Leaf water relations and plant development of three Freeman maple cultivars subjected to drought

Little is known about drought stress resistance of Freeman maples (Acer x freemanii E. Murray), which are hybrids of red maples (A. rubrum L.) and silver maples (A. saccharinum L.). The objective of our study was to measure plant growth and leaf water relations of 'D.T.R. 102' (Autumn Fantasy),'Celzam' (Celebration), and 'Marmo' Freeman maples subjected to drought. Plants grown from rooted cuttings were subjected to four consecutive cycles of water deficit followed by irrigation to container capacity. Average stomatal conductance at container capacity for all cultivars was 255 mmol.s(-1).m(-2) in the first drought cycle and 43 mmol.s(-1).m(-2) during the fourth drought cycle. Predawn and midmorning leaf water potentials of droughted plants at the end of the fourth drought cycle were 1.16 and 0.82 MPa more negative than respective values for control plants. Osmotic potential of leaves at full turgor was -1.05 MPa for controls and -1.29 MPa for droughted plants, indicating an osmotic adjustment of 0.24 MPa. Root and shoot dry mass and leaf area were reduced similarly by drought for all cultivars, while Celebration exhibited the least stem elongation. 'Marmo' treated with drought had the lowest root-to-shoot ratio and the greatest ratio of leaf surface area to root dry mass. Autumn Fantasy had the lowest ratio of leaf area to stem xylem diameter. Specific leaf mass of drought-stressed Autumn Fantasy was 1.89 mg.cm(-2) greater than that of corresponding controls, whereas specific masses of Celebration and 'Marmo' leaves were not affected by drought. Leaf thickness was similar among cultivars, but leaves of droughted plants were 9.6 mu m thicker than leaves of controls. This initial characterization of responses to drought illustrates variation among Freeman maples and suggests that breeding and selection programs might produce superior genotypes for water-deficient sites in the landscape.