Water-conserving Landscapes Research Articles

Morpho-physiological and biochemical responses of four ornamental herbaceous species to water stress

Understanding of water-deficit responses of plants can lead to better establishment and management of water-conserving landscapes. Due to the importance of landscape plants and the need for water relations of field-grown herbaceous species, this study investigated morphological and biochemical responses of Malva sylvestris, Althea rosea, Callistephus chinensis and Rudbeckia hirta under water stress. The main plots were the four plant species and the subplots were irrigation levels of 25%, 50%, 75%, and 100% reference evapotranspiration (ET0). The results indicated that 75% ET0 irrigation treatment had no effect on the relative water content of Althea rosea and R. hirta. Althea rosea and R. hirta had the highest deficit-irrigation tolerance index for root length and root density in 25% ET0. Only A. rosea, exhibited no oxidative stress as reduced chlorophyll content under 75% ET0–50% ET0, and also under 50% ET0–25% ET0. Only in R. hirta, the ratio of chlorophyll a/b was linearly increased. Water stress had no effect on total soluble carbohydrates in C. chinensis, R. hirta and M. sylvestris. Moving from 75 to 25% ET0, R. hirta showed the lowest electrolyte leakage which was followed by A. rosea. Althea rosea and R. hirta displayed a drought-avoidance mechanism.

Elevated soil nitrogen pools after conversion of turfgrass to water-efficient residential landscapes

As a result of uncertain resource availability and growing populations, city managers are implementing conservation plans that aim to provide services for people while reducing household resource use. For example, in the US, municipalities are incentivizing homeowners to replace their water-intensive turfgrass lawns with water-efficient landscapes consisting of interspersed drought-tolerant shrubs and trees with rock or mulch groundcover (e.g. xeriscapes, rain gardens, water-wise landscapes). While these strategies are likely to reduce water demand, the consequences for other ecosystem services are unclear. Previous studies in controlled, experimental landscapes have shown that conversion from turfgrass to shrubs may lead to high rates of nutrient leaching from soils. However, little is known about the long-term biogeochemical consequences of this increasingly common land cover change across diverse homeowner management practices. We explored the fate of soil nitrogen (N) across a chronosequence of land cover change from turfgrass to water-efficient landscapes in privately owned yards in metropolitan Phoenix, Arizona, in the arid US Southwest. Soil nitrate (–N) pools were four times larger in water-efficient landscapes (25 ± 4 kg –N/ha; 0–45 cm depth) compared to turfgrass lawns (6 ± 7 kg –N/ha). Soil –N also varied significantly with time since landscape conversion; the largest pools occurred at 9–13 years after turfgrass removal and declined to levels comparable to turfgrass thereafter. Variation in soil –N with landscape age was strongly influenced by management practices related to soil water availability, including shrub cover, sub-surface plastic sheeting, and irrigation frequency. Our findings show that transitioning from turfgrass to water-efficient residential landscaping can lead to an accumulation of –N that may be lost from the plant rooting zone over time following irrigation or rainfall. These results have implications for best management practices to optimize the benefits of water-conserving landscapes while protecting water quality.

CUTTING PROPAGATION OF LITTLE-LEAF MOUNTAIN MAHOGANY©

Superior selections of little-leaf mountain mahogany (Cercocarpus ledifolius var. intricatus) (CLI) have potential for use in water-conserving landscapes in the Intermountain region of the USA. The potential for propagating CLI by cuttings was determined by selecting specimens from a range of sources and growing conditions at different seasons and with different rooting conditions in a series of individual experiments. Exogenous auxin treatments at high (4000/2000 ppm indolebutryic acid/naphthaleneacetic acid as Dip-N-Grow®) and low (2000/1000 ppm of the same material) were also tested. Selection CLI-1 (wild source, Ephraim, Utah, Jan. 2010) rooted at 0, 33, and 42% with zero, low, and high auxin treatments. Selections CLI-2 and CLI-3 (wild source, Mt. Charleston, Nevada, May, 2010) had results of 0, 0, and 8% and 15, 28, and 52% rooting for the respective auxin treatments and selections. Selection CLI-4 (landscape source, Logan, Utah, July, 2010) had 8, 96, and 100% rooting for similar auxin treatments. Finally selections CLI-5 and CLI-6 (landscape source, Logan, Utah) and CLI-3 (container-grown stock plants) stuck in July, 2012 had 6, 2, and 85% rooting with the low rate of auxin, respectively. Overall, two selections had greater than 90% rooting while one had approximately 40% and three others less than 10%. For the three selections that did root, supplemental auxin increased the percentage of rooted cuttings from 0-15% for untreated controls to 42-100% for treated. In contrast, the three selections with poor rooting had little response to exogenous auxin at the levels used. Propagation of CLI by cuttings is feasible, though variable. The variability may be due to accession genetic differences, stock plant growing conditions, or rooting conditions.

Influence of harvest timing and storage interval on rabbitbrush seed germination, emergence, and viability

Rubber rabbitbrush ( Ericameria nauseosa (Pall. ex Pursh) G.L. Nesom & Baird [Asteraceae]) has potential for use in water-conserving landscapes, but poor seedling emergence can be a problem for nursery production. We evaluated the effects of 1) harvest timing (stage of inflorescence maturity); and 2) duration of storage interval on seed viability, emergence, and germination for 6 geographically diverse populations. Stage of inflorescence maturity (harvest timing) had a statistically significant (P

Influence of stratification, light, and planting depth on rabbitbrush seed germination and emergence

Rubber rabbitbrush ( Ericameria nauseosa (Pall. ex Pursh) G.L. Nesom & Baird) [Asteraceae]) has potential for use as an effective element of water-conserving landscapes. To enhance availability of this species, it is important to optimize nursery seedling production. Our objectives were to determine the influence of 1) stratification (cold-moist); 2) light exposure; and 3) planting depth on germination and emergence of seeds collected from diverse populations of rubber rabbitbrush. Seeds representing a range of environments were collected from Idaho and Utah and were cleaned, sorted, and exposed to germination-enhancing treatments. Following stratification, seeds of 3 of 4 rabbitbrush populations responded with a statistically significant increase in germination percentage. More significant, stratification increased the germination rate, reducing time to culmination from 4 or more wk to 1 wk or less. Compared with seeds germinated in the dark, exposure to sunlight increased germination percentage 1.5- to 3-fold, depending on population. Any amount of seed burial markedly decreased seedling emergence for all 4 populations. Six wk after planting, removal of all but a few mm of soilless substrate resulted in emergence of a portion of the buried seeds, indicating induction and release of conditional dormancy (possibly quiescence) due to a lack of light or other factors. Responses to stratification, light, and seed burial varied by population, thus confirming previously described variability that exists among rubber rabbitbrush populations. Results of this study will help nursery growers provide optimal conditions for producing nursery stock of rubber rabbitbrush.

The social symbolism of water-conserving landscaping

Three studies examined the symbolic and self-presentational meaning of low-water-use residential landscaping in a desert city in the southwestern United States. We hypothesized that owners' water-intensive or water-conserving landscape choices would be seen to convey very different characteristics. Data indicated that these two types of residential landscapes led to substantially different attributions about homeowners and also that potential homeowners could use landscapes to convey an array of characteristics to a social audience. In general, water-intensive landscapes led to more positive attributions than did water-conserving landscapes. The results support the idea that landscaping choice may be guided by self-presentational considerations, and that such considerations might influence the adoption of high- or low-water-use landscapes.

Vegetative propagation of Juniperus osteosperma (Utah Juniper) by cuttings

Utah juniper ( Juniperus osteosperma (Torr.) Little [Cupressaceae]) was vegetatively propagated using tip cuttings from juvenile plants. Rooting was most successful (69%) when cuttings were treated with indole butyric acid (IBA) in talc (0.8% ai), struck in 2:1 perlite:peat (v:v) rooting substrate, provided bottom heat, and kept on a mist bench covered by a white polyethylene tent in a greenhouse environment with supplemental lighting. Utah juniper is highly drought tolerant, and superior accessions may have potential for increased use in water-conserving landscapes. The ability to propagate it by vegetative means should facilitate the selection and development of superior plants for use in the landscape industry.

Selection and Budding Propagation of Native Bigtooth Maple for Water-conserving Landscapes

The potential of bigtooth maple (Acer grandidentatum) as a small, water-conserving landscape tree for the western United States is limited by the selection of superior accessions from a morphologically diverse gene pool and the ability to propagate wild plants in a nursery environment. Superior accessions were selected based primarily on red fall color. Aerial digital images taken during peak fall color in 2007 and 2008 were synchronized with flight global positioning system (GPS) track files using digital image editor software and visually compared with corresponding satellite images to determine the exact latitude and longitude of selected trees on the ground. Trees were physically located using GPS technology then visually evaluated for initial selection. Criteria included fall color, habitat, relative disease and insect resistance, bud quality, and plant form. From 56 observed trees of interest, six were selected for propagation. Through time-course experiments using multistemmed, bigtooth maple seedling rootstocks in a coppiced stoolbed, the optimum time for chip budding scions of wild accessions in northern Utah was determined to be July through mid-August. Further evaluation of accessions for use in the landscape industry is required.

Residential Landscapes, Homeowner Attitudes, and Water-wise Choices in New Mexico

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.

(178) Layering Propagation of Big tooth Maple, Acer grandidentatum

Bigtoothmaple(Acer grandidentatum Nutt.) is of interest for its fall color and potential use in water-conserving landscapes. Clonal propagation of desirable selections would be beneficial. Since bigtooth maple commonly self-propagates by layering, we explored mound layering as a means of vegetative propagation. A stool bed was established in 1999 with seedlings grown from northern Utah seed. Beginning in 2001, seedlings were dormant pruned to their base and shoots allowed to grow until early July, when treatments were applied. At the time of treatment application for the reported experiments, shoot bases were girdled with 24-gauge copper wire, covered with conifer wood shavings, and kept moist during the growing season. The effects of rooting hormones and enclosure of the rooting environment on rooting were examined. On 7 July 2002, 32 trees were randomly selected and the four tallest shoots within each tree were treated with either 0, 1:5, 1:10, or 1:20 (v/v) solutions of Dip-N-Gro© rooting hormone (1% IBA, 0.5% NAA, boron). There was no significant difference in rooted shoots between treatments and 81% of the trees had at least one rooted shoot. On 9 July 2004, 39 trees were selected and two shoots per tree were girdled. One-half of the stool bed area was treated by underlaying the shavings with BioBarrier© (17.5% trifluralin a.i.). Measurements on 12 Nov. 2004 showed no apparent treatment effect on rooting and 90% of the trees had at least one rooted shoot. This research demonstrates that mound layering is an effective means of rooting shoots of juvenile bigtooth maples. Further research will examine the effectiveness of the technique in propagating mature clones.

`Plains' Blackfoot Daisy (Melampodium leucanthum)

Blackfoot Daisy (Melampodium leucanthum Torr. & Gray) is a common wildflower native to much of Arizona, New Mexico, Texas, Oklahoma, Kansas, and Colorado (Stuessy, 1972). This perennial subshrub is characterized by a tight mound of white composite flowers with golden centers and linear leaves. Correll and Johnston (1970) have reported that this attractive native plant flourishes in calcareous gravely soils. Indigenous to regions receiving 40 to 70 cm of annual rainfall, Blackfoot Daisy is found along roadsides in the high plains, shortgrass prairies, uplands, and on limestone outcroppings exhibiting disturbed soils of the southwestern U.S. (Borland, 1998). The long period of bloom and tolerance to the heat and drought of its native environment make this plant desirable for use in water-conserving landscapes. The unusual name Blackfoot Daisy is derived from the foot-shaped bract that surrounds the seed and turns black at maturity (Diggs et al., 1999). Blackfoot Daisy occurs as both a diploid and a tetraploid that are morphologically indistinguishable. Turner and King (1961) suggest the ploidy level does not appear to be influenced by geography or ecologic conditions. Populations of both ploidy levels have been found growing among each other. In 1996, we initiated a breeding project to identify wildflowers with potential for landscape use in demanding environments. Accessions with outstanding attributes were collected and selection trials conducted over several seasons. ‘Plains’ Blackfoot Daisy is the first formal release from our program. It was developed through 6 years of recurrent phenotypic selection for increased branching, compact growth habit and increased floral density. The unique, reflexed flower form is a distinguishing trait that helps to distinguish ‘Plains’ Blackfoot Daisy from other Melampodium leucanthum genotypes. Description

Assessing Public Opinion on Water Conservation and Water Conserving Landscapes in the Semiarid Southwestern United States

A survey instrument was designed to determine public opinion on water conservation, water conserving landscapes, the use of native plants in landscapes, home irrigation systems, and the performance of five Texas native plant species [pink evening primrose (Oenothera speciosa); prairie verbena (Verbena bipinnatifida); red yucca (Hesperaloe parviflora); ceniza (Leucophyllum frutescens); and ruellia (Ruellia nudiflora)] grown in low water use landscapes in the semiarid Southwestern United States. On six occasions during the 1999 growing season, participants viewed landscapes and participated in a survey. Survey data indicate that over 90% of respondents thought water conservation was important to the state of Texas. A majority of participants however, believed water conserving landscapes to be expensive to maintain and not aesthetically pleasing. The survey revealed 79% of participants would use native plants if native plants conserved water, and 86% of participants would use native plants if native plants were attractive. Chi-square approximations revealed participant's opinions regarding water conservation and home irrigation systems were influenced by education level and amount of time they participated in weekly horticulture activities. In an open-ended question, participants indicated flowers and healthy leaves were characteristics indicating a plant was performing well. Throughout the year, species in flower received higher ratings than nonflowering species.

Assessing and Influencing Attitudes toward Water-conserving Landscapes

Implementing water-conserving landscapes is one action that many individuals can take to help ease the nation's water crisis, but few people seem to be exercising this option. Some horticulturists attribute this to a negative attitude toward such landscapes. Our research was designed to assess these attitudes and to see if they could be improved with information. Questionnaires were administered to people in treatment or control groups. Those in the treatment group viewed a short videotape about water issues and water-conserving landscapes. Initial attitudes in both groups were neutral or positive, not negative as predicted. Viewing the videotape was associated with significantly improved attitudes. People in the treatment group described water-conserving landscapes as less hot, more colorful, and more attractive three weeks after viewing the videotape than they had initially.