LEAF WATER RELATIONS AND PLANT DEVELOPMENT OF 3 FREEMAN MAPLE CULTIVARS SUBJECTED TO DROUGHT

Little is known about drought stress resistance of Freeman maples (Ace r x freemanii E. Murray), which are hybrids of red maples (A. rubrum L .) and silver maples (A. saccharinum L.). The objective of our study w as to measure plant growth and leaf water relations of 'D.T.R. 102' (A utumn Fantasy),'Celzam' (Celebration), and 'Marmo' Freeman maples subj ected to drought. Plants grown from rooted cuttings were subjected to four consecutive cycles of water deficit followed by irrigation to con tainer capacity. Average stomatal conductance at container capacity fo r all cultivars was 255 mmol.s(-1).m(-2) in the first drought cycle an d 43 mmol.s(-1).m(-2) during the fourth drought cycle. Predawn and mid morning leaf water potentials of droughted plants at the end of the fo urth drought cycle were 1.16 and 0.82 MPa more negative than respectiv e values for control plants. Osmotic potential of leaves at full turgo r was -1.05 MPa for controls and -1.29 MPa for droughted plants, indic ating an osmotic adjustment of 0.24 MPa. Root and shoot dry mass and l eaf area were reduced similarly by drought for all cultivars, while Ce lebration exhibited the least stem elongation. 'Marmo' treated with dr ought had the lowest root-to-shoot ratio and the greatest ratio of lea f surface area to root dry mass. Autumn Fantasy had the lowest ratio o f leaf area to stem xylem diameter. Specific leaf mass of drought-stre ssed Autumn Fantasy was 1.89 mg.cm(-2) greater than that of correspond ing controls, whereas specific masses of Celebration and 'Marmo' leave s were not affected by drought. Leaf thickness was similar among culti vars, but leaves of droughted plants were 9.6 mu m thicker than leaves of controls. This initial characterization of responses to drought il lustrates variation among Freeman maples and suggests that breeding an d selection programs might produce superior genotypes for water-defici ent sites in the landscape.