The 2012 ASHS Annual Conference

Periodic flooding occurs in many areas where avocado (Persea americana Mill.) trees are commercially grown.  This depletes oxygen from the root zone which can result in severe tree stress or death.  Removing a portion of the canopy has been recommended for rehabilitating flood-damaged avocado trees.  Preliminary studies with plants in containers have shown that removing a portion of the canopy immediately after flooding reduces stress and increases tree survival, whereas removing a portion of the canopy shortly before flooding increases flooding stress.  Our hypothesis is that, leaf removal prior to flooding decreases carbohydrate production and transport to the roots due to a reduction in photosynthesizing area, resulting in reduced root respiration and increased stress of flooded plants. To test the effects of decreasing photosynthesis on stress and recovery of flooded avocado trees, we compared net CO₂ assimilation (A), stomatal conductance (g_s) and growth among avocado trees with: 1) two-thirds of their leaves removed one day before flooding; 2) no leaves removed but sprayed with Freeway®, a chemical adjuvant that inhibits photosynthesis, one day before and during flooding; and 3) non-treated control trees.  Leaf removal or Freeway® application  resulted in significantly lower A, g_s and plant dry weights for flooded trees compared to the control treatment (no leaves removed and not sprayed).  In another experiment, we compared A, g_s, and root carbohydrate concentrations between flooded trees with either two-thirds of their leaves removed one day before flooding, or no leaves removed. In addition to reducing A and g_s, leaf removal prior to flooding resulted in lower total carbohydrate concentrations in roots of flooded trees compared to those with no leaves removed.  These observations support the suggestion that increased flooding stress as a result of leaf removal immediately before flooding may be related to a reduction in net CO₂ assimilation and carbohydrate transport to the roots.