Search Results

You are looking at 1 - 10 of 98 items for

  • Author or Editor: William R. Graves x
Clear All Modify Search

Differences in native habitat and leaf morphological traits have prompted speculation that black maple (Acer nigrum Michx.f.) is more drought resistant than sugar maple (A. saccharum Marsh.). In this study, growth of potted seedlings of the two species irrigated at 10-, 26-, or 42-day intervals was compared. For plants irrigated most frequently, dry mass, shoot: root ratio, stem length, and surface area of lamina were greater for sugar maple than black maple. The impact of drought was more pronounced in sugar maple than in black maple, causing reductions in stem length of ≈ 60% in sugar maple and ≈ 30% in black maple. Specific mass of lamina tended to be greater for black maple than sugar maple, particularly after drought, and it increased over time in both species. The slower growth, lower shoot: root ratio, and greater specific mass of lamina of black maple indicate. it is more drought resistant than sugar maple.

Free access

Growth, dry-matter partitioning, and specific mass of lamina of black maple (Acer nigrum Michx.f.) and sugar maple (A. saccharum Marsh.) irrigated at 10-, 26-, and 42-day intervals were compared. Total dry mass, stem length, and surface area of lamina were greater for sugar maple than for black maple for plants irrigated every 10 days. Reducing irrigation frequency curtailed growth of both species, but the reduction was greater for sugar maple than for black maple. The shoot: root ratio was lower for black maple than for sugar maple and was reduced by drought in both species, particularly among plants irrigated every 26 days. Specific mass of lamina increased as plants aged, was greater for black maple than for sugar maple, and decreased in response to irrigation at 42-day intervals. The slower growth, lower shoot: root ratio, and greater specific mass of lamina of black maple indicate this species has a greater capacity to withstand drought than sugar maple.

Free access

Root hydraulic conductance is often expressed on the basis of dry weight or surface area of leaves or roots of plants produced in solution or aggregate culture. In this study, biomass partitioning and its influence on the interpretation of root hydraulic conductance data were compared in 21- to 63-day-old Gleditsia triacanthos inermis Willd. (honey locust) seedlings grown in solution and sand cultures. The ratio of lamina to root dry weight decreased as seedlings aged but was always greater for solution-grown plants than for sand-grown plants. Expressed on the basis of root dry weight, steady-state water fluxes at applied pressures ≥ 0.28 MPa and hydraulic conductivity coefficients declined with root system age, with a sharp decrease among solution-grown plants between ages 21 and 35 days. Such a difference was not detected using data expressed on lamina surface area or dry weight, illustrating that caution must be exercised when reporting and comparing the conductance of roots cultured in different media.

Free access

Although many species of Alnus Miller grow in wet soils, none is as closely associated with low-oxygen, waterlogged soils as Alnus maritima (Marsh.) Muhl. ex Nutt. (seaside alder). An actinorhizal species with promise for use in horticultural landscapes, land reclamation, and sustainable systems, A. maritima associates with Frankia Brunchorst, thereby forming root nodules in which gaseous nitrogen is fixed. Our objective was to determine how root-zone moisture conditions influence the occurrence, location, and anatomy of nodules on A. maritima. Plants of Alnus maritima subsp. maritima Schrader and Graves were established in root zones with compatible Frankia and subjected to four moisture regimens (daily watered/drained, partially flooded, totally flooded, and totally flooded with argon bubbled through the flood water) for 8 weeks. Oxygen content of the root zone, number and location of nodules on root systems, and dry weight and nitrogen content of shoots were determined. Root-zone oxygen content ranged from 17.3 kPa for daily watered/drained plants to 0.9 kPa for argon-treated plants. Across all treatments, 87% of the nodules were within the upper one-third (4 cm) of the root zone. Although shoot dry weights of daily watered/drained and partially flooded plants were not different, daily watered/drained plants had more nitrogen in their leaves (2.53 vs. 2.21 mg·g-1). Nodulation occurred in all treatments, but nodules on totally flooded roots (with or without argon) were limited to a single lobe; in contrast, multilobed nodules were prevalent on partially flooded and daily watered/drained plants. Frankia infection within submerged nodule lobes was limited to one or two layers of cortical cells. Submerged nodules developed large air spaces between cortical cells, and phenolic-containing cells appeared to inhibit Frankia expansion within the nodule. These data suggest that access to root-zone oxygen is critical to the Frankia-A. maritima subsp. maritima symbiosis, and that plants of this subspecies in the drained soils of managed landscapes may benefit more than plants in native wetland habitats from nodulation and nitrogen fixation.

Free access

Alnus maritima (Marsh.) Muhl. ex Nutt. is a rare woody plant species that exists as three subspecies found in widely disjunct locations in the United States. Although there is a growing interest in the phytogeography, ecology, conservation, and landscape potential of this species, the phylogeny of A. maritima has not yet been resolved by using molecular methods. We have combined a relatively new method of genome fingerprinting, ISSR-PCR, and the automated imaging capabilities of GeneScan technology to investigate the molecular systematics of A. maritima. Based on the molecular evidence from 108 ISSR loci, we confirm that the three disjunct populations of A. maritima have diverged sufficiently to be classified as subspecies. Our molecular phylogeny of the three subspecies of A. maritima agreed in topology with a phylogeny produced from morphological data and showed that subsp. oklahomensis is the most distinct of the three subspecies and was the first to diverge. The simultaneous analysis of molecular and morphological data provides a detailed and balanced phylogeny reconstruction for the three subspecies. Our results support the theory that A. maritima originated in Asia, migrated into North America across the Bering land bridge, and was established over a large range in the New World before being forced into its present meager disjunct distribution.

Free access

Selection of sugar maples (Acer saccharum Marsh.) and black maples (Acer saccharum Marsh. ssp. nigrum Desm. or Acer nigrum Michx. f.) that will be more resilient than existing cultivars in managed landscapes could be facilitated by defining relationships between geographic origin and foliar traits critical to leaf function. We examined variation in leaf morphology and anatomy of both taxa, known collectively as hard maples, near 43 °N latitude and tested for relationships between foliar traits and the longitude of origin from 70 ° to 94 °W longitude. Leaves exposed to direct solar radiation were sampled from up to 20 trees indigenous at each of 42 sites during 1995 and 1996. All leaves from east of 75.84 °W and from 92.73 °W and further west expressed morphological characters associated with sugar maple and black maple, respectively; leaves with intermediate traits were found between these two longitudes. Leaves from 90 ° to 94 °W had the highest surface area due to increases in the areas of middle and proximal portions of laminae. Up to 1162 trichomes/cm2 were present on the abaxial surface of laminae from west of 85 °W, while laminae from further east were glabrous or had ≤300 trichomes/cm2. Laminae from western habitats also had relatively high stomatal frequency, and stomatal apertures of laminae west of 91 °W were particularly narrow. Longitude did not affect specific weight and thickness of laminae, which averaged 5.5 mg·cm-2 and 90 μm, respectively. Principal component analysis of laminar traits showed existence of two clusters. A large group dominated by data from trees in New England also contained data from trees as far west as ≈93 °W longitude; data for trees further west were clustered separately. Although phenotypic continua were defined, laminae west of 93 °W were distinct, which suggests trees selected there may function differently in managed landscapes than trees selected from native populations further east.

Free access

Genotypic variation and horticultural potential of Alnus maritima [Marsh.] Nutt. (seaside alder), a large shrub or small tree found naturally in only three small, disjunct populations, have not been studied. We examined effects of population of origin and environment on seed germination and growth and morphology of seedlings. The first experiment showed that 6 weeks of cold stratification optimized germination of half-sibling seeds from Oklahoma at 73.2%. When this treatment was applied to multiple groups of half-siblings from all populations in a second experiment, seeds from Oklahoma had a higher germination percentage (55.0%) than seeds from Georgia (31.4%) and the Delmarva Peninsula (14.7%). In a third experiment, morphology and growth of multiple groups of half-siblings from all three populations were compared in one environment. Leaves of seedlings from Oklahoma were longer (12.8 cm) and more narrow (2.15 length to width ratio) than leaves of seedlings from Georgia (12.0 cm long; ratio = 1.76) and the Delmarva Peninsula (11.6 cm long; ratio = 1.86). Seedlings from Oklahoma and Georgia accumulated dry weight at higher rates (181 and 160 mg·d-1, respectively) than seedlings from Delmarva (130 mg·d-1), while seedlings from Oklahoma and Delmarva were more densely foliated (0.72 and 0.64 leaves and lateral shoots per centimeter of primary stem, respectively) than those from Georgia (0.46 per cm). These differences indicate genetic divergence among the three disjunct populations and the potential to exploit genetic variation to select horticulturally superior A. maritima for use in managed landscapes.

Free access

Information on the heat resistance of silver maple (Acer saccharinum L.) could help develop stress-resistant Freeman maples (Acer ×freemanii E. Murray). Our first objective was to determine how 26, 30, 32, 34, and 36 °C in the root zone affect growth and water relations of plants from rooted cuttings of a silver maple clone indigenous to Mississippi (33.3 °N latitude). Fresh mass increased over time for plants at all temperatures and was highest for plants with root zones at 30 °C. Quadratic regression functions predicted maximal plant dry mass, leaf surface area, and stomatal conductance at 29, 29, and 28 °C, respectively. Stem xylem water potential (ψ) during the photoperiod decreased linearly with increasing root-zone temperature from -0.83 MPa at 26 °C to -1.05 MPa at 36 °C. Our second objective was to compare six clones of silver maple from the Mississippi location with six clones from 44.4 °N latitude in Minnesota for effects of 35 °C in the root zone on plant growth, stomatal conductance, and stem ψ. Provenance and temperature main effects were significant for most dependent variables, but there were no provenance × temperature interactions. Over both provenances, plant fresh and dry mass, leaf surface area, stomatal conductance, and stem ψ during the photoperiod were higher at 29 than 35 °C. Over both temperatures, plants from Minnesota clones had higher fresh and dry mass and more leaf surface area than plants from Mississippi clones. The lack of temperature × provenance interactions suggests that ecotypic or clinal variation in heat resistance is minimal and will not be useful for identifying superior genotypes for use in interspecific crosses with red maple (Acer rubrum L.).

Free access

Responses of five bottomland tree taxa to drought and flooding were studied to identify those adapted to urban environments. During one experiment, containerized `Franksred' red maple [Acer rubrum L. `Franksred' (trademark = Red Sunset)], sweetbay magnolia (Magnolia virginiana L.), black tupelo (Nyssa sylvatica Marsh.), bald cypress [Taxodium distichum (L.) Rich.], and pawpaw [Asimina triloba (L.) Dunal.] were treated with various irrigation regimes for up to 118 days. Net assimilation rate (NAR) and relative growth rate (RGR) were reduced more by flooding than by drought for plants of all taxa, except pawpaw, which showed similar NAR and RGR during flooding and drought. Only sweetbay magnolia and bald cypress maintained positive NAR and RGR during flooding, and sweetbay magnolia was the only taxon that did not produce significantly less leaf surface area, shoot dry mass, and root dry mass during flooding and drought. Apparent morphological mechanisms of stress resistance included an increase in specific mass of leaves (mg·cm-2) during drought for red maple and bald cypress and a 385% increase in the root: shoot mass ratio for droughted plants of pawpaw. Leaf water relations of drought- and flood-stressed `Franksred' red maple and sweetbay magnolia were determined in a second experiment. Predawn and mid-day leaf water potential (ψ) decreased with decreasing root-zone matric potential for both taxa, and transpiration rate was reduced by drought and flooding. Pressure-volume analysis showed that leaves of `Franksred' red maple responded to drought by shifting symplastic water to the apoplast. Leaves of drought-stressed sweetbay magnolia adjusted osmotically by reducing osmotic potential (ψπ) at full turgor by 0.26 MPa. Our results suggest that sweetbay magnolia and bald cypress will perform well at urban planting sites where episodes of drought and flooding regularly occur.

Free access

Genotypic variation and horticultural potential of Alnus maritima [Marsh.] Nutt. (seaside alder), a large shrub or small tree found naturally in only three small, disjunct populations, have not been studied. We examined effects of population of origin and environment on seed germination and the growth and morphology of seedlings. Our first germination experiment showed that 6 weeks of cold stratification applied to half-siblings from Oklahoma optimized germination at 73.2%. When this treatment was applied to multiple half-sib seed sources from all populations in a second experiment, seeds from Oklahoma had a higher germination percentage (55%) than seeds from both Georgia (31.4%) and the Delmarva Peninsula (14.7%). A third experiment showed that growth of seedlings increased with increasing irradiance intensity up to 258 μmol·m–2·s–1, and survival and growth of seedlings from Oklahoma varied with root media. In a fourth experiment, multiple groups of half-siblings from all three populations were grown in one environment to compare variation in growth and morphology within and among populations. Leaves of Oklahoma seedlings were longer (12.8 cm) and more narrow (2.15 length: width ratio) than leaves of seedlings from Georgia (12.0 cm long, ratio = 1.76) and the Delmarva Peninsula (11.6 cm long, ratio = 1.86). Seedlings from Oklahoma and Georgia had a higher growth rate (180.7 and 160.0 mg/day, respectively) than did seedlings from Delmarva (130.1 mg/day), while Oklahoma and Delmarva seedlings were more densely foliated (0.72 and 0.64 leaves and lateral shoots per cm of primary stem, respectively) than those from Georgia (0.46 per cm). These differences indicate both divergence among the three disjunct populations and potential to exploit genetic variation to select horticulturally superior A. maritima for use in managed landscapes.

Free access