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Abstract

Several field-established broadleaved and coniferous evergreen shrubs and 2 ground covers, Carpobrotus sp. and Hedera helix L., survived, and maintained adequate appearance with greatly restricted growth, without supplemental irrigation from May through September on deep soils at San Jose and Santa Ana, CA. Eugenia uniflora L. at Santa Ana required 1 irrigation (9.4 cm) in July to insure survival and both Coprosma baueri Endl. and Cotoneaster pannosa Franch. required 1 or 2 irrigations to insure adequate foliar density. At San Jose only Nerium oleander L. lost leaves or lost leaf color and turgidity in the non-irrigated plot. The plantings at both locations had viable roots down to 1 m and probably deeper. Non-irrigated and bimonthly irrigated soils were at or below the permanent wilting percentage down to 1 m. Leaf temp in the non-irrigated Xylosma congestum (Lour.) Merr. and Carpobrotus plots were 6 and 15° C, respectively, above ambient and yet no permanent foliar injury was observed. We suggest that leaf temp may be used to measure critical water stress in landscape plants. Our findings indicate that substantial savings in water costs and in controlling vegetative overgrowth can be realized by reducing irrigation frequency in established landscape plantings.

Open Access

The popularity of ornamental grasses for use in urban landscapes, parks, median strips, parking lot borders, and for erosion control on slopes has increased in recent years ( Loram et al., 2008 ; Wilson and Knox, 2006 ). This increase is partially

Free access

Although water conservation programs in the arid southwestern United States have prompted prudent landscaping practices such as planting low water use trees, there is little data on the actual water use of most species. The purpose of this study was to determine the actual water use of two common landscape tree species in Tucson, Ariz., and water use coefficients for two tree species based on the crop coefficient concept. Water use of oak (Quercus virginiana `Heritage') and mesquite (Prosopis alba `Colorado') trees in containers was measured from July to October 1991 using a precision balance. Water-use coefficients for each tree species were calculated as the ratio of measured water use per total leaf area or per projected canopy area to reference evapotranspiration obtained from a modified FAO Penman equation. After accounting for tree growth, water-use coefficients on a total leaf area basis were 0.5 and 1.0 for oak and mesquite, respectively, and on a projected canopy area basis were 1.4 and 1.6 for oaks and mesquites, respectively. These coefficients indicate that mesquites (normally considered xeric trees) use more water than oaks (normally considered mesic trees) under nonlimiting conditions.

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Identification of tree taxa that can thrive on reduced moisture regimes mandated by xeriscape programs of the southwest United States could be facilitated if responses to drought of those taxa are determined. Leaf water relations, plant development, and cuticular wax content of seven taxa maintained as well-irrigated controls or exposed to drought and irrigated based on evapotranspiration were studied. Leaf water potential of drought-stressed Fraxinus velutina Torr. (Arizona ash), Koelreuteria paniculata Laxm. (golden rain tree), Quercus macrocarpa Michx. (bur oak), and Quercus muehlenbergii Engelm. (chinkapin oak) were lower at predawn than the controls. Drought-stressed plants of F. velutina, K. paniculata, and Quercus lobata Née (California white oak) had more negative midday water potential than the control plants. Drought reduced stomatal conductance to as little as 17%, 23%, and 45% of controls in F. velutina, K. paniculata, and Q. macrocarpa, respectively. Drought-stressed plants of F. velutina, K. paniculata, Q. macrocarpa, and Q. muehlenbergii had reduced transpiration rates. Fraxinus velutina had both the highest net assimilation rate (NAR) and relative growth rate (RGR) regardless of irrigation treatment. Mean specific leaf weight (dry weight (DW) of a 1-cm2 leaf disc divided by the weight), trichome density, stomatal density, leaf thickness, and cuticular wax content varied among species but not between irrigation treatments. Leaves of Q. buckleyi Buckl. (Texas red oak) had one of the highest stomatal densities, and also had leaves which were among the waxiest, most dense, and thickest. Abaxial leaf surfaces of F. velutina were the most pubescent. Across species, drought led to lower ratios of leaf surface area to root DW, and leaf DW to root DW. Quercus buckleyi plants subjected to drought had the highest root to shoot DW ratio (3.1). The low relative growth rate of Q. buckleyi might limit widespread landscape use. However, Q. buckleyi may merit increased use in landscapes on a reduced moisture budget because of foliar traits, carbon allocation patterns, and the relative lack of impact of drought on plant tissue water relations.

Free access

Containerized crape myrtle (Lagerstroemia indica L. × Lagerstroemia fauriei Koehne `Tonto') plants were grown for 9 months under various nitrogen fertility regimes, and then transplanted to a sandy loam soil with minimal management to evaluate their landscape establishment and growth performance. During the nursery phase plants were irrigated, except over an overwintering period, with complete nutrient solutions differing in applied N concentration, ranging from 15 to 300 mg·L-1. By 16 weeks after transplanting (WAT) into the landscape soil, plant biomass was significantly higher in the plants that had been grown with higher N supplies and had been among the smallest at transplant. Such plant growth response was linearly and positively correlated to plant N status at transplant. Plant shoot to root ratio and tissue N, Ca, S, and Fe concentrations, which had been significantly affected by the N fertilization regime in the nursery, equalized over time after transplant, with no significant differences observed among treatments by 16 WAT. Flowering response in the landscape was delayed in plants originally grown with the higher N supplies. Plant survival and establishment per se were not affected by treatments; no plants were lost, and aside from the differences in size and flower timing, all plants were considered aesthetically similar.

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Large (≈5 m high) Quercus virginiana Mill. (live oak) trees produced in 0.64-m-diameter in-ground fabric containers were root pruned or not root pruned inside containers before harvest. Harvested trees were grown in two sizes of polyethylene containers for 10 months, then transplanted into a landscape. Water potential (ψT) of small branches (<4 mm in diameter) was measured diurnally during containerization and for 1 year in the landscape. Root pruning had no influence on postharvest survival. Neither root pruning nor container size affected tree water status during containerization or in the landscape. All surviving trees recovered from transplant shock following harvest after 16 weeks in a container, independent of treatment. In the landscape, 35 weeks of daily irrigation were required before dusk ψT declined to within 0.1 MPa of predawn values, a result indicating alleviation of transplant shock. Trunk growth rate during containerization was highest in larger containers. However, in the landscape, root pruning and small containers were associated with higher trunk growth rate. Tree water status during containerization and in the landscape is discussed.

Free access

Abstract

A study of seasonal and landscape effects on residential water application rates used to maintain meso-phytic plants in Las Cruces, New Mexico showed a positive significant correlation between water applied and landscape area maintained. However, only one-half of the variation in water applied was accounted for in the analysis. In 2 years, about 40% more water was applied than the estimated requirement. The principal reason for excessive water use appeared to be consumers’ lack of knowledge about plant water requirements.

Open Access

Shoot and root growth were measured on Chinese juniper (Juniperus chinensis L. `Torulosa', `Sylvestris', `Pfitzeriana', and `Hetzii') 1, 2, and 3 years after planting from 1l-liter black plastic containers. Mean diameter of the root system expanded quadratically, whereas mean branch spread increased linearly. Three years after planting, root spread was 2.75 times branch spread, and roots covered an area 5.5 times that covered by the branches. Percentage of total root length located within the dripline of the plants remained fairly constant for each cultivar during the 3 years following planting. Root length density increased over time but decreased with distance from the trunk. During the first 2 years after planting, shoot mass increased faster than root mass. In the 3rd year, the root system increased in mass at a faster rate than the shoots. Root length was correlated with root weight. Root spread and root area were correlated with trunk cross-sectional area, branch spread, and crown area.

Free access

Research was conducted to investigate how energy balance of bark mulch and turf surfaces influence gas exchange and growth of recently transplanted trees. On several occasions over a 3-year period, stomatal conductance and leaf temperature were measured throughout the day on `Emerald Queen' Norway maple (Acer platanoides L.) and `Greenspire' littleleaf linden (Tilia cordata Mill.) trees growing over each surface. Tree water loss was estimated using a general transport flux equation applied to the tree crown apportioned between sunlit and shade layers. Microclimate variables were measured over each surface with a permanent weather station. Tree growth data were collected at the end of each growing season. Soil heat flux data revealed that a greater portion of incoming radiation was prevented from entering the soil below mulch than below turf. Due to this insulating effect, and consequent lack of evaporative cooling, mulch surface temperature was greater, and emitted more longwave radiation, than turf. Leaves over mulch intercepted more longwave radiation, had greater leaf temperature, and greater leaf-to-air vapor pressure difference than leaves over turf. As a result, leaves over mulch had greater stomatal closure than leaves over turf. Estimated tree water loss varied between surface treatments and with climatic conditions. Trees over turf had greater shoot elongation and leaf area than trees over mulch. These data suggest that gas exchange and growth of recently transplanted trees in an arid climate may be reduced if planted over nonvegetative, urban surfaces.

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Nutrient release from Nutricote Type 100 (100-day N release; 16N-4.4P-8.1K), and from a 1:3 mixture of Nutricote Type 40 (40-day N release; 16N-4.4P-8.1K) and Type 100 was affected by time and temperature. The Type 40/100 mixture released nutrients more rapidly over a 5 to 35C range in laboratory studies. Seasonal growth of containerized cotoneaster (Cotoneaster dammeri C.K. Schneid `Coral Beauty') and juniper (Juniperus horizontalis Moench. `Plumosa Compacta') increased with increasing application rates of either Nutricote Type 100 or a 1:3 mixture of Type 40/100 over the range 2-10 kg·m-3. Between 25 June and 27 July, cotoneaster grew more rapidly in media with Type 40/100 Nutricote, but by the end of the season (27 Sept.), fertilizer type showed no effect on plant dry weight. Shoot N was higher in cotoneaster plants grown with Type 40/100 Nutricote than with the Type 100 formulation during the first 2 months of growth, reflecting the more rapid release and uptake of N from the mixture. During the last month the situation was reversed, as nutrients from the Type 40/100 mixture were depleted. Potassium and P shoot concentrations were not affected by fertilizer type. Juniper growth and shoot concentrations of N, K, and P were not affected by fertilizer type at any time during the season. The results provided no evidence that seasonal growth could be enhanced in either cotoneaster (grows rapidly) or juniper (slower growing) by mixing rapid and more slowly releasing types of Nutricote.

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