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  • 1
    Electronic Resource
    Electronic Resource
    Convergence across biomes to a common rain-use efficiency (2004)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 429 (2004), S. 651-654 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Water availability limits plant growth and production in almost all terrestrial ecosystems. However, biomes differ substantially in sensitivity of aboveground net primary production (ANPP) to between-year variation in precipitation. Average rain-use efficiency (RUE; ANPP/precipitation) also ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature02561
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  • 2
    Electronic Resource
    Electronic Resource
    Elevated CO 2 increases productivity and invasive species success in an arid ecosystem (2000)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 408 (2000), S. 79-82 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Arid ecosystems, which occupy about 20% of the earth's terrestrial surface area, have been predicted to be one of the most responsive ecosystem types to elevated atmospheric CO2 and associated global climate change. Here we show, using free-air CO2 enrichment (FACE) ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35040544
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  • 3
    Electronic Resource
    Electronic Resource
    Photosynthetic responses of Mojave Desert shrubs to free air CO2 enrichment are greatest during wet years (2003)
    Oxford, UK : Blackwell Science, Ltd
    Global change biology 9 (2003), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: It has been suggested that desert vegetation will show the strongest response to rising atmospheric carbon dioxide due to strong water limitations in these systems that may be ameliorated by both photosynthetic enhancements and reductions in stomatal conductance. Here, we report the long-term effect of 55 Pa atmospheric CO2 on photosynthesis and stomatal conductance for three Mojave Desert shrubs of differing leaf phenology (Ambrosia dumosa—drought-deciduous, Krameria erecta—winter-deciduous, Larrea tridentata—evergreen). The shrubs were growing in an undisturbed ecosystem fumigated using FACE technology and were measured over a four-year period that included both above and below-average precipitation. Daily integrated photosynthesis (Aday) was significantly enhanced by elevated CO2 for all three species, although Krameria erecta showed the greatest enhancements (63% vs. 32% for the other species) enhancements were constant throughout the entire measurement period. Only one species, Larrea tridentata, decreased stomatal conductance by 25–50% in response to elevated CO2, and then only at the onset of the summer dry season and following late summer convective precipitation. Similarly, reductions in the maximum carboxylation rate of Rubisco were limited to Larrea during spring. These results suggest that the elevated CO2 response of desert vegetation is a function of complex interactions between species functional types and prevailing environmental conditions. Elevated CO2 did not extend the active growing season into the summer dry season because of overall negligible stomatal conductance responses that did not result in significant water conservation. Overall, we expect the greatest response of desert vegetation during years with above-average precipitation when the active growing season is not limited to ∼2 months and, consequently, the effects of increased photosynthesis can accumulate over a biologically significant time period.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2003.00580.x
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  • 4
    Electronic Resource
    Electronic Resource
    Functional ecology of shrub seedlings after a natural recruitment event at the Nevada Desert FACE Facility (2003)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 9 (2003), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Seedling recruitment is an important determinant of community structure in desert ecosystems. Positive photosynthetic growth and water balance responses to increasing atmospheric carbon dioxide (CO2) concentrations ([CO2]) are predicted to be substantial in desert plants, suggesting that recruitment could be stimulated. However, to date no studies have addressed the response of perennial plant recruitment in natural populations of desert shrubs exposed to elevated [CO2]. In April 1997, we employed Free-Air Carbon Dioxide Enrichment (FACE) in order to increase atmospheric [CO2] in an undisturbed Mojave Desert ecosystem from ambient (∼∼ 370 µmol mol−1) to elevated CO2 (∼∼ 550 µmol mol−1). From 1997 to 2001 we seasonally examined survival, growth, gas exchange and water potential responses of Larrea tridentata and Ambrosia dumosa seedlings that germinated in Fall, 1997. Recruitment densities were not influenced by [CO2] in either species, although a two-fold higher adult Ambrosia density under elevated [CO2] resulted in two-fold higher seedling density (0.87 vs 0.40 seedlings m−2). Mortality was greatest for both species during the first summer (1998), despite above-average rainfall during the previous Winter–Spring. A significant [CO2] × time interaction revealed that early survival was greater under elevated CO2, whereas a significant species time interaction revealed that overall survival was greater for Ambrosia (28%) than for Larrea (15%), regardless of [CO2]. Microsite (understorey or interspace) alone had no significant influence on survival. Significant species, microsite and species × microsite effects on growth (seedling height, stem diameter and canopy size) were found, but elevated CO2 had minimal impact on these parameters. Photosynthetic rates (Asat) for both species were higher at elevated [CO2] during certain seasons, but not consistently so. These results suggest that increased atmospheric [CO2] may enhance carbon (C) assimilation and survival of aridland perennial shrubs during favourable growing conditions, but that it may not counteract the effects of prolonged drought on mortality.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2003.00618.x
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  • 5
    Electronic Resource
    Electronic Resource
    Net ecosystem CO2 exchange in Mojave Desert shrublands during the eighth year of exposure to elevated CO2 (2005)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 11 (2005), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Arid ecosystems, which occupy about 35% of the Earth's terrestrial surface area, are believed to be among the most responsive to elevated [CO2]. Net ecosystem CO2 exchange (NEE) was measured in the eighth year of CO2 enrichment at the Nevada Desert Free-Air CO2 Enrichment (FACE) Facility between the months of December 2003–December 2004. On most dates mean daily NEE (24 h) (μmol CO2 m−2 s−1) of ecosystems exposed to elevated atmospheric CO2 were similar to those maintained at current ambient CO2 levels. However, on sampling dates following rains, mean daily NEEs of ecosystems exposed to elevated [CO2] averaged 23 to 56% lower than mean daily NEEs of ecosystems maintained at ambient [CO2]. Mean daily NEE varied seasonally across both CO2 treatments, increasing from about 0.1 μmol CO2 m−2 s−1 in December to a maximum of 0.5–0.6 μmol CO2 m−2 s−1 in early spring. Maximum NEE in ecosystems exposed to elevated CO2 occurred 1 month earlier than it did in ecosystems exposed to ambient CO2, with declines in both treatments to lowest seasonal levels by early October (0.09±0.03 μmol CO2 m−2 s−1), but then increasing to near peak levels in late October (0.36±0.08 μmol CO2 m−2 s−1), November (0.28±0.03 μmol CO2 m−2 s−1), and December (0.54±0.06 μmol CO2 m−2 s−1). Seasonal patterns of mean daily NEE primarily resulted from larger seasonal fluctuations in rates of daytime net ecosystem CO2 uptake which were closely tied to plant community phenology and precipitation. Photosynthesis in the autotrophic crust community (lichens, mosses, and free-living cyanobacteria) following rains were probably responsible for the high NEEs observed in January, February, and late October 2004 when vascular plant photosynthesis was low. Both CO2 treatments were net CO2 sinks in 2004, but exposure to elevated CO2 reduced CO2 sink strength by 30% (positive net ecosystem productivity=127±17 g C m−2 yr−1 ambient CO2 and 90±11 g C m−2 yr−1 elevated CO2, P=0.011). This level of net C uptake rivals or exceeds levels observed in some forested and grassland ecosystems. Thus, the decrease in C sequestration seen in our study under elevated CO2– along with the extensive coverage of arid and semi-arid ecosystems globally – points to a significant drop in global C sequestration potential in the next several decades because of responses of heretofore overlooked dryland ecosystems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2486.2005.00948.x
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  • 6
    Electronic Resource
    Electronic Resource
    Self-Selection and Discrimination in Credit Markets (2005)
    Oxford, UK and Boston, USA : Blackwell Publishing, Inc.
    Real estate economics 33 (2005), S. 0 
    Details
    ISSN: 1540-6229
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: In this article we make two contributions toward a better understanding of the causes and consequences of discrimination in credit markets. First, we develop an explicit theoretical model of loan underwriting in which lenders use a simple Bayesian updating process to evaluate applicant creditworthiness. Using a signal correlated with an applicant's true creditworthiness and their prior beliefs about the distribution of credit risk in the applicant pool, lenders are able to evaluate an applicant's expected or “inferred” creditworthiness to determine which loans to approve and which to deny. Second, we explicitly model the self-selection behavior of individuals. Because these decisions shape lenders' prior beliefs about the distribution of credit risk, they also affect the Bayesian posterior from which lenders compute an applicant's inferred creditworthiness, implying that statistical discrimination can arise endogenously. As an example, we show that in a market in which only some lenders have Beckerian tastes for discrimination there are conditions under which lenders without racial animus will also discriminate. Our model's flexibility makes it ideal for analyzing a wide variety of empirical and policy questions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1540-6229.2005.00118.x
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  • 7
    Electronic Resource
    Electronic Resource
    Evidence of drought-induced stress on biotic crust moss in the Mojave Desert (2005)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 28 (2005), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Widespread bleaching (chlorosis) of patches of the dominant desert moss Syntrichia caninervis was observed across the northern Mojave Desert in the winter of 2002–03 following an extended period of drought interrupted by small rain events. These rain events were more frequent during the warmer months just prior to the appearance of chlorosis. We hypothesized that the patches were experiencing physiological stress due to partial hydration/rapid dehydration cycling during the warmer months. Compared to unbleached (green) shoots, chlorotic shoots exhibited significantly reduced photochemical performance, photosynthetic pigments, regenerational potential, sex expression, and lower rates of growth and productivity. However, age-specific analyses revealed older leaves from chlorotic shoots did not show the typical decline in vigour, suggesting that stress may primarily affect younger tissues. It is concluded that this chlorosis phenomenon is indicative of physiological stress presently occurring in the Mojave Desert, and is likely due to exposure to a higher than normal frequency of light rain events (〈 3.5 mm), which serve to partially hydrate moss patches that then rapidly desiccate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.2005.01346.x
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  • 8
    Electronic Resource
    Electronic Resource
    The b Subunit of Escherichia coli ATP Synthase (2000)
    Springer
    Journal of bioenergetics and biomembranes 32 (2000), S. 347-355 
    Details
    ISSN: 1573-6881
    Keywords: ATP synthase ; second stalk ; b subunit ; stator ; rotational catalysis ; coiled-coil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract The b subunit of ATP synthase is a major component of the second stalk connecting the F1and F0 sectors of the enzyme and is essential for normal assembly and function. The156-residue b subunit of the Escherichia coli ATP synthase has been investigated extensivelythrough mutagenesis, deletion analysis, and biophysical characterization. The two copies ofb exist as a highly extended, helical dimer extending from the membrane to near the top ofF1, where they interact with the δ subunit. The sequence has been divided into four domains:the N-terminal membrane-spanning domain, the tether domain, the dimerization domain, andthe C-terminal δ-binding domain. The dimerization domain, contained within residues 60–122,has many properties of a coiled-coil, while the δ-binding domain is more globular. Sites ofcrosslinking between b and the a, α, β, and δ subunits of ATP synthase have been identified,and the functional significance of these interactions is under investigation. The b dimer mayserve as an elastic element during rotational catalysis in the enzyme, but also directly influencesthe catalytic sites, suggesting a more active role in coupling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005571818730
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  • 9
    Electronic Resource
    Electronic Resource
    HIV-related services for persons with severe mental illness: Policy and practice in new hampshire community mental health (2000)
    Springer
    The journal of behavioral health services & research 27 (2000), S. 347-353 
    Details
    ISSN: 1556-3308
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine , Psychology
    Notes: Abstract Rates of HIV and HIV risk behaviors are elevated among people with severe mental illnesses (SMI). Little is known about the extent to which community mental health (CMH) centers screen, refer, and educate their clients regarding HIV and sexually transmitted diseases (STDs). The authors surveyed CMH administrators and clinicians in New Hampshire regarding HIV/STD policy, practices, knowledge, and attitudes. HIV/STD service availability varied, and the amount of services provided was unrelated to the prevalence of HIV and AIDS in that region. Clinicians were knowledgeable about general HIV information but lacked specific knowledge about HIV related to persons with SMI. CMH staff had positive attitudes about helping clients with HIV issues. Administrators were interested in receiving training. Policy leadership, CMH practice guidelines, and training are warranted in light of the pressing public health implications of HIV/STDs among people with SMI.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02291746
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  • 10
    Electronic Resource
    Electronic Resource
    Anoxia tolerance of con-familial tiger beetle larvae is associated with differences in energy flow and anaerobiosis (2000)
    Springer
    Journal of comparative physiology 170 (2000), S. 307-314 
    Details
    ISSN: 1432-136X
    Keywords: AbbreviationLt50 time to 50% mortality
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract In this study, we compared survivorship, heat dissipation and biochemical features of anaerobiosis of two tiger beetle species (Coleoptera: Cicindelidae) exposed to anoxia. One species commonly experiences environmental immersion from rainfall and snowmelt (Cicindela togata), and the habitat of the other (Amblycheila cylindriformis) is not prone to flooding. The ancestral genus, A. cylindriformis, survives anoxia for only 2 days at 25 °C. In response to anoxia, these larvae immediately lose locomotory abilities, tissue concentrations of ATP fall precipitously within 12 h, and significant amounts of lactate are quickly produced. In contrast, C. togata larvae tolerate anoxia for 5 days. Heat dissipation is downregulated to a greater degree than that seen in A. cylindriformis (3.4% versus 14% of standard normoxic rate, respectively), the ability for locomotion is maintained and normoxic levels of ATP are defended for at least 24 h. Lactate is not accumulated until well into anoxic bout, and significant amounts of alanine are also produced. This study provides evidence that tiger beetles differ in physiological responses to anoxia, and that these differences are correlated with flooding risk and with species distribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003600000104
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