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  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 361 (1993), S. 24-24 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR - There have been several reports suggesting that non-field-based studies of plant responses to elevated atmospheric CO2 may be compromised because small rooting volumes limit a plant's ability to respond to elevated CO2 (refs 1-3). This hypothesis calls into question most of our present ...
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 376 (1995), S. 559-560 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR - Genome size, as measured by the content of nuclear DNA per cell, varies over 2,500-fold among species of angiosperm plants1. As genome size is positively correlated with cell size and with the duration of cell cycle2, it may have direct effects on the evolutionary strategy3, life history, ...
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 34 (1975), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Detached corn and sunflower leaves supplied with PbCl2 via the transpiration stream exhibited reduced rates of photosynthesis. The difference between species in the amount of Pb taken up was in direct proportion to their respective transpiration rates. For both species the reduction in photosynthesis and the amount of Pb taken up increased with increasing treatment concentrations. A corresponding reduction occurred in the rate of transpiration suggesting that stomatal resistance may be increased by Pb contamination. The pathways of CO2 and water vapor exchange are discussed in relation to the effects of Pb on photosynthesis and transpiration.
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  • 4
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Detached corn and sunflower leaves exposed to various concentrations of Cd, supplied as CdCl2, exhibit reduced photosynthesis and transpiration. The reduction is dependent on the concentration of CdCl2 solution and generally becomes more pronounced with time. In sunflower, net photosynthesis and transpiration are completely inhibited within 45 min after the introduction of 18 mM Cd. Within two hours net photosynthesis is reduced to 40% and 70% of maximum after the introduction of 9 and 4.5 mM Cd respectively. In corn the trend of photo-synthetic response to Cd is similar to that in sunflower except that the inhibition in corn is more pronounced at all treatment levels. A strong linear relationship between photosynthesis and transpiration inhibition is obtained in both species suggesting that Cd contamination induces stomatal closure.
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  • 5
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 279 (1979), S. 554-555 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Inflorescences, flowers or fruits with a 3-5-cm piece of stem were excised from plants, sealed in vials containing water, and the rate of CO2 exchange of the inflorescence was determined, first in the light (700 ? m2 s"1) and then in the dark (1 ? m 2 s *) (rf. 7). Carbon dioxide exchange was ...
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  • 6
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: We investigated how light and CO2 levels interact to influence growth, phenology, and the physiological processes involved in leaf senescence in red oak (Quercus rubra) seedlings. We grew plants in high and low light and in elevated and ambient CO2. At the end of three years of growth, shade plants showed greater biomass enhancement under elevated CO2 than sun plants. We attribute this difference to an increase in leaf area ratio (LAR) in shade plants relative to sun plants, as well as to an ontogenetic effect: as plants increased in size, the LAR declined concomitant with a decline in biomass enhancement under elevated CO2Elevated CO2 prolonged the carbon gain capacity of shade-grown plants during autumnal senescence, thus increasing their functional leaf lifespan. The prolongation of carbon assimilation, however, did not account for the increased growth enhancement in shade plants under elevated CO2. Elevated CO2 did not significantly alter leaf phenology. Nitrogen concentrations in both green and senesced leaves were lower under elevated CO2 and declined more rapidly in sun leaves than in shade leaves. Similar to nitrogen concentration, the initial slope of A/Ci curves indicated that Rubisco activity declined more rapidly in sun plants than in shade plants, particularly under elevated CO2. Absolute levels of chlorophyll were affected by the interaction of CO2 and light, and chlorophyll content declined to a minimal level in sun plants sooner than in shade plants. These declines in N concentration, in the initial slope of A/Ci curves, and in chlorophyll content were consistent with declining photosynthesis, such that elevated CO2 accelerated senescence in sun plants and prolonged leaf function in shade plants. These results have implications for the carbon economy of seedlings and the regeneration of red oak under global change conditions.
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  • 7
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Increased atmospheric carbon dioxide supply is predicted to alter plant growth and biomass allocation patterns. It is not clear whether changes in biomass allocation reflect optimal partitioning or whether they are a direct effect of increased growth rates. Plasticity in growth and biomass allocation patterns was investigated at two concentrations of CO2 ([CO2]) and at limiting and nonlimiting nutrient levels for four fast- growing old-field annual species. Abutilon theophrasti, Amaranthus retroflexus, Chenopodium album, and Polygonum pensylvanicum were grown from seed in controlled growth chamber conditions at current (350 μmol mol−1, ambient) and future- predicted (700 μmol mol−1, elevated) CO2 levels. Frequent harvests were used to determine growth and biomass allocation responses of these plants throughout vegetative development. Under nonlimiting nutrient conditions, whole plant growth was increased greatly under elevated [CO2] for three C3 species and moderately increased for a C4 species (Amaranthus). No significant increases in whole plant growth were observed under limiting nutrient conditions. Plants grown in elevated [CO2] had lower or unchanged root:shoot ratios, contrary to what would be expected by optimal partitioning theory. These differences disappeared when allometric plots of the same data were analysed, indicating that CO2-induced differences in root:shoot allocation were a consequence of accelerated growth and development rates. Allocation to leaf area was unaffected by atmospheric [CO2] for these species. The general lack of biomass allocation responses to [CO2] availability is in stark contrast with known responses of these species to light and nutrient gradients. We conclude that biomass allocation responses to elevated atmospheric [CO2] are not consistent with optimal partitioning predictions.
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  • 8
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Rising levels of atmospheric CO2 may alter patterns of plant biomass production. These changes will be dependent on the ability of plants to acquire sufficient nutrients to maintain enhanced growth. Species-specific differences in responsiveness to CO2 may lead to changes in plant community composition and biodiversity. Differences in species-level growth responses to CO2 may be, in a large part, driven by differences in the ability to acquire nutrients. To understand the mechanisms of how elevated CO2 leads to changes in community-level productivity, we need to study the growth responses and patterns of nutrient acquisition for each of the species that comprise the community.In this paper, we present a study of how elevated CO2 affects community-level and species-level patterns of nitrogen uptake and biomass production. As an experimental system we use experimental communities of 11 co-occurring annuals common to disturbed seasonal grasslands in south-western U.S.A. We established experimental communities with approximately even numbers of each species in three different atmospheric CO2 concentrations (375, 550, and 700 ppm). We maintained these communities for 1, 1.5, and 2 months at which times we applied a 15N tracer (15NH415NO3) to quantify the nitrogen uptake and then measured plant biomass, nitrogen content, and nitrogen uptake rates for the entire communities as well as for each species.Overall, community-level responses to elevated CO2 were consistent with the majority of other studies of individual- and multispecies assemblages, where elevated CO2 leads to enhanced biomass production early on, but this enhancement declines through time. In contrast, the responses of the individual species within the communities was highly variable, showing the full range of responses from positive to negative. Due to the large variation in size between the different species, community-level responses were generally determined by the responses of only one or a few species. Thus, while several of the smaller species showed trends of increased biomass and nitrogen uptake in elevated CO2 at the end of the experiment, community-level patterns showed a decrease in these parameters due to the significant reduction in biomass and nitrogen content in the single largest species.The relationship between enhancement of nitrogen uptake and biomass production in elevated CO2 was highly significant for both 550 ppm and 700 ppm CO2. This relationship strongly suggests that the ability of plants to increase nitrogen uptake (through changes in physiology, morphology, architecture, or mycorrhizal symbionts) may be an important determinant of which species in a community will be able to respond to increased CO2 levels with increased biomass production. The fact that the most dominant species within the community showed reduced enhancement and the smaller species showed increased enhancement suggest that through time, elevated CO2 may lead to significant changes in community composition.At the community level, nitrogen uptake rates relative to plant nitrogen content were invariable between the three different CO2 levels at each harvest. This was in contrast to significant reductions in total plant nitrogen uptake and nitrogen uptake relative to total plant biomass. These patterns support the hypothesis that plant nitrogen uptake is largely regulated by physiological activity, assuming that physiological activity is controlled by nitrogen content and thus protein and enzyme content.
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  • 9
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: This study investigated simultaneous plant and soil feedbacks on growth enhancement with elevated [CO2] within microcosms of yellow birch (Betula alleghaniensis Britt.) in the second year of growth. Understanding the integrated responses of model ecosystems may provide key insight into the potential net nutrient feedbacks on [CO2] growth enhancements in temperate forests. We measured the net biomass production, C:N ratios, root architecture, and mycorrhizal responses of yellow birch, in situ rates gross nitrogen mineralization and the partitioning of available NH4+ between yellow birch and soil microbes. Elevated atmospheric [CO2] resulted in significant alterations in the cycling of N within the microcosms. Plant C/N ratios were significantly increased, gross mineralization and NH4+ consumption rates were decreased, and relative microbial uptake of NH4+ was increased, representing a suite of N cycling negative feedbacks on N availability. However, increased C/N ratios may also be a mechanism which allows plants to maintain higher growth with a constant or reduced N supply. Total plant N content was increased with elevated [CO2], suggesting that yellow birch had successfully increased their ability to acquire nutrients during the first year of growth. However, plant uptake rates of NH4+ had decreased in the second year. This discrepancy implies that, in this study, nitrogen uptake showed a trend through ontogeny of decreasing enhancement under elevated [CO2]. The reduced N mineralization and relatively increased N immobilization are a potential feedback which may drive this ontogenetic trend. This study has demonstrated the importance of using an integrated approach to exploring potential nutrient-cycling feedbacks in elevated [CO2].
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  • 10
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Sap-feeding insects such as aphids are the only insect herbivores that show positive responses to elevated CO2. Recent models predict that increased nitrogen will increase aphid population size under elevated CO2, but few experiments have tested this idea empirically. To determine whether soil nitrogen (N) availability modifies aphid responses to elevated CO2, we tested the performance of Macrosiphum euphorbiae feeding on two host plants; a C3 plant (Solanum dulcamara), and a C4 plant (Amaranthus viridis). We expected aphid population size to increase on plants in elevated CO2, with the degree of increase depending on the N availability.We found a significant CO2× N interaction for the response of population size for M. euphorbiae feeding on S. dulcamara: aphids feeding on plants grown in ambient CO2, low N conditions increased in response to either high N availability or elevated CO2. No population size responses were observed for aphids infesting A. viridis. Elevated CO2 increased plant biomass, specific leaf weight, and C : N ratios of the C3 plant, S. dulcamara but did not affect the C4 plant, A. viridis. Increased N fertilization significantly increased plant biomass, leaf area, and the weight : height ratio in both experiments. Elevated CO2 decreased leaf N in S. dulcamara and had no effect on A. viridis, while higher N availability increased leaf N in A. viridis and had no effect in S. dulcamara. Aphid infestation only affected the weight : height ratio of S. dulcamara.We only observed an increase in aphid population size in response to elevated CO2 or increased N availability for aphids feeding on S. dulcamara grown under low N conditions. There appears to be a maximum population growth rate that M. euphorbiae aphids can attain, and we suggest that this response is because of intrinsic limits on development time and fecundity.
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