Autecology of Atriplex Canescens (Pursh) Nutt. In Southwestern United States

Atriplex oanescens, a facultatively evergreen dioecious shrub inhabiting cold and warm winter deserts of western United States, was studied at four sites in the Great Basin. The species was commonly a co-dominant in communities throughout its distribution, and was frequently found with other members of the Chenopodiaceae and members of Compositae. It was found to resprout vigorously and experiments indicated that seeds from all sites germinated easily in wetted, well 3 aerated soil. The mean plant size ranged from 0.62±0.48 to 7.05±2.19 m . 3 -1 Density and cover ranged from 400 to 1.022 X 10 plants ha , and from 5.7 to 38.4% of the ground space, respectively. Atviplex oanescens had a significant influence on the chemical and physical properties of the soil. Vegetated soils had significantly higher moisture content, organic matter, electrical conductivity, alkaline earth carbonates, nitrogen, potassium, sodium, calcium, magnesium and manganese than unvegetated soils. Both organic matter and nitrogen of unvegetated soils from the four study sites were typical of semi- arid environments, generally below 0.7 and 0.03%, respectively. Fertile islands beneath the shrub canopies provided microclimates favorable to the growth of ephemeral grass species. Major cations in plant parts were in the order K \u3e Ca \u3e Mg \u3e Na. Concentrations of these cations in plant parts decreased thus: leaves, fruits, twigs, middle and old growth. The mean of major cations in leaf tissue was 317.96±42.78 me 100 g_1 dry weight. Major anions in leaf tissue followed the order Cl \u3e C20^ \u3e N \u3e P. The mean sum of major anions in leaf tissue was 116.15±15.54 me 100 g-* dry weight. High K/Na ratios were found in plant tissue, in contrast to low K/Na ratios in unvegetated soils. Leaf chloride content of Atriplex oanesoens was negatively correlated with total oxalate but positively correlated with the sum of major cations in the leaf. Water potential (^) measurements of Atriplex oanesoens at Tipton revealed a range of -15.5 to -45.1 bars. Minimum values coincided with the lowest air and soil temperatures, maximum with the greatest atmospheric evaporative demand. Change in $ exceeded 12 bars hr-1 during periods of rapidly moving storm systems. Changes in ^ appeared to be independent of plant size, age, sex and the spatial location of plants. Chemical analyses revealed that expressed sap was up to three times more concentrated at high than at low \p. The increase in water movement accounted for the dilution of the concentration of sap solutes. Together, K, Ca, Mg and Na contributed 58% of the mean osmolality of the expressed sap; the dominant ions, however, were K and Cl. Productivity of Atriplex oanesoens at southern warm-desert sites was significantly greater than that at the cold-desert locations. Net annual productivity estimated from species-specific prediction equations ranged from 0.203 X 10^ to 2.482 X 10^ kg ha * yr Potassium had the highest rate of return of any single element in plant litter. Rates of potassium mobilization from leaf litter at the cold-desert site ranged from 3.94 to 11.12 g K yr ■* . Data suggest that K and N, and possibly other elements are redistributed to other plant parts from leaves prior to leaf senescence

Autecology of Atriplex Canescens (Pursh) Nutt. In Southwestern United States

Atriplex oanescens, a facultatively evergreen dioecious shrub inhabiting cold and warm winter deserts of western United States, was studied at four sites in the Great Basin. The species was commonly a co-dominant in communities throughout its distribution, and was frequently found with other members of the Chenopodiaceae and members of Compositae. It was found to resprout vigorously and experiments indicated that seeds from all sites germinated easily in wetted, well 3 aerated soil. The mean plant size ranged from 0.62±0.48 to 7.05±2.19 m . 3 -1 Density and cover ranged from 400 to 1.022 X 10 plants ha , and from 5.7 to 38.4% of the ground space, respectively. Atviplex oanescens had a significant influence on the chemical and physical properties of the soil. Vegetated soils had significantly higher moisture content, organic matter, electrical conductivity, alkaline earth carbonates, nitrogen, potassium, sodium, calcium, magnesium and manganese than unvegetated soils. Both organic matter and nitrogen of unvegetated soils from the four study sites were typical of semi- arid environments, generally below 0.7 and 0.03%, respectively. Fertile islands beneath the shrub canopies provided microclimates favorable to the growth of ephemeral grass species. Major cations in plant parts were in the order K \u3e Ca \u3e Mg \u3e Na. Concentrations of these cations in plant parts decreased thus: leaves, fruits, twigs, middle and old growth. The mean of major cations in leaf tissue was 317.96±42.78 me 100 g_1 dry weight. Major anions in leaf tissue followed the order Cl \u3e C20^ \u3e N \u3e P. The mean sum of major anions in leaf tissue was 116.15±15.54 me 100 g-* dry weight. High K/Na ratios were found in plant tissue, in contrast to low K/Na ratios in unvegetated soils. Leaf chloride content of Atriplex oanesoens was negatively correlated with total oxalate but positively correlated with the sum of major cations in the leaf. Water potential (^) measurements of Atriplex oanesoens at Tipton revealed a range of -15.5 to -45.1 bars. Minimum values coincided with the lowest air and soil temperatures, maximum with the greatest atmospheric evaporative demand. Change in $ exceeded 12 bars hr-1 during periods of rapidly moving storm systems. Changes in ^ appeared to be independent of plant size, age, sex and the spatial location of plants. Chemical analyses revealed that expressed sap was up to three times more concentrated at high than at low \p. The increase in water movement accounted for the dilution of the concentration of sap solutes. Together, K, Ca, Mg and Na contributed 58% of the mean osmolality of the expressed sap; the dominant ions, however, were K and Cl. Productivity of Atriplex oanesoens at southern warm-desert sites was significantly greater than that at the cold-desert locations. Net annual productivity estimated from species-specific prediction equations ranged from 0.203 X 10^ to 2.482 X 10^ kg ha * yr Potassium had the highest rate of return of any single element in plant litter. Rates of potassium mobilization from leaf litter at the cold-desert site ranged from 3.94 to 11.12 g K yr ■* . Data suggest that K and N, and possibly other elements are redistributed to other plant parts from leaves prior to leaf senescence

Determining the Novel Pathogen Neodothiora populina as the Causal Agent of the Aspen Running Canker Disease in Alaska

Neodothiora populina Crous, G.C. Adams & Winton was determined to be a new pathogen of trembling aspen (Populus tremuloides) growing in Alaska, based on completion of Koch’s Postulates in replicated forest and growth chamber inoculation trials. The pathogen is responsible for severe damage and widespread rapid mortality of sapling to mature aspen (≥ 80 years) in the boreal forests of interior Alaska, due to large diffuse annual (1–2 years) cankers. Isolation of the pathogen was challenging, and identification based on cultural characters was difficult. Fruiting bodies were not found on wild diseased trees, but erumpent pycnidia were found in bark overlying cankers on several stems inoculated with pure cultures

Nesting Biology of Lesser Canada Geese, Branta canadensis parvipes, along the Tanana River, Alaska

Lesser Canada Geese (Branta canadensis parvipes) are widespread throughout interior regions of Alaska and Canada, yet there have been no published studies documenting basic aspects of their nesting biology. We conducted a study to determine reproductive parameters of Lesser Canada Geese nesting along the Tanana River near the city of Fairbanks, in interior Alaska. Fieldwork was conducted in May of 2003, and consisted of locating nests along the riparian corridor between Fairbanks and Northpole, Alaska. Nests were found on gravel islands and shore habitats along the Tanana River, and were most commonly observed among driftwood logs associated with patches of alder (Alnus spp.) and willow (Salix spp.). Peak of nest initiation was 3-8 May, with a range from 27 April to 20 May; renesting was likely. Clutches ranged in size from 2 to 7 eggs and averaged 4.6 eggs. There was a negative correlation between clutch size and date of nest initiation. Egg size (mean mass = 128 g) was similar to other medium-sized Canada Geese. A positive correlation between egg size and clutch size was likely related to female age. Nineteen of 28 nests (68%) were active when visited; nests located on islands with nesting Mew Gulls (Larus canus) were more likely to be active than nests located elsewhere. Evidence at nest sites implicated Bald Eagles (Haliaeetus leucocephalus) and Red Foxes (Vulpes vulpes) as nest predators

Widespread Mortality of Trembling Aspen (Populus tremuloides) Throughout Interior Alaskan Boreal Forests Resulting from a Novel Canker Disease

Over the past several decades, growth declines and mortality of trembling aspen throughout western Canada and the United States have been linked to drought, often interacting with outbreaks of insects and fungal pathogens, resulting in a “sudden aspen decline” throughout much of aspen’s range. In 2015, we noticed an aggressive fungal canker causing widespread mortality of aspen throughout interior Alaska and initiated a study to quantify potential drivers for the incidence, virulence, and distribution of the disease. Stand-level infection rates among 88 study sites distributed across 6 Alaska ecoregions ranged from \u3c 1 to 69%, with the proportion of trees with canker that were dead averaging 70% across all sites. The disease is most prevalent north of the Alaska Range within the Tanana Kuskokwim ecoregion. Modeling canker probability as a function of ecoregion, stand structure, landscape position, and climate revealed that smaller-diameter trees in older stands with greater aspen basal area have the highest canker incidence and mortality, while younger trees in younger stands appear virtually immune to the disease. Sites with higher summer vapor pressure deficits had significantly higher levels of canker infection and mortality. We believe the combined effects of this novel fungal canker pathogen, drought, and the persistent aspen leaf miner outbreak are triggering feedbacks between carbon starvation and hydraulic failure that are ultimately driving widespread mortality. Warmer early-season temperatures and prolonged late summer drought are leading to larger and more severe wildfires throughout interior Alaska that are favoring a shift from black spruce to forests dominated by Alaska paper birch and aspen. Widespread aspen mortality fostered by this rapidly spreading pathogen has significant implications for successional dynamics, ecosystem function, and feedbacks to disturbance regimes, particularly on sites too dry for Alaska paper birch

Existence and asymptotic behavior of solutions for neutral stochastic partial integrodifferential equations with infinite delays

In this work we study the existence, uniqueness and asymptotic behavior of mild solutions for neutral stochastic partial integrodifferential equations with infinite delays. To prove the results, we use the theory of resolvent operators as developed by R. Grimmer [12] R. Grimmer. Resolvent operators for integral equations in a banach space. Transactions of the American Mathematical Society, 273(1): 333-349, 1982, as well as a version of the fixed point principle. We establish sufficient conditions ensuring that the mild solutions are exponentially stable in pth-moment. An example is provided to illustrate the abstract results.Fondo Europeo de Desarrollo RegionalMinisterio de Economía y CompetitividadConsejería de Innovación, Ciencia y Empresa (Junta de Andalucía

New results on rewrite-based satisfiability procedures

Program analysis and verification require decision procedures to reason on theories of data structures. Many problems can be reduced to the satisfiability of sets of ground literals in theory T. If a sound and complete inference system for first-order logic is guaranteed to terminate on T-satisfiability problems, any theorem-proving strategy with that system and a fair search plan is a T-satisfiability procedure. We prove termination of a rewrite-based first-order engine on the theories of records, integer offsets, integer offsets modulo and lists. We give a modularity theorem stating sufficient conditions for termination on a combinations of theories, given termination on each. The above theories, as well as others, satisfy these conditions. We introduce several sets of benchmarks on these theories and their combinations, including both parametric synthetic benchmarks to test scalability, and real-world problems to test performances on huge sets of literals. We compare the rewrite-based theorem prover E with the validity checkers CVC and CVC Lite. Contrary to the folklore that a general-purpose prover cannot compete with reasoners with built-in theories, the experiments are overall favorable to the theorem prover, showing that not only the rewriting approach is elegant and conceptually simple, but has important practical implications.Comment: To appear in the ACM Transactions on Computational Logic, 49 page

Subspecies Variation of Daucus carota Coastal (“Gummifer”) Morphotypes (Apiaceae) Using Genotyping-by-Sequencing

The genus Daucus is widely distributed worldwide, but with a concentration of diversity in the Mediterranean Region. The D. carota complex presents the greatest taxonomic problems in the genus. We focus on a distinctive phenotypic group of coastal morphotypes of D. carota, strictly confined to the margins to within about 0.5 km of the Mediterranean Sea and the Atlantic Ocean, which we here refer to as coastal morphotypes or D. carota subsp. “gummifer” complex. They are loosely morphologically coherent, sharing a relatively short stature, thick, broad, sometimes highly glossy leaf segments, and usually flat or convex fruiting umbels. We analyzed 288 accessions obtained from genebanks in England, France, and the USA, and an expedition to Spain in 2016, covering the Mediterranean and Atlantic coasts and Balearic Islands, where much of the gummifer complex variation occurs. Our study includes 112 accessions not examined before in this context. Genotyping-by-sequencing identified 29,041 filtered SNPs. Based on high bootstrap support from maximum likelihood and Structure analysis we highlight three main clades. The gummifer morphotypes are intercalated with members of Daucus carota subspecies carota and subspecies maximus in two of these main clades, including a clade containing accessions from Tunisia (also including D. carota subsp. capillifolius) and a clade containing accessions from western Europe (including the British Isles), southern Europe (including the Balearic Islands and the Iberian Peninsula) and Morocco. These results support five independent selections of the gummifer morphotypes in these restricted maritime environments in the Mediterranean and nearby Atlantic coasts. Daucus annuus (=Tornabenea annua) and Daucus tenuissimus (=Tornabenea tenuissima) also fall firmly within D. carota, supporting their classification as morphologically well-defined subspecies of D. carota, which are accepted here under the new combinations Daucus carota subsp. annuus and D. carota subsp. tenuissimus , respectively. Types are indicated for most of treated names, including designation of four lectotypes and three epitypes, which fix their further use.This research was partly funded by the research grant UA2004-47056131 (University of Alicante) to FMF and by the USDA

Scanning-probe spectroscopy of semiconductor donor molecules

Semiconductor devices continue to press into the nanoscale regime, and new applications have emerged for which the quantum properties of dopant atoms act as the functional part of the device, underscoring the necessity to probe the quantum structure of small numbers of dopant atoms in semiconductors[1-3]. Although dopant properties are well-understood with respect to bulk semiconductors, new questions arise in nanosystems. For example, the quantum energy levels of dopants will be affected by the proximity of nanometer-scale electrodes. Moreover, because shallow donors and acceptors are analogous to hydrogen atoms, experiments on small numbers of dopants have the potential to be a testing ground for fundamental questions of atomic and molecular physics, such as the maximum negative ionization of a molecule with a given number of positive ions[4,5]. Electron tunneling spectroscopy through isolated dopants has been observed in transport studies[6,7]. In addition, Geim and coworkers identified resonances due to two closely spaced donors, effectively forming donor molecules[8]. Here we present capacitance spectroscopy measurements of silicon donors in a gallium-arsenide heterostructure using a scanning probe technique[9,10]. In contrast to the work of Geim et al., our data show discernible peaks attributed to successive electrons entering the molecules. Hence this work represents the first addition spectrum measurement of dopant molecules. More generally, to the best of our knowledge, this study is the first example of single-electron capacitance spectroscopy performed directly with a scanning probe tip[9].Comment: In press, Nature Physics. Original manuscript posted here; 16 pages, 3 figures, 5 supplementary figure