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Brian H. Hurd, Rolston St. Hilaire, and John M. White

Residential landscapes are responsible for a large share of the water use of New Mexico communities. Water conservation plans and programs are being promulgated throughout New Mexico and the western U.S. as concern grows over the sufficiency and variability of present supplies, sustainability of current population growth rates, and desire for enhanced economic development. Household attitudes, choices, and behaviors ultimately underlie the success and performance of community water conservation programs. Homeowners in three New Mexico cities were surveyed concerning their attitudes and behavior toward water use, water conservation, and residential landscapes. Findings suggest that New Mexico's homeowners are mindful of the water resource challenges faced by communities, and are prepared to shoulder responsibility for stewarding the state's water resources. There is broad community support to limit traditional turfgrasses [e.g., kentucky bluegrass (Poa pratensis)] and to increase the areas planted to native, natural, and water-conserving landscapes; for example, 92% favored limiting turfgrass to less than 25% of the area around public buildings. Evidence showing that 40% are not “content” with their current landscape suggests that significant impediments remain and limit still greater adoption of water-conserving landscapes and subsequent potential for increased household water savings.

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Rolston St. Hilaire, William R. Graves, and Randall L. Small

Morphological distinctions between sugar maples and black maples are not consistently evident, and molecular assessment of genetic diversity is lacking for these taxa. We examined restriction-site polymorphisms in the ndhA intron of the chloroplast DNA (cpDNA) in populations of sugar maples and black maples representing their zones of allopatry and sympatry in eastern North America. Restriction-site analysis of the ndhA intron after digestion with HinfI and Sau3AI yielded no polymorphisms. Restriction digestion of the ndhA intron with TaqI revealed two cpDNA haplotypes that were neither geographically localized nor taxon specific. Although testing additional accessions of sugar maples and black maples for cpDNA variation will further elucidate patterns of genetic variation, our initial results suggest that the taxa are either exchanging genes or share an ancestral cpDNA polymorphism.

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Yahia Othman, Caiti Steele, Dawn VanLeeuwen, and Rolston St. Hilaire

For large fields, remote sensing might permit plant low moisture status to be detected early, and this may improve drought detection and monitoring. The objective of this study was to determine whether canopy and soil surface reflectance data derived from a handheld spectroradiometer can detect moisture status assessed using midday stem water potential (ψsmd) in pecan (Carya illinoinensis) during cyclic flood irrigations. We conducted the study simultaneously on two mature pecan orchards, one in a sandy loam (La Mancha) and the other in a clay loam (Leyendecker) soil. We were particularly interested in detecting moisture status in the −0.90 to −1.5 MPa ψsmd range because our previous studies indicated this was the critical range for irrigating pecan. Midday stem water potential, photosynthesis (A) and canopy and soil surface reflectance measurements were taken over the course of irrigation dry-down cycles at ψsmd levels of −0.40 to −0.85 MPa (well watered) and −0.9 to −1.5 MPa (water deficit). The decline in A averaged 34% in La Mancha and 25% in Leyendecker orchard when ψsmd ranged from −0.9 to −1.5 MPa. Average canopy surface reflectance of well-watered trees (ψsmd −0.4 to −0.85 MPa) was significantly higher than the same trees experiencing water deficits (ψsmd −0.9 to −1.5 MPa) within the 350- to 2500-nm bands range. Conversely, soil surface reflectance of well-watered trees was lower than water deficit trees over all bands. At both orchards, coefficient of determinations between ψsmd and all soil and canopy bands and surface reflectance indices were less than 0.62. But discriminant analysis models derived from combining soil and canopy reflectance data of well-watered and water-deficit trees had high classification accuracy (overall and cross-validation classification accuracy >80%). A discriminant model that included triangular vegetation index (TVI), photochemical reflectance index (PRI), and normalized soil moisture index (NSMI) had 85% overall accuracy and 82% cross-validation accuracy at La Mancha orchard. At Leyendecker, either a discriminant model weighted with two soil bands (690 and 2430 nm) or a discriminant model that used PRI and soil band 2430 nm had an overall classification and cross-validation accuracy of 99%. In summary, the results presented here suggest that canopy and soil hyperspectral data derived from a handheld spectroradiometer hold promise for discerning the ψsmd of pecan orchards subjected to flood irrigation.

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Emad Bsoul, Rolston St. Hilaire, and Dawn M. VanLeeuwen

Ecological traits such as an extensive range of natural distribution and tolerance to varying soil conditions, suggest that bigtooth maples (Acer grandidentatum Nutt.) could be popular landscape trees. But information on the tolerance of bigtooth maples to environmental stresses, such as drought, is virtually nonexistent. We studied physiological, growth and developmental traits of bigtooth maple plants from 15 trees native to Arizona, New Mexico, Texas, and Utah. Plants were grown in pots in a greenhouse and maintained as well-irrigated controls or exposed to drought and irrigated in cycles based on evapotranspiration. The ratio of variable to maximal fluorescence (Fv/Fm) was not different between drought-stressed and control plants, but the low Fv/Fm in plants designated as LM2 from the Lost Maples State Natural Area in Vanderpool, Tex., suggests these plants were relatively inefficient in capturing energy at PSII. Plants from another tree (LM5) originating from Lost Maples State Natural Area maintained similar predawn water potentials between drought-stressed and control plants after five cycles of drought. Plants from Dripping Springs State Park in Las Cruces, N.M., and those from LM2 had a strong, significant linear relationship between transpiration and stomatal conductance. Drought-stressed plants from Dripping Springs State Park, two plant sources from the Guadalupe Mountains in Salt Flat, Tex., designated as GM3 and GM4, and plants from trees designated as LM1 and LM2, had high relative growth rates and net assimilation rates. Drought-stressed plants from three of the four Guadalupe Mountain sources (GM1, GM3, GM4) had among the longest and thickest stems. Drought reduced shoot and root dry weight (DW). Although bigtooth maples showed several provenance differences in drought adaptation mechanisms, the lack of an irrigation effect on biomass allocation parameters such as root to shoot DW ratio and leaf area ratio implies that altered biomass allocation patterns may not be a common drought adaptation mechanism in bigtooth maples. Plants from selected provenances from the Guadalupe Mountains and Lost Maples State Natural Area in Texas, and to a lesser extent, provenances from Dripping Springs State Park in New Mexico might hold promise for selecting bigtooth maples for arid environments.

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Dawn M. VanLeeuwen, Rolston St. Hilaire, and Emad Y. Bsoul

Statistical analysis of data from repeated measures experiments with missing factor combinations encounters multiple complications. Data from asynchronous cyclic drought experiments incorporate unequal numbers of drought cycles for different sources and provide an example of data both with repeated measures and missing factor combinations. Repeated measures data are problematic because typical analyses with PROC GLM do not allow the researcher to compare candidate covariance structures. In contrast, PROC MIXED allows comparison of covariance structures and several options for modeling serial correlation and variance heterogeneity. When there are missing factor combinations, the cross-classified model traditionally used for synchronized trials is inappropriate. For asynchronous data, some least squares means estimates for treatment and source main effects, and treatment by source interaction effects are inestimable. The objectives of this paper were to use an asynchronous drought cycle data set to 1) model an appropriate covariance structure using mixed models, and 2) compare the cross-classified fixed effects model to drought cycle nested within source models. We used a data set of midday water potential measurements taken during a cyclic drought study of 15 half-siblings of bigtooth maples (Acer grandidentatum Nutt.) indigenous to Arizona, New Mexico, Texas, and Utah. Data were analyzed using SAS PROC MIXED software. Information criteria lead to the selection of a model incorporating separate compound symmetric covariance structures for the two irrigation treatment groups. When using nested models in the fixed portion of the model, there are no missing factors because drought cycle is not treated as a crossed experimental factor. Nested models provided meaningful F tests and estimated all the least squares means, but the cross-classified model did not. Furthermore, the nested models adequately compared the treatment effect of sources subjected to asynchronous drought events. We conclude that researchers wishing to analyze data from asynchronous drought trials must consider using mixed models with nested fixed effects.

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Jane E. Spinti, Rolston St. Hilaire, and Dawn VanLeeuwen

We surveyed homeowners with residential landscapes in Las Cruces, N.M., to determine design features participants valued in their landscapes, their attitudes toward the landscape use of desert plants and opinions on factors that would encourage respondents to reduce landscape water use. We also determined whether the willingness to use desert plants in their landscapes related to the length of residency in the southwestern United States. At least 98% of respondents landscaped to enhance the appearance of their home and increase their property value. About half (50.6%) of the participants strongly agreed or agreed that the main reason to landscape was to display their landscape preferences. Many participants indicated they would use desert plants to landscape their front yard (80.3%) and back yard (56.3%), but relatively lower percentages of participants actually had desert landscapes in their front yard and back yard. Regardless of their property value, respondents were more likely to use desert plants in their backyard the shorter their stay in the desert. Data revealed that participants rank water shortages as the factor that would most likely cause them to reduce the amount of water they applied to their landscapes. We conclude that homeowners report willingness to use desert plants but desert-type landscapes are not a widespread feature of managed residential landscapes. Furthermore, water shortages and the length of time respondents spent in a desert environment would most likely influence water use in their landscapes.

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Malik G. Al-Ajlouni, Dawn M. VanLeeuwen, and Rolston St. Hilaire

Linking an urban residential landscapes type to a specific landscape water budget is important to water resource management in a desert environment. Yet, no research that we are aware of has effectively associated a specific water budget with a quantitatively determined urban landscape type. The objective of this research was to determine whether a landscape water budget and residential urban landscape type could be related. We previously quantitatively classified urban residential landscapes in the desert environment of Las Cruces, NM, into hard-surface shade-structure, mulch, hard-surface, hard-surface-mulch, mulch tree, turf mulch, turf, tree mulch turf, and turf tree landscape types. In this study, we determined water budget, landscape coefficient, and the portion of the coverage of irrigated and nonirrigated elements for each landscape type. Landscape types in Las Cruces grouped into four distinct water budget groups: no-water, low-, moderate-, and high-water budget. Because of the heterogeneity of the coefficients for grass, plants, and water surfaces that constituted it, the landscape coefficient correlated weakly (r 2 = 0.3) with the water budget. Coverage of the irrigated elements correlated highly (r 2 = 0.95) with the water budget. Our results suggest that the coverage of irrigated elements in a desert urban landscape is a major driver of landscape water budgets.

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Emad Bsoul, Rolston St. Hilaire, and Dawn M. VanLeeuwen

Although bigtooth maple (Acer grandidentatum Nutt.) is an ornamental plant that might thrive in managed landscapes in arid and semiarid regions, little information on the drought tolerance of bigtooth maples appears to be available. We studied water relations, plant development, and carbon isotope composition of bigtooth maples indigenous to New Mexico, Texas, and Utah that were field-grown in New Mexico using a pot-in-pot nursery production system. Plants were maintained as well-irrigated controls or irrigated after the weight of pots decreased by 35% due to evapotranspiration. Bigtooth maples subjected to drought had more negative predawn leaf water potentials (−0.76 MPa) than the plants in the control treatment (−0.64 MPa). Drought did not affect midday leaf water potential of seed sources. Trees native to the Lost Maples State Natural Area in Vanderpool, TX (designated LMP5), had the greatest leaf area (1236 cm2) among plants from all sources, while those native to Logan Canyon in Cache County, UT (designated UW2), had among the smallest leaf area (216 cm2). Leaf area ratio (LAR) was highest in plants from LMP5 (24.23 cm2·g−1), which suggests that they have potential for more carbon assimilation than the other plants tested. Plants from LMP5 had the highest leaf area/xylem diameter ratio (135 cm−2·mm−1). This ratio was 5.8 times higher than that of UW2, which had among the lowest leaf area/xylem diameter ratios. The high leaf area/xylem diameter ratio of LMP5 plants relative to UW2 plants indicates that LMP5 plants had a larger surface area of tissues that transpire relative to those that transport water. Treatment did not affect stomatal conductance (g S) or transpiration, but g S and transpiration were positively correlated for both drought-stressed (r 2 = 0.801) and well-irrigated plants (r 2 = 0.759). Plants from New Mexico (designated DS) had the lowest transpiration rate (2.32 mmol·m−2·s−1), lowest g s (52.1 mmol·m−2·s−1), largest xylem diameter (11 mm), and had among the largest shoot dry weight (DW) and plant height. Plants did not differ either among sources or between treatments in the ratio of variable to maximal fluorescence (mean = 0.64), relative water content (averaged 57%), specific leaf weight, stem DW, root DW, and plant DW. Carbon isotope discrimination (Δ) averaged −26.53‰ and did not differ among plant sources or irrigation treatments. This suggests that Δ might not be effective in screening bigtooth maples for drought tolerance. Low transpiration rate, g S, and high shoot dry weight in DS plants and traits, such as a high LAR in plants from LMP5, suggest that plants selected from these provenances might effectively endure deficit irrigation.

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Joshua Sherman, Richard J. Heerema, Dawn VanLeeuwen, and Rolston St. Hilaire

Southwestern U.S. pecan [Carya illinoinensis (Wangenh.) K. Koch] orchard soils are typically alkaline and calcareous, making micronutrients such as manganese (Mn) poorly available for root uptake. Manganese is essential to the light reactions of photosynthesis (Pn), but the level of leaf Mn for optimum Pn in pecan is unknown. Our objective was to characterize the relationships of foliar Mn fertilizer applications and leaf Mn nutrition with Pn over a broad range of leaf Mn concentrations. Two experiments were conducted from 2011 to 2012 (Expt. 1) and in 2013 (Expt. 2) in immature, nonbearing ‘Pawnee’ and ‘Western’ pecan orchards near Las Cruces, NM. To create differential leaf tissue Mn concentrations, four Mn spray concentrations were applied foliarly: 0.00, 0.34, 0.68, and 1.3 g Mn/L (Control, Low, Medium, and High, respectively). In Expt. 2, we added a higher Mn concentration (2.7 g Mn/L). Repeated measurements of leaf Pn were made beginning 1 week following a Mn application using a portable Pn system. Across treatments in both studies, final leaf Mn concentrations ranged from 21 to 1488 µg·g−1. Leaves treated with 0.68 g Mn/L had higher Pn than the other treatments in each experiment. In 2013, Pn rates of the leaves treated with 0.68 g Mn/L increased 7.1% and 10.4% over the Control for ‘Pawnee’ and ‘Western’, respectively. Our data confirm an association between leaf tissue Mn and Pn; the leaf tissue Mn concentration at which Pn rates are optimized in immature pecan trees was estimated to be 151.64 (±17.3 se) µg·g−1 Mn.

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Rolston St. Hilaire, Carlos A. Fierro Berwart, and Carlos A. Pérez-Muñoz

Mussaendas (Mussaenda spp.) are ornamental shrubs, and some cultivars are difficult to root. This study was conducted to explore how adventitious roots initiate and develop in the cultivar Rosea and to determine if anatomical events are associated with difficulty in rooting stem cuttings. Stem cuttings were treated with 5, 10, 15 mmol IBA, or distilled water, and sampled every 2 days over 26 days to observe adventitious root formation and development. Adventitious roots initiated from phloem parenchyma cells. Cuttings treated with 15 mmol IBA had a mean of 18 root primordia per basal 1 cm of cutting after 10 days. Primordia were absent in nontreated cuttings at 10 days. These results suggest that nontreated cuttings are difficult to root because few primordia are produced. Chemical name used: 1H-indole-3-butyric acid (IBA).