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- Author or Editor: William R. Graves x
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.
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
Alnus maritima (Marsh.) Muhl. ex Nutt. is a large shrub or small tree with potential for use in managed landscapes. Because the three subspecies of A. maritima are indigenous only to areas with mild winter temperatures (USDA hardiness zones 7a and 7b), knowledge of their cold acclimation and cold hardiness is vital if they are to be used where winters are more harsh. Phenology and depth of cold hardiness were assessed by collecting stem samples seven times from 25 Sept. 2000 to 23 Apr. 2001, subjecting the samples to cold temperature ramping, and determining the lowest survival temperature (LST) via the tissue discoloration method. Samples were collected from indigenous plants of the three subspecies and from plants growing in a common garden near Ames, Iowa (USDA zone 5a). Results indicated that some plants from all three subspecies can survive midwinter extremes as low as -80 °C; that plants grown in Ames achieved a greater depth of cold hardiness for most of the winter and were more uniform in cold hardiness than plants growing in warmer native sites; and that the three subspecies did not differ in phenology or depth of cold acclimation. Results of field trials with plots of 150 plants each installed in three northern hardiness zones (USDA zones 5a, 4a, and 3a) supported these conclusions by showing survival of all 450 plants. We resolved differences among subspecies by rating the percentage of stem tissue survival for each plant in the field plots. Subspecies maritima, from the northernmost provenance (the Delmarva Peninsula), showed the least stem death across all three plots (3.9% tissue death), followed by subsp. georgiensis from northwestern Georgia (10% tissue death), and subsp. oklahomensis from southern Oklahoma (12.8% tissue death). Our results suggest that low temperatures should not limit the use of A. maritima in areas as harsh as USDA zone 3a. Selections based on cold hardiness may allow the use of A. maritima in areas with even colder winters.
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.
Symbiotic associations between Alnus maritima (Marsh.) Muhl. ex Nutt. (seaside alder) and the actinomycete Frankia result in root nodules in which atmospheric nitrogen (N) is fixed. This has led to interest in producing seaside alders with minimal N fertilizer and in using the species on low-N soils. Our objectives were to determine how applied N influences nodulation and to characterize how short-term changes in root-zone N affect the function of established nodules. Seaside alders native to the Delmarva Peninsula (Alnus maritima subsp. maritima) were grown in perlite inoculated with soil from roots of indigenous plants. Plants were treated with N-free Hoagland solution supplemented with ammonium nitrate at 0, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 2, 4, and 8 mm for 10 weeks. Nodulation decreased as applied N increased. While plants treated with ammonium nitrate at 4 and 8 mm formed nearly no nodules, 0.5 mM resulted in vigorous, healthy plants that formed, on average, 70 nodules. In a second experiment, a nodulated population of seaside alders was established by treating seedlings with 0.5-mm ammonium nitrate in otherwise N-free Hoagland solution for 6 weeks. Plants then were provided ammonium nitrate at 0.5, 2, or 4 mm for two weeks. Acetylene-reduction assays showed that ammonium nitrate at 4 mm suppressed nodule activity. Daily irrigation with N-free solution subsequently led to a rapid depletion of root-zone N and a concomitant resurgence of nodule activity among plants previously provided 2- and 4-mm ammonium nitrate. These results provide useful information on how to manage fertility to optimize nodulation and show suppression of nodule activity caused by N fertilization can be temporary if excess N is leached from the root zone.
Horticulturists have not promoted use of Dirca palustris L. (eastern leatherwood) despite its suite of traits valued by gardeners and landscapers. Horticultural production of D. palustris may be hindered by slow shoot growth and sensitivity of plants to edaphic conditions. Because of discrepancies in reported tolerances of D. palustris to root-zone pH, we assessed whether pH of soils supporting indigenous populations in Florida, Maine, and North Dakota corresponded to responses of seedlings from the three provenances to root-zone pH of 4.5 to 7.3 in soilless media. Regression showed that root zones at pH 5.8 promoted maximum stem length of seedlings from Florida and North Dakota, whereas root zones at pH 4.5 led to maximum stem length of seedlings from Maine. Root-zone pH 5.6 and 5.5 fostered maximum root and shoot dry weight, respectively, for seedlings from Florida, whereas root zones at pH 4.5 promoted maximum root and shoot dry weights of seedlings from Maine and North Dakota. Averaged over provenance, relative leaf greenness decreased by 62%, and foliar nitrogen, iron, manganese, and zinc decreased by 49%, 70%, 95%, and 48%, respectively, as root-zone pH increased from 4.5 to 7.3. Foliar phosphorus decreased at both low and high pH. The pH of soils where seeds were collected did not predict optimal root-zone pH for stem length or biomass accrual in soilless media; genotypes from soils with a pH of 7.4 in North Dakota did not exhibit greater tolerance to high pH than genotypes from Maine or Florida, where pH of indigenous soil was 6.1 and 5.2, respectively. Averaged over pH treatments, seedlings from Florida showed the greatest stem length and formed the most shoot biomass, whereas seedlings from North Dakota had stouter stems, greater root biomass, and greater root-to-shoot ratios than did seedlings from Florida and Maine. Our results illustrate that acidic media facilitate horticultural production of D. palustris, that further evaluation of provenance differences could facilitate selection of genotypes for horticulture, and that tolerances of genotypes to root-zone pH do not strictly correspond to the pH of soils on which they were indigenous.
Traits associated with drought resistance vary with provenance of hard maples (Acer sp.), but the stability of differences ex situ and over time is unknown. We compared growth, dry-matter partitioning, leaf anatomy, and water relations of seedlings from central Iowa, eastern Iowa, and the northeastern United States over 2 years. Some seedlings from each of the three provenances were used as well-irrigated controls. The remaining seedlings were drought-stressed and irrigated based on evapotranspiration. Across irrigation treatments, plants from Iowa had shorter stems and higher specific weight of lamina, root: shoot dry-weight ratios, and root: lamina dry-weight ratios than did plants from the northeastern United States when treatments began. Biomass partitioning did not differ based on provenance after irrigation treatment for 2 years, but leaves from central Iowa had a higher specific weight, and their abaxial surfaces had more stomates and trichomes, than did leaves from the Northeast. Drought stress reduced conductance only in plants from central Iowa. Across provenances, drought stress reduced stomatal frequency, surface area of laminae, and dry weights of laminae and roots, and increased root: shoot dry-weight ratio. Leaf water potential of plants subjected to drought was lower at predawn and higher at midday than that of control plants. Drought did not cause osmotic adjustment in leaves. We conclude that the stability of foliar differences among provenances of hard maples validates using these traits as criteria for selecting ecotypes for use in managed landscapes prone to drought.
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.