Variation among red and Freeman maples in response to drought and flooding

Freeman maples (Acer xfreemanii E. Murray) are marketed as stress-resistant alternatives to red maples (Acer rubrum L.). Our objective was to compare two cultivars of Freeman maple ['Jeffersred' (Autumn Blaze(x)) and 'Indian Summer'] and five red maples ['Franksred' (Red Sunset(x)), 'Autumn Flame', 'PNI 0268' (October Glory(x)), 'Fairview Flame', and unnamed selection 5990 4] for effects of flooding and water deficit on plant growth, biomass parti tioning, stomatal conductance, and leaf osmotic potential. Plants grown fro m rooted cuttings in containers were subjected to three consecutive cycles during which root-zone water content decreased to 0.12, 0.08, and 0.02 m(3) .m(-3), respectively. Additional plants were flooded for 75 days, while pla nts in a control treatment were irrigated frequently. Stomatal conductance immediately before imposing drought and after three drought cycles did not differ among genotypes and averaged 220 and 26 mmol.s(-1).m(-2) respectivel y. Differences in stomatal conductance after recovery from the first drough t cycle and at the end of the second drought cycle did not vary with specie s. Drought reduced estimated leaf osmotic potential similarly for all genot ypes; means for drought-stressed and control plants were -1.92 and -1.16 MP a, respectively. Freeman maples had a higher mean root : shoot weight ratio and a lower leaf surface area : root dry-weight ratio than did red maples. Across genotypes, stomatal conductance of flooded plants initially increas ed by approximate to 20% and then fell to and remained below 50 mmol.s(-1). m(-2). Stomatal conductance of 'Indian Summer' decreased to approximate to 20 mmol.s(-1).m(-2) after 8 days of flooding, indicating that this cultivar may be particularly sensitive to root-zone saturation.