Water relations,mineral nutrition,growth, and13C discrimination in two apple cultivars under daily episodes of high root-medium temperature

Although high soil temperatures can occur in apple orchards throughout the world, there is little information on their effect. This investigation was conducted to determine the influence of various durations of root exposure to 34 °C on the growth and physiology of the apple plant. Roots of Royal Gala and McIntosh cultivars were exposed to 34 °C for 0, 8, 16, and 24 hours/day for seven weeks. Royal Gala grown at the 24 hours/day treatment exhibited significant decreases in leaf, shoot, and root growth; chlorophyll concentration of the older leaves; transpiration; discrimination against¹³C in leaves; and an increase in leaf temperature. In McIntosh, root growth and chlorophyll concentration of leaves were not affected. For both cultivars compared to the control treatment, the continuous high temperature treatment resulted in lower levels of P, Mg, and Mn in leaves. Royal Gala at this treatment showed significantly higher values of foliar N and K and lower values of Ca, Fe, and Zn. For McIntosh the levels of Cu and B decreased significantly in this treatment as compared to the control treatment. We conclude that 34 °C in the root-zone does not stress these cultivars unless it persists throughout the day/night cycle.