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Chris A. Martin

This study evaluated the influence of social economic rank (SER) and neighborhood and park age on the composition and place of origin of trees in residential neighborhoods and embedded small urban parks in Phoenix, Ariz. During 2000 and 2001, trees were surveyed within an array of 16 residential neighborhoods and embedded small urban parks that spanned a range of socioeconomic rank (SER) and age. Parks were embedded within residential neighborhoods of similar density across three SER classifications, high, moderate, or low. Neighborhoods and parks ranged in age from about 1947 to 1997. Counts of all trees in each park were made and neighborhood tree composition was approximated by tree counts along four transects, distributed away from each park along streets in a northerly, easterly, southerly, or westerly direction, respectively. Transect widths extended about the depth of a front yard residence on both sides of the street. Park and surrounding neighborhood tree composition was calculated as total frequency (abundance) and taxa frequency (diversity) per hectare of landscape surface area. Tree abundance in parks was highest when surrounded by neighborhoods of high SER. Neighborhoods of high SER had greater tree diversity than neighborhoods of low SER. Distinct patterns of tree origin, dictated by both classifications of SER and age, were found. Overall, trees in residential neighborhoods and embedded parks tended to be indigenous to arid regions of North America, South America, Australia, south Asia, and China.

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Chris A. Martin and Dewayne L. Ingram

A three-dimensional computer model was developed to simulate numerically the thermal environment of a polyethylene container-root medium system. An energy balance was calculated at the exterior container wall and the root medium top surface. Thermal energy exchanges at the system's boundaries were a function of radiation, convection, evaporation, and conduction energy flaxes. A forward finite difference form of a transient heat. conduction equation was used to calculate rates of temperature changes as a result of thermal energy exchanges at the system's boundaries. The χ2“goodness-to-fit” test was used to validate computer-generated values to actual measured temperature data. Probabilities for the null hypothesis of no association ranged from P = 0.45 (Julian day 271), to P = 0.81 (Julian day 190), with P ≥ 0.70 on nine of 10 validation days in 1989. Relative to net radiation and convection, conduction and evaporation had little effect on thermal energy exchanges at the root medium top surface during sunlight hours. The rate of movement of thermal energy (thermal diffusivity) was slower and generally resulted in lower temperatures in a pine bark medium than in a pine bark medium supplemented with sand when volumetric water content (VMC) ranged from 0.25 to 0.45.

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Chris A. Martin and Jean C. Stutz

A distance learning course called Southwest Home Horticulture was developed and implemented at Arizona State University using video and Internet technologies to give nonhorticulture students an overview of urban horticulture in the southwestern United States. Fourteen, one-half-hour video programs about topics in southwestern residential landscaping, plants materials and landscape best-management practices were produced in ≈800 working hours. The video programs are now telecast weekly, each academic semester, on the regional public television station and the educational channel of several cable television systems. We found that students who enrolled in the course were most likely to tape the programs on a video cassette recorder and watch them at their own convenience, one to three times. A World Wide Web (Web) site on the Internet was developed as a supplement to the video programs. The Web site was organized into a modular format giving students quick access to auxiliary course-related information and helpful resources. When asked, ≈90% of the students indicated that the Web site was a helpful supplement to the video programs. Use of video and Internet technologies in tandem has enabled nonhorticulture major students to learn about home horticulture in an asynchronous or location and time independent fashion.

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Matthew W. Fidelibus and Chris A. Martin

Four AM fungal isolates (Glomus sp.) from disparate edaphic conditions were screened for effects on leaf gas exchange of `Volkamer' lemon (Citrus volkameriana Ten. and Pasq.) plants of similar size under conditions of increased soil water deficit stress and recovery from stress. Mycorrhizal and non-mycorrhizal plants were grown in 8-L containers for 10 weeks under well-watered conditions in a glasshouse and then subjected to three consecutive soil-drying episodes of increased severity (mean soil water tension reached –0.02, –0.06, and –0.08 MPa, respectively). Gas exchange measurements were made on the last day of each soil-drying episode. Plants were irrigated after each soil-drying episode, and measurements were repeated on the following 2 recovery days, when soil remained moist. All measurements were made at mid-day with a LI-COR 6200 portable photosynthesis system. The effect of AM fungi on leaf gas exchange fluxes varied depending on the isolate and the intensity of soil water stress. Leaf gas exchange fluxes always were highest for plants colonized by Glomus mosseae (Nicol. & Gerde.) isolate 114C, except during the third soil-drying episode, when all mycorrhizal plants had similar, and lower, gas exchange fluxes compared with non-mycorrhizal plants. During recovery from the third soil-drying episode, Glomus mosseae isolate 51C had lower leaf gas exchange fluxes compared with all other plants. Our results show that AM fungi can alter leaf gas exchange fluxes of citrus, under conditions of optimal P nutrition, in an isolate-specific manner.

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Chris A. Martin and Jean C. Stutz

Sour orange (Citrus aurannum L.) seedlings were inoculated with geographic isolates of an endomycorrhizal fungus, Glomus intraradices Smith and Schneck, from a xeric (New Mexico) or mesic (Florida) climate or not inoculated as controls, and were grown for 5 months under high (soil water potential more than or equal to –0.1 MPa, irrigated once every 3 days) or low (more than or equal to –1.0 MPa, irrigated once every 12 to 15 days) irrigation frequency regimens. Similar leaf P concentrations were achieved in all plants by giving more P fertilizer to nonmycorrhizal plants than mycorrhizal plants. Plants inoculated with the xeric isolate had more arbuscules and fewer vesicles than those inoculated with the mesic isolate. Mycorrhizal fungi had little affect on plant growth under high irrigation frequency. Low irrigation frequency reduced plant growth compared with high irrigation frequency. Under low irrigation frequency, shoot and root growth increased for mycorrhizal plants; however, the magnitude of increase of shoot growth was greatest for plants inoculated with the xeric isolate. Additionally, low irrigation frequency was associated with a dramatic decrease in vesicle formation in roots inoculated with the mesic isolate. This study showed that sour orange plants especially benefited from inoculation with an isolate from a xeric climate under low irrigation frequency, independent of P nutrition.

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Chris A. Martin and Dewayne L. Ingram

Root growth of Magnolia grandiflora Hort. `St. Mary' was studied for 16 wk after an 8-wk exposure period to 30°, 34°, 38°, or 42°±0.8°C root-zone temperature (RZT) treatments applied 6 hr daily, Immediately after the RZT treatment period, total root length was similar for trees exposed to 30°, 34°, and 38°C and was reduced 45% at 42° compared to 38°C. For weeks eight and 18 of the post-treatment period, response of total root length to RZT was linear. Total root length of trees exposed to 28°C was 247% and 225% greater than those exposed to 42°C RZT at week eight and 16, respectively. Root dry weight from the 42°C RZT treatment was 29% and 48% less than 38° and 34°C RZT treatment, respectively, at week eight. By week 16, root dry weight as a function of RZT had changed such that the 42°C RZT was 43% and 47% less than 38° and 34°C RZT, respectively. Differences in root growth patterns between weeks eight and 16 suggest that trees were able to overcome the detrimental effects of the 38°C treatment whereas growth suppression by the 42°C treatment was still evident after 16 wk. Previous exposure of tree roots to supraoptimal RZT regimens may have long-term implications for suppressing growth and lengthening the establishment period of trees in the landscape,

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Chris A. Martin and Dewayne L. Ingram

Root growth of Magnolia grandiflora Hort. `St. Mary' was studied for 16 wk after an 8-wk exposure period to 30°, 34°, 38°, or 42°±0.8°C root-zone temperature (RZT) treatments applied 6 hr daily, Immediately after the RZT treatment period, total root length was similar for trees exposed to 30°, 34°, and 38°C and was reduced 45% at 42° compared to 38°C. For weeks eight and 18 of the post-treatment period, response of total root length to RZT was linear. Total root length of trees exposed to 28°C was 247% and 225% greater than those exposed to 42°C RZT at week eight and 16, respectively. Root dry weight from the 42°C RZT treatment was 29% and 48% less than 38° and 34°C RZT treatment, respectively, at week eight. By week 16, root dry weight as a function of RZT had changed such that the 42°C RZT was 43% and 47% less than 38° and 34°C RZT, respectively. Differences in root growth patterns between weeks eight and 16 suggest that trees were able to overcome the detrimental effects of the 38°C treatment whereas growth suppression by the 42°C treatment was still evident after 16 wk. Previous exposure of tree roots to supraoptimal RZT regimens may have long-term implications for suppressing growth and lengthening the establishment period of trees in the landscape,

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Chris A. Martin and Richard L. Garcia

Eureka lemon (Cirrus limon L. `Eureka') trees were grown in factorial combinations of low (L) or high (H) temperature [day/night temperature regimens of 29.4C/21.1C or 40.5C/32.2C] and ambient (C380) or enriched (C680) atmospheric CO2 concentrations [380 umol mol-1 or 680 umol mol-1, respectively]. After growth under these conditions for 5 months, morning and afternoon leaf carbon assimilation measurements were made with a temperature-controlled cuvette attached to a portable photosynthesis system. Net (P3) and gross (Pg) photosynthesis were measured at 30 umol mol-1 intervals as leaves were exposed to cuvette CO2 drawndowns from 700 to 300 umol mol-1 at 21% and 1% O2, respectively. Photorespiration (Rp) was estimated as the difference between Pg and Pn. Generally, Rp increased as cuvette CO2 decreased. Morning and afternoon Rp of leaves adapted to LC380 conditions were similar. Morning Rp was higher than afternoon Rp for leaves adapted to LC680 conditions. Morning Rp was higher for leaves adapted to HC380 conditions as compared to HC680-adapted leaves. In contrast, afternoon Rp was higher for leaves adapted to HC680 conditions than for H&,-adapted leaves.

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Chris A. Martin and Dewayne L. Ingram

Computer modeling was used to study the effect of container volume and shape on summer temperature patterns for black polyethylene nursery containers filled with a 4 pine bark: 1 sand (v/v) rooting medium and located in Phoenix, Ariz. (lat. 33.5°N, long. 112°W) or Lexington, Ky. (lat. 38.0°N, long. 84.4°W). For both locations, medium temperatures were highest at the east and west container walls, halfway down the container profile, regardless of container height (20 to 50 cm) or volume (10 to 70 liters). The daily maximum medium temperature (Tmax) at the center was lower and occurred later in the day as container volume was increased because of an increased distance to the container wall. For both locations, predicted temperature patterns in rooting medium adjacent to the container wall decreased as the wall tilt angle (TA) increased. Predicted temperature patterns at the center of the container profile were lowered in response to the interaction of increased container height and wall TA. As container height decreased, the container wall TA necessary to lower center Tmax to ≤ 40C increased; however, the required increase in TA was greater for Phoenix than for Lexington, principally because of higher ambient air temperatures.

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Chris A. Martin and L. Brooke McDowell

Seedlings of Olneya tesota A. Gray (desert ironwood) were grown in 12-L containers filled with a peatmoss and pumice substrate (1:1 v/v) for 3 months under simulated summer or winter Sonoran Desert conditions in a walk-in growth chamber. Growth room irradiance (550 mmol•m-2•s-1) was provided with an even mixture of mercury vapor and high-pressure sodium high-intensity discharge lamps. Growth room air temperature and relative humidity were ramped hourly to approximate typical summer or winter weather conditions based on mean seasonal climatological data for Phoenix, Ariz. For simulated summer conditions, maximum/minimum air temperature range was 40/28 °C and maximum/minimum relative humidity range was 25%/12%. Photoperiod was 16 h. For simulated winter conditions, maximum/minimum air temperature and relative humidity were 20/5 °C and 80%/35%, respectively. Photoperiod was 10 h. After 2 months, desert ironwood root systems were cleaned of substrate by floatation in a water bath, pruned to a length of 15 cm, repotted, and then grown for an additional month under the same conditions. Only 41% of desert ironwood survived root pruning under summer conditions compared with a 100% survival rate under winter conditions. For surviving desert ironwood, shoot and root extension growth was significantly greater under summer conditions.