Chrysothamnus Nauseosus Research Articles

Phytochemical Composition and Biological Activity of the Essential Oil from Ericameria nauseosa Collected in Southwestern Montana, United States.

Ericameria nauseosa (Pall. ex Pursh) G.L. Nesom & G.I. Baird) is used in traditional medicine to treat various diseases; however, little is known about the immunomodulatory activity of essential oil from this plant. Thus, we isolated essential oil from the aerial parts of E. nauseosa and evaluated their chemical composition and biological activity. Compositional analysis of E. nauseosa essential oil revealed that the main (>2%) components were γ-decalactone (13.3%), cryptone (9.4%), terpinen-4-ol (9.3%), (E)-methyl cinnamate (6.0%), T-cadinol (4.7%), spathulenol (3.6%), 8Z-2,3-dihydromatricaria ester (3.1%), β-phellandrene (3.0%), p-cymen-8-ol (2.2%), 3-ethoxy-2-cycloocten-1-one (2.2%), and trans-p-menth-2-en-1-ol (2.1%). Distinctive features were the lactones (up to 15%) and polyacetylenes (up to 3.1%), including (2Z,8Z)-matricaria ester and 8Z-2,3-dihydromatricaria ester. A comparison with other reported E. nauseosa essential oil samples showed that our samples were distinct from those collected in other areas of the country; however, they did have the most similarity to one sample collected in North Central Utah. Pharmacological studies showed that E. nauseosa essential oil activated human neutrophil Ca2+ influx, which desensitized these cells to subsequent agonist-induced functional responses. Based on our previously reported data that nerolidol, β-pinene, spathulenol, sabinene, and γ-terpinene were active in human neutrophils, these compounds are the most likely constituents contributing to this immunomodulatory activity. However, the relatively high amount of polyacetylenes may also contribute, as these compounds have been characterized as potent immunomodulators.

Environment predicts the maintenance of reproductive isolation in a mosaic hybrid zone of rubber rabbitbrush.

Widely distributed plants of western North America experience divergent selection across environmental gradients, have complex histories shaped by biogeographic barriers and distributional shifts and often illustrate continuums of reproductive isolation. Rubber rabbitbrush (Ericameria nauseosa) is a foundational shrub species that occurs across diverse environments of western North America. Its remarkable phenotypic diversity is currently ascribed to two subspecies-Ericameria nauseosa nauseosa and Ericameria nauseosa consimilis-and 22 named varieties. To understand how genetic variation is partitioned across subspecies, varieties, and environments, we used high throughput sequencing of reduced representation libraries. We found clear evidence for divergence between the two subspecies, despite largely sympatric distributions. Numerous locations exhibiting admixed ancestry were not geographically localized but were widely distributed across a mosaic hybrid zone. The occurrence of hybrid and subspecific ancestries was strongly predicted by environmental variables as well as the proximity to major ecotones between ecoregions. Although this repeatability illustrates the importance of environmental factors in shaping reproductive isolation, variability in the prevalence of hybridization also indicates these factors likely differ across ecological contexts. There was mixed evidence for the evolutionary cohesiveness of varieties, but several genetically distinct and narrow endemic varieties exhibited admixed subspecific ancestries, hinting at the possibility for transgressive hybridization to contribute to phenotypic novelty and the colonization of new environments in E. nauseosa.

The Essential Oils of Rubber Rabbitbrush (Ericameria nauseosa) from North-Central Utah and Southwestern Idaho

Background: Rabbitbrush ( Ericameria nauseosa) is a conspicuous member of plant communities in the deserts of western North America. The plant is an important winter forage for several ungulates in the region and has been used in Native American ethnopharmacology. Methods: Several specimens were collected from North Central Utah (8 samples) and Southwestern Idaho (6 samples). The essential oils were obtained by hydrodistillation and analyzed by gas chromatographic techniques. The data were analyzed using agglomerative hierarchical cluster analysis (HCA), principal component analysis (PCA), and Pearson correlation analysis. Results: Essential oil yields ranged from 0.030% to 2.011%. The major components in the essential oils were β-phellandrene (1.8%-56.5%), β-pinene (0.%3-23.3%), limonene (0.7%-22.3%), and ( Z)-β-ocimene (0.0%-29.3%). With the exception of 1 sample from Utah, the essential oils showed greater than 50% similarity in composition. There were significant differences in percentages of some components, however. Sabinene, β-phellandrene, cosmene, 1,3,8- p-menthatriene, terpinen-4-ol, and β-eudesmol concentrations were higher in the Idaho samples while myrcene, limonene, geranyl acetate, ( E)-β-caryophyllene, γ-curcumene, germacrene D, α-muurolene, γ-cadinene, and δ-cadinene concentrations were significantly higher in the Utah samples. Chiral gas chromatography–mass spectrometry showed the chiral monoterpenoids to be dominated by the (−)-enantiomers, but there were some differences in enantiomeric distribution in the essential oils from Utah compared to those from Idaho. Conclusion: The essential oil compositions in this work are qualitatively similar to those reported previously. However, there were quantitative differences in chemical composition and enantiomeric distributions between the Utah samples and the Idaho samples. Additional research is needed to compare essential oil composition from other geographical locations in western North America.

Distribution, morphology, and karyotype of San Joaquin pocket mice from the western Mojave Desert

The San Joaquin pocket mouse (Perognathus inornatus) is endemic to California and currently includes three subspecies (P. i. inornatus, neglectus, and psammophilus). P. inornatus from the western Mojave Desert have been assigned to the subspecies neglectus based on similar morphology. During the course of live-trapping projects between 1990 and 2017, we captured P. inornatus at several locations in the Mojave Desert and gathered information on habitat associations, relative abundance, seasonal activity, and field identification. P. inornatus was found at elevations ranging from 668–1,109 m above mean sea level in creosote bush scrub, allscale scrub, Joshua tree woodland, rubber rabbitbrush scrub, spinescale scrub, and California juniper woodland. The capture locations and our review of museum specimens indicate that, at a minimum, the species’ range in the Mojave Desert encompasses approximately 7,000 km2 primarily in the Antelope Valley, extending at least as far north as the Rand Mountains, east to the vicinity of Hinkley, south to Palmdale, and west to near Gorman. P. inornatus capture rates were typically low relative to other nocturnal rodents, and it was not found consistently at localities at which it had been captured previously. Adults were sexually dimorphic, with males significantly larger than females. P. inornatus was significantly larger than the sympatric little pocket mouse (P. longimembris) for length of head-body, total length and body mass, and possessed a relatively shorter tail. We collected 15 specimens of P. inornatus from nine localities in the western Mojave Desert for cytogenetic analysis and each possessed the same karyotype, characterized by a diploid complement of 52 chromosomes, which has not been previously described for the genus. We argue that the 52-chromosome form should be considered distinct for conservation purposes, because it occupies a relatively small geographic area that is being subjected to increasing habitat loss and fragmentation due to residential, commercial, and renewable energy development.

Irrigation and fertilization of Chrysothamnus nauseosus (Asteraceae) affect the attack and gall growth of Rhopalomyia chrysothamni (Cecidomyiidae)

The quality of the environment and the host plant influence the development of the galls as well as the performance of gall inducing insects. The effect of nutrients and water availability on the development of galls induced by Rhopalomyia chrysothamni (Diptera: Cecidomyiidae) on Chrysothamnus nauseosus subsp. hololeucus (Asteraceae) was tested. The study was conducted in a xeric area with no signs of disturbances in Coconino National Forest, Arizona, USA. Individuals of C. nauseosus randomly selected underwent three treatments of water and nutrients availability. At the end of the growing season, the number of attacked plants, abundance and the development of galls in each treatment were evaluated. The differences in habitat quality simulated by the fertility and humidity conditions influenced both the number of attacked plants and the growth of galls. Plants with lower hydric-nutritional quality were more attacked by the galling insect. Otherwise, when both water and nutritional stresses were relieved plants developed galls with higher dry biomass and density. Therefore, this field experimental study indicates that while galling females attacked plants more in xeric environments, the galls grew larger in relatively more mesic conditions. The results showed a trade-off between the quantity and quality of galls of R. chrysothamni depending on the nutritional quality of the host plants.

Genomic and common garden approaches yield complementary results for quantifying environmental drivers of local adaptation in rubber rabbitbrush, a foundational Great Basin shrub.

The spatial structure of genomic and phenotypic variation across populations reflects historical and demographic processes as well as evolution via natural selection. Characterizing such variation can provide an important perspective for understanding the evolutionary consequences of changing climate and for guiding ecological restoration. While evidence for local adaptation has been traditionally evaluated using phenotypic data, modern methods for generating and analyzing landscape genomic data can directly quantify local adaptation by associating allelic variation with environmental variation. Here, we analyze both genomic and phenotypic variation of rubber rabbitbrush (Ericameria nauseosa), a foundational shrub species of western North America. To quantify landscape genomic structure and provide perspective on patterns of local adaptation, we generated reduced representation sequencing data for 17 wild populations (222 individuals; 38,615 loci) spanning a range of environmental conditions. Population genetic analyses illustrated pronounced landscape genomic structure jointly shaped by geography and environment. Genetic‐environment association (GEA) analyses using both redundancy analysis (RDA) and a machine‐learning approach (Gradient Forest) indicated environmental variables (precipitation seasonality, slope, aspect, elevation, and annual precipitation) influenced spatial genomic structure and were correlated with allele frequency shifts indicative of local adaptation at a consistent set of genomic regions. We compared our GEA‐based inference of local adaptation with phenotypic data collected by growing seeds from each population in a greenhouse common garden. Population differentiation in seed weight, emergence, and seedling traits was associated with environmental variables (e.g., precipitation seasonality) that were also implicated in GEA analyses, suggesting complementary conclusions about the drivers of local adaptation across different methods and data sources. Our results provide a baseline understanding of spatial genomic structure for E. nauseosa across the western Great Basin and illustrate the utility of GEA analyses for detecting the environmental causes and genetic signatures of local adaptation in a widely distributed plant species of restoration significance.

Variations in Groundwater Level and Microtopography Influence Desert Plant Communities in Shallow Aquifer Areas

An improved understanding of the relationships among vegetation, groundwater level, and microtopography is crucial for making well-informed management decisions in areas with shallow groundwater resources. We measured plant species abundance/composition and richness in relation to depth to groundwater (DTW) and microtopography in Owens Valley, California, particularly in areas where DTW ranged from 0 to 4 m. Sampling occurred along 67 vegetation transects across three community types. Relationships between DTW and community composition were evaluated using non-metric multidimensional scaling (NMS), while non-parametric multiplicative regression was used to relate DTW and microtopography to species abundance. The dominant gradient in species composition (NMS Axis 1) explained ~51% of variation in our distance matrix and was most strongly associated (r = 0.55) with DTW. The graminoids Juncus arcticus, Leymus triticoides, and Distichlis spicata had strong affinities toward areas with the shallowest DTW (<1.5 m). One salt-adapted species Sporobolus airoides and one shrub Ericameria nauseosa dominated areas with intermediate DTW (1.5-2.0 m), whereas the shrubs Atriplex torreyi, Sarcobatus vermiculatus, and Artemisia tridentata were dominant in areas with deeper DTW (>2.0 m). Variation in microtopography affected species abundance and increased species richness for vegetation communities at either extreme of the water table gradient, shallow, and deep DTW but not the intermediate DTW. Findings indicate that desert plant communities from shallow aquifers have adapted to different DTW and microtopography conditions and that considering those adaptations may be important to manage groundwater and vegetation resources in these areas.

Water Stress Patterns of Xerophytic Plants in an Urban Landscape

Efficient water use in urban landscapes is a common objective throughout the western United States. Vegetative species promoted for their drought tolerance characteristics are often included in landscapes designed for resource conservation. However, water requirements of most common landscape species have not been quantified. This is especially true for xerophytic species. This lack of landscape plant water requirement data is a significant constraint on the design of efficient irrigation systems and management practices affecting urban landscape water use. Current irrigation practices often fail to consider the unique physiology of xerophytic species, and irrigation scheduling models may not be appropriate for xeric landscapes using xerophytic vegetation as the primary method of reducing water use. This work describes the seasonal patterns of growth and xylem water status for four regionally native xeric shrub species planted in an unirrigated urban landscape in the semi-arid environment of central Oregon. The four species (Artemisia tridentata, Holodiscus microphyllus, Ericameria nauseosa, and Ribes cereum) exhibited substantial growth over the course of 18 months without irrigation in a heavily modified urban soil profile. Water potential of the four species was strongly correlated with surface (10 cm) soil moisture (r ≥ 0.90), less so with reference monthly evapotranspiration (r ≤ 0.55), and only weakly with water vapor deficit (r ≤ 0.22). In A. tridentata and H. microphyllus, xylem water potential became more negative during the growing season and tracked the seasonal decline in soil moisture. In contrast, the xylem water potential of E. nauseosa and R. cereum tracked soil moisture early in the season but became less responsive to soil moisture in the driest months, suggesting different drought adaptation strategies in these species. Three of the four species showed no visual signs of drought stress and maintained acceptable aesthetics even as soil moisture decreased to less than 10%. However, R. cereum exhibited a drought dormancy strategy that made it less aesthetically desirable. These results suggest that extreme xerophytic shrubs provide an opportunity for significant reductions in water use in urban landscapes.

Insects of Dominant Shrub Communities at Pawnee and Comanche National Grasslands, Colorado

Terrestrial insects associated with shrubs at Pawnee National Grassland in northeastern Colorado and Comanche National Grassland in southeastern Colorado were identified to family or genus with some taxa to species. Six species of grassland shrubs were sampled using a funnel-bucket method each month from June-September 2014 and 2015. Insect diversity and abundance differed between the grasslands. Chrysomelidae, Cicadellidae, Cleridae, Formicidae, Meloidae, and Miridae were abundant at Pawnee National Grassland, primarily from four-winged saltbush (Atriplex canescens) (Pursh.) Nutt). Acrididae, Aphididae, Chrysomelidae, Cleridae, Coccinellidae, Formicidae, Lygaeidae, Miridae, and Reduviidae collected from sandsage (Artemisia filifolia Torr.), four-winged saltbush, rabbitbrush (Ericameria nauseosa (Pallas ex. Pursh), greasewood (Sarcobatus vermiculatus (Hook) Torr.), skunkbush (Rhus trilobata Nutt.), and one-seed juniper (Juniperus monosperma (Engelm.) were abundant at Comanche National Grassland.

Development and Survival ofChlosyne acastus sterope(Lepidoptera: Nymphalidae) Larvae on Three Host Plants in South Central Washington

Post-diapause third instar larvae of Chlosyne acastus sterope from shrub-steppe habitat near Benton City in central Washington were reared to adulthood at 25 oC on Chrysothamnus viscidiflorus, Erigeron linearis and a hitherto unrecorded host, Ericameria nauseosa. Larvae developed successfully on all host plants but survival was highest on C. viscidiflorus and E. linearis and lowest on E. nauseosa. Mean larval duration from post-diapause entry into laboratory conditions until pupation was shortest when fed C. viscidiflorus and longest on E. nauseosa or E. linearis. Mean pupal duration was longest on E. linearis and shortest on E. nauseosa and C. viscidiflorus. Mean forewing lengths of adults were shorter when larvae were reared on E. linearis. Ericameria nauseosa is sub-optimal for C. a. sterope in terms of larval survival but produces optimally-sized pupae and adults. Feeding on E. linearis is optimal for survival but slow-developing larvae produce small pupae and adults. Possible fitness implications of this host plant-mediated variation in larval survival, pupal weight, duration and adult size in C. a. sterope are discussed.

Community Structure and Demography in a Saline Pan-Dune Mosaic in the Western Mojave Desert

A unique saline ecological system formed by an extensive mosaic of small clay pans and low stable dunes exists within Edwards Air Force Base in the western Mojave Desert of California. This ecosystem lies between the large Rosamond and Rogers dry lakes on the old Pleistocene lakebed of Lake Thompson. Plant communities on the low and relatively stable dunes were broadly classed as saltbush scrub, with a total canopy cover of 30–36%. Atriplex confertifolia was the typical dominant, with Ericameria nauseosa as an important associate. Taller dunes of younger age and less saline soils had similar plant cover, but a distinct plant community with Atriplex canescens and Krascheninnikovia lanata as dominants and Yucca brevifolia as a common associate. Flat areas adjacent to the dunes were dominated by a virtual monoculture of Atriplex confertifolia. Aboveground shrub and bunchgrass biomass including dead material varied from 503 to 1204 kg ha−1, low in comparison to similar plant communities in the Great Basin. The absence of small saplings and seedlings of many shrub species suggests successful establishment is highly episodic. Seedlings were abundant only in Isocoma acradenia.

Plant Phenology and Water Relations in a Saline Pan-Dune Mosaic in the Western Mojave Desert

An extensive mosaic of small clay pans and low stable dunes exists within Edwards Air Force Base in the western Mojave Desert of California. This pan-dune ecosystem, positioned between the large Rosamond and Rogers dry lakes on the old Pleistocene lakebed of Lake Thompson, provides an opportunity to study the seasonal patterns in growth and flowering phenology and water relations in a saltbush scrub community dominated by a mix of C3 and C4 species. C3 shrubs initiated vegetative growth in February, with current shoot and leaf production largely ceasing in most species by mid-April. The deeply rooted Tetradymia stenolepis and Ericameria nauseosa continued vegetative growth through May. C4 species including Atriplex and the grass Distichilis spicata typically began vegetative growth in mid- to late March, 2–6 weeks later than the first group and continued this growth in most cases through June and July. Reproductive growth commonly did not begin until June and continued into July and/or August. Shrub species showed a general pattern of slowly declining water potentials (increased stress) through the late spring and summer months, reflecting more limited soil water availability. Smaller changes in predawn water potential over this period were seen in the deeply rooted species. Soil moisture availability in the widespread Atriplex confertifolia showed a pattern of variation between pan, dune and open flat microhabtats.

Performance of the Rangeland Hydrology and Erosion Model for runoff and erosion assessment on a semiarid reclaimed construction site

The ability to assess the impact of management actions on soil and water resources is crucial to sustainable land management. The Rangeland Hydrology and Erosion Model (RHEM) was developed as an assessment and decision support tool for resource management agencies and has been used to estimate soil erosion at national, regional, and local scales for both disturbed and undisturbed rangeland soil and vegetation conditions. In this paper, runoff, sediment, and microtopography data were collected during a series of rainfall simulation experiments aimed at evaluating the effectiveness of revegetation on a shrub-dominated post-construction hillslope where the soil has had time to reconsolidate. RHEM9s input parameters are simple to collect and consist of soil texture, slope configuration, and canopy and ground cover. Experimental results showed that a mix of the shrub species rabbitbrush (<i>Chrysothamnus nauseosus</i>) and the invasive annual grass cheatgrass (<i>Bromus tectorum</i>) were more effective at reducing runoff and soil loss than rabbitbrush alone. Plots with more than 45% of residue cover produced as much as 2.1 times less runoff and 16 times less sediments than those with less than 15% of litter. Microtopographic changes information allowed partitioning the erosion process into diffuse and concentrated flow processes. Analysis of this 3D data highlighted the central role of concentrated flow erosion in sediment delivery on rangeland hillslopes. RHEM9s performance as expressed by the coefficient of determination, <i>R</i>², and the Nash-Stucliffe Efficiency (NSE) was <i>R</i>² = 0.84 and NSE = 0.27 for runoff and <i>R</i>² = 0.81 and NSE = 0.26 for sediments. This study demonstrates that RHEM can be effectively used by land managers and project managers to estimate soil erosion as a function of precipitation event on construction sites that have been revegetated to rangeland plant communities.

Hydrothermal Carbonization (HTC) and Pelletization of Two Arid Land Plants Bagasse for Energy Densification

In this study, bagasse from two arid land plants, grindelia and rabbitbrush, were hydrothermally carbonized (HTC) along with their raw biomass at 200–260 °C for 5 min. Prior to HTC, biocrude was extracted from grindelia (Grindelia squarrosa), whereas rubber was extracted from rabbitbrush (Ericameria nauseosa). Solid hydrochars and HTC process liquids of extracted feedstocks were characterized by ultimate, proximate, fiber, FTIR, higher heating value (HHV), and GC–MS analyses and the results were compared with their corresponding unextracted conditions. Hydrochars were pelletized in a single-press pelletizer and mass and energy densities of the pellets were measured. From the proximate, ultimate, FTIR, and fiber analyses, the bagasse show similar properties of the raw biomass, although the HHV was slightly increased with crude extraction from grindelia and decreased with rubber extraction from rabbitbrush. With the increase of HTC temperature, solid mass yield was decreased up to 44% for grindelia bagasse ...

Life form-specific gradients in compound-specific hydrogen isotope ratios of modern leaf waxes along a North American Monsoonal transect.

The use of hydrogen isotope ratios (δ(2)H) of sedimentary n-alkanes from leaf waxes has become an important tool for reconstructing paleoenvironmental and ancient hydrologic conditions. Studies of modern plant waxes can elucidate driving ecological mechanisms behind geologic deposits. Here, we used a transect across the North American Monsoon region of the western USA from Tucson, Arizona to Salt Lake City, Utah to study variations in leaf wax δ(2)H among co-occurring plants. Three co-occurring life forms were selected: perennial shrub (rabbit brush, Chrysothamnus nauseosus; sagebrush, Artemisia tridentata); tree (Gambel's oak tree, Quercus gambelii); and annual (sunflower, Helianthus annuus). Our results showed that the distributions and abundances of n-alkanes in perennial plants were similar across all sites and generally did not vary with environmental conditions (e.g., precipitation and temperature). In contrast, variations in n-alkane δ(2)H were significantly correlated with the fraction of the annual precipitation coming during the summer monsoon period. We use a modified Craig-Gordon model to speculate on the possible drivers of the δ(2)H values of leaf wax n-alkanes of plants across the region. The model results suggest that the most likely explanation for variation in wax δ(2)H values was a combination of seasonal source water usage and subsequent environmental conditions.

Bidirectional recovery patterns of Mojave Desert vegetation in an aqueduct pipeline corridor after 36 years: I. Perennial shrubs and grasses

We studied recovery of 21 perennial plant species along a severely disturbed aqueduct corridor in a Larrea tridentata-Ambrosia dumosa plant alliance in the Mojave Desert 36 years after construction. The 97-m wide corridor contained a central dirt road and buried aqueduct pipeline. We established transects at 0 m (road verge), 20 m and 40 m into the disturbance corridor, and at 100 m in undisturbed habitat (the control). Although total numbers of shrubs per transect did not vary significantly with distance from the verge, canopy cover of shrubs, species richness, and species diversity were higher in the control than at the verge and other distances. Canopy cover of common shrubs (Ericameria nauseosa, Ambrosia salsola, A. dumosa, L. tridentata, Grayia spinosa) and perennial grasses (Elymus elymoides, Poa secunda) also varied significantly by location. Discriminant analysis clearly separated the four distances based on plant composition. Patterns of recovery were bidirectional: secondary succession from the control into the disturbance corridor and inhibition from the verge in the direction of the control. Time estimated for species composition to resemble the control is dependent on location within the disturbance corridor and could be centuries at the road verge. Our findings have applications to other deserts.

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.

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

Patterns of Water Use by Great Basin Plant Species Under Summer Watering

We analyzed temporal and spatial patterns of water use by a functionally-diverse group of Great Basin plant species and determined their water use rates at the whole-plant and individual-leaf scales under variable summer watering. Species studied were the desert grasses Distichlis spicata and Sporobolus airoides, the desert shrubs Artemisia tridentata, Ericameria nauseosa, and Atriplex confertifolia; the wetland/riparian plants Juncus arcticus, Leymus triticoides, and Salix exigua; and the annual exotic Salsola tragus. Plant species were individually grown in 5.8 m2 plots in a common garden in eastern California. Three irrigation treatments in the form of monthly pulses were applied during the summer: low (1.3 cm), medium (2.6 cm), and high (3.9 cm), in addition to a nonirrigated control. Whole-plant water uptake characteristics were determined by soil water depletion at different soil depths, while leaf transpiration was determined by gas exchange. Whole-plant water extraction and leaf transpiration varied similarly among species. Desert shrubs had low water extraction (35 to 395 g m−2 day−1) and were not affected by irrigation. The desert grasses and riparian/wetland species had higher water extraction, increasing with irrigation levels. L. triticoides and J. arcticus had the highest water extraction overall (>2,000 g m−2 day−1). Desert shrubs relied 10 times more on deeper water sources than herbaceous species. The average T/ET was 31%, but varied by species. Summer available water in environments such as the Great Basin favors desert grasses and riparian/wetland species, but not desert shrubs. The observed species differences provide alternatives for water and vegetation management.

Community Structure Affects Annual Grass Weed Invasion During Restoration of a Shrub–Steppe Ecosystem

AbstractEcological restoration of shrub–steppe communities in the western United States is often hampered by invasion of exotic annual grasses during the process. An important question is how to create restored communities that can better resist reinvasion by these weeds. One hypothesis is that communities comprised of species that are functionally similar to the invader will best resist invasion, while an alternative hypothesis is that structurally more complex and diverse communities will result in more effective competitive exclusion. In this field experiment, we examined the effects of restored community structure on the invasion success of three annual grass weeds (downy brome, jointed goatgrass, and cereal rye). We created replicated community plots that varied in species composition, structural complexity and density, then seeded in annual grass weeds and measured their biomass and seed production the following year, and their cover after 1 and 3 yr. Annual grass weeds were not strongly suppressed by any of the restored communities, indicating that it was difficult for native species to completely capture available resources and exclude annual grass weeds in the first years after planting. Perennial grass monocultures, particularly of the early seral grass bottlebrush squirreltail, were the most highly invaded communities, while structurally complex and diverse mixtures of shrubs (big sagebrush, rubber rabbitbrush), perennial grasses (bluebunch wheatgrass and bottlebrush squirreltail) and forbs (Lewis flax, Utah sweetvetch, hairy golden aster, gooseberryleaf globemallow) were more resistant to invasion. These results suggest that restoration of sagebrush steppe communities resistant to annual grass invasion benefits from higher species diversity; significant reduction of weed propagule pressure prior to restoration may be required.