Leaf removal before flooding influences recovery of avocado (Persea americana Mill.) trees from flooding stress

Three experiments (Expts. 1, 2 and 3) were conducted to test the effects of removing a portion of the leaf canopy of avocado trees (Persea americana Mill.) prior to flooding on plant stress, survival and recovery from short-term flooding. 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 in Expt. 1: (1) approximately two-thirds of the canopy removed by pruning, or (2) non-pruned (control). In Expt. 2, trees in each flooding treatment were divided into three “canopy” treatments: (1) removal of two-thirds of the total number of leaves from the bottom of the canopy upward (2/3 LR), (2) foliar application of a chemical photosynthetic inhibitor and no leaf removal (CP), or (3) no leaf removal or photosynthetic inhibitor applied (control). Trees in each flooding treatment in Expt. 3 were divided into two treatments: (1) two-thirds of the total number of leaves removed from the bottom of the canopy upward, or (2) no leaves removed (control). In each experiment, net CO2 assimilation (A) and stomatal conductance of water vapor (gs) were determined daily during the flooding period and periodically after the flooding period until trees were harvested. Plant survival and tissue dry weights were determined several weeks after plants were removed from flooding (unflooded) in Expts. 1 and 2. Root carbohydrate concentrations were determined immediately after the flooding period in Expt. 3. Pruning, leaf removal or foliar application of a chemical photosynthetic inhibitor immediately prior to flooding resulted in significantly lower A of flooded compared to non-flooded trees. Concentration of the C7 sugar, d-mannoheptulose, was higher in non-flooded than in flooded plants. In flooded plants, concentration of the C7 sugar alcohol, perseitol, was higher in plants with no leaves removed than those in the 2/3 LR treatment. Reducing photosynthesis of avocado trees prior to flooding, either by pruning, leaf removal, or the application of a chemical photosynthetic inhibitor, makes trees more susceptible to flooding stress. Reducing A prior to flooding limits carbohydrate transport to the roots, thereby limiting the amount of substrate for respiration of flooded roots, making the plants more susceptible to flooding stress.

► Pruning, leaf removal or foliar application of a chemical photosynthetic inhibitor prior to flooding lowered net CO2 assimilation and tissue dry weights of flooded compared to non-flooded avocado trees.
► Concentration of the C7 sugar, d-mannoheptulose, was higher in non-flooded than in flooded avocado trees.
► In flooded avocado trees, concentration of the C7 sugar alcohol, perseitol, was higher in plants with no leaves removed than those with 2/3 of their leaves removed before flooding.
► Reducing photosynthesis of avocado trees prior to flooding, either by pruning, leaf removal, or the application of a chemical photosynthetic inhibitor, makes trees more susceptible to flooding stress.