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Abstract

Only a few species are capable of colonizing extreme environments, whereas more moderate environments can support many more. The diversity of species in a habitat is thus controlled by the environment, whether by soil fertility, altitude or any other factor. This diversity reflects the number of species adapted to grow in a habitat, and the nature of this adaptation must be examined in light of the physiological effect of the environmental factors making up the habitat, and their variation in time and space (11).

Open Access

Plant development, leaf morphology, leaf cuticular wax content, and leaf water relations were determined for seven tree species exposed to consecutive cycles of drought. The objective of the experiment was to identify plant taxa suitable for landscapes prone to drought. On the day drought treatments began, plant development traits and leaf morphology varied among species. Leaf cuticular wax content was different among species and ranged from 0.053 mg·cm–2 in California white oak (Quercus lobata Née), to 0.200 mg·cm–2 in Texas red oak (Quercus buckleyi Buckl.). Was content in Bur oak (Quercus macrocarpa Michx.) and Shumard oak (Quercus shumardii Buckl.) averaged 0.105 and 0.11 mg·cm–2, respectively. At harvest, Texas red oak plants treated with drought had the highest root-to-shoot dry weight ratio which averaged 3.1. In contrast, plants of Arizona ash (Fraxinus velutina Torr.) and California white oak that were frequently irrigated had the lowest root-to-shoot dry weight ratio. Drought did not affect stem elongation, total lamina area, leaf dry weight, and specific leaf weight. Abaxial leaf surfaces of Arizona ash were the most pubescent and averaged1836 trichomes/cm2. Drought-stressed plants of golden rain tree (Koelreuteria paniculata Laxm.) had the most negative midday leaf water potential, which averaged –2.5 MPa. Plants of Chinkapin oak (Quercus muehlenbergii Engelm.) that were irrigated frequently had the least negative predawn leaf water potentials. Predawn leaf water potentials tended to be more negative for Arizona ash and golden rain tree than for the oak species. These results suggest that some species of oak might perform well in landscapes prone to drought.

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Effects of landscape design and land use history on gas exchange parameters were evaluated for woody plants in a factorial site matrix of formerly desert or agricultural land uses and xeric or mesic residential landscape designs within the metropolitan area of Phoenix, Ariz. Remnant Sonoran Desert sites and an alfalfa agricultural field functioned as controls. Residential landscapes and the alfalfa field were irrigated regularly. Monthly instantaneous measurements of maximum leaf and stem carbon assimilation (A), conductance (gs), and transpiration (E) were made within three replicates of each site type during 1998 and 1999. Measurements were repeated monthly on three woody plant life forms: trees, shrubs, and ground covers. Assimilation fluxes were not related to former land use, but were lower for plants in xeric compared with those in mesic landscapes. Transpiration fluxes were higher for plants in formerly agricultural sites than in formerly desert sites, and were lower in xeric than in mesic landscape design. Compared with plants in residential landscapes, A and E fluxes were generally higher for plants in the agricultural control sites and were lower for plants at the desert control sites. Plant instantaneous transpiration efficiency (ITE = A/E) was higher in formerly agricultural sites than in formerly desert sites but was not affected by landscape design. Patterns of A, gs, and shoot temperature at irrigated sites suggest that maximum plant carbon assimilation was not limited by shoot conductance but was more responsive to shoot temperature. Similarities in patterns of ITE between plants in the different landscape design types suggest that xeric and mesic landscape plants do not differ in terms of water use efficiency.

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A proposed Center for Horticulture within the College of Agricultural and Environmental Sciences of The University of Georgia will target both Environmental Horticulture professionals and homeowners. To be headquartered at the Georgia Experiment Station in Griffin, Ga., with satellite units in Atlanta, Athens, Tifton, and Savannah, the Center will utilize advanced communications technology in developing and delivering educational outreach programs for clientele. Distance learning via fiber optics telecommunications will be used to provide educational short courses and seminars to clientele across the state. Distance imaging will be used for plant problem solving and plant identification. Newsletters, pest alerts, program announcements and other information will be sent electronically to clients via fax, e-mail, or the World Wide Web. Marketing of Georgia-grown crops will be a major thrust of the Center. A second component of the Center will be a public outreach unit, staffed by trained Master Gardeners, professional coordinator, and computer technician housed at the various satellite units. Citizens throughout the state will be able to phone one of the satellite units to get their gardening questions answered. Information will be sent directly to clients via fax, e-mail, or from the local county Extension agent when prompted via the computer to send the client an informational bulletin. A central server and database of information to support the Center will be maintained at the Georgia Experiment Station. The Center will utilize an interdisciplinary approach, involving teaching, research, and Extension personnel in responding to industry and consumer needs.

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Two tree species, Acer rubrum `October Glory' (October Glory red maple) and Quercus phellos (willow oak) were planted in Columbus, GA and Mobile, AL. Variables evaluated were location (park vs residential) and tree size (1.5 vs 3.0 inch caliper). Greater shoot elongation occurred with 1.5 inch red maples and willow oaks than with 3.0 inch caliper trees. First year growth differences were not related to photosynthesis, night respiration, leaf water potential, or foliar nitrogen levels. Little height or caliper change occurred with either species. Red maple shoot elongation was greater in Mobile than into Columbus. Growth was not affected by location within either city.

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Spanish moss (Tillandsia usneoides) samples were deployed at 36 locations in a 6 × 6-grid system in northeastern Texas during the summer months of 1989 and again in the winter months of 1990. Analytical methods, including inductively coupled plasma emission spectrometry (ICP) and neutron activation analysis (NAA), were used in analyzing samples for sulfur, selenium, arsenic, sodium, and aluminum. Concentrations of most elements in Spanish moss samples were much higher in summer than winter. The highest concentrations of sulfur were found in Van Zandt, Wood, Titus, and Bowie counties. These results suggest that on average sulfur stays in the region in which it was generated. Potassium and sodium were highly correlated with latitude and seem to originate from the Gulf of Mexico.

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Abstract

Two home vegetable gardens (77.4 and 58.3 m2) in Tucson, Ariz., yielded an average of 1.24 and 2.31 kg/m2 of produce per year over 3 and 2.5 years, respectively. Average net returns were $109 and $123 per year, $0.72 and $1.11 per hour, or $8.80 and $7.75 per dollar of water used. Thus, in the southwest desert, a weekly investment of 2-to-3 hours in a home garden can provide savings.

Open Access

The Univ. of Arizona Cooperative Extension home horticulture World Wide Web site for Maricopa County, “Environmentally responsible gardening and landscaping in the low desert,” provides the public with timely, research-based, regionally appropriate information. This delivery method enables self-service access to prepared text information and high-quality images that could not be economically distributed via traditional print methods, and interactive opportunities for submitting questions.

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We investigated gas-exchange response of norway maple and crabapple to the energy balance of turf, bark-mulch, and asphalt surfaces. In each surface stomatal conductance, leaf temperature (T1), and photosynthesis, were measured during two dawn-to-dusk studies concurrent with soil (To), top surface (Ta), and air temperature (Ta) measurements. Different properties affected the energy balance of each surface. Turf transpiration moderated To and Ts while low thermal conductivity of the mulch resulted in To similar to turf but Ts23C higher. Higher thermal conductivity of the asphalt resulted in higher To but Ts intermediate to mulch and turf surfaces. We did not detect differences in Ta, probably due to close proximity to one another that allowed substantial air mixing between treatments. Higher Ts increased longwave radiation flux that raised midday T1 of trees in the mulch and asphalt 3 to 8C higher than trees in the turf. Differences in T1 between the asphalt and mulch were minimal. Stomatal conductance declined with increasing leaf-to-air vapor pressure gradient in all trees, and was consistently lower for trees in the mulch and asphalt through the day due to larger gradients induced by higher T1. Midday photosynthesis was highest for trees in the turf and lowest for those in the mulch. Foliar interception of higher energy fluxes from mulch and asphalt surfaces apparently limited gas exchange in both species due to over-optimal leaf temperatures as compared to trees in the turf

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