Pruning after flooding hastens recovery of flood-stressed avocado (Persea americana Mill.) trees

Two experiments (Expts. 1 and 2) were conducted at different times with avocado (Persea americana Mill. cv. Choquette) trees in containers to test the effects of leaf pruning immediately after removing trees from short-term flooding on tree recovery. Trees in each experiment were divided into two flooding treatments: (1) flooded, or (2) non-flooded. Trees in each flooding treatment were divided into two pruning treatments: (1) pruned; approximately two-thirds of the canopy removed by pruning immediately after trees were removed from flooding (unflooded), or (2) non-pruned. In each experiment, net CO2 assimilation (A), stomatal conductance of water vapor (gs), transpiration (E), water use efficiency (WUE, calculated as A/E) and xylem sap flow (in Expt. 2) were determined daily during the flooding period and periodically after trees were unflooded until harvest time in each flooding/pruning treatment. Tissue dry weights were determined for trees in all treatments at the end of the experiment (several weeks after trees were unflooded). Net CO2 assimilation, gs, E and WUE of flooded trees decreased after 2 and 5 days and trees were unflooded after 3 and 6 days in Expts. 1 and 2, respectively. After trees were unflooded, A, gs, E and WUE were lower in flooded trees than in non-flooded trees for a few weeks, but these reductions were greater for pruned than non-pruned trees. Eventually, A, gs, E and WUE of flooded trees in both the pruned and non-pruned treatments returned to values similar to those of non-flooded trees. After trees were unflooded, for trees in the pruned treatment, xylem sap flow was generally not significantly affected by flooding. However, for non-pruned trees, xylem sap flow was usually lower in the flooded than non-flooded trees. In each experiment, leaf dry weight and total plant dry weight were significantly lower for flooded than non-flooded trees only in the non-pruned treatments. In Expt. 2, root and stem dry weights were also lower in flooded than non-flooded trees only in the non-pruned treatment. The results indicate that pruning the canopy of avocado immediately after trees are removed from short-term flooding hastens plant recovery. It is postulated that the hastened recovery was due to pruning bringing the shoot to root ratio of flooded trees (with damaged roots) and the subsequent supply and demand for water and nutrients into better equilibrium in flooded trees, allowing pruned trees to recover more quickly from flooding compared to non-pruned trees.