Leaf Net CO2 Assimilation and Electrolyte Leakage and Alcohol Dehydrogenase Activity in Roots of Mamey Sapote (Pouteria sapota) Trees as Affected by Root Zone Oxygen Content

Net CO2 assimilation (A) of leaves and root electrolyte leakage (EL) and alcohol dehydrogenase enzyme (activity) (ADH) in roots of mamey sapote (Pouteria sapota) trees were assessed in response to different oxygen concentrations in the root zone. In separate experiments, ‘Pantin’ and ‘Magana’ scions on mamey sapote seedling rootstocks were grown hydroponically with an oxygen concentration of 7–8 mg O2·L–1H2O in the root zone maintained by bubbling air into the hydroponic medium (aerated treatment) or with an oxygen concentration of 0–1 mg O2·L–1H2O maintained by purging O2from a hydroponic medium with N2 gas (O2-purged treatment). Net CO2 assimilation of ‘Magana’ leaves from the O2-purged treatment declined over time and was at or near zero 8 days after treatment (DAT). Net CO2 assimilation of ‘Pantin’ leaves in the aerated treatment was higher than that of leaves in the O2-purged treatment at 2–6 DAT only. Electrolyte leakage from roots was significantly greater in the O2-purged treatment than in the aerated treatment. Two days after treatments, root ADH activity in both cultivars tended to be consistently higher in the O2-purged than aerated treatment. The ADH activity of mamey sapote roots appears to be up-regulated as a result of root-zone hypoxia. However, increased ADH activity alone is apparently not sufficient to limit low soil oxygen stress of mamey sapote trees as evidenced by decreased A of leaves and increased EL from roots of trees exposed to low oxygen content in the root zone.