studies of a new hybrid taxon in the Artemisia tridentata asteraceae anthemideae complex

Members of the Artemisia tridentata complex (ASTERACEAE: Anthemideae: Artemisia subgen. Triden- tatae) have adapted to changing environmental conditions through geographic migration, introgression, and hybridiza- tion. These processes have resulted in morphologic and genetic variation. A presumed hybrid (“Bonneville” big sage- brush) of the complex occurs in the moister ranges of A. t. ssp. wyomingensis and can be found growing with shrub species commonly associated with A. t. ssp. vaseyana. These populations appear to be preferred habitat for sage-grouse and are more heavily grazed by ungulates than the parental populations. We determined ploidy levels and conducted a detailed morphological analysis to determine if “Bonneville” is a hybrid entity. Sixteen populations (12 in Oneida Co., ID, and 4 in Rich Co., UT) were selected for the study, representing the putative hybrid (Taxon B) and the putative parents— A. t. ssp. vaseyana (2n = 18), A. t. ssp. wyomingensis (2n = 36), and A. t. ssp. tridentata (2n = 36). Each population con- sisted of 25 randomly selected individuals for a total of 400 samples. Our analysis showed 3 populations with morpho- logical and chemical characteristics indicating introgression of A. t. ssp. wyomingensis with populations containing A. t. ssp. vaseyana. Based on these results, we designate the Bonneville sagebrush with formal hybrid status of nothotaxon: Artemisia tridentata ssp. ×bonnevillensis H. Garrison, L. Shultz, and E.D. McArthur (pro subsp.), 2n = 36. RESUMEN.—Los arbustos que forman parte del complejo Artemisia tridentata (ASTERACEAE: Anthemideae: Artemisia subgenero tridentatae) se han adaptado a las condiciones ambientales cambiantes a traves de la migracion geografica, la introgresion y la hibridacion, lo cual ha dado como resultado variacion morfologica y genetica. Un supuesto hibrido (Artemisia “Bonneville”) del complejo habita en sitios humedos de A. t. ssp. wyomingensis y se puede encontrar creciendo entre las especies de arbustos que habitualmente se asocian con A. t. ssp. vaseyana. Estas pobla- ciones parecen ser el habitat preferido del gallo de salvia y donde pastan mas los ungulados, en comparacion con las poblaciones parentales. Determinamos niveles de ploidia y realizamos un analisis morfologico exhaustivo para determi- nar si “Bonneville” es una entidad hibrida. Se seleccionaron dieciseis poblaciones para realizar el estudio, que represen- tan el hibrido potencial (Taxon B) y los parentales potenciales: A. t. ssp. vaseyana (2n = 18), A. t. ssp. wyomingensis (2n = 36), A. t. ssp. tridentata (2n = 36): doce en el condado de Oneida, Idaho y cuatro en el condado de Rich, Utah. Cada poblacion consistio de veinticinco individuos seleccionados al azar con un total de cuatrocientas muestras. Nuestro analisis mostro tres poblaciones con caracteristicas morfologicas y quimicas que indican introgresion de A. t. ssp. wyomingensis con poblaciones de A. t. ssp. vaseyana. Con base en estos estudios, asignamos a la Artemisia Bonneville la condicion de hibrido formal de un nototaxon, como Artemisia tridentata ssp. ×bonnevillensis H. Garrison, L. Shultz, y E.D. McArthur (pro subsp.), 2n = 36.

stress induced metabolic differences between populations and subspecies of Artemisia tridentata sagebrush from a single hillside

Abstract Big sagebrush or Artemisia tridentata Nutt. ssp. vaseyana grows at slightly higher, cooler, and drier sites than does A. tridentata ssp. tridentata . The two sagebrush subspecies and natural hybrids between them are found along an elevational gradient in Salt Creek Canyon, near Nephi, UT, USA, where the parent populations are separated by 85 m in elevation and 1.1 km along the transect. In 1993, three gardens were established with seedlings from five populations from different elevations planted in each garden. Physiological measurements of carbon isotope ratios, chlorophyll fluorescence, and respiratory heat and CO 2 production show adaptation to the site of origin. When transplanted to foreign sites, stress was noted. Sagebrush has persistent leaves that are metabolically active all year. Seasonal changes in temperature promote metabolic responses in sagebrush that differ with population and garden.

narrow hybrid zone between two subspecies of big sagebrush Artemisia tridentata asteraceae vi respiration and water potential

Respiration and stem water potential (ψ) were examined in parental and hybrid big sagebrush (Artemisia tridentata Nutt. ssp. tridentata and Artemisia tridentata Nutt. ssp. vaseyana (Rydb.) Beetle) grown in common gardens within each parental zone and in the hybrid zone. Plants were sampled in July, August, and September, i.e., immediately before, during, and after flowering. The habitats differed from one another, and there were significant garden by date interactions. The source populations also differed significantly from one another. There were no significant garden by source interactions. Hybrid plants had intermediate respiration rates and did not suffer greater water stress than parental plants. Hybrid plants showed no apparent decrease in adaptation in the important physiological traits respiration and water stress in the hybrid zone.

shifts in depth of water extraction and photosynthetic capacity inferred from stable isotope proxies across an ecotone of juniperus osteosperma utah juniper and Artemisia tridentata big sagebrush

Summary

1
In western North America, juniper trees (Juniperus spp.) are apparently encroaching into numerous communities including sagebrush-dominated (Artemisia tridentata) valleys, where, as density of juniper increases, the density and condition of sagebrush decline but juniper condition appears unaffected.

2
We examined stable isotope proxies of plant gas exchange and relative depth of soil water extraction of Juniperus osteosperma and Artemisia tridentata as their relative densities changed across a transition zone in northern Utah, USA. Measurement of 13C and 18O of foliage allowed separation of the contributions of stomatal and biochemical factors to differences in mean intercellular CO2 concentration, while deuterium composition of stem water served as an indicator of the relative depth of water extraction.

3
Leaf δ13C of juniper and, to a lesser extent, of sagebrush increased with decreasing density of juniper. Foliage 18O did not vary significantly with juniper density, indicating that this was primarily caused by an increase in photosynthetic capacity rather than decreased supply of CO2. Increased foliage nitrogen concentration of both species with decreasing juniper density is also consistent with increased photosynthetic capacity.

4
The much greater mean age of juniper trees in the high juniper density plots may explain their lower photosynthetic capacity.

5
Averaged across densities, juniper always extracted water deeper in the profile than did sagebrush, but in June and August, only the high juniper density plots showed an effect. Sagebrush is either restricted from using water at greater depth in the presence of juniper at high density or was in such poor condition that deep-water sources were not necessary to maintain their reduced function.

6
Ecotones can serve as useful, spatially constrained stages for examining resource partitioning and relationships among plant species. We observed spatial and temporal variation in resource use and partitioning of limited resources that will enable better design of manipulative experiments to explicitly examine competition.

water conservation in Artemisia tridentata through redistribution of precipitation

Water conservation is important for plants that maintain physiologically active foliage during prolonged periods of drought. A variety of mechanisms for water conservation exist including stomatal regulation, foliage loss, above- and below-ground allocation patterns, size of xylem vessels and leaf pubescence. Using the results of a field and simulation study with Artemisia tridentata in the Great Basin, USA, we propose an additional mechanism of water conservation that can be used by plants in arid and semi-arid environments following pulses of water availability. Precipitation redistributed more uniformly in the soil column by roots (hydraulic redistribution of water downward) slows the rate at which this water can subsequently be taken up by plants, thus prolonging water availability during periods of drought. By spreading out water more uniformly in the soil column at lower water potentials following precipitation events, water use is reduced due to lower soil conductivity. The greater remaining soil water and more uniform distribution result in higher plant predawn water potentials and transpiration rates later in the drought period. Simulation results indicate that plants can benefit during drought periods from water storage following both summer rain events (small summer pulses) and overwinter recharge (large spring pulse). This mechanism of water conservation may aid in sustaining active foliage, maintaining root-soil hydraulic connectivity, and increasing survival probability of plants which remain physiologically active during periods of drought.

rapid soil moisture recharge to depth by roots in a stand of Artemisia tridentata

The temporal patterns of soil water potential in a stand of Artemisia tridentata in central Utah, USA, were monitored during the summer, which included small periodic rainfall events, and over the winter, when most of the soil recharge occurs in this environment. The pattern of recharge, when compared to an area cleared of aboveground vegetation, strongly indicated that the downward movement of water to 1.5 m was primarily conducted via roots by the process known as hydraulic redistribution. Rainwater was moved rapidly downward shortly after the rain event and continued over a period of a few days. For rainwater reaching a 0.3–1.5 m depth, the portion redistributed by roots was estimated to range from 100% for small rainfall events (<8 mm) to 74% for a 36-mm event. Simulations with a model of soil water movement that compared situations with and without hydraulic redistribution by roots, indicated that during the fall–spring recharge period, 67% of all water moved downward below 0.1 m was via roots, while...

water relations and photosynthesis along an elevation gradient for Artemisia tridentata during an historic drought

Quantifying the variation in plant-water relations and photosynthesis over environmental gradients and during unique events can provide a better understanding of vegetation patterns in a future climate. We evaluated the hypotheses that photosynthesis and plant water potential would correspond to gradients in precipitation and soil moisture during a lengthy drought, and that experimental water additions would increase photosynthesis for the widespread evergreen shrub Artemisia tridentata ssp. vaseyana. We quantified abiotic conditions and physiological characteristics for control and watered plants at 2135, 2315, and 2835 m near Mammoth Lakes, CA, USA, at the ecotone of the Sierra Nevada and Great Basin ecoregions. Snowfall, total precipitation, and soil moisture increased with elevation, but air temperature and soil N content did not. Plant water potential (Ψ), stomatal conductance (g s), maximum photosynthetic rate (A max), carboxylation rate (V cmax), and electron transport rate (J max) all significantly increased with elevations. Addition of water increased Ψ, g s, J max, and A max only at the lowest elevation; g s contributed about 30 % of the constraints on photosynthesis at the lowest elevation and 23 % at the other two elevations. The physiology of this foundational shrub species was quite resilient to this 1-in-1200 year drought. However, plant water potential and photosynthesis corresponded to differences in soil moisture across the gradient. Soil re-wetting in early summer increased water potential and photosynthesis at the lowest elevation. Effects on water relations and photosynthesis of this widespread, cold desert shrub species may be disproportionate at lower elevations as drought length increases in a future climate.

sensitivity of water relations and photosynthesis to summer precipitation pulses for Artemisia tridentata and purshia tridentata

For much of the western USA, precipitation occurs in pulses, the nature of which determine soil water potential and plant physiological performance. This research utilized three experiments to examine the sensitivity of photosynthesis and water relations for two widespread Great Basin Desert shrub species, Artemisia tridentata (which has both deep and shallow roots) and Purshia tridentata (which reportedly has only deep roots), to (1) variation in pulse magnitude size, (2) the kinetics of responses to pulses, and (3) the relationship between pulse-size and antecedent soil water content. At the study site in the southwestern Great Basin Desert, USA, summer rainfall exhibits a greater frequency of larger-sized events, and longer inter-pulse intervals, compared to annual patterns. Compared to pre-watering values, stem water potential initially increased by about 2.00 MPa for A. tridentata and 1.00 MPa for P. tridentata following watering to simulate an 11.5 mm rainfall pulse. For the same water addition, stomatal conductance increased by 0.3 mol m−2 s−1 and photosynthetic CO2 assimilation increased 8-fold for A. tridentata and 6-fold for P. tridentata. Water potential and photosynthetic gas exchange were maximal for both species 2–3 days following a pulse addition. In comparison to P. tridentata, the increase in photosynthesis for A. tridentata was more pronounced for plants treated incrementally with several small pulses compared to plants treated with one pulse of an equivalent total volume. The results indicate that both species can respond to a range of summer rainfall pulse magnitudes within about 2 days, with A. tridentata generally exhibiting larger responses in comparison to the co-dominant shrub species P. tridentata, which at this study site does indeed have shallow roots. In a future climate, the timing and magnitude of summer rainfall pulses will determine the extent to which these two species undergo changes in water status and photosynthetic carbon uptake, with implications for their fitness.

combined drought and episodic freezing effects on seedlings of low and high elevation subspecies of sagebrush Artemisia tridentata

Big sagebrush (Artemisia tridentata) is a dominant shrub throughout much of the arid western United States. Several recognized subspecies differ in physiology, morphology and in their distribution in relation to soil water availability. While several studies have compared mature individuals of these subspecies, there is little information on seedling physiological tolerance to physical stresses. Understanding seedling physiology is essential for predicting how species may respond to changes in temperature and precipitation regimes. Our objective was to examine the drought and freezing tolerance of seedlings of two A. tridentata subspecies: ssp. tridentata, which is found in low-elevation dry sites, and ssp. vaseyana, found in higher, moister sites. We examined growth, gas exchange and quantum yield of chlorophyll a fluorescence from photosystem II (PSII) for seedlings grown in a greenhouse and exposed to two different levels of moisture availability in combination with a simulated growing season freezing event. We found that ssp. tridentata possessed several drought-tolerant characteristics, such as rapid growth rates, thick leaves and low stomatal conductance. Both subspecies shared similar physiological tolerance to the low-moisture treatment but experienced relatively more stress under the freezing treatment. Subspecies vaseyana was more sensitive to freezing when grown with low soil moisture, resulting in reduced stomatal conductance and PSII quantum yield. In contrast, the low-soil moisture treatment did not increase the susceptibility of ssp. tridentata to freezing. These results demonstrate that drought tolerance may be an important trait for seedlings of A. tridentata, but stress because of freezing damage of seedlings may limit the distribution of the species.