Chilopsis Research Articles

Effect of Reclaimed Water and Drought on Salt-sensitive Perennials

Four species of salt-sensitive perennials (Chilopsis linearis, Tecoma stans, Salviagreggii, and Verbena pulchella gracilior) were grown in containers and were irrigated with potable or reclaimed water. Electrical conductivity (EC) was 0.3 dS·m-1 for potable irrigation water and 1.0 dS·m-1 for reclaimed irrigation water. After 12 weeks of growing plants with reclaimed vs. potable water, C. linearis leaf dry weight was reduced by 15%, T. stans root dry weight was reduced by 41%, V. puchella gracilior stem dry weight was reduced by 35%, and S. greggii total dry weight was reduced by 56%. The increase in canopy size was calculated 4, 8, and 12 weeks after treatments began and was not affected by water source for C. linearis and T. stans, but was reduced for S. greggii and V. pulchella gracilior treated with reclaimed water. Up to 12% dieback and reduced flowering were observed on S. greggii irrigated with reclaimed water. Within 4 weeks of treatments, EC in the root zone was 0.5 dS·m-1 for plants irrigated with potable water and 1.9 dS·m-1 for those irrigated with reclaimed water. When exposed to drought, C. linearis and T. stans grown with reclaimed water maintained a more negative water potential as soil moisture was depleted. Osmotic potential started to increase significantly for both irrigation treatments when more than 25% moisture from fully saturated containers were lost. In general, plants irrigated with potable water sustained more damage than those irrigated with reclaimed water after recovering from a drought cycle.

Foliar Damage, Spectral Reflectance, and Tissue Ion Concentrations of Trees Sprinkle Irrigated with Waters of Similar Salinity but Different Chemical Composition

We investigated foliar damage to five landscape species sprinkler irrigated with either reuse water or one of five synthesized saline waters that contained elevated single salts mixed with Colorado River water, all having similar electrical conductivities. The experiment allowed us to compare the impact of elevated concentrations of Na, Mg, Ca, Cl, and SO4 on an index of visual damage (IVD), tissue ion concentrations, and spectral reflectance. Waters containing elevated concentrations of MgCl2 or NaCl caused greater foliar damage than did MgSO4, Na2SO4, CaSO4, or reuse water, as recorded in higher IVD values (p < 0.05). Privet and elm were damaged to a greater extent (higher IVD values) than were desert willow, guava and laurel (p < 0.05). Higher IVD values were recorded for all species irrigated with the MgCl2 waters, with mortality recorded in privet. Tissue nutrient concentrations were correlated with the IVD values. In the case of guava, 61% of the variability in the IVD could be accounted for based on N, P and K (P < 0.01). On a treatment basis, the single salts added to the municipal water showed little correlation with the IVD values, except in the case of MgCl2, where Mg was included in the regression equation (r2 = 0.82, P < 0.01, IVD↑ as S04↓, Mg and P↑). Eleven different spectral indices separated based on treatment and/or species (P < 0.05). In elm, 70% of the variability in the IVD could be accounted for by including Red Edge, Normalized Difference Vegetation Index (NDVI) and Water Band Index (WBI)/NDVI. A mixed response was observed to a post 30-day irrigation rinse in an attempt to reduce IVD values. Based on our results, care should be given to monitoring not only the EC (and osmotic potential) but also the ionic composition when saline waters are blended with other water sources, with the aim of minimizing the concentration of Mg, Cl, and Na.

Use of ICP and XAS to determine the enhancement of gold phytoextraction by Chilopsis linearis using thiocyanate as a complexing agent

Under natural conditions gold has low solubility that reduces its bioavailability, a critical factor for phytoextraction. Researchers have found that phytoextraction can be improved by using synthetic chelating agents. Preliminary studies have shown that desert willow (Chilopsis linearis), a common inhabitant of the Chihuahuan Desert, is able to extract gold from a gold-enriched medium. The objective of the present study was to determine the ability of thiocyanate to enhance the gold-uptake capacity of C. linearis. Seedlings of this plant were exposed to the following hydroponics treatment: (1) 5 mg Au L(-1) (2.5x10(-5) mol L(-1)), (2) 5 mg Au L(-1) + 10(-5) mol L(-1) NH4SCN, (3) 5 mg Au L(-1) + 5x10(-5) mol L(-1) NH4SCN, and (4) 5 mg Au L(-1) + 10(-4) mol L(-1) NH4SCN. Each treatment had its respective control. After 2 weeks we determined the effect of the treatment on plant growth and gold content by inductively coupled plasma-optical emission spectroscopy (ICP-OES). No signs of shoot-growth inhibition were observed at any NH4SCN treatment level. The ICP-OES analysis showed that addition of 10(-4) mol L(-1) NH4SCN increased the concentration of gold by about 595, 396, and 467% in roots, stems, and leaves, respectively. X-ray absorption spectroscopy (XAS) studies showed that the oxidation state of gold was Au(0) and that gold nanoparticles were formed inside the plants.

Benefits and costs of floral visitors to Chilopsis linearis: pollen deposition and stigma closure

In pollination mutualisms, nectar‐robbers are usually considered antagonists; visitors that enter flowers (legitimate visitors) are usually considered mutualists. However, nectar‐robbers may provide some benefits to plants, whereas legitimate visitors may inflict some costs. The costs and benefits of floral visitors to Chilopsis linearis (desert willow) were compared by number of pollen grains deposited and their effect on stigmas. Because these plants are self‐incompatible and pollen‐limited, they depend on visitors for services by pollinators to reproduce. On a per‐visit basis, only one legitimate visitor, Bombus sonorus (bumblebees) generally benefited plants in terms of pollen deposition. However, no species of visitor was consistently beneficial; every one was at least sometimes ineffective in terms of pollen deposition. Chilopsis had sensitive stigmas that closed immediately upon touch and sometimes reopened later. Whether stigmas remained permanently closed or reopened depended on number of pollen grains deposited and tended also to be affected by source either, outcross or self. Legitimate visitors sometimes cost plants by causing stigma closure without depositing enough pollen to set a fruit. When abundant, a visitor such as Apis mellifera (honeybees) that was only occasionally beneficial on a per‐visit basis may have provided a greater benefit to plants as a population than a more effective, but rare visitor. In contrast, nectar‐robbers did not benefit plants by depositing pollen grains, but they also did not inflict costs on plants by causing stigmas to close without adequate pollen. There are two general implications of these results. First, individuals of species that appear to be mutualists can vary greatly in the benefits that they give to their partners. Second, apparent mutualists can inflict costs on plants that apparent exploiters (nectar‐robbers) do not.

Plant water relations and photosynthesis during and after drought in a Chihuahuan desert arroyo

In order to understand the physiology and ecology of perennial shrub species occupying the banks of ephemeral streams we studied the plant water relations and gas-exchange characteristics of six perennial shrub species growing along an ephemeral stream (arroyo) in the northern Chihuahuan Desert. Two of the species are restricted to riparian habitats ( Brickellia laciniata and Chilopsis linearis), three are classified as semi-riparian ( Fallugia paradoxa, Prosopis glandulosa, and Rhus microphylla) and one is considered to be non-riparian ( Flourensia cernua). Differences in gas-exchange patterns and water relations emerged among these six species, yet differences among obligate, semi-riparian, and non-riparian classes of species were evident, but not universal. Chilopsis and Brickellia did not develop the low plant water potentials that characterized some semi-riparian ( Rhus) and non-riparian species ( Flourensia) during periods of drought. Rates of photosynthesis and transpiration were highest in Prosopis throughout the study, and were relatively constant in Chilopsis during and after drought. Whether water became available as channel flow or direct rainfall appeared to play a role in the physiology of these arroyo shrubs.

Are nectar-robbers mutualists or antagonists?

As "exploiters" of plant-pollinator mutualisms, nectar-robbers remove rewards (nectar) without providing pollination services. Though one might expect nectar-robbing to be costly to plants, it may instead benefit plants by indirectly increasing pollen dispersal. I investigated the direct effects of nectar-robbing bees ( Xylocopa californica) on floral rewards and behaviors of pollinators visiting desert willow ( Chilopsis linearis) and indirect effects of robbing on the reproductive success of the plant. Nectar-robbers reduced nectar; while unrobbed and robbed flowers were equally likely to contain nectar, nectar volumes were smaller in robbed flowers with nectar. Apis mellifera (honeybees), ineffective pollinators in terms of pollen deposition, avoided robbed flowers. In contrast, Bombus sonorus (bumblebees), effective pollinators, did not avoid robbed flowers. While bumblebees tended to spend less time in robbed flowers, the time that they spent in flowers was not correlated with pollen deposition. Using powder mimicking pollen, I found that on some days, powder was dispersed farther or to more flowers from robbed flowers, indicating that robbing may sometimes benefit plants by increasing male reproductive success. Powder movement suggested that the effect of robbing on male reproductive success ranged from costly to beneficial. The outcome for flowers that were marked early each morning was a function of prevalence of robbing and abundances of effective pollinators, but not a function of spatial variability among trees in prevalence of robbing or the abundance of ineffective honeybees. Unlike powder dispersal, female reproductive success, measured by fruit set and the number of pollen tubes growing in styles, was not affected by robbing. Thus, robbers did not reduce plants' female reproductive success either directly by damaging flowers or indirectly by reducing pollen deposition by pollinators. Overall, this study indicates that nectar-robbers were not often costly to plants, and sometimes even benefited plants.

Effect of Commercial Arbuscular Mycorrhizal Fungi on Growth, Survivability, and Subsequent Landscape Performance of Selected Container Grown Nursery Crops

Abstract This research evaluated the effects of commercially available arbuscular mycorrhizal fungi (AMF) on growth of selected ornamental plant species grown under a nursery-container production system. Subsequent plant survivability and growth in the landscape was also evaluated for two seasons. Acacia greggii, Chilopsis linearis, Diospyros virginiana, Platanus occidentalis, Ipomoea carnea and Plumbago auriculata were inoculated with commercial AMF: EndoNet®, MycorisePro®, or non-inoculated (NonAMF). Platanus occidentalis had a fourth mycorrhizal treatment, which included BioterraPLUS®. EndoNet® and MycorisePro® enhanced growth of C. linearis, I. carnea and P. auriculata during nursery-container production. Growth enhancement of P. occidentalis was significant with BioterraPLUS®, EndoNet® and MycorisePro® compared to NonAMF. During the container phase, greatest colonization (total arbuscules, vesicles/endospores, and intraradical hyphae) occurred with I. carnea and P. auriculata inoculated with EndoNet® and MycorisePro®. After the 1st growing season following out planting, AMF inoculated P. occidentalis and C. linearis had greater growth and AMF inoculated P. auriculata had higher survival than NonAMF plants. However, by the end of the 2nd growing season there were no differences in survival or growth among AMF treatments. The similarity in plant growth during the 2nd season was due in part to a high and active indigenous AMF population in the landscape site that colonized the NonAMF plants after transplanting.

Impact of Water Treatment on Foliar Damage of Landscape Trees Sprinkle Irrigated with Reuse Water

Abstract An experiment was conducted on four container-grown tree species placed under five different irrigation reuse water treatments to determine the extent of foliar damage after a 14.5-month period. The tree species included Heritage oak (Quercus virginiana Mill. ‘Heritage’), desert willow (Chilopsis linearis (Cav.)/Sweet), flowering plum (Prunus cerasifera Ehrh ‘Atropurpurea’), and Chinese pistache (Pistacia chinensis Bunge). Plant response and an index of visual damage (IVD) were assessed at different times throughout the experiment. Ion concentrations in the leaf tissue were different for species (S) (p < 0.001), treatment (T) (Na, K, SO4, p < 0.05) and by a species by treatment interaction (S × T) (Na, Ca, Mg, K and SO4, p < 0.05). SPAD measurements varied by S (p < 0.001), T (p < 0.001) and by an S × T interaction (p < 0.045). SPAD measurements decreased as the leaf tissue Na concentration increased (SPAD = 47.49 – 12.46(Na), r2 = 0.38, p < 0.01). The IVD varied by S (p < 0.001), T (p < 0.001) and by an S × T interaction (p < 0.001). Na, Ca and SO4 tissue ion concentrations could account for 52% of the variability in the IVD (IVD =−1.93 + 4.63(Na) + 2.60(Ca)−0.001(SO4), p < 0.01). Because the irrigation treatment resulting in the lowest IVD was species dependent, irrigation treatment selection should be based upon an evaluation of the landscape species composition and the potential cost of implementing a given strategy. The response observed in this study suggests that a single universal irrigation strategy does not exist, indicating that emphasis must be placed on initial and replacement plant selection.

Nutrient resorption in shrubs growing by design, and by default in Chihuahuan Desert arroyos

In the northern stretches of the Chihuahuan Desert, the margins of ephemeral stream channels called arroyos support a unique vegetation dominated by a guild of winter-deciduous shrubs. To explore the dynamics of nutrient conservation in this assemblage of arroyo shrubs, we measured nitrogen (N) and phosphorus (P) resorption efficiency and proficiency in six species of shrubs growing in arroyos in southern New Mexico. Collectively, these six species were no more efficient or proficient at resorbing N and P from senescing leaves than shrubs growing in other environments. Resorption efficiency averaged 53% and 50% for N and P, respectively, and resorption proficiency averaged 0.80% and 0.06% for N and P, respectively. However, resorption varied significantly between species specifically restricted in their distribution to riparian habitats (obligate riparian species), and those that were not. The two obligate riparian species combined (Brickellia laciniata, Chilopsis linearis) were significantly more efficient and proficient at resorbing N than the non-obligate riparian species combined (Fallugia paradoxa, Flourensia cernua, Prosopis glandulosa, Rhus microphylla). Additionally, both Brickellia and Chilopsis were individually significantly more proficient at resorbing N than any of the other four species. The dichotomy in resorption between obligate riparian species and those that were not may have been the result of the interplay between hydrology, geomorphology, and biology. Because arroyos move in space as the movement of water erodes banks and changes channel location, some plants are found along arroyos only because the arroyos have moved to them. These plants (plants growing by default) may be less well adapted to arroyo margins than obligate riparian species (plants growing by design). Significant differences in resorption between obligate and non-obligate riparian species suggested that evolutionary history and habitat specificity may be added to the list of factors known to influence resorption. Selected life history traits of the six species did not appear to be related to any measure of resorption, but leaf surface area, specific leaf mass, and nutrient concentrations in green leaves were all correlated with resorption efficiency or proficiency in one or more species. The only species capable of symbiotic N fixation, Prosopis glandulosa, retained at least 2.3 times more N in its senesced leaves than any other species. Patterns of resorption in arroyo shrubs strongly indicated that efficiency and proficiency are fundamentally different, complementary measures of resorption.

Arroyo water storage and soil nutrients and their effects on gas-exchange of shrub species in the northern Chihuahuan Desert

A variable fraction of the rain falling on desert landscapes runs off and accumulates in ephemeral channels (arroyos), where some of the water is transported downslope. Relatively large amounts of water are stored in arroyo sediments. This water may support high rates of gas-exchange in some riparian species. We examined differences in the timing of flow events, soil water storage, and soil nutrients on gas-exchange rates of shrubs growing on arroyo margins and in adjacent piedmont areas in the Chihuahuan Desert of southern New Mexico, USA. The semi-riparian shrub, Fallugia paradoxa (Apache plume), had very different photosynthetic rates between two arroyos, but transpiration rates did not differ. This may result from nutrient limitation differences between arroyos. At one site, the semi-riparian shrub, Prosopis glandulosa (mesquite), on arroyo margins had access to more water and showed higher rates of gas-exchange compared with non-arroyo mesquite located on nearby piedmont areas. The obligate riparian shrub, Chilopsis linearis (desert willow), had intermediate gas-exchange rates when compared with Apache plume and mesquite, and neither soil water nor nutrient concentrations appeared to affect photosynthesis during the growing season. Variation between and within arroyos was high; however, our data suggest that stored water enabled mesquite of arroyo margins to maintain relatively high rates of gas-exchange. When water was relatively abundant, nutrient availability appeared to limit photosynthetic rates of Apache plume.

Effects of Mulch on Soil Moisture and Growth of Desert Willow

The objective of this research was to consider the effects of gravel, wood chip, and tire mulches and turf on soil moisture and root and shoot growth of Chilopsis linearis (Cav.) `Burgundy' (desert willow). Gravel, wood chip, and tire mulches retained greater soil moisture than bare soil (control) with little difference in soil moisture between the mulches. Mulched trees and bare soil had greater height and shoot and root dry weights than trees in turf. Turf conserved soil moisture better than bare soil but appeared to compete with desert willow for water and nutrients resulting in less growth. Trees with gravel and tire mulches had greater shoot dry weight in the second year of growth and greater root dry weight, root length, and root area in both the first and second years of growth after transplanting.

Chemical and nutritional composition of tree legume seeds and pods from southwestern United States and Sonora Mexico

Ten different types of legume tree seeds and pods collected from legume trees growing in the desert area of Tucson, Arizona were analyzed for proximate composition, acid detergent (ADF), dietary fiber, phytic acid (PA), trypsin inhibitor activity (TIA), minerals, and amino acids composition. Protein content of seeds ranged from 19.09% for desert willow to 25.66% for feather tree. The lipid content of seeds ranged from 1.7% for mesquite to 34.25% for ironwood. The soluble fiber content of seeds ranged from 4.23% for ironwood to 23.16% for green palo verde, while the insoluble fiber ranged from 19.71% for Acacia angustissima to 45.67% for sweet acacia. PA levels varied from 1.4mg/g for feather tree seeds to 7.4mg/g for blue palo verde seeds. TIA was extremely high in feather tree and Acacia angustissima seeds (27,323 and 26,338 TIU/g, respectively). Mineral content varied among seeds, calcium and phosphorus being consistently the highest. Amino acid content was similar to that of other legumes with cysteine and methionine being low.

Implications of Using Kenaf Stalk Core and Coconut Coir Pith as Nursery Container Media

Four underutilized small trees, Chilopsis linearis, Rhus lanceolata, Acacia wrightii, ×Chitalpa tashkentensis, and a commercial control Fraxinus velutina, were grown outdoors in 15-L containers. Four media combinations, 3 pine bark: 1 sand, 3 pine bark: 1 coconut coir pith, 3 kenaf stalk core: 1 sphagnum peat, and 3 kenaf stalk core: 1 coconut coir pith (v/v), were amended with Sierrablen 18N–2.6P–10K at three rates, 3.6, 7.1, and 10.7 kg·m-3. Fraxinus velutina and C. linearis seedlings were transplanted to the field to evaluate initial landscape establishment. Growth was typically reduced, in both the field and container, when kenaf media was used during production. EC was greatest early and with higher fertility rates. Leachate pH decreased over time, and was lower at high fertility rates. Soil particle size >6.0 mm decreased substantially in kenaf media over time. Water holding capacity increased, while air space and total root volume decreased in kenaf media. Physical characteristics and growth responses were similar with coconut coir and peat moss.

Leaf carbon isotope ratios in three landscape species growing in an arid environment

The effect of leaching fraction (LF = drainage volume/irrigation volume) and tree planting size on the carbon isotope ratio measured in leaves of live oak (Quercus virginiana), desert willow (Chilopsis linearis) and tall fescue (Festuca arundinacea; LF only) were investigated in an arid climate. Irrigations were applied to maintain LFs of +0·25, 0·00 or −0·25 (theoretical). Live oak and desert willow were planted as 3·8, 18·9 or 56·8 l nursery container plants in lysimeters where hydrologic balances were maintained weekly. Leaf carbon isotope ratios varied by species across the three LFs (live oak>desert willow>tall fescue). In live oak, leaf carbon isotope ratios increased as LF decreased but did not change with planting size. In desert willow the ratios increased with decreasing LF and with increasing planting size. In tall fescue the leaf carbon isotope ratio decreased as the LF increased. Leaf carbon isotope ratios also varied with stomatal conductance, leaf xylem water potentials and water-use efficiency (WUE). In live oak, both average midday stomatal conductance and leaf xylem water potential decreased with increasing leaf carbon isotope ratio. Average stomatal conductance for live oak was negatively correlated with average leaf WUE. Average leaf WUE in live oak and tall fescue were correlated with average leaf carbon isotope ratios. However, in tall fescue leaf WUE increased as the leaf carbon isotope ratio became more negative. In live oak the ratio became more positive as leaf WUE increased. This study has demonstrated that leaf carbon isotope ratios can be used as a way of screening plant response for low water-use landscapes, but only after careful correlations for each species have been established between growth form and growing conditions.

Implications of Genotypic Selection and Production Practices on Root Regeneration Potential and Field Establishment of Container-grown Trees

Transplant studies were conducted on Taxodium distichum L., Platanus occidentalis L., Quercus shumardii Buckl., Fraxinus velutina Torr., and Chilopsis linearis (Cav.) Sweet seedlings grown in 2.2- to 9.1-L black plastic containers. Effects of half-sib family selection on post-transplant root regeneration potential (RRP) and field establishment were investigated with P. occidentalis. Taxodium distichum, Q. shumardii, and P. occidentalis were used to determine seasonal variation in relationships among RRP characteristics and measures of successful transplant establishment. Post-transplant effects of avoidance of circling root development vs. remediation practices were investigated with Q. shumardii. Effects of container media composition on field establishment and RRP of container-grown plants were studied using F. velutina and C. linearis. Impacts of rotation time on RRP and field establishment were investigated with T. distichum. Rates of RRP were the measure most consistently linked to improved post-transplant shoot growth of P. occidentalis. Utilization of locally adapted genotypes and avoidance of summer transplant were important in establishment of P. occidentalis and T. distichum. Increased small diameter root regeneration was linked to reduced water stress during transplanting of Q. shumardii. Physical characteristics of the container media impacted initial post-transplant growth of F. velutina and C. linearis.

CONTAINER PRODUCTION OF UNDERUTILIZED URBAN TREES USING KENAF AND COCONUT COIR PITH

Growth responses during nursery production in 2.2- and 11.4-liter plastic containers to conventional and alternative media of four species of small trees of limited availability for potential use in urban sites in the southwest United States (Acacia wrightii, Chilopsis linearis, × Chitalpa tashkentensis, and Rhus lanceolata) were compared to that of a commercially available small tree (Fraxinus velutina). Four media combinations, at 3:1 (v/v) of bark: sand (conventional), bark: coconut coir pith, kenaf stalk core: peatmoss, and kenaf: coir, with three fertilizer concentrations (3.6, 7.2, and 10.7 kg·m–3 of 18N–2.6P–10K Osmocote) were tested with each species. All species exhibited commercially acceptable growth (80 to 167 cm mean heights in 11.4-liter containers in 240 days) with near 100% survival in most media and fertilizer combinations with the following exceptions: shoot extension of Rhus lanceolata was reduced by 20 to 30 cm and survival by 20% to 50% in kenaf media with high fertility rates; and Acacia wrightii had acceptable shoot extension but exhibited poor trunk diameter growth across media relative to the other species. Slightreductions in growth of some species were noted with kenaf media and slight increases with coconut coir, but differences were not likely of commercial significance. Kenaf media was significantly lighter (20% to 80%) than bark media, but had elevated initial electrical conductivity (EC) and shrank to 60% to 70% of its initial volume after 240 days. Kenaf: peatmoss media had a slightly lower mean pH (6.34) compared to the other media (pH 6.41–6.49).

Rapid Micropropagation of xChitalpa tashkentensis

×Chitalpa tashkentensis (Chilopsis linearis × Catalpa bignonoides) is an attractive small tree producing lavender to white orchid like flowers. Micropropagation would allow for the rapid clonal propagation of new hybrids for testing cold hardiness and landscape performance. The rapid growth response of Chitalpa shoot cultures also makes it an excellent subject for the study of in vitro growth parameters of woody plants. Shoot cultures were initiated from shoot tips on Anderson's rhododendron medium with MS vitamins, 3% sucrose, 1 μm BA, pH 5.6 and solidified with 0.6% phytagar. Shoot cultures stabilized rapidly. Two-node microcuttings were placed on modified MS media (200.1 μm Na2 EDTA and 200.5 μm FeSO47H2O), MS vitamins, 3% sucrose, pH 5.6, 0.6% phytagar and supplemented with NAA (0 0.5, 1.5, or 3 μm) in combination with BA (0, 1, 5, 10, 15, 20, 30, or 40 μm). Cultures grown on media supplemented with 1 mm BA produced the longest shoots and the most nodes per shoot. Cultures grown on media supplemented with 10 μm BA produced the most shoots. Microshoots readily rooted on plant growth regulator free MS medium and were easily acclimated.

Comparative Water Use of Turfgrasses and Ornamental Trees in an Arid Environment

Monthly evapotranspiration (ETa) of Argentine mesquite (Prosopis alba Grisebach), desert willow (Chilopsis linearis (Cav.) Sweet var. linearis) and southern live oak (Quercus virginiana Mill., nursery seedling selection) were compared with tall fescue (Festuca arundinacea Schreb.) and common bermudagrass (Cynodon dactylon (L.) Pers.) overseeded with perennial ryegrass (Lolium perene L.) over a two-year period at a field site in Las Vegas, NV. Immature trees (56.8 L container nursery stock) and tall fescue were grown in 190 L plastic lysimeters in which weekly hydrologic balances were maintained. Evapotranspiration of bermudagrass/ryegrass was estimated from crop coefficients (Kc) and potential evapotranspiration (ETo) predictions. ETa of the trees and tall fescue (L/lysimeter) was shown to increase as the leaching fraction (LF = drainage/irrigation) increased. The ETa data were compared on an area basis by dividing tree ETa by measured basal canopy areas and turfgrass ETa by the land area on which the gra...

Relative Drought Resistance Among Selected Southwestern Landscape Plants

A method of determining drought resistance appears to have promise in identifying superior plants for minimal irrigation landscapes. Under conditions of this test, desert willow had greater resistance to drought than either fruitless mulberry or yellow bells. This can be attributed to a greater tolerance rather than a greater avoidance. Drought tolerance of both desert willow and yellow bells was over 1.5 times that of fruitless mulberry. Fruitless mulberry had as great or greater drought avoidance than the xeric species under dry conditions. Based on these results, desert willow and yellow bells are tolerant water spenders that can convert to water savers. Fruitless mulberry is a relatively intolerant water spender that may not convert to a water saver. If this is confirmed in further studies, then the success of mulberry in the arid Southwest may be attributed to an ability to increase water uptake in times of drought.

Evapotranspiration and Growth Response of Three Woody Ornamental Species Placed under Varying Irrigation Regimes

A 2-year study was conducted to quantify the actual evapotranspiration (ETa) of three woody ornamental trees placed under three different leaching fractions (LFs). Argentine mesquite (Prosopis alba Grisebach), desert willow [Chilopsis linearis (Cav.) Sweet var. linearis], and southern live oak (Quercus virginiana Mill.) (nursery seedling selection) were planted as 3.8-, 18.9-, or 56.8-liter container nursery stock outdoors in 190-liter plastic lysimeters in which weekly hydrologic balances were maintained. Weekly storage changes were measured with a portable hoist-load cell apparatus. Irrigations were applied to maintain LFs of +0.25, 0.00, or -0.25 (theoretical) based on the equation irrigation (I) = ETa/(1 - LF). Tree height, trunk diameter, canopy volume, leaf area index, total leaf area (oak only) and dry weight were monitored during the experiment or measured at final harvest. Average yearly ETa was significantly influenced by planting size (oak and willow, P ≤ 0.001) and leaching fraction imposed (P ≤ 0.001). Multiple regressions accounting for the variability in average yearly ETa were comprised of different growth and water management variables depending on the species. LF, trunk diameter, and canopy volume accounted for 92% (P ≤ 0.001) of the variability in the average yearly ETa of oak. Monthly ETa data were also evaluated, with multiple regressions based on data from nonwater-deficit trees, such that LF could be ignored. In the case of desert willow, monthly potential ET and trunk diameter accounted for 88% (P ≤ 0.001) of the variability in the monthly ETa. Results suggest that irrigators could apply water to arid urban landscapes more efficiently if irrigations were scheduled based on such information.