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  • 1
    Digitale Medien
    Digitale Medien
    Widespread foliage δ15N depletion under elevated CO2: inferences for the nitrogen cycle (2003)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 9 (2003), S. 0 
    Details
    ISSN: 1365-2486
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Energietechnik , Geographie
    Notizen: Leaf 15N signature is a powerful tool that can provide an integrated assessment of the nitrogen (N) cycle and whether it is influenced by rising atmospheric CO2 concentration. We tested the hypothesis that elevated CO2 significantly changes foliage δ15N in a wide range of plant species and ecosystem types. This objective was achieved by determining the δ15N of foliage of 27 field-grown plant species from six free-air CO2 enrichment (FACE) experiments representing desert, temperate forest, Mediterranean-type, grassland prairie, and agricultural ecosystems. We found that within species, the δ15N of foliage produced under elevated CO2 was significantly lower (P〈0.038) compared with that of foliage grown under ambient conditions. Further analysis of foliage δ15N by life form and growth habit revealed that the CO2 effect was consistent across all functional groups tested. The examination of two chaparral shrubs grown for 6 years under a wide range of CO2 concentrations (25–75 Pa) also showed a significant and negative correlation between growth CO2 and leaf δ15N. In a select number of species, we measured bulk soil δ15N at a depth of 10 cm, and found that the observed depletion of foliage δ15N in response to elevated CO2 was unrelated to changes in the soil δ15N. While the data suggest a strong influence of elevated CO2 on the N cycle in diverse ecosystems, the exact site(s) at which elevated CO2 alters fractionating processes of the N cycle remains unclear. We cannot rule out the fact that the pattern of foliage δ15N responses to elevated CO2 reported here resulted from a general drop in δ15N of the source N, caused by soil-driven processes. There is a stronger possibility, however, that the general depletion of foliage δ15N under high CO2 may have resulted from changes in the fractionating processes within the plant/mycorrhizal system.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2486.2003.00679.x
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  • 2
    Digitale Medien
    Digitale Medien
    Influence of atmospheric CO2 enrichment on methane consumption in a temperate forest soil (2001)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 7 (2001), S. 0 
    Details
    ISSN: 1365-2486
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Energietechnik , Geographie
    Notizen: Rates of atmospheric CH4 consumption of soils in temperate forest were compared in plots continuously enriched with CO2 at 200 µL L−1 above ambient and in control plots exposed to the ambient atmosphere of 360 µL CO2 L−1. The purpose was to determine if ecosystem atmospheric CO2 enrichment would alter soil microbial CH4 consumption at the forest floor and if the effect of CO2 would change with time or with environmental conditions. Reduced CH4 consumption was observed in CO2-enriched plots relative to control plots on 46 out of 48 sampling dates, such that CO2-enriched plots showed annual reductions in CH4 consumption of 16% in 1998 and 30% in 1999. No significant differences were observed in soil moisture, temperature, pH, inorganic-N or rates of N-mineralization between CO2-enriched and control plots, indicating that differences in CH4 consumption between treatments were likely the result of changes in the composition or size of the CH4-oxidizing microbial community. A repeated measures analysis of variance that included soil moisture, soil temperature (from 0 to 30 cm), and time as covariates indicated that the reduction of CH4 consumption under elevated CO2 was enhanced at higher soil temperatures. Additionally, the effect of elevated CO2 on CH4 consumption increased with time during the two-year study. Overall, these data suggest that rising atmospheric CO2 will reduce atmospheric CH4 consumption in temperate forests and that the effect will be greater in warmer climates. A 30% reduction in atmospheric CH4 consumption by temperate forest soils in response to rising atmospheric CO2 will result in a 10% reduction in the sink strength of temperate forest soils in the atmospheric CH4 budget and a positive feedback to the greenhouse effect.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1354-1013.2001.00432.x
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  • 3
    Digitale Medien
    Digitale Medien
    The influence of elevated atmospheric CO2 on fine root dynamics in an intact temperate forest (2001)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 7 (2001), S. 0 
    Details
    ISSN: 1365-2486
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Energietechnik , Geographie
    Notizen: Root dynamics are important for plant, ecosystem and global carbon cycling. Changes in root dynamics caused by rising atmospheric CO2 not only have the potential to moderate further CO2 increases, but will likely affect forest function. We used FACE (Free-Air CO2 Enrichment) to expose three 30-m diameter plots in a 13-year-old loblolly pine (Pinus taeda) forest to elevated (ambient + 200 µL L−1) atmospheric CO2. Three identical fully instrumented plots were implemented as controls (ambient air only). We quantified root dynamics from October 1998 to October 1999 using minirhizotrons. In spite of 16% greater root lengths and 24% more roots per minirhizotron tube, the effects of elevated atmospheric CO2 on root lengths and numbers were not statistically significant. Similarly, production and mortality were also unaffected by the CO2 treatment, even though annual root production and mortality were 26% and 46% greater in elevated compared to ambient CO2 plots. Average diameters of live roots present at the shallowest soil depth were, however, significantly enhanced in CO2-enriched plots. Mortality decreased with increasing soil depth and the slopes of linear regression lines (mortality vs. depth) differed between elevated and ambient CO2 treatments, reflecting the significant CO2 by depth interaction. Relative root turnover (root flux/live root pool) was unchanged by exposure to elevated atmospheric CO2. Results from this study suggest modest, if any, increases in ecosystem-level root productivity in CO2-enriched environments.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1354-1013.2001.00457.x
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  • 4
    Digitale Medien
    Digitale Medien
    Archival photographs show no climate-induced changes in woody vegetation in the Sudan, 1943–1994 (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Global change biology 2 (1996), S. 0 
    Details
    ISSN: 1365-2486
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Energietechnik , Geographie
    Notizen: An archive of satellite and aircraft photographs of the western Sudan showed no longterm (1943–1994) trends in the abundance of trees despite several decades of recent drought in this region. These data extend the extant historical record of vegetation change in the African Sahel, where recent fluctuations in vegetation greenness have been monitored with the NOAA Advanced Very High Resolution Radiometer since 1980. Despite substantial population turnover, woody vegetation is not yet indicative of the recent climate changes in this region.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1365-2486.1996.tb00058.x
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  • 5
    Digitale Medien
    Digitale Medien
    Desertification alters patterns of aboveground net primary production in Chihuahuan ecosystems (2002)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 8 (2002), S. 0 
    Details
    ISSN: 1365-2486
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Energietechnik , Geographie
    Notizen: Abstract The Chihuahuan desert of New Mexico, USA, has changed in historical times from semiarid grassland to desert shrublands dominated by Larrea tridentata and Prosopis glandulosa. Similar displacement of perennial grasslands by shrubs typifies desertification in many regions. Such structural vegetation change could alter average values of net primary productivity, as well as spatial and temporal patterns of production. We investigated patterns of aboveground plant biomass and net primary production in five ecosystem types of the Jornada Basin Long-Term Ecological Research (LTER) site. Comparisons of shrub-dominated desertified systems and remnant grass-dominated systems allowed us to test the prediction that shrublands are more heterogeneous spatially, but less variable over time, than grasslands.We measured aboveground plant biomass and aboveground net primary productivity (ANPP) by species, three times per year for 10 years, in 15 sites of five ecosystem types (three each in Larrea shrubland, Bouteloua eriopoda grassland, Prosopis dune systems, Flourensia cernua alluvial flats, and grass-dominated dry lakes or playas). Spatial heterogeneity of biomass at the scale of our measurements was significantly greater in shrub-dominated systems than in grass-dominated vegetation. ANPP was homogeneous across space in grass-dominated systems, and in most growing seasons was significantly more patchy in shrub vegetation. Substantial interannual variability in ANPP complicates comparison of mean values across ecosystem types, but grasslands tended to support higher ANPP values than did shrub-dominated systems. There were significant interactions between ecosystem type and season.Grasslands demonstrated higher interannual variation than did shrub systems. Desertification has apparently altered the seasonality of productivity in these systems; grasslands were dominated by summer growth, while sites dominated by Larrea or Prosopis tended to have higher spring ANPP. Production was frequently uncorrelated across sites of an ecosystem type, suggesting that factors other than season, regional climate, or dominant vegetation may be significant determinants of actual NPP.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2486.2002.00473.x
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  • 6
    Digitale Medien
    Digitale Medien
    Primary productivity of planet earth: biological determinants and physical constraints in terrestrial and aquatic habitats (2001)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 7 (2001), S. 0 
    Details
    ISSN: 1365-2486
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Energietechnik , Geographie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2486.2001.00448.x
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  • 7
    Digitale Medien
    Digitale Medien
    Genetic variation in germination, growth, and survivorship of red maple in response to subambient through elevated atmospheric CO2 (2004)
    Oxford, UK : Blackwell Publishing
    Global change biology 10 (2004), S. 0 
    Details
    ISSN: 1365-2486
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Energietechnik , Geographie
    Notizen: Genetic variation in plant response to atmospheric carbon dioxide (CO2) may have influenced paleo-vegetation dynamics and could determine how future elevated CO2 drives plant evolution and ecosystem productivity. We established how levels of relatedness – the maternal family, population, and provenance – affect variation in the CO2 response of a species. This 2-year growth chamber experiment focused on the germination, growth, biomass allocation, and survivorship responses of Acer rubrum to four concentrations of CO2: 180, 270, 360, and 600 μL L−1– representing Pleistocene through potential future conditions. We found that all levels of relatedness interacted with CO2 to contribute to variation in response. Germination responses to CO2 varied among families and populations, growth responses depended on families and regions of origin, and survivorship responses to CO2 were particularly affected by regional identities. Differences among geographic regions accounted for 23% of the variation in biomass response to CO2. If seeds produced under subambient CO2 conditions behave similarly, our results suggest that A. rubrum may have experienced strong selection on seedling survivorship at Pleistocene CO2 levels. Further, this species may evolve in response to globally rising CO2 so as to increase productivity above that experimentally observed today. Species responses to future atmospheric CO2 and the accompanying biotic effects on the global carbon cycle will vary among families, populations, and provenances.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2486.2004.00726.x
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  • 8
    Digitale Medien
    Digitale Medien
    Species control variation in litter decomposition in a pine forest exposed to elevated CO2 (2002)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 8 (2002), S. 0 
    Details
    ISSN: 1365-2486
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Energietechnik , Geographie
    Notizen: Net primary production and the flux of dry matter and nutrients from vegetation to soils has increased following four years of exposure to elevated CO2 in a southern pine forest in NC, USA. This has increased the demand for nutrients to support enhanced rates of NPP and altered the conditions for litter decomposition on the forest floor. We quantified the chemistry and decomposition dynamics of leaf litter produced by five of the most abundant tree species in this ecosystem during the third and fourth growing seasons under elevated CO2. The objectives of this study were to determine (i) if there were systemic or species-specific changes in leaf litter chemistry associated with a sustained enhancement of plant growth under elevated CO2; and (ii) whether the process of litter decomposition was altered by increased inputs of energy and nutrients to the forest floor in the plots under elevated CO2. Leaf litter chemistry, including various C fractions and N concentration, was virtually unchanged by elevated CO2. With few exceptions, plant litter produced under elevated CO2 lost mass or N at the same relative rate as that produced under ambient CO2. The relationship between initial litter chemistry and decomposition was not altered by elevated CO2. The greater forest floor mass and nutrient content in the plots under elevated CO2 had no consistent or long-term effect on litter decomposition. Thus, we found no evidence that plant and microbial processes under elevated CO2 resulted in systemic changes in mass loss or N dynamics during decomposition. In contrast to the limited effects of elevated CO2 on litter chemistry and decomposition, there were large differences among species in initial litter chemistry, mass loss and N dynamics during decomposition. If the species composition of this forest community is altered by elevated CO2, the indirect effect of a change in species composition will exert greater control over the long-term rate of nutrient cycling than the direct effect of elevated CO2 on litter chemistry and decomposition dynamics alone.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2486.2002.00551.x
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  • 9
    Digitale Medien
    Digitale Medien
    Effects of elevated atmospheric CO2 on fine root production and activity in an intact temperate forest ecosystem (2000)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 6 (2000), S. 0 
    Details
    ISSN: 1365-2486
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie , Energietechnik , Geographie
    Notizen: We investigated the effects of elevated atmospheric CO2 concentrations (ambient + 200 ppm) on fine root production and soil carbon dynamics in a loblolly pine (Pinus taeda) forest subject to free-air CO2 enrichment (FACE) near Durham, NC (USA). Live fine root mass (LFR) showed less seasonal variation than dead fine root mass (DFR), which was correlated with seasonal changes in soil moisture and soil temperature. LFR mass increased significantly (by 86%) in the elevated CO2 treatment, with an increment of 37 g(dry weight) m−2 above the control plots after two years of CO2 fumigation. There was no long-term increment in DFR associated with elevated CO2, but significant seasonal accumulations of DFR mass occurred during the summer of the second year of fumigation. Overall, root net primary production (RNPP) was not significantly different, but annual carbon inputs were 21.7 gC m−2 y−1 (68%) higher in the elevated CO2 treatment compared to controls. Specific root respiration was not altered by the CO2 treatment during most of the year; however, it was significantly higher by 21% and 13% in September 1997 and May 1998, respectively, in elevated CO2. We did not find statistically significant differences in the C/N ratio of the root tissue, root decomposition or phosphatase activity in soil and roots associated with the treatment. Our data show that the early response of a loblolly pine forest ecosystem subject to CO2 enrichment is an increase in its fine root population and a trend towards higher total RNPP after two years of CO2 fumigation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.1365-2486.2000.00374.x
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  • 10
    Digitale Medien
    Digitale Medien
    Limited carbon storage in soil and litter of experimental forest plots under increased atmospheric CO 2 (2001)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 411 (2001), S. 466-469 
    Details
    ISSN: 1476-4687
    Quelle: Nature Archives 1869 - 2009
    Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik
    Notizen: [Auszug] The current rise in atmospheric CO2 concentration is thought to be mitigated in part by carbon sequestration within forest ecosystems, where carbon can be stored in vegetation or soils. The storage of carbon in soils is determined by the fraction that is sequestered in persistent ...
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1038/35078060
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