Red Maple Cultivars Research Articles

Physiological response and resistance of three cultivars of Acer rubrum L. to continuous drought stress

Red maple (Acer rubrum L.) is a fast-growing tree of medium height that is indigenous to the eastern United States and southern Canada. The tree furnishes reasonably strong, close-grained wood that is used extensively for inexpensive furniture, in the manufacture of baskets and crates, for mine props, railroad ties, and fuel wood. Many cultivars have been selected, of which almost all are selections for leaf color characteristics. In this study, three cultivars of red maple (Acer rubrum ‘October Glory’, Acer × freemanii ‘Jeffersred’, and Acer rubrum ‘Brandywine’) were selected to compare their physiological response and resistance to continuous drought stress. Before the experiment, two-year-old seedlings were grown at respective day/night temperatures of 25/18°C and 70%/80% RH without water limitation. The drought treatment was initiated by ceasing water supply until the seedlings showed visible signs of wilting. Drought is a common environmental stress that severely limits plant growth and development. Plants have evolved many mechanisms to adapt to environmental stresses via changes at the physiological, morphological, and molecular levels. In the present study, nine physiological indices, namely concentration of proline, soluble protein, and soluble sugar, activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), malondialdehyde (MDA) concentration, relative chlorophyll concentration, and relative conductivity of cell membranes, were measured to investigate the tolerance mechanism of red maple during the whole drought stress. Water deficit caused a progressive spread of tissue damage, as indicated by the physiological indices monitored, which was always observed first in the young leaves. October Glory experienced severe damage, whereas injury to Brandywine developed more slowly and was less severe, and Jeffersred showed an intermediate level of injury. A significant increase in the levels of osmoregulatory substances was observed in seedlings of all cultivars. Soluble protein and soluble sugar contents showed the same trends, namely a decrease after a rapid transient increase, whereas proline contents showed no significant changes during the drought-stress treatment. Osmoregulatory responses to drought stress of Jeffersred and Brandywine were initiated from the 6th day of treatment, whereas in October Glory responses were observed from the 13th day of treatment. October Glory showed the best osmoregulatory capability of the three cultivars. The activities of SOD and CAT initially increased, and thereafter rapidly decreased, in response to drought stress, whereas POD activity showed the opposite trend. Brandywine showed the most active antioxidant system in which activities of SOD, CAT, and POD were higher than those of the other cultivars throughout the experiment. Antioxidant activity of Jeffersred was higher than that of October Glory, in which only POD activity was maintained at a high level. Continuous drought damaged the cell membrane systems of seedlings, with gradual increases in relative membrane conductivity and MDA concentrations of cells closely associated with the duration of drought stress. Relative membrane conductivity and MDA concentration did not differ significantly between Jeffersred and Brandywine, whereas in October Glory both indices increased significantly at advanced stages of drought stress (P<0.05). Among the three cultivars, damage to the cell membrane system was most severe in October Glory over the duration of the experiment. Chlorophyll concentration decreased gradually with increasing duration of drought stress, but significant variation in response among the cultivars was observed; chlorophyll concentration was most stable in ‘Jeffersred’, whereas October Glory showed the most dramatic loss of chlorophyll and Brandywine showed an intermediate response. Chlorophyll loss with increasing duration of drought stress was consistent with the damage observed to the cell membrane system. Combining the membership function with the physiological observations for assessment of the drought resistance of the three red maple cultivars, we concluded that the relative drought stress resistance of the cultivars was Brandywine>Jeffersred>October Glory.

Cyclanilide Differentially Affects Branching in Red Maple Cultivars and Hybrids

Abstract Development of the canopy is an important aspect of ornamental shade tree production. Branching can be induced by pruning the apical meristem, but this process is time consuming and costly to growers. Cyclanilide is an auxin transport inhibitor that has been successfully used to eliminate apical dominance and increase branching in a number of tree species. In this study, we tested the effects of cyclanilide application in two years on branching, canopy form, and trunk diameter. Cyclanilide did not cause phytotoxicity symptoms in any cultivar at any rate. Two cultivars, Celebration® (Acer × freemanii A.E. Murray ‘Celzam’) and Sienna Glen® (Acer × freemanii ‘Sienna’) Freeman maples responded to cyclanilide treatments with increased primary and secondary shoots, whereas Red Sunset® red maple (Acer rubrum L. ‘Franksred’) and Autumn Blaze® Freeman maple (Acer × freemanii A.E. Murray ‘Jeffersred’) did not respond to any treatments. Responsive cultivars had approximately double the number of growing points and larger total branch length after second year applications, but this did not result in an increase in trunk caliper. Despite the increased number of shoots produced, overall canopy ratings did not differ among treatments. Cyclanilide had a limited affect on branching in red and Freeman maple whips. Furthermore, if growers choose to utilize this product, they should be aware that cultivar response is likely to vary, and initial testing should be done before making large-scale applications.

Evaluation of a Single Application of Neonicotinoid and Multi-Application Contact Insecticides for Flatheaded Borer Management in Field Grown Red Maple Cultivars

Abstract Two trials evaluated insecticides for flatheaded borer control and effect on red maple (Acer rubrum L.) cultivar growth over 4 years. Chrysobothris femorata (Olivier) was the only species reared from borer damaged maples during the study. Soil-applied systemic insecticides (acephate, imidacloprid, clothianidin, dinotefuran, and thiamethoxam) and trunk-applied contact insecticides (chlorpyrifos and bifenthrin) were tested. In the 2005 trial, a one-time drench of Allectus (imidacloprid + bifenthrin) or Discus (imidacloprid + cyfluthrin) provided 2 to 4 years of protection with ‘Autumn Flame’ and ‘Franksred’ from C. femorata. Soil-applied experimental imidacloprid tablets prevented borer damage in the third and fourth post-treatment years, but were not as effective as imidacloprid drenches in the first two years. Soil applied acephate tablets, chlorpyrifos (Dursban 4E) trunk sprays, or untreated control plants had borer damage each year, which totaled up to 41.7% damage by year 4 in ‘Autumn Flame’. Trunk diameter growth and tree canopy size was greater with Discus drench or imidacloprid tablet treatments than other treatments. In the 2006 trial, drenches of Allectus, Discus, or Safari 20SG (dinotefuran) applied in May and Discus or Arena 50WDG (clothianidin) drenches applied in March provided complete protection from C. femorata the first year in ‘Fairview Flame’, ‘Franksred’, and ‘October Glory’. Discus (March) drench provided four years of complete protection among the three cultivars, while other neonicotinoid drenches had 3.7–6.3% (Arena March), 3.7–12.5% (Arena May), 0–6.3% (Discus May), 0–10.3% (Safari), and 12.5–20.5% (Flagship) total damage. Ineffective treatments included an experimental imidacloprid gel (7.4–18.8% damage), acephate tablets (18.5–75.0%), Onyx Pro Insecticide (5.1–18.8%), Dursban 2E (11.1–31.3%), one imidacloprid tablet (15.4–43.8%), or untreated plants (32.1–41.0%). This study demonstrates a single application of some neonicotinoid treatments can provide multi-year C. femorata prevention, increased maple trunk growth, and provide borer protection superior to trunk sprays.

Evaluation of Systemic Insecticides for Potato Leafhopper Control in Field-Grown Red Maple

Abstract Systemic insecticides and application methods were evaluated in two trials that began in 2005 and 2006 for control of potato leafhopper (Empoasca fabae [Harris]) on four red maple (Acer rubrum L.) cultivars and rated annually through 2007. Treatments evaluated in this study included surface drenches of imidacloprid plus cyfluthrin (Discus) or imidacloprid plus bifenthrin (Allectus SC), clothianidin (Arena 50WDG), dinotefuran (Safari 20SG), or thiamethoxam (Flagship 25WG); soil inserted treatments of imidacloprid formulated as an experimental tablet or as an experimental gel; or a plant root dip of Discus + Terra-Sorb hydrogel. In the 2005 trial, a one-time drench of Discus or two imidacloprid tablets significantly reduced leafhopper damage to red maple for a 3-year period. In the 2006 trial, a one-time drench of Allectus, Discus, Arena, Flagship, and Safari significantly reduced leafhopper damage for 2 years. In most cases, the Discus drench and root dip treatments were initially more effective than the imidacloprid tablets or the gel treatment. However, in general, the efficacy of imidacloprid tablet or gel treatments increased in subsequent years. Two imidacloprid tablets were more effective than one. Likewise, higher imidacloprid drench rates were more effective than lower rates. Most insecticide treatments significantly increased red maple trunk diameter, although this effect varied with cultivar and time. Allectus and Discus drench treatments significantly increased the branch and internode length of ‘Franksred’ maple in the 2005 trial. Results of this study indicate long-term potato leafhopper control with systemic insecticides and enhanced growth in red maple.

Leaf Abscisic Acid Accumulation in Response To Substrate Water Content: Linking Leaf Gas Exchange Regulation with Leaf Abscisic Acid Concentration

Quantitative differences in leaf abscisic acid (ABAL) among four cultivars of red maple (Acer rubrum L.) and one freeman maple (Acer ×freemanii E. Murray) cultivar were investigated. This study tested the hypothesis that ABAL concentration can be used to compare the effects of water stress on the gas exchange response of five different maple genotypes, including four red maple cultivars [`Summer Red', `October Glory', `Autumn Flame', and `Franksred' ('Red Sunset')] and one hybridized freeman maple cultivar ['Jeffersred' ('Autumn Blaze')]. Two-year-old cloned genotypes of red maple and freeman maple were subjected to two treatments: irrigated daily to container capacity or irrigation withheld for one drought and recovery cycle. Leaf abscisic acid concentration, gas exchange, and wholetree sap flow measurements were conducted under well-watered and drought stress conditions. Over the course of the drought stress and recovery phase, net photosynthesis (Anet), stomatal conductance (gs), and transpiration (E) declined as ABAL and instantaneous water use efficiency (A/gs) increased. Until severe water stress conditions were prominent, water use was higher in `Summer Red' as compared to `October Glory'. This study found that ABAL tracked gs and that stomatal responsiveness to substrate moisture deficit is likely mediated by ABA accumulation in leaf tissue. This research demonstrates a leaf level physiological response to substrate volumetric water content that appears to depend on ABAL concentration. In addition, the evidence in this study indicates that ABAL may be used as a potential surrogate for the gs response to substrate water stress and could become part of a cultivar drought tolerance selection strategy for red maple and freeman maple.

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 quantifies 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 five different maple cultivars of marketable size including four red maple genotypes, `Summer Red', `October Glory' (October Glory), `Autumn Flame', 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 fluorescence 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 significant main effect that reduced the amount of light absorption in four of the five 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) efficiency of dark-adapted leaves (Fv/Fm) was lowered by the water stress condition. The efficiency 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 deficit caused an increase in PSII efficiency 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.

Chilling and Heat Unit Levels Affect Foliar Budbreak of Selected Red and Freeman Maple Cultivars

The effects of six levels of chilling (temp &lt;7°C) on foliar budbreak of red maple (Acer rubrum) cultivars October Glory® and 'Franksred' (Red Sunset®) and Freeman maple (A. ´ freemanii) cultivar 'Autumn Fantasy' were evaluated in a study conducted from December 14, 1999, to April 7, 2000. October Glory had a greater minimum chilling hour requirement to initiate budbreak than 'Autumn Fantasy' and 'Franksred' (Red Sunset). However, once optimal chilling had been satisfied (near 600 hours), October Glory required fewer heat units than the other cultivars to reach 20% and 25% budbreak. For example, estimates for heat units required to reach 25% budbreak for October Glory were less than half that required for 'Autumn Fantasy' and 'Franksred' following 1,200 hours of chilling. Chilling was a determining factor in foliar budbreak for all cultivars, and with all three cultivars, increasing chilling produced greater budbreak percentages and the rate at which budbreak was initiated. All cultivars required fewer heat units for budbreak as chilling increased. All cultivars required over 1,700 heat units to initiate budbreak after 200 hours of chilling, but only 780 to 970 heat units after 600 hours and between 200 and 400 following 1,000 hours of chilling. Information from this and future studies may be used to facilitate the development of models for regional planting recommendations based on the amount chilling received in a given location. Calculated r2 values indicated the models provided a good fit to the data for all cultivars.

Nitrate uptake kinetics for rooted cuttings of Acer rubrum L.

Red maple (Acer rubrumL.) occurs in a broad spectrum of both woodland and managed landscapes in much of eastern North America. Earlier work has indicated considerable plasticity within the species in water use efficiency, as well as dry mass accumulation and tertiary root extension when grown in a solution in which all N was supplied as NO3 -. Nitrogen uptake is largely a function of N supply, soil water availability and root surface area. Therefore, compensatory mechanisms could have evolved among cultivars to compensate for site differences. The objective of this study was to define NO3 - uptake parameters for red maple in a hydroponic system through the use of two cultivars known to differ in root production and water use efficiency. Green wood stem cuttings of two red maple cultivars, `Autumn Flame' and `Franksred', were rooted and then transferred to solution culture. Using established techniques, three separate experiments were conducted to define ranges of Imax, Km and Cmin values and to determine root mass, length, mean radius and surface area. Estimates of Imax exhibited considerable variation between experiments with means ranging from 1.57E-5 to 5.91E-5 μmol cm-2 s-1. However, cultivar differences in Imax were statistically significant in only one of the three experiments. Means for Km ranged from 2.04E-1 to 5.23E-1 μmol cm-3, while Cmin values were consistent at 0.001 μmol cm-3 (the limit of analytical detection) across all experiments. While data on variation among red maple cultivars are not conclusive, some evidence exists for genotype differences that may relate to the broad range of site conditions under which red maple is successfully grown.

Growth Periodicity for Container-Grown Red and Freeman Maple Cultivars in AHS Heat-Zone 8

Abstract Growth patterns of seven red maple (Acer rubrum L.) and three Freeman maple (Acer x freemanii E. Murray) cultivars grown in containers in Alabama were evaluated using monthly destructive harvests. The effectiveness of a growth modeling technique not previously described is demonstrated using the data presented for both the Freeman maple (red maple xsilver maple interspecific cross) and red maple categories. Freeman maple cultivars ‘Armstrong’, ‘Celzam’ (Celebration™), and ‘Jeffersred’ (Autumn Blaze™); and red maple cultivars ‘Autumn Flame’, ‘Fairview Flame’, ‘Landsburg’ (Firedance™), ‘Franksred’ (Red Sunset™), ‘Olson’ (Northfire™), ‘Northwood’, and ‘October Glory®’ were studied. Uniform liners of each cultivar were planted in 9.1-liter (#3) containers in March 1996. More than 75% of seasonal height and diameter growth was complete for most cultivars before mid-August, while only 25% of root growth had occurred by the end of August. The remaining 75% of root growth occurred from August through November. The greatest overall growth (based on height, diameter, and root growth increase) was for ‘Autumn Flame’ and ‘October Glory®’, both red maple cultivars; and Freeman maple cultivars ‘Celzam’ and ‘Jeffersred’. The least overall growth (based on height, diameter, and root growth increase), was for red maple cultivars ‘Northwood’ and ‘Landsburg’.

Root membrane thermostability of red maple cultivars

Nine red maple cultivars originating in different USDA hardiness zones were grown in containers in 1995 and 1996 prior to laboratory procedures to determine root cell membrane thermostability. Electrolyte leakage from excised root tissue exposed for 30 min to temperatures ranging from 20 to 63°C, was used to assess cellular injury of unsuberized, current season, fine roots. Electrolyte leakage was an effective means for measuring cell membrane thermostability in root tissue. The critical killing temperatures of root tissue of cultivars evaluated ranged from 52.0±0.8°C to 53.3±0.5°C, indicating minimal differences in root membrane thermostability. Critical temperatures for cultivars selected from the northern part of the native range did not differ from cultivars originating elsewhere.

Flood-Tolerance Ranking of Red and Freeman Maple Cultivars

Red maple (Acer rubruni) is often recommended for use in wet soils, yet its extensive native range suggests there may be genetic variation for traits associated with flood tolerance. Likewise, genetic variation for flood tolerance may be captured within red maple cultivars making some more appropriate than others for use in wet or low oxygen soils. Seven red maple cultivars (2-year-old trees)—'Autumn Flame'®, 'Bowhall', 'Karpick', 'Northwood', 'October Glory'®, Red Sunset®, and 'Schlesinger— and 4 Freeman maple (A. xfreemanii) cultivars—' Armstrong', 'Autumn Blaze', 'Morgan', and Scarlet Sentinel™, were ranked for flood tolerance by flooding the trees and characterizing photosynthesis, lenticel intumescence, and survival. Indicator trees representing the wet extreme of red maple's native range were also included for comparison. Net photosynthesis declined for all cultivars; however, 'Schlesinger', Red Sunset and 'Bowhall' had the highest net photosynthetic rates (ranging from 1.94 to 1.71 umol/m2s) after 45 days of flooding. In contrast, 'Karpick', 'Autumn Flame', and 'Northwood' had net photosynthetic rates near 0. The extent of lenticel intumescence also varied among the cultivars with 'Schlesinger' and 'Bowhall' producing the longest lenticels. All of the 'Northwood' trees died, as did two-thirds of the Autumn Flame' trees. The cultivars were separated into 3 overall flood-tolerance rankings: high ('Schlesinger', Red Sunset, and 'Bowhall'), intermediate (Armstrong1, 'Morgan', 'October Glory', Scarlet Sentinel, and Autumn Blaze'), and low ('Karpick', Autumn Flame', and 'Northwood').

Evaluation of Various Traits of 40 Selections and Cultivars of Red Maple and Freeman Maple Growing in Maryland

Abstract Thirty-seven red maple (Acer rubrum L.) and three Freeman maple (A. x freemanii E. Murray) selections and commercial cultivars were evaluated for six years in a replicated field plot at Glenn Dale, MD. Significant differences among clones occurred for growth rate; for time, intensity, and duration of autumn color; for time of growth initiation in the spring; and for injury sustained from potato leafhopper (PLH) [Empoasca fabae (Harris)] feeding. The red maple cultivars showing the best red color over three years time were ‘Autumn Flame,’ ‘Brandywine,’ ‘Cumberland,’ ‘Red Rocket,’ ‘Somerset,’ ‘Sun Valley,’ and ‘Van.’ The cultivar ‘Bowhall’ was the least reddish. Of the three Freeman maples evaluated, ‘ Jeffersred’ and ‘Indian Summer’ manifested the best red color and also low PLH injury; whereas ‘Armstrong’ consistently showed the least reddish color of all 40 clones tested, and intermediate PLH injury. Those cultivars and selections from northern seed sources reached their peak color the earliest, but often dropped their leaves more quickly after showing their best color, compared to clones originating in more southerly locations. The clones showing the least PLH injury over several years included the Freeman maples ‘Jeffersred’ and ‘Indian Summer,’ and red maple clones and cultivars selected by the U.S. National Arboretum either from full-sib progenies (e.g., ‘Brandywine,’ ‘Somerset,’ ‘Sun Valley’) or from an Ohio provenance-progeny test (e.g., ‘Cumberland,’ ‘Red Rocket’). Those clones initiating growth (or “flushing”) earliest in the spring generally showed the least PLH injury; correlations between lateness of flushing and degree of PLH injury were highly significant.

Differences in Growth of Container-Grown Red Maple Cultivars in Different Hardiness Zones

Abstract Growth of eight container-grown red maple cultivars was evaluated at four locations under dissimilar environmental conditions/hardiness zones in Georgia and Alabama for two years. Rooted cuttings and tissue cultured plantlets were planted in #3 (9.1 liter) containers in one location in the same substrate in April 1995. Trees were transported the second week of June to Blairsville, GA; Muscle Shoals, AL; Auburn, AL; and Tifton, GA in USDA hardiness zones 6b, 7a, 8a, and 8a, respectively. Dormant trees were transplanted to #10 (38 liter) containers the second week of December 1995. At the conclusion of the study, December 1996, growth differed by location and cultivar. Height and stem diameter increase, and root and stem dry weights were greatest at the two Alabama locations for most cultivars and were least at the two Georgia locations. Root:shoot ratios were greatest at the two Georgia locations, an indication of increased carbon partitioning of photoassimilates to roots over stems under dryer growing conditions. Irrigation rates and different environmental conditions among locations have a significant impact on growth response of container-grown red maple cultivars.

Membrane Thermostability for Root Tissue of Red and Freeman Maple Cultivars

Six red (Acer rubrum `Autumn Flame', `Fairview Flame', `Franksred', `Landsburg', `Northwood', and `October Glory') and three Freeman (A. × freemanii `Armstrong', `Celzam', and `Jeffersred') maple cultivars originating in different parts of the United States were grown in containers in 1995 and 1996 prior to laboratory procedures to determine root cell membrane thermostability. Electrolyte leakage from excised root tissue exposed for 30 min to temperatures ranging from 20 to 63 °C, was used to assess cellular injury of unsuberized, current season, fine roots. The critical killing temperatures of root tissue of cultivars evaluated ranged from 52.0 ± 0.8 °C to 53.3 ± 0.5 °C, indicating minimal differences in root membrane thermostability among the selections evaluated. Critical temperatures for cultivars selected from the northern part of the native range did not differ from cultivars originating elsewhere. Implications of these differences for container production will be discussed.

Growth of `October Glory' Red Maple in Multiple Locations in the Southeast

Limited information exists for container production of red maple cultivars. The objective of this study was to evaluate first-year growth of container-grown `October Glory' at 3 locations with disparate climates in Georgia and Alabama (Tifton, Ga., Blairsville, Ga., and Auburn, Ala.). Rooted cuttings were planted in 9.2-L containers in one location in the same substrate in April 1995. Trees were transported to each location in mid-June and irrigated from overhead risers at 1.3 cm/day for 6 months until dormant, then transported to a single location for harvest. Despite weather differences among locations, final heights were not different (Blairsville 59.8 cm; Auburn 53.0 cm; and Tifton 60.2 cm). Shoot diameter increase and shoot dry weight was greatest at Tifton (8.4 mm, 17.5 g), least at Blairsville (6.3 mm, 9.2 g), with Auburn similar to both locations (6.8 mm, 12.2 g). Root dry weight and root: shoot ratio was greater in Tifton (17.2 g, 0.97) than Blairsville 14.9 g, 0.51) and Auburn (7.0 g, 0.64).

Photosynthetic Response of Selected Red Maple Cultivars to Light

Four red maple {Acer rubrum L.) cultivars ('FranksrecT - Red Sunset™, 'Northwood', 'October Glory', and 'Schlesingeri') grown in containers were evaluated for response to different photosynthetically active radiation (PAR) levels. As PAR increased, there was a linear increase in net photosynthesis (Pn) and transpiration (E) for 'Franksred' and 'October Glory'. In contrast, Pn and E for 'Northwood' and 'Schlesingeri' increased as PAR increased to about 1375 |imol-m'2-s'1 and 1350 u.mol-m~2-s\ respectively and declined thereafter. PAR had no relationship to water use efficiency (calculated as Pn/E) for the four cultivars. Mesophyll resistance ( r j to CO2 (Cl/Pn) decreased linearly as PAR increased for 'October Glory'; but'Franksred', 'Northwood', and 'Schlesingeri' exhibited a quadratic response to PAR (with estimated lows of 17.61 cm-sec1 at 1600 PAR, and 16.45 cm-sec1 and 16.36 cm-sec1 at 1400 PAR, respectively). The enhanced photosynthetic mechanism for rm as PAR levels increased suggests that 'October Glory' is the most adapted cultivar of the four selections in this study for high PAR environments. Furthermore, adaptive ranges of red maple cultivars may be predicted during developmental stages by establishing light curves for Pn, E, and r.

Sensitivity of Red Maple Cultivars to Acute and Chronic Exposures of Ozone

Five red maple (Acer rubrum) cultivars, 'Autumn Flame', 'Fairview Flame', 'Franksred' (Red Sunset™), 'Northfire' and 'October Glory', and 1 Freeman maple cultivar (Acer°° freemanii 'Autumn Blaze', an interspecific cross between red maple and silver maple) were exposed to 0,100, 200, or 300 ppb ozone for 4 hours on 2 consecutive days. Visible foliar injury, characterized as a stipple on the upper leaf surface, was observed in all ozone treatments except the control, and occurred on the oldest leaves only. 'Autumn Flame' had the least visible injury (less than 1% of the leaves injured), while 'Northfire' had the most (4% of the leaves injured). In a chronic ozone exposure experiment, 3 red maple cultivars ('Autumn Flame', 'Fairview Flame', and 'October Glory'), and 1 Freeman maple cultivar ('Autumn Blaze') were exposed to sub-ambient, ambient, or twice-ambient ozone levels for 9 weeks. No visible foliar injury developed in any of the ozone treatments. No differences for plants in the 3 ozone treatments occurred for height, caliper, leaf, shoot, or root dry weight. Photosynthesis was lower for sub-ambient plants and similar for twice-ambient and ambient plants 4 weeks after treatment initiation, while at 8 weeks no differences occurred. These data indicate that red maple cultivars are relatively tolerant to elevated acute and chronic ozone exposures.

Root-zone Stress Effects on Water Relations and Growth of Silver, Red, and Freeman Maples

Freeman maples (Acer ×freemanii E. Murray) are suspected to be more resistant to environmental stress than red maples (A. rubrum L.) because the lineage of Freeman maple includes silver maple (A. saccharinum L.). Little is known, however, about stress resistance of silver maple, and few data from direct comparisons of red and Freeman maples are available. Our objectives were to determine effects of root-zone heat on silver maples from northern and southern provenances, and to compare red and Freeman maple cultivars for resistance to rootzone heat stress and drought. There were no provenance-by-temperature interactions when silver maples from 33.3°N (Mississippi) and 44.4°N (Minnesota) latitude were grown with root zones at 29 and 35°C. Plants from 44.4°N latitude had 36% higher fresh mass, 43% more leaf surface area, and 35% and 59% higher, respectively, root and shoot dry masses than plants from 33.3°N latitude. Midday xylem water potential was 68% more negative for plants at 35°C than for plants at 29°C, and transpiration rate was 129% less for plants with root zones at 35°C than for those with root zones at 29°C. During preliminary work with Autumn Flame and Franksred red maple and Indian Summer and Jeffersred Freeman maples, rooted cuttings were grown in 25 and 37°C root zones under both drought and nondrought conditions. Reductions in growth at 37°C were similar for all cultivars. Results of this work could influence development, marketing, and use of Freeman maples.

Styrene-lined and Copper-coated Containers Affect Production and Landscape Establishment of Red Maple

Growth response of two red maple cultivars (Acer rubrum L. `October Glory' and `Northwood') to styrene lining or copper hydroxide coating of 23.3-liter black plastic containers was evaluated. After the first growing season, plants were left in their original container, repotted into 51.2-liter nontreated containers, or transplanted into the landscape. Copper hydroxide effectively reduced circling of roots of both cultivars at the medium–container interface during the first year of production, but was less effective during the second growing season. Repotting from copper-treated containers into 51.2-liter containers or transplanting into the landscape resulted in more fibrous root development and enhanced root regeneration outside the original rootball relative to transplanting from nontreated containers. However, when copper hydroxide was applied to styrene lining, root regeneration after transplanting was reduced. Roots of plants grown in styrene-lined containers covered the medium–container interface more thoroughly than those in nonlined containers, but height, trunk diameter, and root regeneration were similar. `October Glory' had a larger trunk diameter, more branching, and better root regeneration than `Northwood'.

Gas Exchange Rates for Selected Red Maple Cultivars Grown in Alabama

Abstract The objective of this study was to develop a rapid screening technique to characterize selected red maple (Acer rubrum L.) cultivars based on their gas exchange capacities. Evaluations were conducted in Alabama under ambient conditions on an established, irrigated field trial. In preliminary evaluations 9 red maple cultivars (‘Autumn Flame’, ‘Fairview Flam’, ‘Franksred’, ‘Karpick’, ‘Northwood’, ‘October Glory’, ‘Redskin’, ‘Schlesingeri’, and ‘Tilford’) and 3 Freeman maple (Acer x freemanii E. Murray) selections (‘Autumn Blaze’, ‘Morgan’, and ‘Scarsen’) were observed for differences in net photosynthesis (Pn), transpiration (E), and stomatal conductance (Cs). Based on these results, 4 cultivars of A. rubrum were selected and evaluated intensively over 2 years. Throughout the study, growth rates for the 4 selections failed to correspond with gas exchange observations.