Abstract

Two experiments were conducted to determine whether genotypes of red maple (Acer rubrum L.) and Freeman maple (A. x freemanii E. Murray) differ in responses to high root-zone temperature. During the first experiment, dry mass of ‘Franksred’, ‘October Glory’, and ‘Schlesinger’ red maple, ‘Indian Summer’ Freeman maple, and selections from Arkansas, Maine, and Wisconsin were similar at 24, 28, and 32C (75, 82, and 90F), but dry mass at 36C (97F) was only 22% of that at 28C (82F). ‘Autumn Flame’, ‘Franksred’, ‘October Glory’, and ‘Schlesinger’ red maple and ‘Indian Summer’ and ‘Jeffersred’ Freeman maple differed in responses to 34C (93F) during the second experiment. Stem length and plant dry mass were higher at 28C (82F) than at 34C (93F) for all cultivars except ‘Autumn Flame’ and ‘Jeffersred’, and the extent to which 34C (93F) decreased the length of the longest third-order root ranged from 50% for ‘Autumn Flame’ to 90% for ‘Indian Summer’. The higher root-zone temperature decreased transpiration by as little as 25% for ‘Jeffersred’ to as much as 89% for ‘Franksred’, and 34C (93F) reduced leaf chlorophyll content of only ‘Indian Summer’ and ‘Jeffersred’. These results indicate that ‘Franksred’ and ‘Indian Summer’ are relatively sensitive while ‘Autumn Flame’, ‘Jeffersred’, and ‘Schlesinger’ are relatively resistant to high root-zone temperature.