Genotypic Variability in Photosynthesis, Water Use, and Light Absorption among Red and Freeman Maple Cultivars in Response to Drought Stress

Cultivars of red (Acer rubrum L.) and Freeman maple (Acer ×freemanii E. Murray) are popular ornamental plants which are commonly placed in a variety of landscapes. To date, little information quantifi es the capacity to tolerate and recover from drought among cultivars of red and Freeman maple. The objective of this study was to compare the effects of water stress on the physiology of fi ve different maple cultivars of marketable size including four red maple genotypes, ‘Summer Redʼ, ‘October Glory ̓(October Glory), ‘Autumn Flameʼ, and ‘Franksred ̓(Red Sunset), as well as one hybridized Freeman maple genotype, ‘Jeffersred ̓(Autumn Blaze). Two-year-old cloned genotypes of red and Freeman maple were subjected to two treatments: irrigated daily to container capacity or irrigation withheld for one drought and recovery cycle. Light absorption, gas exchange, and chlorophyll fl uorescence measurements were conducted under well-watered and drought stress conditions that approached 0.070 m3·m–3. Compared to well-watered conditions, drought stress conditions of 0.090 m3·m–3 had a signifi cant main effect that reduced the amount of light absorption in four of the fi ve genotypes. Additionally, absorption among genotypes was different under both well-watered and water stress conditions. Over the course of drought stress and a recovery phase, net photosynthesis and stomatal conductance were different among genotypes. Maximum photosystem II (PSII) effi ciency of dark-adapted leaves (Fv/Fm) was lowered by the water stress condition. The effi ciency of excitation capture by open PSII reaction centers (Fv'/Fm') was variable among genotypes. Photochemical quenching was higher in Autumn Blaze, October Glory, and ‘Summer Red ̓under drought conditions, which corresponded with a low degree of closure of PSII centers. Additionally, the fraction of excess excitation energy was also lower. Lastly, water defi cit caused an increase in PSII effi ciency in all genotypes except Autumn Blaze. This research demonstrated physiological variation among commercially available red and Freeman maple genotypes that may be selected for drought tolerance based on site moisture characteristics. drought are known to exist among genotypes of red maple (Abrams and Kubiske, 1990), and it may be possible to select for this variability to manage cultivars in nursery and landscape conditions. The intent to tailor other tree species to soil conditions (e.g., Populus) through selective breeding, interspecifi c hybridization, and cloning has been based on genetic diversity within species (Stettler et al., 1988). Red maple (Acer rubrum L.) occurs naturally along a hydrologic continuum from wet to dry (Golet et al., 1993; Walters and Yawney, 1990) and has shown genotypic variability among sites of different soil moisture availability (Abrams and Kubiske, 1990; Anella and Whitlow, 1998, 2000; Townsend and Roberts, 1973). In addition to the potential genetic diversity within the species, red maple can cross-pollinate with silver maple (Acer saccharinum L.), the hybrid of which is known as Freeman maple (Acer ×freemanii E. Murray). The high adaptability of red maple to different soils and climates together with its wide distribution across the eastern United States, and its ability to cross-pollinate with silver maple, could favor differentiation, providing a basis for cultivar development. Variations in photosynthesis and transpiration rates coupled with chlorophyll fl uorescence and light absorption parameters provide a quick and noninvasive way to characterize plant responses to water stress. Photoprotective processes are thought to occur in light-harvesting antenna of PS II (Horton et al., 1996). Fluorescence can decipher the amount of quenching within the PS II reaction center and, therefore, quantify damage to the PS II antenna. The technique quantifi es the response of the photosynthetic apparatus to stress and variability within the measured Container-grown plants are often subjected to periods of severe drought. Drought-induced depression of photosynthesis can be the consequence of patchy stomatal closure and/or collapse of the mesophyll due to loss of turgor as a result of low lateral CO2 diffusion capacity (Cornic and Massacci, 1996). As a result, leaf photosynthetic effi ciency and capacity can be compromised. During periods of drought when stomata close and CO2 assimilation is reduced, the photosynthetic reduction of O2 via photorespiration increases and serves as a sink for excess excitation energy in the photosynthetic apparatus (Cornic and Briantais, 1991). The photorespiratory increase in O2 reduction may not be suffi cient to dissipate excess excitation energy in PSII antennae and as a consequence, energy dissipation occurs as heat in order to minimize damage to PSII reaction centers (Baker, 1993). Such effects can have signifi cant consequences on the photosynthetic productivity of plants (Long et al., 1994). Analyzing changes in chlorophyll fl uorescence emission via a pulse modulated fl uorescence system (Schreiber et al., 1994) has been used to study both photosynthetic electron transport and thermal dissipation in leaves (Demmig-Adams and Adams, 1992; Genty et al., 1989) and can elucidate photo-damage to PSII reaction centers in response to stress. Variation in water stress tolerance of photosynthetic and respiratory systems can be a principal factor in differential growth under drought stress. Considerable differences in response to Received for publication 8 Aug. 2002. Accepted for publication 15 Jan. 2003. We thank Caula Beyl and Douglas Archbold for helpful suggestions on earlier drafts of this manuscript. J. AMER. SOC. HORT. SCI. 128(3):337–342. 2003.