potential was not affected by root pruning and irrigation regimes while the xylem ABA concentration was higher in the RP compared to NP as well as in the DI and NI compared to the FI, which could account for the lower stomatal conductance in those treatments. Conclusively, root pruning not only decreased water uptake but also nutrient uptake by the pear trees, and both could have caused reduced vegetative and generative growth of the trees. Supplemental irrigation partially improved the tree water status but not nutrient uptake in the root pruned trees.