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.
Dawn M. VanLeeuwen, Rolston St. Hilaire, and Emad Y. Bsoul
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.
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.
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.
Rolston St. Hilaire, Theodore W. Sammis, and John G. Mexal
We integrated the construction and operation of hoop houses into a general education course to provide students with basic agriculture skills such as basic agricultural construction, greenhouse crop production, and greenhouse environmental data collection, while immersing them in an experiential learning environment. Students in the class constructed three 12 × 15-ft hoop houses, installed an irrigation system and climate data acquisition system, and grew radish (Raphanus sativus ‘Cherry Belle’) and lettuce (Lactuca sativa ‘Black-Seeded Simpson’) within each hoop house. At the end of the exercise, 86% of students agreed that they knew the basic techniques of hoop house construction, and 89% agreed that they understood the practical application of building a hoop house. More instruction on calculating crop fertilizer requirements would benefit students because only 43% of students agreed or strongly agreed that they understood how to compute crop fertilizer requirements. Climate data demonstrated that air temperature within the unvented hoop houses exceeded the optimal growing temperature for lettuce and radish. We conclude that construction and operation of hoop houses provided practical agricultural skills in an experiential learning environment while revealing subject areas that warrant further instruction.
Rolston St. Hilaire, Dawn M. VanLeeuwen, and Patrick Torres
We surveyed homeowners with residential landscapes in Santa Fe, NM, to determine their attitudes toward high desert plants and to assess their preferences for urban landscapes and water conservation strategies in a high desert urban environment. While there was low acceptance for the traditional turf lawn, 64% of residents agreed that high desert plants provided the variety they needed in their residential landscapes and 92% of residents would use high desert plants to landscape their front yard. Homeowners had a strong preference for retaining their current desert landscapes and converting traditional landscapes to high desert-adapted landscapes. Logistic regression revealed a negative relationship between length of residency in the southwestern United States and the willingness to use high desert plants. When homeowners who irrigated their landscape were asked whether water shortages, environmental concerns, information on water, city regulations, high water bills, or water rate increases would cause them to use less water on their landscapes, the highest level of agreement (94%) was for water shortages. Eighty-eight percent of respondents agreed that they liked any type of landscape that contains interesting features and is well planned. We conclude that homeowners have a preference for desert-adapted landscapes and agree that high desert plants provide an adequate palette of plants for urban landscapes. Additionally, the length of residency in the southwestern U.S. and the possibility of water shortages have the potential to impact water conservation strategies in high desert urban landscapes.
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.
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.
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.
Richard J. Heerema, Dawn VanLeeuwen, Rolston St. Hilaire, Vince P. Gutschick, and Bethany Cook
Photosynthetic function in nut trees is closely related to nitrogen (N) nutrition because much of tree N is held within the leaf photosynthetic apparatus, but growing fruit and seeds also represent strong N sinks. When soil N availability is low, nut trees remobilize and translocate N from leaves to help satisfy N demand of developing fruit. Our objective was to describe shoot-level impacts of pecan [Carya illinoinensis (Wangenh.) K. Koch.] fruiting on leaf N and photosynthesis (Pn) during kernel fill under a range of tree N statuses. Our study was conducted in a mature ‘Western’ pecan orchard near Las Cruces, NM. In 2009, 15 trees showing a range of N deficiency symptom severity were grouped according to leaf SPAD into low, medium, and high N status categories. Differential N fertilizer rates were applied to the soil around high and medium N trees to accentuate differences in N status among the three categories. Light-saturated leaf Pn was measured on fruiting and non-fruiting shoots during kernel fill in 2009 and 2010. After measurement of Pn, the leaflet and its leaflet pair partner were collected, dried, and analyzed for tissue N. Leaf N concentration was significantly lower on fruiting shoots than non-fruiting shoots on all three sampling dates. The tree N status main effect was also significant, whereas the two-way interaction of shoot fruiting status and tree N status was not. Photosynthesis of leaves on fruiting shoots was significantly lower than that of non-fruiting shoots on all sampling dates. These data suggest that N demand by the growing kernel reduced N in leaves on the same shoot. Consequently, Pn of those leaves was reduced. The effect of tree N status and shoot fruiting status was best summarized with an additive model where there is a larger relative reduction in leaf N and Pn for fruiting shoots on trees with low N status.