High rates of photosynthesis in the desert shrub Chrysothamnus nauseosus ssp. albicaulis

  Basic aspects of photosynthesis were investigated in white rubber rabbitbrush ( Chrysothamnus nauseosus (Pallas) Britt. ssp. albicaulis ), a common C 3 deciduous shrub native to arid regions of the western U.S. Under favorable field conditions, net photosynthesis (P n ) ranged from 36 to 73 mgCO 2 · dm – 2 · hr – 1 , which is relatively high for a woody species. The leaves from the actively growing flowering shoots exhibited higher P n than those on the vegetative shoots. P n also varied according to the age of the leaves and the location of the plants. P n did not light saturate even at quantum flux densities (QFD) equivalent to full sunlight. The light compensation point was relatively high (ca 100 μ mol · m – 2 · S – 1 ), perhaps due to the presence of a tomentose vestiture on the leaf surface. At high QFD's, the stomatal conductance was high (ca 520 mmol · m – 2 · s – 1 ) for a woody species. RUBP - carboxylase content of the leaves ranged from 20 to 22 mg per gram F.W., which is similar to that found in most C 3 crop species. These results suggest that rabbitbrush is able to maintain high rates of P n , at least under nonstressed conditions.           

Chrysothamnus nauseosus ssp. uintahensis: a stabilized hybrid

Chrysothamnus nauseosus ssp. uintahensis (Asteraceae) is formally described and illustrated. The new subspecies represents stabilized hybrids that most probably have C. nauseosus ssp. hololeucus x C. parryi ssp. attenuatus ancestry. Morphological and anatomical comparisons are made among the putatively related taxa.        

Seasonal changes of selected secondary plant products in Chrysothamnus nauseosus ssp. turbinatus

Previously, physiological studies of rubber and resin production during the growing season of Chrysothamnus nausceosus ssp. turbinatus indicated a negative correlation between rubber and resin content. The resin was highest in the spring and lowest in the summer, whereas rubber was highest in the summer and lowest in the spring. Individual compounds were followed during the growing season to see if they correlated with the rubber or resin trend. The total compounds in the cyclohexane fraction followed the resin pattern. Individual compounds varied in their changes during the growing season. Limonene, for example, was negatively correlated with rubber production, whereas β cubebene was positively correlated. The possible metabolic pathways between resin and rubber are discussed.     

Seed germination characteristics of Chrysothamnus nauseosus ssp. viridulus (Astereae, Asteraceae)

Rubber rabbitbrush ( Chrysothamnus nauseosus [Pallas] Britt. ssp. viridulus ) may prove to be a source of high-quality cis-isoprene rubber, but its establishment is limited by a lack of information on seed germination. Consequently, seeds were germinated at alternating temperatures (5–15, 5–25, 15–25, and 20–30 C) in light and dark as well as constant temperatures (15–40 C with 5-C increments) to determine temperature response. Seeds were also germinated in solutions of polyethylene glycol 6000 (0 to –5 bar), salinity regimes (1, 17, 51, and 86 mM) at all the above-mentioned temperatures to determine salinity and temperature interaction. The hormones GA 3 (0, 2.9, 29.0, and 58.0 um) and kinetin (0, 4.7, 23.5, and 47.0 um) were used to study their effect on overcoming salt- and temperature-induced germination inhibition. Seeds of C. nauseosus ssp. viridulus were very sensitive to low temperature. Best germination was achieved at 25 and 30 C, but these seeds also germinated at a higher temperature (35 C). The seeds of rabbitbrush germinated at both constant and alternating temperatures. Light appears to play little or no role in controlling germination of the seeds of rubber rabbitbrush. However, seeds of rabbitbrush were sensitive to salinity, and seed germination was progressively inhibited by increase in salt concentration, although a few seeds still germinated at the highest saline level. Progressively higher concentrations of polyethylene glycol also progressively inhibited germination. Suppression of seed germination induced by high salt concentrations and high temperatures can be partially alleviated by the application of either GA 3 or kinetin.     

Chrysothamnus nauseosus ssp. iridis (Asteraceae): a new endemic from Utah

Chrysothamnus nauseosus ssp. uintahensis (Asteraceae) is formally described and illustrated. The new subspecies represents stabilized hybrids that most probably have C. nauseosus ssp. hololeucus x C. parryi ssp. attenuatus ancestry. Morphological and anatomical comparisons are made among the putatively related taxa.        

Natural polyploidization within tetraploid and hexaploid populations of the desert shrub Atriplex confertifolia

Shadscale ( Atriplex confertifolia ) is a wind-pollinated dioecious shrub of western North America with an unusual development of apparently autoploid races, showing all even ploidy levels from 2x to 12x (base x = 9). Of these, tetraploid races are the most frequently encountered, with octoploids the next most common, and hexaploids being much less common. In this study, the occurrence of neopolyploid individuals within tetraploid and hexaploid populations of shadscale was examined at natural sites in order to investigate the pathways by which octoploids may be formed and to find a possible explanation for the predominance of octoploids over hexaploids. The frequencies of apparent neopolyploid individuals among adults and the frequencies of their backcrosses were tabulated, as was the occurrence of neopolyploidy among seeds of female plants from some of the same populations. The neopolyploids encountered in these surveys were almost exclusively those expected from unions involving single unreduced gametes. 6x presumed neopolyploid plants were observed in tetraploid populations at a frequency of 0.20%, and 6x seeds were observed at a frequency of 1.91%. Within examined hexaploid populations, 9x adults were not encountered, but 9x seeds were observed at a rate of 0.52%. Evidence was obtained for the operation of some postulated autoploid pathways for generation of octoploids, but these routes did not operate at rates comparable to those for the production of hexaploids. Although the question needs to be studied by genetic methods, the most probable reason for scarcity of hexaploids in nature appears to be that some tetraploid races are diploidized, which would result in irregularities of meiosis in their neohexaploids and a failure to form new races due to infertility and inviability. El “shadscale” ( Atriplex confertifolia ) es un arbusto dioico del oeste de Norteamérica polinizado por el viento que exhibe el desarrollo inusual de razas aparentemente poliploides, con todos los niveles pares de ploidía desde 2x hasta 12x (x base = 9). De éstos, los más comunes son los tetraploides y luego los octoploides. Los hexaploides son mucho menos comunes. En este estudio, examinamos la presencia de individuos neopoliploides entre poblaciones tetraploides y hexaploides del shadscale en sitios naturales para investigar los medios por los cuales se pueden formar los octoploides y para encontrar una posible explicación para el predominio de los octoploides sobre los hexaploides. Tabulamos la frecuencia de individuos aparentemente neopoliploides entre adultos y su descendencia retrocruzada, así como la presencia de neopoliploides entre semillas de las plantas femeninas de algunas de las mismas poblaciones. Los neopoliploides encontrados en estos muestreos fueron casi exclusivamente los que se esperarían de la unión de un gameto no reducido y un gameto reducido. Observamos plantas 6x presunta mente neopoliploides en poblaciones tetraploides con una frecuencia del 0.20%, o del 1.91% en las semillas. Entre las poblaciones examinadas de hexaploides, no encontramos adultos 9x, aunque los observamos con una frecuencia del 0.52% en las semillas. Obtuvimos evidencia de la operación de algunos procesos autoploides postulados para explicar la generación de octoploides, pero estos procesos no operan a frecuencias comparables a aquellas para la producción de hexaploides. Aunque es preciso investigar el tema mediante métodos genéticos, la causa más probable para la escasez de los hexaploides en entornos naturales parece ser que algunas razas tetraploides son diploidizadas, produciendo irregularidades meióticas en sus neohexaploides, los cuales no logran formar razas nuevas debido a su infertilidad o inviabilidad.     

Standing crops and dynamics of phytomass and minerals in two salt desert shrub communities

Of two salt desert shrub communities studied in Curlew Valley, Utah, the Atriplex confertifolia- dominated community had 15% greater total midsummer phytomass than the Ceratoides lanata community. The larger Atriplex shrubs contained much more woody tissue for support of photosynthetic tissues than did Ceratoides. Atriplex aboveground phytomass and litter were about twice those of Ceratoides. Ceratoides litter was generally fine and easily decomposable, but Atriplex litter contained about equal proportions of coarse, resistant woody tissues and fine, easily decomposable material. Atriplex root phytomass was 1.3 times that of Ceratoides at the 2–30 cm depth, but at depths below 30 cm, Ceratoides exhibited up to three times greater root phytomass and had 23% more root mass overall. Net aboveground community primary production was estimated to be about one-third greater in the Atriplex than Ceratoides community. Turnover times for readily decomposable aboveground litter were quite similar, but, because Atriplex produced coarser litter, its overall rate was somewhat slower than that of Ceratoides. Analyses of selected minerals in plant parts, litter, and soil revealed that about 90% of the mineral capital is in the soil, mostly within organic matter. Nearly equivalent pools of mineral elements were found in the two communities, except for greater Na in the Atriplex community.     

Observations on the distribution of microorganisms in desert soil

Population estimates of fungi, bacteria, and actinomycetes in desert soil were determined with respect to soil depth and distance from shrubs. In general the highest numbers of microbes were found at the shrub base; the lowest numbers were found in the interspaces. While the total number of organisms usually declined in deeper soil, the relative importance of the actinomycetes increased. These population trends are attributed to substrate availability and utilization and interspecific interactions. As the soils became drier and warmer the total number of microorganisms decreased. Mold populations remained at about the same level during the study. While the numbers of both bacteria and actinomycetes declined, the relative importance of the actinomycetes increased.        

Temperature-related behavior of some migrant birds in the desert

Behavior of migrant birds in relation to temperature was studied and compared to that of resident species in the northern Mojave Desert. Migrants reduced foraging intensity above 30 C, but resident species showed no striking decrease in intensity of foraging at temperatures up to 35 C. Migrant species shifted activities to shaded microhabitats at temperatures between 20 and 30 C; the resident Verdin showed a similar shift at 35 C. Most migrants decreased the amount of time spent foraging at temperatures above 30; Verdins showed a similar but stronger response to temperatures about 30 C. Significant reductions in the use of hovering and hawking maneuvers were found among migrants at temperatures above 30 C. Migrants showed similar types of behavioral adjustments to temperatures as did resident desert species, but they responded earlier in the daily temperature cycle. Desert birds appear to correlate their daily activity strongly with temperature, but nondesert species may respond either to temperature or time of day.     

Competition between harvester ants and rodents in the cold desert

Local distribution patterns of three rodent species ( Perognathus parvus, Peromyscus maniculatus, Reithrodontomys megalotis ) were studied in areas of high and low densities of harvester ants ( Pogonomyrmex owyheei ) in Raft River Valley, Idaho. Numbers of rodents were greatest in areas of high ant-density during May, but partially reduced in August; whereas, the trend was reversed in areas of low ant-density. Seed abundance was probably not the factor limiting changes in rodent populations, because seed densities of annual plants were always greater in areas of high ant-density. Differences in seasonal population distributions of rodents between areas of high and low ant-densities were probably due to interactions of seed availability, rodent energetics, and predation.     

Sprouting and seedling establishment in plains silver sagebrush ( Artemisia cana Pursh. ssp. cana )

The importance and nature of vegetative reproduction was compared with seedling establishment in plains silver sagebrush ( Artemisia cana Pursh. ssp. cana ). Sixty-three percent of plants excavated originated from rhizomes. Sites that experienced habitat disturbance did not have a significantly different number of plants originating from vegetative reproduction than did undisturbed sites. Parent rhizomes were significantly older than taproots, which were significantly older than aboveground stems. Rhizome systems were spread 3.3 times that of plant height. Seventy-nine percent of rhizomatous daughter plants were 100 cm or less from parent plants. Up to 52 sprouts were found on one rhizome. Seedling establishment was greatest during wet growing seasons, and vegetative reproduction was greatest during dry years.     

Vegetation changes after livestock grazing exclusion and shrub control in the southern Chihuahuan Desert

Vegetation cover and production were evaluated after nearly 7 years of livestock grazing exclusion and shrub control in an area with a long history of heavy livestock grazing in the southern Chihuahuan Desert, Mexico. An exclosure was established to prevent livestock grazing. In half of the excluded area, the main shrub, Larrea tridentata , was mechanically controlled. Outside the exclosure, heavy livestock grazing occurred as customary and shrubs were not controlled. Absence of grazing resulted in 50% higher grass cover and 35% higher total biomass. Larrea tridentata cover was twice as high on the grazed area as on the ungrazed area. Vegetation cover was dominated by grasses (42%) in the ungrazed area, whereas in the grazed area, cover was equally divided between grasses (28%) and shrubs (27%). Shrub control did not affect vegetation cover or herbage production. Multivariate analysis confirmed that inside the excluded area, shrub control had little impact on the plant community. The effect of grazing, however, clearly distinguished the community outside the exclosure from that inside the exclosure.     

Carbon isotope discrimination in the C 4 shrub Atriplex confertifolia along a salinity gradient

Carbon isotope discrimination (Δ) was measured for leaves of Atriplex confertifolia along a salinity gradient in northern Utah. Over this gradient, the variation of Δ values was high for a C 4 species, and the Δ values were positively correlated with salinity in both years of study. Of the possible explanations for this patter, the Δ results are consistent with the notion that salinity induces an increase in the bundle sheath leakiness of these C 4 plants.     

Nest site selection in raptor communities of the eastern Great Basin desert

Measures of niche breadth and overlap were used to compare nest site selection in a community of 10 raptor species and the Raven nesting in the eastern Great Basin Desert. Three variables were examined: nest site type, elevation, and exposure. Results suggest a division of component raptor species into relatively abundant core species that show wide niche breadths and uncommon fringe species with narrow niche breadths. Differences in use of each resource are most pronounced along elevation gradient in which three guilds are evident that correspond to raptor species groupings that nest at higher, middle, and lower elevations. Each guild is comprised of a mix of core and fringe species. Raptor species with highest overlap along one or more nest site variables examined are separated by differences in activity patterns.     

Studies in nearctic desert sand dune Orthoptera. Part XV: Eremogeography of Spaniacris with bioecological notes

Four decades of the author's records indicate that Spaniacris deserticola (Bruner) is confined within the periphery of the Colorado Desert. It is usually found, near or within a few hundred feet of sea level, marking the shore line of ancient Lake Cahuilla (except for the Dale Lake record). The preferred host plant is Coldenia palmeri growing on the lower fringes of bajadas, with C. plicata on drift sand being second in preference. Spaniacris can tolerate sand and rock temperatures of 60 C. (believed to be a maximum for Colorado Desert life). Mating takes place at that and lower temperatures. When they are disturbed while on the tops of host plants, their flight is low and direct and of short duration, and they come to rest on the torrid soil for long periods of time. The female, much larger than the male, can sustain the male in flight while mating. The study verified spatial longevity of Spaniacris at Indio, California, after approximately 70 years and for the Kane Springs area after 52 years.     

Inter-simple sequence repeat (ISSR) variation in three populations of Gaura neomexicana ssp. coloradensis (Onagraceae), F.E. Warren Air Force Base, Cheyenne, Wyoming

We investigated genetic variation within and between 3 populations of Gaura neomexicana ssp. coloradensis , a federally listed threatened species, using inter-simple sequence repeats. The data matrix included 24 individuals scored for 88 bands, with 3.4% missing data. Cluster analysis showed that members of the 3 populations are very similar and are intermixed in the phenogram. Principal coordinate analysis indicated that members of the Crow Creek population are different from the Diamond Creek and ""unnamed drainage"" populations. This could be the result of historic differences, current changes in vegetation at the Crow Creek site, or an artifact of limited sampling. In any case, for management purposes it is best to preserve the dwindling population at Crow Creek as well as the thriving populations at the other 2 sites.     

Diamond Pond, Harney County, Oregon: vegetation history and water table in the eastern Oregon desert

Cores obtained in 1978 from Diamond Pond, Diamond Craters, Harney County, Oregon, as part of the Steens Mountain Prehistory Project, provide a record of vegetation change on the sagebrush/shadscale ecotone and of local and perhaps regional water tables. Pollen, macrofossils, sediments, and charcoal from these radiocarbon-dated cores were analyzed. Varying abundance of juniper, grass, sagebrush, and greasewood pollen, and of aquatic to littoral plant macrofossils reflects changing regional effective moisture and local water table since 6000 B. P. Eleven dates spanning 5200 radiocarbon years and four regionally correlated volcanic ashes establish the dating of seven periods of different moisture regimes: 1. Greasewood and saltbush pollen dominance before 5400 B. P. indicates shadscale desert. Rapid accumulation of alternating silts and medium sands lacking aquatic plant macrofossils and pollen reflects periods of ephemeral ponds with water table 17 m below the present level and considerable erosion of maar slopes. 2. Increasing sagebrush pollen from 5400 to 4000 B. P. indicates sagebrush expansion into shadscale desert. Scirpus, Rumex, Ceratophyllum, and Polygonum persicaria macrofossils and finely laminated clayey silts evidence perennial pond. 3. From 4000 to 2000 B. P. abundant juniper and grass pollen reflects extensive juniper grasslands (juniper seeds from trees growing nearby fell into the pond during this period). Rising charcoal values indicate greater importance of fire. Deepest late-Holocene pond ca 3700 B. P. corresponds with postulated intensive human occupation of northern Great Basin marsh and lake locales. 4. Between 2000 and 1400 B. P. increased sagebrush pollen mirrors reduced effective moisture and reexpanding sagebrush steppe. More abundant Scirpus and Rumex macrofossils evidence shallow pond. 5. From 1400 to 900 B. P. more numerous grass pollen indicates returning greater effective moisture resulting in deeper water with abundant Potamogeton . 6. About 500 B. P. increased greasewood and saltbush pollen evidences drought. Ruppia seeds and pollen and the mollusk Musculium indicate shallow, brackish water. 7. Abundant juniper and grass pollen reflects moister conditions between 300 and 150 B. P. Numerous Ceratophyllum fruits indicate deeper, freshened water. Since the mid- 1800s man and changing climate have encouraged sagebrush reexpansion. Increased Scirpus macrofossils indicate shallower water.     

Studies in Nearctic desert sand dune Orthoptera, Part XVI: A new black Stenopelmatus from the Mescalero Sands

Stenopelmatus mescaleroensis is described from New Mexico as new to science. A key to the Stenopelmatus of the United States is presented with notes on chaetotaxy used for these crickets.     

Differing morphology and ultrastructure of the male copulatory apparatus in species-groups of Anagrus Haliday (Hymenoptera: Mymaridae)

Male genitalia of 13 members of the mymarid wasp genus Anagrus have been studied: Anagrus (Anagrella) mymaricornis (Bakkendorf), Anagrus (Paranagrus) unilinearis Soyka, A. (Anagrus) ustulatus Haliday, A. (A.) erythroneurae Trjapitzin and Chiappini, A. (A.) atomus (Linnaeus), A. (A.) aegyptiacus Soyka, A. (A.) vilis Donev, A. (A.) sensillatus Viggiani and Jesu, A. (A.) breviphragma Soyka, A. (A.) incarnatus Haliday, A. (A.) obscurus Förster sensu Soyka, A. (A.) fennicus Soyka and A. (A.) avalae Soyka. Taxonomically significant differences between subgenera and the atomus and incarnatus species-groups are described. The functional significance of various features, and in particular, the arrangment of sensilla are discussed.     

Phylogenetic divergence in a desert fish: differentiation of speckled dace within the Bonneville, Lahontan, and upper Snake river basins

Historical events have had a great impact on the biogeography of fishes of western North America. We examined the genetic variation of the speckled dace ( Rhinichthys osculus ) to determine the effects on this species of extensive hydrological changes during the last 10 million years in the Bonneville and Lahontan basins of the Great Basin and the upper Snake River Basin. Eight hundred sixty-nine base pairs of the mitochondrial gene cytochrome b were sequenced from 97 individuals representing 22 populations within these 3 basins, as well as from 2 individuals of longnose dace ( Rhinichthys cataractae ) that served as outgroups. Additionally, 13 speckled dace sequences representing 3 Bonneville populations were used from GenBank. Phylogenetic relationships were reconstructed using maximum parsimony and maximum likelihood criteria. Analysis of molecular variance was used to determine population structure and to estimate the amount of gene flow across the community boundaries. Three distinct clades were reconstructed representing the Lahontan Basin, the northern Bonneville and upper Snake River basins, and the southern Bonneville Basin. Additionally, most of the population structuring was explained by variation among basins (65.33%). Speckled dace demonstrated high genetic variation. As hypothesized, the northern and southern Bonneville specimens formed separate clades; however, the southern Bonneville clade was basal to a sister clade formed by the northern Bonneville/upper Snake River and Lahontan clades. These relationships indicate that Pliocene connections between the Snake, Lahontan, and Bonneville drainages, rather than more recent Pleistocene connections, best explain population structuring in speckled dace.