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Amur maackia (Maackia amurensis Rupr. & Maxim.) has potential as a more widely grown nursery crop, but little information is available on effects of media and nutrition on growth of containerized plants. We compared growth of seedlings in five media and determined growth responses to two fertility regimes. After 35 days, total dry mass of plants grown in 1 perlite: 1 vermiculite (by volume) or in 5 sphagnum peat: 3 perlite: 2 soil was 3.2 times the dry mass of plants grown in three soilless media that contained composted bark; and after 70 days, growth was greater in the medium with soil than in 1 perlite: 1 vermiculite. Plants grown in solution culture with N at 0.75 mm had 1.8 times the dry mass of those provided N at 3.75 mm. Form of N in solution did not affect dry mass, but N content of leaves of plants grown with >50% NH 4 + was 1.3 times as great as that of plants provided only NO 3 . Plants in containers attained maximal dry mass when fertilized with solutions containing N at 10.8 mm from NO 3 , NH 4 + , and urea or N at 7.5 mm with equal amounts of NO 3 and NH 4 + . None of the soilless media used consistently evoked growth similar to growth of plants in the soil-based medium.

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The capacity to form nitrogen-fixing symbioses with rhizobia is common among species in the Papilionoideae subfamily of the Leguminosae, but nodulation and nitrogen fixation have never been documented in Cladrastis kentukea (Dum.-Cours.) Rudd (American yellowwood). The purpose of this study was to test the hypothesis that C. kentukea is nodulated by rhizobia. Seedlings were grown in sterile vermiculite and irrigated with a nitrogen-free nutrient solution. In one experiment, the vermiculite was inoculated with rhizobia that nodulate Maackia amurensis Rupr. & Maxim., a closely related tree species. During a second experiment, the vermiculite was inoculated with samples of soil collected near trees of C. kentukea in a native stand in Alexander County, Illinois. There were no nodules on roots of seedlings harvested 6 weeks after inoculation in either experiment. These results represent strong additional evidence that C. kentukea does not form nitrogen-fixing symbioses with rhizobia.

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Maackia amurensis Rupr. & Maxim. associates with N2-fixing rhizobia, but variation in N2 fixation among genotypes of this species is not known. We determined the effect of N2 fixation on growth of plants from seven half-sib families known to differ in seed mass and seedling growth when provided N. Seedlings were grown in Leonard jars for 12 weeks in a greenhouse. Mass of control plants provided N and nodule mass on plants inoculated with rhizobia (USDA 4349) and not provided N differed among families. Among plants not provided N, inoculation did not increase dry matter but did reduce chlorosis. Therefore, plant N content also will be discussed as an indicator of efficiency of N2 fixation. Results indicate N2 fixation improves plant quality in low-N soils but will not eliminate the need for N applications during seedling production.

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Commercial production of Maackia amurensis Rupr. & Maxim. (Amur maackia) is very limited despite the ornamental and nitrogen (N2)-fixing potential of this tree species. The goal of this on-going project is foster production efforts by selecting genotypes based on growth rate, morphology, stress resistance, and efficiency of N2 fixation. To establish a collection of plants with diverse genetic backgrounds, we requested half-sib lots of seed from arboreta, public gardens, and zoos in 1991. Mean seed mass of the 38 lots that were obtained ranged from 35 to 99 mg. Germination ranged from 67 to 100% and was 78% for the oldest lot, which was harvested at least 66 years ago. Over 2500 seedlings representing the 38 lots were grown in a greenhouse during the 1992 season. The mean epicotyl length and number of compound leaves varied among seedlings in the different lots. Results to date indicate that selecting genotypes based on growth rate and morphological features will be possible.

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Scotch laburnum [Laburnum alpinum (Mill.) Bercht.], Amur maackia (Maackia amurensis Rupr. & Maxim.), and Chinese wisteria [Wisteria sinensis (Sims) Sweet] were inoculated with compatible rhizobia and treated with leaching fractions (LF) of 0, 0.2, and 0.4 using fertilizer solutions with 3.6 and 10.7 mol N/m3 for 10 weeks. LF did not affect plant dry mass, leaf area, or stem length. Growth was higher among plants provided 10.7 mol N/m3, but only plants provided 3.6 mol N/m3 formed root nodules. We conclude that growth is not reduced by eliminating leaching during the first 10 weeks of seedling development, and that application of 10.7 mol N/m3 prevents nodulation of these species.

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The objective of this study was to determine the efficacy of plant growth regulators applied as foliar sprays on height and branching of seashore mallow (Kosteletzkya virginica). Five chemical plant growth regulators were applied: ancymidol [15, 25, and 50 mg·L–1 (ppm)] (A-Rest; Elanco Products Co., Indianapolis), dikegulac sodium (500, 1000, and 1500 mg.L–1) (Atrimmec; PBI/Gordon Corp., Kansas City, Mo.), paclobutrazol (10, 20, and 60 mg·L–1) (Bonzi; Uniroyal Chemical Co., Middlebury, Conn.), chlormequat chloride (CCC) (750, 1000, and 1500 mg·L–1) (Cycocel; Olympic Horticultural Products, Mainland, Pa.), and CCC/daminozide mixes (1000/2500, 1000/5000, and 1500/5000 mg·L–1) (Cycocel and B-Nine; Uniroyal Chemical Co.). Ten replicate plants of each concentration were evaluated weekly for plant height and number of branches for 8 weeks. Plants that received CCC and CCC/daminozide treatments at all concentrations and paclobutrazol at 60 mg·L–1 were 60%, 60%, and 48% shorter than control plants and had 113%, 100%, and 75% more branches than control plants, respectively. All concentrations of ancymidol and dikegulac sodium-treated plants were similar to control plants. Paclobutrazol was applied twice, and only the highest concentration was effective for height control. Chlormequat chloride at the lowest concentration was as effective as all other concentrations of CCC and CCC/daminozide.

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Honey locust (Gleditsia triacanthos var. inermis Wind.) and tree-of-heaven Ailanthus altissima (Mill.) Swingle] sometimes are exposed to high root-zone temperatures in urban microclimates. The objective of this study was to test the hypothesis that seedlings of these species differ in how elevated root-zone temperature affects growth, leaf water relations, and root hydraulic properties. Shoot extension, leaf area, root: shoot ratio, and root and shoot dry weights were less for tree-of-heaven grown with the root zone at 34C than for those with root zones at 24C. Tree-of-heaven with roots at 34C had a lower mean transpiration rate (E) than those grown at 24C, but leaf water potential (ψ1) was similar at both temperatures. In contrast, shoot extension of seedlings of honey locust grown with roots at 34C was greater than honey locust at 24C, E was similar at both temperatures, and ψ1 was reduced at 34C. Hydraulic properties of root systems grown at both temperatures were determined during exposure to pressure in solution held at 24 or 34C. For each species at both solution temperatures, water flux through root systems (Jv) grown at 34C was less than for roots grown at 24C. Roots of tree-of-heaven grown at 34C had lower hydraulic conductivity coefficients (Lp) than those grown at 24C, but Lp of roots of honey locust grown at the two temperatures was similar.

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Freeman maples (Ace×freemanii 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®) and `Indian Summer'] and five red maples [`Franksred' (Red Sunset®), `Autumn Flame', `PNI 0268' (October Glory®), `Fairview Flame', and unnamed selection 59904] for effects of flooding and water deficit on plant growth, biomass partitioning, stomatal conductance, and leaf osmotic potential. Plants grown from 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 m3·m–3, respectively. Additional plants were flooded for 75 days, while plants 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, respectively. Differences in stomatal conductance after recovery from the first drought cycle and at the end of the second drought cycle did not vary with species. Drought reduced estimated leaf osmotic potential similarly for all genotypes; means for drought-stressed and control plants were –1.92 and –1.16 MPa, respectively. Freeman maples had a higher mean root: shoot weight ratio and a lower leaf surface area: root dryweight ratio than did red maples. Across genotypes, stomatal conductance of flooded plants initially increased by ≈20% and then fell to and remained below 50 mmol·s–1·m–2. Stomatal conductance of `Indian Summer' decreased to ≈20 mmol·s–1·m–2 after 8 days of flooding, indicating that this cultivar may be particularly sensitive to root-zone saturation.

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The limited use of the katsura tree (Cercidiphyllum japonicum Sieb. & Zucc.) in the landscape may be due to its reputed, but uncharacterized, intolerance of drought. We examined the responses of katsura trees subjected to episodes of drought. Container-grown trees in a greenhouse were subjected to one of three irrigation treatments, each composed of four irrigation phases. Control plants were maintained under well-hydrated conditions in each phase. Plants in the multiple-drought treatment were subjected to two drought phases, each followed by a hydration phase. Plants in the single-drought treatment were exposed to an initial drought phase followed by three hydration phases. Trees avoided drought stress by drought-induced leaf abscission. Plants in the multiple- and single-drought treatments underwent a 63% and 34% reduction in leaf dry weight and a 60% and 31% reduction in leaf surface area, respectively. After leaf abscission, trees in the single-drought treatment recovered 112% of the lost leaf dry weight within 24 days. Leaf abscission and subsequent refoliation resulted in a temporary reduction in the leaf surface area: root dry weight ratio. After relief from drought, net assimilation rate and relative growth rate were maintained at least at the rates associated with plants in the control treatment. We conclude that katsura is a drought avoider that abscises leaves to reduce transpirational water loss. Although plants are capable of refoliation after water becomes available, to maintain the greatest ornamental value in the landscape, siting of katsura should be limited to areas not prone to drought.

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