bluuebunny/crossref_metadata_2025 huggingface dataset:
The patterning of plant communities and edaphic factors along a high arctic coastline: implications for succession
Authors: Bliss L. C. , Gold W. G.
Published: July 2010

Isostatic rebound and the periodic development of ice-push beach ridges have created topography suitable for development of biologically rich polar oases along the northeast coast of Devon Island, Canada. Distinct patterning of both plant communities and edaphic factors from coastal shoreline areas inland indicate primary succession with a directional species replacement At Rocky Point (emergent < 2000 BP) biological development along the shore is initiated by marine algae that are invaded by cyanobacteria. These organic mats are colonized by Puccinellia on the shoreline of these brackish lagoons. Where the topography grades upslope, via concave areas, the toposequence from Puccinellia proceeds through Dupontia → Carex → Salix hummocks → cushion plant–lichen communities. In drier, convex areas Puccinellia proceeds through rosette-herb hummocks → cushion plant–lichen communities as a toposequence. Reduced levels of salinity and of nitrogen fixation upslope (from the shore) along with increased depth of organic soils and ability of soils to hold more soil water appear important in the conversion of Puccinellia- to Dupontia- to Carex-dominated meadows. This is the major chronosequence at Rocky Point and it is these Carex meadows that occupy most of the wetlands of Truelove Lowland. The Salix hummocks and cushion plant–lichen communities of all drier habitats resemble communities of similar species composition on the beach ridges of the lowland. Key words: arctic Canada, succession, plant communities, soil factors, polar oasis.
Mating systems in the Xerulaceae: Xerula
Authors: Petersen Ronald H. , Methven Andrew S.
Published: July 2010

Mating systems in Xerula australis, Xerula furfuracea, Xerula incognita (sp.nov.), Xerula megalospora, Xerula rugosoceps, and the Xerula radicata complex are described, with notes on culture morphology and biogeographic distribution. All taxa tested were bifactorial (i.e., tetrapolar) and genetically isolated from one another. Multiple collections of X. furfuracea and X. megalospora were found to interbreed in vitro. Two collections of putative European X. radicata were found to be haploid, monokaryotic, nonmeiotic basidiomes genetically isolated from each other and from all other tested taxa, including X. radicata. Neohaploidization experiments with Xerula rufobrunnescens failed. A discussion comparing mating systems in Xerula to those in other genera of the Xerulaceae is included. Key words: mating systems, interbreeding, biological species, intersterility groups, biogeography, Xerula, basidiomycetes.
Morphology of infection of onion leaves by Alternaria porri
Authors: Aveling Theresa A. S. , Snyman Heidi G. , Rijkenberg F. H. J.
Published: July 2010

Conidial germination of Alternaria porri, formation of prepenetration structures, penetration of the onion leaf surface, and the postpenetration processes were studied using light, scanning electron, and transmission electron microscopy. Ninety-six percent of conidia germinated at 25 °C within 24 h of inoculation. Each conidium formed several germ tubes that grew in any direction across the leaf surface. Each germ tube usually terminated in a bulbous appressorium formed directly on the epidermal cell (52.4% of appressoria) or on a stoma (48.6% of appressoria). Following direct penetration of the outer epidermal cell wall or the stoma, bulbous primary hyphae developed below the appressoria. Secondary hyphae developed from the primary hyphae within 48 h after inoculation and grew within the intercellular spaces penetrating mesophyll cells. The changes in ultrastructure of cells in close proximity to hyphae and of infected cells are described. Key words: Allium cepa, electron microscopy, infection process, purple blotch.
Long-term recovery of vegetation on two experimental crude oil spills in interior Alaska black spruce taiga
Authors: Racine Charles H.
Published: July 2010

Vegetation was sampled on two black spruce taiga sites in interior Alaska, 15 and 20 years after crude oil was experimentally applied as low-volume sprays or high-volume point spills. Low volume spray spills that uniformly covered the ground caused initial damage to vegetation, but after 20 years recovery of the understory vegetation was almost complete, with dramatic recovery and expansion of fruticose lichens. High-volume point spills created small areas of surface oil saturation with dead vegetation and little sign of recovery but spread out mostly belowground with little or no apparent effect on the shallowly rooted vegetation above even after 15–20 years. Because winter point spills created a much greater area of surface oil, their effects were more damaging. After 15 years on the saturated surface oiled areas, only Eriophorum vaginatum tussocks survive and grow. At both sites with surface oil, black spruce mortality was high, with no evidence of long-term recovery and with continuing chronic effects after 15 years. However, from a long-term perspective the black spruce taiga ecosystem appears to be able to recover from low volume spray spills and to retain large amounts of crude oil from high-volume point spills belowground with minimal damage to the vegetation. Because of the permafrost, removal of crude oil from this ecosystem by soil excavation is undesirable. In situ acceleration of oil breakdown using fertilizers and bacteria is a possible option; seeding or planting of E. vaginatum on surface-oiled areas may also provide some cover and belowground biomass. Key words: oil spills, taiga, black spruce, interior Alaska, vegetation recovery.
Modeling the potential for boron amelioration of aluminum toxicity using the Weibull function
Authors: Taylor Gregory J. , Macfie Sheila M.
Published: July 2010

Several recent reports have suggested that boron (B) may alleviate the toxic effects of aluminum (Al) on plant growth, providing improved plant performance on acid soils. To test this hypothesis, an Al-sensitive cultivar of Triticum aestivum L. (cv. Neepawa) was grown in solution culture with 10 concentrations of Al (0–300 μM), in the presence of deficient (0 μM), sufficient (6 μM), luxury (75 μM), or toxic (750 μM) concentrations of B. The effects of both Al and B on the response of roots and leaves to Al was accurately modeled (R2 < 0.99) using a modified Weibull function. Comparison of best fit function parameters for the response to Al under varying conditions of B supply failed to reveal any evidence of B amelioration of Al toxicity. The combined effects of Al and B were adequately explained by a multiplicative model. Although formation of stable Al-borate complexes could occur in growth solutions under our experimental conditions, varying the supply of B had little effect on accumulation of Al in roots and leaves. In contrast, increasing Al concentrations in solution resulted in increased immobilization of B in roots and decreased accumulation of B in leaves. Growth of plants with elevated B supply resulted in higher concentrations of B in roots and leaves without improving growth. We suggest that previous reports of B amelioration of Al toxicity must reflect the unique characteristics of soil-based media, and (or) differences among species in internal requirements for B and the effects of Al on B nutrition. Key words: amelioration, aluminum, boron, toxicity, Weibull function, wheat.
Absorption de l'eau atmosphérique par la partie aérienne d'un chaméphyte de la Tunisie présaharienne : l’Anthyllis henoniana (Fabaceae)
Authors: Ourcival Jean-Marc , Berger André , Floc'h Édouard Le
Published: July 2010

Measurements of predawn water potential made in the presaharian Tunisia (Médenine) on A. henoniana suggest that this species is able to absorb directly atmospheric water through its leaves and (or) stems. Measurements of water potential were also made on several plants in controlled conditions. Cross sections of stems of various ages and of leaves were examined. There was a good correlation between the thickness of the cortical parenchymatous tissue in leaves and young stems and the ability of a plant to maintain a less negative water potential in conditions of high atmospheric humidity. The water is apparently taken up by the vascular system. This ability would allow A. henoniana to benefit from the many dew days observed in its area of distribution and would improve its water balance. Key words: Anthyllis henoniana, dew, water potential, water absorption, water balance.
Symptomless endophytic colonization of maize byFusarium moniliforme
Authors: Bacon C. W. , Hinton D. M.
Published: July 2010

Fusarium moniliforme Sheldon is a nonobligate parasite of maize that produces several mycotoxins. This fungus causes systemic infections of maize kernels, which then serve as dissemination vehicles and inoculum sources. Infected plants may or may not show disease symptoms. Symptomless infection was studied in maize plants and was compared with plants that eventually showed symptoms of seedling disease. Three isolates of F. moniliforme, a hygromycin-resistant mutant of two of these isolates, and Fusarium fujikuroi were used to infect surface and internally sterilized maize kernels, and symptomatic and symptomless infections were observed for 8 weeks. The results indicated that in symptomless infected plants, hyphae were intercellular only and distributed throughout the plant, whereas in plants showing disease symptoms, the fungus was both intercellular and intracellular. Symptomless plants remained symptomless throughout the observation period, and at the ultrastructural level there was no evidence of an antagonistic relationship. This indicates that the symptomless state persists beyond the seedling stage and could contribute, without visual signs, to the total mycotoxin contaminants of maize both before and during kernel development. Keywords: Gibberella fujikuroi, endophyte, toxic fungus, maize, fusarium toxins, corn disease.
Regression-based focal point seed zones for Picea mariana from northwestern Ontario
Authors: Parker William H. , Niejenhuis Annette van
Published: July 2010

The results of a recent study of adaptive variation of black spruce in northwestern Ontario, together with additional freezing damage data, were used to produce regression-based focal point seed zones for this species. The procedure required two data bases as follows: (i) the biological data derived from two common garden growth trials, one greenhouse trial, and freezing trials of 75 black spruce seed sources and (ii) climatic data for the period 1951 – 1980. Principal components analysis (PCA) was used to summarize the main components of growth and freezing variation, and the PCA axis scores for the seed sources were regressed against climatic variables. The regression equations were used to model the patterns of adaptive variation, and these patterns were graphically reproduced as contour maps by a geographic information system (GIS). A series of focal point seed zone maps for black spruce was produced by GIS intersection of the regression-based contour maps. Focal point seed zones were more restricted in the south near Lake Superior, reflecting the more rapidly changing climate in this part of the study area. Since black spruce is closely adapted to local climate, these results will be useful to formulate successful seed transfers in this area. There are additional potential applications for matching seed sources to changing climates and for the identification of genetically unique populations. Keywords: black spruce, Picea mariana, adaptive variation, focal point seed zones.
Cellular mechanisms of callose deposition in response to fungal infection or chemical damage
Authors: Škalamera Dubravka , Heath Michèle C.
Published: July 2010

Cellular mechanisms of callose deposition induced in cowpea (Vigna unguiculata) leaves by the living cowpea rust fungus (Uromyces vignae), boric acid, or the fungus killed by polyoxin D, were investigated by the use of chemical inhibitors. Effects of the inhibitors were observed in both a resistant and a susceptible cowpea cultivar. The effect of inhibitors differed depending on the type of callose-inducing stimulus and cultivar used. Inhibitors of transcription (actinomycin D) and protein synthesis (blasticidin S, cycloheximide) lowered the incidence of fungus-induced callose deposits in both cultivars. Inhibitors of protein synthesis also reduced deposits induced by boric acid or fungal death. Callose deposition induced by the living fungus in the resistant cultivar was reduced by inhibitors of protein glycosylation (tunicamycin, deoxynojirimycin) and microfilament function (cytochalasins B and E), but these inhibitors had no effect on callose deposition in the susceptible cultivar or on chemical or fungal death-induced deposition in either cultivar. No reduction in callose deposits was observed in plants treated with inhibitors of Golgi-associated vesicle transfer (brefeldin A, monensin) or microtubule polymerization (colchicine, oryzalin). The results suggest that the cellular processes involved in callose deposition differ with differing triggering stimuli and that callose deposition triggered by the living fungus in a resistant host cultivar is not a typical wound or damage response. Keywords: callose, infection, inhibitors, resistance, rust fungi.
Pollen deposition in the boreal forest of west-central Canada
Authors: Lee Eun Ju , Kenkel Norm C. , Booth Thomas
Published: July 2010

Deposition of tree and tall shrub pollen was examined along a 5.5-km transect in mixed boreal forest in west-central Manitoba, Canada. Annual pollen deposition averaged ca. 6850 grains/cm2 in 1992, with jack pine contributing 67.3% and spruce 24.5% of the total. In general, flowering plant species released their pollen in early to late May, while conifer (spruce and pine) pollen release occurred in early to mid-June. Pollen deposition was poorly correlated with relative species abundance in the community, with some species (e.g., jack pine) being over-represented in the pollen rain and others (e.g., aspen poplar) being under-represented. In 1993, spruce pollen deposition was 63% of that in 1992. By contrast, total pollen deposition by jack pine showed little variation from 1991 to 1993. However, pollen release dates varied between years, occurring earlier in years with warmer spring temperatures. Jack pine pollen release exhibited diurnal variation, with the majority of pollen being released during daylight hours on warm, sunny days. Keywords: Manitoba, jack pine, black spruce, boreal forest, pollen rain, palynology.
Ultrastructure of the vascular responses of tobacco to Fusarium oxysporum f.sp. nicotianae
Authors: Mueller W. C. , Morgham A. T.
Published: July 2010

The reactions of a broadleaf tobacco variety polygenically resistant to Fusarium wilt were compared with a susceptible variety. Symptoms of wilting, yellowing, and eventual death of leaves in the susceptible variety were associated with rapid movement of the fungus through the plant, whereas in the resistant variety the fungus was confined to the lower portion of the plant and symptoms occurred only on the lowermost leaves. The responses in the vascular tissue were similar in both varieties but appeared more intense in the resistant variety. Lipoidal wall coatings and occlusions occurred in the initially infected vessels. Apposition layers containing callose were deposited in the contact cells within 1 day of inoculation. Lipoidal occlusions occurred in the secondarily infected vessels, but apposition layers were not detected in the contact cells. Tyloses were not observed. Resistance is associated with the localization and slower movement of the fungus that is reflected in the observable differences in symptom development. Keywords: contact cells, Nicotiana tabacum, polygenic resistance, vascular occlusion.
Colonization of tomatoes byVerticillium dahliae: determinative phase II
Authors: Gold Julie , Lee Barbara , Robb J.
Published: July 2010

To investigate the relationship between stem colonizing ability of Verticillium and wilt disease development, the colonization capacities of Verticillium dahliae, race 1 or race 2, were compared in near-isolines of the cultivar Craigella, with (Ve+) and without (Ve−) Ve-gene resistance, and in the cultivar IRAT-L3, which also lacks the Ve-gene. Only the Ve+/V.d.1 interaction was resistant to disease. Lateral and vertical invasiveness of the pathogen were assessed cytologically and fungal biomass was monitored by PCR-based diagnostics. The pathogen was most aggressive in the Ve−/V.d.1 interaction; colonization capacity was reduced in the other five combinations, but most severely, and equivalently, in Ve+/V.d.1, IRAT/V.d.1, and IRAT/V.d.2. Further study of the development and role of the vascular coating response in IRAT-L3 indicated a pattern of expression similar to that observed in other susceptible plants, and it was concluded that the reduced colonization of this cultivar by V. dahliae resulted from another unknown defensive mechanism. Stem colonizing ability that is compatible with resistance in one cultivar and race combination may promote symptom expression and even death in another. Keywords: tomato, Verticillium dahliae, vascular coating, resistance.
Spatial and temporal genetic structure ofAsclepias verticillata(whorled milkweed) among prairie patches in a forested landscape
Authors: Foré S. A. , Guttman S. I.
Published: July 2010

We examined the spatial scale of genetic structure of Asclepias verticillata L. (whorled milkweed) populations in a landscape where suitable habitat is fragmented by woodlands to determine if the distance between patches influences genetic differentiation. In addition, we sampled over 2 years to determine if there are temporal genetic differences. This forb is found in prairie habitat in the Edge of Appalachia Preserve System, Ohio. Prairie patches have a clumped distribution with patches within a region located < 150 m apart and regions located > 1.5 km apart. Allozyme electrophoresis was used to collect genetic data from reproductive individuals in nine patches representing four regions. Observed heterozygosity was not significantly different among patches or between years, even though population sizes varied. Rogers' genetic distance and hierarchical F-statistics indicated that there was little genetic differentiation among patches within a region. Although genetic differentiation was greater among regions, it was relatively low. Between years, genetic differentiation within a patch was as great as genetic differentiation between patches. Conditional allele frequencies suggest that loss of one patch within a region will increase genetic differentiation within a region. Data suggest that prairie management could focus on a few regions with large numbers of patches. Keywords: habitat fragmentation, allozyme, genetic diversity, prairie management.
Components of resistance in barley to stem rust: receptivity, urediniospore production, latent period, and infection response in adult plants
Authors: Liu J. Q. , Harder D. E.
Published: July 2010

Resistance in barley (Hordeum vulgare) to stem rust, caused by Puccinia graminis f.sp. tritici, is often variably expressed. This study was undertaken to evaluate several components of stem rust resistance in the barley cultivars or lines Tupper, Robust, Q21861, SB90585, SB91702, and Harrington and to compare them with the susceptible wheat cultivar Little Club (Triticum aestivum). Stems of adult plants were quantitatively inoculated with urediniospores of races QCC, QFC, and TPM of P. graminis tritici. Significant differences in receptivity, urediniospore production, and latent period were observed among the barley lines and between all barley lines and Little Club wheat. The degrees of receptivity and the levels of urediniospore production on the barley lines were related to the presence or absence of the specific resistance genes Rpg1, rpg4, and possibly additional noncharacterized gene(s). Receptivity was the most strongly expressed of all of the components measured. Receptivity, spore production, and infection response were highly correlated to each other, but only infection response was significantly correlated to latent period. The usefulness of measuring these components to evaluate resistance in barley breeding is discussed. Keywords: barley, Hordeum vulgare, stem rust, Puccinia graminis tritici, resistance, components.
Marking salmon fry with strontium chloride solutions
Authors: Schroder Steven L. , Knudsen Curtis M. , Volk Eric C.
Published: July 2010

Chum (Oncorhynchus keta) and sockeye salmon (O. nerka) fry immersed in strontium chloride solutions for 24 h had greater amounts of strontium in their otoliths, vertebrae, and opercula than controls. Exposure to a hyperosmotic bath prior to marking, and dimethyl sulfoxide and heat during the immersion period, slightly increased the uptake of strontium in some cases. Hemisections of otoliths taken from treated fish possessed a highly visible ring of deposited strontium when viewed with backscattered electron microscopy. The peak concentration of strontium in a ring was often two orders of magnitude higher than that found in otoliths taken from control fish or in preexisting growth areas of a treated otolith. Treated fish that had been reared for 21 months in freshwater were easily identified when their otoliths were examined with backscattered electron microscopy or Wavelength Dispersive Spectrometry. When marked fish weighed less than 15 g their otoliths were also distinguished from control specimens by using bulk Inductively Coupled Plasma Mass Spectrometry. This study showed that 24-h immersion in strontium chloride solutions produced easily detected and long-lived marks in Pacific salmon fry.
Quantitative ultrastructure of gill epithelial cells in the larval lampreyPetromyzon marinus
Authors: Mallatt Jon , Lampa Steven J. , Bailey J. Franklin , Evans Marc A. , Tate Wayne
Published: July 2010

Cells and organelles in the respiratory epithelium of the sea lamprey (Petromyzon marinus) gill were measured in electron micrographs of plastic-embedded sections to provide baseline data for future quantitative studies of how toxicants affect gill morphology. Stereology was used, based on the [Formula: see text] method for determining cell volumes. The method was checked against unbiased methods and was shown to be accurate within 12%. We found that cells in the basal layer of the epithelium, basal cells, are smaller (averaging 338 μm3) and contain smaller volumes of most organelles, than cells in the superficial layer. These features suggest that basal cells are either undifferentiated or differentiating cells. The superficial layer contains larger, more specialized cells: presumed ion-uptake cells (817 μm3) and mucous-pavement cells (548 μm3). Ion-uptake cells contain the largest volume of mitochondria (270 μm3), consistent with the high energy demands of ion transport. Mucous-pavement cells contain the largest volume of secretory vesicles (55 μm3), presumably for coating the lamellae with protective mucus. A new cell type was discovered, with features intermediate between basal cells and mucous-pavement cells, suggesting that the former cells transform into the latter. Volumes of gill epithelial cells are independent of animal size.
A fish gill system for quantifying the ultrastructural effects of environmental stressors: methylmercury, Kepone®, and heat shock
Authors: Mallatt Jon , Lampa Steven J. , Bailey J. Franklin , Evans Marc A. , Brumbaugh Steve
Published: July 2010

In previous histopathological studies, fish gills have been used to study nonspecific responses of tissue to injury; however, such studies have revealed little about the specific effects of different toxicants on cells. Here, we used transmission electron microscopy plus a morphometric technique (stereology) to determine how several types of gill cells are specifically altered by three stressors: methylmercury, heat shock, and the insecticide Kepone®(chlordecone). Larval sea lampreys, Petromyzon marinus, were exposed to various concentrations of waterborne stressor (ranging from the incipient lethal concentrations to a 24-h LC50) for different periods (half a day or 3 weeks). Methylmercury increased the volumes of gill epithelial cells and their nuclei and mitochondria, presumably by inducing ambient water to leak into these structures. Heat shock, by contrast, decreased the volumes of most cells and their organelles, presumably by causing cells to shed pieces of cytoplasm. Kepone had almost no effect, but the few changes that were recorded (increased mitochondrial volume in one cell type) are consistent with known actions of Kepone®(alteration of mitochondrial respiration). The results prove that a fish gill can be used to probe the specific actions of different toxicants and pollutants.
Respiratory quotients predict increases in reducing products in the hypolimnion of a stratified lake
Authors: Murray Thomas E. , Rich Peter H.
Published: July 2010

The benthic respiration of Crystal Lake, Connecticut, was modeled with two respiratory quotients, the volumetric respiratory quotient (VRQ) and the fundamental respiratory quotient (FRQ). The VRQ is defined as the quotient of the increase in dissolved inorganic carbon (DIC) and the decrease in dissolved oxygen (DO) resulting from respiration at a given depth. Those changes are relative to concentrations determined early in spring. The FRQ is the slope of the regression of DIC against DO at all depths not chronically anoxic. Respiratory quotients describe the predominance of anaerobic over aerobic metabolism and should, therefore, predict the accumulation of the products of anaerobic metabolism (i.e., Fe2+, H2S). VRQs successfully predicted the increase in reduced products in the hypolimnion of Crystal Lake. FRQs successfully predicted the rate of increase of reduced products early in stratification. FRQ was unsuccessful in predicting the continued accumulation of reducing products later in the summer, which may reflect a steady state between the production of DIC and reduced products and the diffusion of oxygen across the thermocline, or may reflect methodological constraints imposed by the calculation of FRQ. Both models were successful to a limited extent in predicting the accumulation of the products of anaerobic metabolism.
Trends in nutrient concentrations in Hatchery Bay, western Lake Erie, before and after Dreissena polymorpha
Authors: Holland Ruth E. , Johengen Thomas H. , Beeton Alfred M.
Published: July 2010

Concentrations of soluble reactive phosphorus, ammonium-nitrogen, nitrate-nitrogen, silica, and chloride have all increased since the establishment of the zebra mussel (Dreissena polymorpha) in Hatchery Bay, western Lake Erie, in 1988. Total phosphorus concentrations have changed little. These results are from 188 samples collected weekly and year round before the establishment of Dreissena (1984–1987) and 192 samples post-Dreissena (1990–1993). The mean annual total phosphorus concentration for the three complete post-Dreissena years was 35 μg∙L−1 strikingly similar to the concentration of 36 μg∙L−1, which in 1959 helped to define the waters of Lake Erie as eutrophic. The relative steadiness in total phosphorus may reflect sediment reflux, because Hatchery Bay is a polymictic system. The slight increase in the biologically conservative ion, chloride, in the 1990s, is probably due to the increased precipitation and runoff in the western Lake Erie watershed. Decreased phytoplankton and associated increased water clarity caused by efficient filtering by D. polymorpha, have lessened symptoms of eutrophication and produced a situation where nutrients are not fully utilized, i.e., biological oligotrophy.
Variability of the mitochondrial control region in populations of the harbour porpoise, Phocoena, on interoceanic and regional scales
Authors: Rosel P. E. , Dizon A. E. , Haygood M. G.
Published: July 2010

The harbour porpoise, Phocoena phocoena, experiences a high degree of incidental mortality owing to interactions with commercial fisheries. To properly manage the species, it is necessary to assess levels of inter- and intra-populational variation so that management units can be accurately defined. A portion of the mitochondrial DNA control region was amplified and sequenced to characterize the amount of genetic variation within harbour porpoise populations in the Northeast Pacific, North Atlantic, and Black Sea. In addition, the utility of the control region to discriminate among putative populations of harbour porpoises along the west coast of North America was investigated. The resultant data were analyzed phylogenetically using a neighbour-joining algorithm and statistically for population subdivision using an analysis of variance approach. No shared haplotypes were found among the three ocean basins, and the estimated sequence divergence among them was high. Within the Northeast Pacific, several distinct groupings of haplotypes were found, but no phylogenetic concordance between sequence type and geographic location was found. However, differences in the geographic distributions among and genetic diversity within matrilineal groups, and indications of significant genetic heterogeneity among the sampling locales in the Northeast Pacific argue for management strategies on a regional basis.
Was an increase in natural mortality responsible for the collapse off northern cod?
Authors: Myers Ransom A. , Cadigan Noel G.
Published: July 2010

The collapse of the northern Atlantic cod (Gadus morhua) fishery off southern Labrador and to the northern Grand Bank of Newfoundland, once the largest cod fishery in the world, was a social and economic disaster for the region. An analysis of traditional catch-at-age data in conjunction with research surveys, which assumed that research survey estimation errors of abundance by age and year were independent, led assessment biologists to the conclusion that the collapse was caused by an increase in natural mortality in the first half of 1991. We constructed a statistical model to test this hypothesis. The results do not support the hypothesis. There is ambiguous evidence that natural mortality has increased since 1991; however, these results are found only in a model that has extraordinary patterns in the residuals. Our analysis suggests that even if natural mortality has been higher in recent years (as estimated using a model with correlated errors for research surveys), overfishing was sufficiently high to cause a collapse of this population. We also demonstrate that the usual assumption that estimation errors from research trawl surveys are independent is not valid, and can lead to invalid inference and unreasonable estimates of abundance.
Comparative review of Pacific salmon survival rates
Authors: Bradford Michael J.
Published: July 2010

I collated estimates of survival from the literature for naturally reproducing populations of the five major commercially harvested species of Pacific salmon (Oncorhynchus spp.) and compared the mean and variability of survival across species and life-history stages. The conclusion that survival rates can be described with a lognormal distribution was extended to include both the marine and freshwater stages. Average egg–fry survival of pink (O. gorbuscha), chum (O. keta), and sockeye (O. nerka) salmon was similar (average 7%) but was significantly lower than that of coho salmon (O. kisutch, 19%). The egg–smolt survival of chinook (O. tshawytscha) was much higher than coho or sockeye that also rear in freshwater for similar periods (7 compared with 1–2%). No direct estimates exist for the marine survival rate of naturally spawning chinook stocks; however, from fecundity and freshwater survival data a species average of 1–2% was derived. Across all species freshwater contributes slightly more to total variation in egg–adult survival than does the ocean, and the schedule of mortality during the egg–adult interval depends on the natural history of each species.
A finite element approach to elastic soil–structure interaction
Authors: Smith Ian M.
Published: July 2010

An application of the displacement finite element method to axisymmetric soil–structure interaction problems is described. Since the structure and foundation are analyzed as an entity, the distribution of contact pressure does not have to be assumed. The accuracy of the method is first assessed in the analysis of some simple problems to which other solutions exist. Then a series of laboratory results and one field case record, all involving flexible structures bearing on cohesionless foundations are analyzed, the foundations being treated as elastic but inhomogeneous. Both "Winkler" and elastic solid foundations are considered and it is shown that for the latter type physically reasonable distributions of the elastic modulus do not lead to very good predictions of the deflections of the structure although the deflections within the foundation itself are in agreement with observed values.
An alternative approach to goal programming
Authors: Walker H. Douglas
Published: July 2010

An alternative approach to goal programming is described. The approach incorporates both cardinal weighting and ordinal ranking of deviation variables, and does not require apriori specification of goal target levels. Ordinal rankings are used to describe feasible and optimal policy spaces. Cardinal weightings are then adjusted through an interactive procedure until the decision makers are satisfied with the weightings and with the resulting compromise solution. The procedure is demonstrated using a hypothetical reforestation budget allocation problem.
Changes in bark beetle susceptibility indicators in a lightning-struck loblolly pine
Authors: Blanche C. A. , Hodges J. D. , Nebeker T. E.
Published: July 2010

Xylem resin flow in a lightning-struck loblolly pine was too low to be measured for the first few days after the strike, but flow was restored after 3 weeks. The content of α-pinene, camphene and myrcene in the oleoresin increased 3 weeks after the strike while the level of β-pinene showed a dramatic decline. Limonene and β-phellandrene also decreased, but not as dramatically as the decline in β-pinene. The implications of these changes to known bark beetle attack behavior are discussed.
Physiological ecology of lodgepole pine (Pinuscontorta) in an enriched CO2 environment
Authors: Higginbotham K. O. , Mayo J. M. , L'Hirondelle S. , Krystofiak D. K.
Published: July 2010

Relatively little work has been done to evaluate the effects of chronically high levels of carbon dioxide on growth and physiology of woody plants. In this study, seedlings of lodgepole pine (Pinuscontorta Dougl. var. latifoliaEngelm.) were grown for 5-month periods at 330, 1000, or 2000 μL CO2•L−1. Height growth; leaf area production; biomass of leaves, stems, and roots; and photosynthetic responses to changing light, moisture, and CO2 concentration were measured. Significant differences between treatments were found in mean seedling height on all measurement dates. Seedlings grown at 1000 μL CO2•L−1 were tallest, with seedlings grown in 2000 μL•L−1 intermediate between the control (330 μL•L−1) and 1000 μL•L−1 treatments. The same relationship was found in production of total leaf surface area. Increased leaf surface area yields a productive advantage to seedlings grown at concentrations of CO2 up to 2000 μL•L−1 even if no increase in net photosynthesis is assumed. Biomass of stems, roots, and secondary leaves was increased in both elevated CO2 conditions, with root biomass approximately 15 times greater in seedlings grown at 1000 μL•L−1 than in those grown at 330 μL•CO2•L−1. Stomatal resistances were essentially the same for all treatments, indicating no CO2-induced stomatal closure to at least 2000 μL•L−1. Photosynthetic Vmax (milligrams per square decimetre per hour) for light response curves varied with CO2 concentration. If results are extrapolated beyond a 5-month period and into field conditions, it appears that size of trees, interactions with competitors, and ecological role of the species might be altered.
Xylem sap analysis for determining nutritional status of trees: Pseudotsugamenziesii
Authors: Stark N. , Spitzner C. , Essig D.
Published: July 2010

Xylem sap extraction of branches as a new field problem-solving technique in forestry, environmental pollution, and botany is described. The influence of extraction pressure, crown aspect, height into the crown, tree age, time of year and day, and soil chemistry on the ion concentrations in xylem sap are discussed. Xylem sap extraction with a pressure chamber provides a good indication of the nutrient status of a species if the trees are of similar age, and if they are sampled at the same aspect, crown height, time of day, time of year, and on the same soils. Pseudotsugamenziesii (Mirb.) Franco (Douglas-fir), growing on nutrient-poor acid soils and moderately fertile alkaline soils showed significant differences in growth rate and ion concentrations in the xylem sap and soil. Trees on the faster growth site (< 12 rings/2.54 cm) had significantly more Ca, K, Mn, P, and N in the xylem sap. Trees on the poor growth site had high levels of Mg in the sap. Trees growing on the poor site which was also K deficient transpired more rapidly than those with faster growth. It is hypothesized that insufficient plant K could reduce the ability of the guard cells to control water loss. The stem water potential was slightly, but not significantly, higher on the poor growth site. Although there is no proof that the deficient ions are the cause of poor growth, they are suspect, given the similar water availability on the two sites. The concept of nutrient supplying potential of a tree, or its ability to supply its needles and meristems with water and nutrients is discussed. Distilled water soil extracts and foliar analyses would not have reflected the same ion relationships (deficiencies or excesses) that are evident in the xylem sap. Evidence for the factors controlling growth in these stands is being sought through fertilizer tests.
Factors influencing generation times of spruce beetles in Alaska
Authors: Werner Richard A. , Holsten Edward H.
Published: July 2010

Direct solar radiation to the bark surface of white spruce, Piceaglauca (Moench) Voss, is the primary environmental factor influencing the developmental rate of spruce beetles, Dendroctonusrufipennis (Kirby), in Alaska. A phloem threshold temperature of 16.5 °C is required to initiate the development of 1 year life cycle beetles. Tree location within a stand and stand aspect in relation to direct solar radiation determine which trees or areas of the tree support beetles with 1- and 2-year life cycles. Two-year cycles normally developed on the north and west sides of standing trees and the north and bottom sides of felled trees, which were characterized by an average phloem temperature of 10.6 °C. One-year cycles normally developed on the south sides of standing trees and the south and top sides of felled trees, which were characterized by an average phloem temperature of 16.5 °C.
Long-term atmospheric CO2 enrichment affects the growth and development of Liquidambarstyraciflua and Pinustaeda seedlings
Authors: Sionit N. , Strain B. R. , Hellmers H. , Riechers G. H. , Jaeger C. H.
Published: July 2010

Growth and development of native species of trees in response to long-term increases in atmospheric CO2 concentration were studied. Seedlings of two competing perennials, Pinustaeda L. and Liquidambarstyraciflua L., were obtained from germinated seeds and grown through one complete growing season at 350, 500, and 650 μL•L−1 CO2. The plants were grown in CO2 controlled greenhouses under natural photoperiods and light regimes, with temperature controlled to simulate mean local climate. Stem length and basal stem diameter increased with increasing CO2 in both species. Liquidambarstyraciflua maintained size dominance in all concentrations. The dry weights of stems, roots, and leaves increased in both species. In P. taeda, however, the seedlings reached maximum size at 500 μL•L−1 while L. styraciflua continued to increase up to 650 μL•L−1. Liquidambarstyraciflua produced significantly more branches and leaves at the higher CO2 concentrations than at 350 μL L−1. Differences in plant shape and responses in growth rate of these two naturally competing tree species suggest that continuing atmospheric CO2 enrichment could affect future interactions between the species and might produce changes in community composition.
DYNAMICS OF A PARTICULAR LORENZ TYPE SYSTEM
Authors: TESTONI GIORGIO E. , RECH PAULO C.
Published: July 2010

In this paper we analytically and numerically investigate the dynamics of a nonlinear three-dimensional autonomous first-order ordinary differential equation system, obtained from paradigmatic Lorenz system by suppressing the y variable in the right-hand side of the second equation. The Routh–Hurwitz criterion is used to decide on the stability of the nontrivial equilibrium points of the system, as a function of the parameters. The dynamics of the system is numerically characterized by using diagrams that associate colors to largest Lyapunov exponent values in the parameter-space. Additionally, phase-space plots and bifurcation diagrams are used to characterize periodic and chaotic attractors.
EMPIRICAL ANALYSIS OF ATTENTION BEHAVIORS IN ONLINE SOCIAL NETWORKS
Authors: DU FANG , XUAN QI , WU TIE-JUN
Published: July 2010

Studying attention behavior has its social significance because such behavior is considered to lead the evolution of the friendship network. However, this type of behavior in social networks has attracted relatively little attention before, which is mainly because, in reality, such behaviors are always transitory and rarely recorded. In this paper, we collected the attention behaviors as well as the friendship network from Douban database and then carefully studied the attention behaviors in the friendship network as a latent metric space. The revealed similar patterns of attention behavior and friendship suggest that attention behavior may be the pre-stage of friendship to a certain extent, which can be further validated by the fact that pairwise nodes in Douban network connected by attention links beforehand are indeed far more likely to be connected by friendship links in the near future. This phenomenon can also be used to explain the high clustering of many social networks. More interestingly, it seems that attention behaviors are more likely to take place between individuals who have more mutual friends as well as more different friends, which seems a little different from the principles of many link prediction algorithms. Moreover, it is also found that forward attention is preferred to inverse attention, which is quite natural because, usually, an individual must be more interested in others that he is paying attention to than those paying attention to him. All of these findings can be used to guide the design of more appropriate social network models in the future.
DYNAMIC MAINTENANCE OF SUPPORT COVERAGE IN SENSOR NETWORKS
Authors: DASH DINESH , GUPTA AROBINDA , BISHNU ARIJIT
Published: July 2010

Ensuring different types of coverage is an important problem in many wireless sensor applications. In this paper, we address the problem of maintaining support coverage in the presence of sensor failures. Given a placement of n sensors in an area A, and any two points i and f in A, the support value of any path between i and f is the maximum distance of any point on the path from its closest sensor. The path with the minimum support value is called the maximal support path. The support value of a path may increase if a sensor fails. Given a maximal support path with a support value ψ, we first present two centralized approximation algorithms that, on failure of a single sensor, compute a new path with a support value close to ψ by moving exactly one nearby sensor. The first algorithm assumes that the sensors are allowed to move in any direction, and the second one assumes that the sensors are constrained to move in any of the four directions east, west, north, and south. Both the support value for the new path computed and the movement necessary are shown to be within a constant-factor of the initial support value. We then show that even in case of multiple sensor failures, a new path with a bounded support value can be computed. Detailed simulation results are provided to show that the algorithms result in significant improvement in many cases in practice, and the improvements obtained are significantly better than the worst case bounds given by the analysis. We also discuss distributed implementations of the algorithms.
EXTENDED SKYRME INTERACTION IN THE SPIN CHANNEL
Authors: MARGUERON J. , GORIELY S. , GRASSO M. , COLÒ G. , SAGAWA H.
Published: July 2010

Most of the Skyrme interactions are known to predict spin or isospin instabilities beyond the saturation density of nuclear matter which contradict predictions based on realistic interactions. A modification of the standard Skyrme interaction is proposed so that the ferromagnetic instability is removed. The new terms are density dependent and modify only the spin p - h interaction in the case of spin-saturated system. We have shown that these new terms change the total binding energy of odd-nuclei by only few tenths of keV. From the analysis of the spin instabilities of nuclear matter, restrictions on the parameters governing the spin-density dependent terms are evaluated. We conclude that with the extended Skyrme interaction, the Landau parameters G0 and [Formula: see text] could be tuned with a large flexibility without changing the ground-state properties in nuclei and in nuclear matter.
EFFECT OF TENSOR INTERACTION ON HEAVY AND SUPERHEAVY NUCLEI
Authors: ZHOU XIAN-RONG , SAGAWA HIROYUKI
Published: July 2010

The effect of tensor interaction is discussed on the deformation and the shell structure of heavy and superheavy nuclei within the deformed Skyrme Hartree-Fock+BCS model. The importance of the tensor correlations is shown for the single particle spectra of protons in 249 Bk . The large shell gaps of superheavy nuclei are found at Z = 114 and Z = 120 for protons and N = 184 for neutrons with the spherical shape irrespective of the tensor correlations. It is also shown that Z = 114 and N = 164 shell gaps are more pronounced by the tensor correlations in the case of SLy 5+ T interaction.
SYSTEMATIC CALCULATION OF ELECTRIC DIPOLE STRENGTH WITH SKYRME-HF PLUS RPA
Authors: INAKURA TSUNENORI , NAKATSUKASA TAKASHI , YABANA KAZUHIRO
Published: July 2010

We show some results of systematic calculation on electric dipole responses of even-even nuclei, employing a Hartree-Fock plus RPA approach. For an easy implementation of the fully self-consistent calculation, a finite amplitude method which we proposed recently is employed. We show a systematic comparison of calculated peak energies of giant dipole resonances and an importance of low-angular momentum orbit for emergence of pygmy dipole resonances.
Crystal Polarity Effects on Magnesium Implantation into GaN Layer
Authors: Liu Kuan-Ting , Chang Shoou-Jinn , Wu Sean , Horikoshi Yoshiji
Published: July 2010

Crystal polarity effects on Mg implantation into GaN layers for p-type doping have been systematically investigated. It is found that we can observe a smaller X-ray diffraction full-width at half-maximum and a stronger Mg-acceptor bound exciton emission for the Mg implantation into N-polarity GaN layer than Ga-polarity one after a proper post-implantation annealing treatment. Raman experiment demonstrates that the tensile stress occurs on the as-grown N-polarity GaN layer, which can be resulting from the Ga vacancy. Hall measurement results further indicate that the p-type conductivity can be successfully obtained for N-polarity GaN compared with Ga-polarity one after Mg implantation regardless of under the identical implantation and post-implantation annealing conditions. These phenomena can all be attributed to the more Ga vacancies in the as-grown N-polarity GaN layer that enhances Mg acceptor substitution and eventually achieve p-type conductive characteristics by an appropriate postimplantation annealing treatment.