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The effects of two rooting media [5 pine bark : 1 soil (v/v) and 5 Tufflite (a volcanic pumice) : 1 soil (v/v)] and (+ or -) phosphorus fertilizer [Ca(H2PO4)2H2O @ 6.58 g P per pot] on root architecture of Colorado mesquite (Prosopis alba Grieb. 'Colorado') were studied. Rooted cuttings were transplanted into 10-liter containers, topdressed with 45 g of 20N-0P-16.5K (IBDU slow release formulation) and 3 g Micromax micronutrient fertilizer, grown outdoors on black polyproplyene fabric, and irrigated daily to container capacity for three months. With or without P, specific root length was less for mesquite roots in Tufflite than for those in pine bark. Without P fertilizer, extended path length and root altitude were higher for roots grown in Tufflite than for those in pine bark. Adding P fertilizer decreased specific root length regardless of media type. In the pine bark medium, root altitude and extended path length were highest for trees fertilized with P; however, P fertilizer did not affect root altitude and lowered the extended path length when trees were grown in the Tufflite medium. These results indicate that roots were thicker and more branched in the Tufflite medium compared to pine bark and that P fertilizer caused a more herringbone branching pattern for mesquite roots when grown in pine bark, but resulted in a slightly more dichomatous branching pattern for roots when grown in Tufflite.

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Heightened awareness of ecological concerns have prompted many municipalities to promote water conservation through landscape design. In central Arizona, urban residential landscapes containing desert-adapted plant species are termed xeriscapes, while those containing temperate or tropical species and turf are termed mesoscapes. Research was conducted to ascertain landscape plant species diversity, tree, shrub, and ground cover frequency; landscape canopy area coverage; and monthly irrigation application volumes for xeric and mesic urban residential landscapes. The residential urban landscapes were located in Tempe and Phoenix, Ariz., and all were installed initially between 1985 and 1995. Although species composition of xeric and mesic landscapes was generally dissimilar, both landscape types had comparable species diversity. Mesoscapes had significantly more trees and shrubs and about 2.3 times more canopy area coverage per landscaped area than xeriscapes. Monthly irrigation application volumes per landscaped surface area were higher for xeriscapes. Even though human preference for xeric landscape plants may be ecological in principle, use of desert-adapted species in central Arizona urban residential landscape settings might not result in less landscape water use compared with mesic landscapes.

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Trees were grown for 2 years as a function of three container volumes (10, 27, and 57 liter) the first year and six shifting treatments (10 liter both years, 10 to 27 liter, 10 to 57 liter, 27 liter both years, 27 to 57 liter, or 57 liter both years) the second year when containers were spaced 120 cm on center, Height and caliper were greatest for magnolias grown in 27- or 57-liter containers both years. Caliper was greater for trees shifted from 10-liter containers to the larger container volumes compared to trees grown in 10-liter containers both years, Trees grown in 10-liter containers both years tended to have few roots growing in the outer 4 cm at the eastern, southern, and western exposures in the grow medium, During the second year, high air and growth medium temperatures may have been primary limiting factors to carbon assimilation during June and August. Using large container volumes to increase carbon assimilation and tree growth may be even more important when daily maximum air temperatures are lower during late spring or early fall compared to midsummer.

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Trees were grown for 2 years as a function of three container volumes (10, 27, and 57 liter) the first year and six shifting treatments (10 liter both years, 10 to 27 liter, 10 to 57 liter, 27 liter both years, 27 to 57 liter, or 57 liter both years) the second year when containers were spaced 120 cm on center, Height and caliper were greatest for magnolias grown in 27- or 57-liter containers both years. Caliper was greater for trees shifted from 10-liter containers to the larger container volumes compared to trees grown in 10-liter containers both years, Trees grown in 10-liter containers both years tended to have few roots growing in the outer 4 cm at the eastern, southern, and western exposures in the grow medium, During the second year, high air and growth medium temperatures may have been primary limiting factors to carbon assimilation during June and August. Using large container volumes to increase carbon assimilation and tree growth may be even more important when daily maximum air temperatures are lower during late spring or early fall compared to midsummer.

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Leucophyllum frutescens I. M. Johnst. (Texas sage) and Nerium oleander L. (oleander) shrubs grown for 2 years in the southwest United States under well-watered conditions in outdoor field plots were either sheared every 6 weeks or not pruned (control) to determine if frequent shearing had an effect on root growth and mycorrhizal colonization. During February and June of the second year after transplanting, leaf gas exchange, shoot and root growth, and arbuscular mycorrhizal fungi (AMF) colonization of shrubs were studied. Shearing reduced shrub volume of Texas sage and oleander by 84% and 82%, respectively. Leaf carbon assimilation (A) and conductance of both shrub taxa were stimulated by frequent shearing, especially during June. Shearing decreased root mass density (RMD) and root length density (RLD) of Texas sage but had no impact on RMD or RLD of oleander. Shearing decreased the length of Texas sage roots colonized by AMF but increased AMF colonization of oleander roots. Soil respiration and temperatures were less under all shrubs that were frequently sheared than those that were not pruned and were higher under all shrubs in June than in February. From these data we conclude that under well-watered conditions, the rejuvenative capacity and resilience of oleander to the practice of frequent shearing is greater than Texas sage and recommend that Texas sage shrubs not be frequently sheared in southwest landscapes.

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Four AM fungal isolates (Glomus sp.) were screened for effects on growth of `Volkamer' lemon (Citrus volkameriana Ten. and Pasq.) under well-watered conditions. Plants were inoculated with an isolate of AM fungi, or non-inoculated. Non-mycorrhizal plants received more phosphorus (P) fertilizer than mycorrhizal plants because mycorrhizae enhance P uptake. Mycorrhizal and non-mycorrhizal plants were grown in 8-liter containers for 3 months in a glasshouse. Plants were then harvested, and root length colonized by mycorrhizal fungi, leaf P concentration, and plant growth were determined. Root length colonized by AM fungi differed among isolates; control plants were non-mycorrhizal. Leaf P concentration was in the optimal range for all plants; however, plants colonized by Glomus mosseae Isolate 51C had higher leaf P concentration than non-mycorrhizal plants. Plants colonized by Glomus AZ112 had higher leaf P concentration than all other plants. All plants had similar canopy leaf area, shoot length, and shoot dry mass. Plants colonized with AM fungi, except Glomus mosseae Isolate 51C, had longer root length and greater root dry mass than non-mycorrhizal plants. All mycorrhizal plants had lower shoot:root dry mass and leaf area:root length ratios than non-mycorrhizal plants. Our results showed that under optimal P nutrition and well-watered conditions, AM fungal isolates differentially altered the morphology of citrus plants by stimulating root growth.

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Pepper (Capsicum sp. L.) seedlings were inoculated with either Glomus sp. AZ 112 (isolated from Wickman, Ariz.), Glomus intraradices Smith and Schneck (isolated from Santa Theresa, N.M.), a mixture of the two isolates, or a nonmycorrhizal control, and were grown for 8 weeks in a moderate (20.7 to 25.4C) or high temperature (32.1 to 38.0C) environment. Plants in moderate temperatures were larger and had lower specific soil respiration (Rspsoil) (μmol CO2/m2/s per gram root tissue dry weight) compared with those in high temperatures. In moderate temperatures, mycorrhizal plants were smaller and had higher Rspsoil than nonmycorrhizal controls. In high temperatures, plants inoculated with the isolate mixture grew nearly twice as large and had lower Rspsoil compared with plants inoculatedwith the individual isolates or the nonmycorrhizal control. Results suggest an improved carbon economy and a synergistic enhancement of pepper growth caused by the mixture of VAM fungal isolates that was not achieved by inoculation with single isolates alone under conditions of high-temperature stress.

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Pepper (Capsicum sp. L.) seedlings were inoculated with either Glomus sp. AZ 112 (isolated from Wickman, Ariz.), Glomus intraradices Smith and Schneck (isolated from Santa Theresa, N.M.), a mixture of the two isolates, or a nonmycorrhizal control, and were grown for 8 weeks in a moderate (20.7 to 25.4C) or high temperature (32.1 to 38.0C) environment. Plants in moderate temperatures were larger and had lower specific soil respiration (Rspsoil) (μmol CO2/m2/s per gram root tissue dry weight) compared with those in high temperatures. In moderate temperatures, mycorrhizal plants were smaller and had higher Rspsoil than nonmycorrhizal controls. In high temperatures, plants inoculated with the isolate mixture grew nearly twice as large and had lower Rspsoil compared with plants inoculatedwith the individual isolates or the nonmycorrhizal control. Results suggest an improved carbon economy and a synergistic enhancement of pepper growth caused by the mixture of VAM fungal isolates that was not achieved by inoculation with single isolates alone under conditions of high-temperature stress.

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Eureka lemon (Citrus limon L. `Eureka') trees were inoculated with ecotypes of VAM fungi isolated from either a subtropical desert (HVAM) or a temperate grassland (LVAM), and grown for five months at 40.5C/32.2C (high) or 29.4C/21.1C (low) day/night, respectively. Diurnal measurements of leaf carbon assimilation (A), transpiration (E) and stomatal conductance (gs) were then made with a portable photosynthesis system. At high temperatures, afternoon A, E and gs were highest for trees inoculated with LVAM and lowest for trees inoculated with HVAM. At low temperatures, afternoon A, E and gs were highest for trees inoculated with HVAM and lowest for trees inoculated with LVAM. Compared to controls, trees inoculated with HVAM and LVAM displayed rapid mid-day fluctuations in stomatal conductance. At low temperatures, water use efficiency (WUE) during the morning was lowest for trees inoculated with LVAM; whereas, afternoon WUE was not affected by HVAM or LVAM. HVAM and LVAM did not affect WUE at high temperatures. Results indicate that long-term physiological adaptations of lemon trees to temperature are uniquely affected by different VAM fungal ecotypes.

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Tomato (Lycopersicon esculentum Mill. `Heinz 1350 VF 402') seedlings were inoculated with populations of vesicular–arbuscular mycorrhizal (VAM) fungi collected from saline or nonsaline soil or remained nonmycorrhizal as a control. Plants then were salinated for 8 weeks at 1.0, 2.0, 5.0, or 10.0 dS·m–1 produced by dilutions of 1 m NaCl: 1 m CaCl2 in deionized water. Inoculation with VAM fungi from nonsaline soil enhanced shoot growth, while VAM fungi from saline soil suppressed shoot and root growth. Plants inoculated with VAM fungi from nonsaline soil and non-VAM control plants showed a quadratic increase in leaf Cl concentration in response to an increased salinity level, whereas plants inoculated with VAM fungi from saline soil showed a linear increase in leaf Cl concentration. Mycorrhizal-induced growth responses and changes in leaf Cl concentration were not associated with any apparent alterations in tomato plant P status. Although VAM fungi originating from saline soil did not promote plant growth, reduction in leaf Cl concentration mediated by these VAM fungi at moderate salinity levels may have beneficial implications for plant survival in saline soil.

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