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Hydroponic culture of tree seedlings is commonly used to study root biology; however, we have found that species differ in their responses to this practice. Responses of 2-week-old seedlings of Amur maackia (Maackia amurensis Rupr. & Maxim.) and black locust (Robinia pseudoacacia L.) to 1%, 5%, 10%, 25%, 50%, and 100% Hoagland solution #1 were determined over 5 weeks. Dry mass of black locust increased with increasing solution concentration up to 50%. For Amur maackia, dry mass was highest in 5% solution, and dry mass declined by ≈50% in 50% solution. Purpling, chlorosis, and necrosis occurred on leaves of Amur maackia in solutions ≥10%, and symptom severity increased with solution strength. Amur maackia leaf ion content increased dramatically with increasing solution strength; for instance, leaf P content increased 688% as solution strength increased from 5% to 50%. No symptoms occurred on Amur maackia grown in a soil-based medium and irrigated with 50% solution. These data indicate that black locust can be grown hydroponically using standard methods. However, growth of Amur maackia is inhibited at high solution concentrations, suggesting a sensitivity to the availability of ions, and perhaps an enhanced ability to sequester ions from its media.

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Amur maackia (Maackia amurensis Rupr. & Maxim.) is a nodulating leguminous tree with potential for increased use in cities and in the dry, cold climates of the upper Midwest and Great Plains of North America. There has been little research on nutritional requirements and production methods of this species. We determined the effect of growth medium and form of applied N on seedling growth. Amur maackia attained 3.3-times more dry mass in a medium of 5 peat: 3 perlite: 2 soil (by volume) and in coarse 1 vermiculite: 1 coarse perlite (v/v) than in three soil-less mixes that contained large proportions of composted bark. When seedlings were grown in an aerated nutrient solution, dry mass after 5 weeks was similar regardless of whether NO 3 , NH 4 + , or a combination of these was supplied. But, leaf N content was 1.3-times greater in plants grown in a solution that contained at least 50% NH 4 + compared to plants provided with all NO 3 . Plants grown in solution with 750 μm N had 1.8-times more dry mass than those grown in solution with 3.75 μm N. Seedlings grown for 70 days in 5 peat: 3 perlite: 2 soil (by volume) attained the greatest dry mass when fertilized with Excel all purpose fertilizer that contained N at 10.8 mol·m–3, or with a nutrient solution that contained N at a 1.5 μm, at least half of which was NH 4 + . For container-grown Amur maackia, we recommend using a soil-based medium and providing N as either all NH 4 + or as a mixture of NH 4 + and NO 3 .

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Its more westerly native range and apparent xeromorphic foliar traits have led to speculation that black maple (Acer nigrum Michx.f.) is more drought resistant than sugar maple (Acer saccharum Marsh.). We examined differences in morphology and anatomy of leaves of trees of these species indigenous near the 43°N latitude in the midwestern and eastern United States. Leaves were collected during July, Aug., and Sept. 1995, from 10 trees in each of 24 sites at longitudes of 71°W in Maine to 94°W in Iowa. Density of trichomes on abaxial surfaces and lamina surface area showed quadratic relationships with longitude and were greatest for leaves from westerly sites in Iowa. The percentage of total lamina surface area partitioned in the two most basipetal lobes increased linearly with longitude. Abaxial surfaces had 6 to 960 trichomes/cm2, lamina surface area was 28 to 176 cm2, and surface area partitioned in basipetal lobes was 5% to 9%. A quadratic regression function related increases in trichome density to decreasing mean annual rainfall at collection sites. Specific leaf mass ranged from 3.5 to 7.6 mg·cm–2 and did not relate to longitude. Scanning electron microscopy showed leaves throughout the range had similar trichome morphology, and light microscopy is being used to examine variation in leaf anatomy and stomatal traits.

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A subirrigation method for rooting stem cuttings was compared to intermittent mist. Both methods resulted in 100% rooting of `Charm' chrysanthemum [Dendranthema × grandiflorum (Ramat.) Kitamura] and coleus (Coleus × hybridus Voss.) after 2 weeks. Subirrigated cuttings of `Charm' chrysanthemum had a lower mean root dry mass than misted cuttings, but root dry mass of coleus was not affected. Percentage rooting and mean root dry mass of subirrigated cuttings of `Franksred' red maple (Acer rubrum L.) were 95% and 321 mg, whereas the mean root dry mass of the 33% of cuttings that rooted under mist was 38 mg. For Japanese tree lilac [Syringa reticulata (Blume) Hara], the percentage of cuttings with living callus, mean callus diameter, and percentage rooting were higher for subirrigated cuttings than for misted cuttings. In a second study, cuttings of `Franksred' red maple were subirrigated with a solution containing 0 to 7.2 mol N/m3 and not misted. Cuttings given 3.6 or 7.2 mol N/m3 had > 90% rooting after 2 weeks, whereas only 8% of unfertilized cuttings had rooted, and root mass and chlorophyll content were highest for cuttings given 7.2 mol N/m3. Subirrigation can replace mist during propagation of some florist and nursery crops, and subirrigating with fertilizer solution improves rooting of `Franksred' red maple.

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Long regarded as a genus of two species, Dirca L. was expanded to include a third North American shrub discovered in 1994 as one population in the Sierra Madre Oriental of Tamaulipas in northeastern Mexico. The designation of Dirca mexicana Nesom & Mayfield as a third species in the genus was based in part on geographical separation from Dirca palustris L. and Dirca occidentalis Gray, which occur farther north in eastern North America and in a small region of California, respectively. Morphologically, D. mexicana was regarded as more similar to D. occidentalis than to D. palustris. Our objectives were to obtain fruits of all species, germinate seeds, and compare the three species genetically through analyses of seedling DNA. Drupes of D. mexicana, D. palustris (from populations in Iowa), and D. occidentalis were collected as they abscised naturally from plants in native habitats in mid-May, late May to early June, and mid-June, respectively. Embryo extraction, gibberellin, and cold stratification were used to promote germination, and DNA was extracted from leaves of seedlings by using the fully automated Autogen Autogenprep 740 DNA extraction system. Genomic DNA templates were used to compare sequences of the internal transcribed spacers (ITS) and the 5.8S coding region of the nuclear ribosomal DNA repeat and to examine polymorphisms in inter-simple sequence repeats (ISSRs). These analyses reinforce the present morphologically based classification of the three Dirca species by confirming species-level divergence at the molecular level. ITS sequences and ISSR banding patterns also enabled us to reconstruct the phylogenetic relationship among the three extant species of Dirca.

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Carolina buckthorn (Rhamnus caroliniana Walt.) is ornamental and could be promoted as a stress-resistant shrub for horticultural landscapes. Its status as a relative of invasive species, including common buckthorn (Rhamnus cathartica L.), raises concerns regarding the environmental consequences of planting Carolina buckthorn outside of its natural habitat. To assess the ease of propagating Carolina buckthorn from seed, and to gather data relevant to assessments of invasiveness, we compared seed-germination characteristics between the two species. Seeds of Carolina buckthorn were collected from native populations in Missouri, Oklahoma, and Texas. Seeds of common buckthorn were collected from populations in Iowa. We stratified seeds of both species for up to 112 days at 4 °C. Germination at 20 °C then was evaluated for 56 days. Over stratification durations, 40% and 71% of seeds of Carolina buckthorn and common buckthorn germinated, respectively. Stratification for 112 days optimized germination value for Carolina buckthorn, but stratification for 42, 56, 84, and 112 days evoked similar germination percentages. Seeds of Carolina buckthorn from Oklahoma germinated at a higher percentage (56%) than did seeds from Missouri (25%). Neither germination value nor germination percentage of common buckthorn was influenced by stratification. We conclude that seeds of Carolina buckthorn are more recalcitrant than are seeds of common buckthorn. This suggests that Carolina buckthorn, particularly those from Missouri with low reproductive success, may be less invasive than their Eurasian kin. Horticulturists can optimize germination percentage of Carolina buckthorn by cold-stratifying seeds for as little as 42 days, but 112 days optimizes germination value.

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A rapid, easy, and economical way to root softwood cuttings of red maple (Acer rubrum L. and A. × freemanii E. Murray) has been developed. Single-node cuttings were treated with 8 g IBA/kg and inserted in flats of perlite. Flats were placed in larger trays without drainage holes. Cuttings were subirrigated by adding a complete solution with 100 mg N/L to trays, saturating perlite at the bottom of the flat, below the cuttings. After 3 weeks, 94, 98, 100, and 100% of cuttings of `Indian Summer', `Autumn Flame', `Red Sunset', and `Autumn Blaze' had rooted, respectively. Leaves on cuttings remained turgid without mist or fog. In a subsequent study of `Red Sunset', 0, 50, and 100 mg N/L in the subirrigation solution resulted in 37, 100, and 100% rooting with 8 g IBA/kg and 0, 43, and 67% rooting without IBA. Rooting was fastest and chlorophyll in leaves was highest with both IBA and nutrients. Subirrigation can replace mist or fog when rooting cuttings of red maple.

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Rhamnus caroliniana Walt. (carolina buckthorn or indian cherry) is an attractive small tree or shrub found in diverse habitats in the United States. Because the species occurs in both mesic and xeric soils, we questioned whether selections of carolina buckthorn could be marketed as new nursery crops resistant to both drought and flooding. Our first objective was to characterize how soil water affects growth and gas exchange of carolina buckthorn. We studied potted plants subjected to soil moistures that ranged from complete submersion of the root zone to severe drought (7% soil water by volume). The maximal photosynthetic rate occurred at 27% soil water content, and complete submersion killed plants. Our second objective was to compare responses of carolina buckthorn to those of the invasive common buckthorn (Rhamnus cathartica L.) when potted plants were treated with partial flooding of root zones and drought. Carolina buckthorn resisted deleterious effects of partial flooding. In contrast, leaves of common buckthorn became epinastic, and rates of photosynthesis were low (2.14 μmol CO2/m2/s) after 17 days of treatment. Mean photosynthesis of common buckthorn increased to 5.52 μmol CO2/m2/s, a rate similar to that of carolina buckthorn, after 55 days of treatment. Drought reduced net photosynthesis by 52% and 68%, respectively, for carolina buckthorn and common buckthorn relative to rates of plants in the control treatment. We conclude that carolina buckthorn is capable of maintaining carbon fixation and growth over a wide range of soil water contents, and unlike common buckthorn, is not dependent upon morphological, anatomical, or physiological adjustments to optimize growth and net photosynthesis in extremely wet soil. Use of carolina buckthorn as an ornamental is warranted if invasiveness and other potential problems with the species are not identified.

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Attributes of Leitneria floridana Chapman have been recognized, but this North American shrub remains rare in commerce, and little information on propagation is available. We studied germination of seeds collected from several disjunct populations of L. floridana in 2002 and 2003. In 2002, ≤5% germination occurred when ripe drupes from Missouri and Florida were sown soon after collection. Effects of GA3 (750 mg·L-1 for 24 hours) were assessed on stored drupes leached with water and on seeds excised from stored drupes. Germination percentages were 21 and 32 for leached drupes and excised seeds from Florida, respectively, but ≤5% germination occurred among germplasm from Missouri and among untreated drupes from both provenances. Viability of ungerminated seeds among treatments ranged from 0% to 7%. In 2003, fleshy, apparently unripe drupes from Texas, which were scarified with H2SO4 and then treated with 1000 mg·L-1 GA3 showed 48% germination (germination value = 3.9). Up to 29% germination (germination value = 2.7) occurred when seeds were excised from unripe drupes from Arkansas and Missouri and then were treated for 24 hours with 750 or 1000 mg·L-1 GA3. We conclude that provenance, developmental stage of drupes when collected, storage, and pregermination treatments influence viability and germination of seeds of L. floridana. Barriers to germination may be avoided by collecting drupes when they are green and fleshy.

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