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  • 1
    Electronic Resource
    Electronic Resource
    Mechanisms of long-distance dispersal of seeds by wind (2002)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 418 (2002), S. 409-413 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Long-distance dispersal (LDD) is central to species expansion following climate change, re-colonization of disturbed areas and control of pests. The current paradigm is that the frequency and spatial extent of LDD events are extremely difficult to predict. Here we show that mechanistic models ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature00844
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  • 2
    Electronic Resource
    Electronic Resource
    Soil fertility limits carbon sequestration by forest ecosystems in a CO 2 -enriched atmosphere (2001)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 411 (2001), S. 469-472 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Northern mid-latitude forests are a large terrestrial carbon sink. Ignoring nutrient limitations, large increases in carbon sequestration from carbon dioxide (CO2) fertilization are expected in these forests. Yet, forests are usually relegated to sites of moderate to poor fertility, ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/35078064
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  • 3
    Electronic Resource
    Electronic Resource
    Hydrologic balance in an intact temperate forest ecosystem under ambient and elevated atmospheric CO2 concentration (2002)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 8 (2002), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Abstract Increasing atmospheric CO2 concentration decreases stomatal conductance in many species, but the savings of water from reduced transpiration may permit the forest to retain greater leaf area index (L). Therefore, the net effect on water use in forest ecosystems under a higher CO2 atmosphere is difficult to predict. The free air CO2 enrichment (FACE) facility (n = 3) in a 14-m tall (in 1996) Pinus taeda L. stand was designed to reduce uncertainties in predicting such responses. Continuous measurements of precipitation, throughfall precipitation, sap flux, and soil moisture were made over 3.5 years under ambient (CO2a) and elevated (CO2e) ambient + 200 µmol mol−1). Annual stand transpiration under ambient CO2 conditions accounted for 84–96% of latent heat flux measured with the eddy-covariance technique above the canopy. Under CO2e, P. taeda transpired less per unit of leaf area only when soil drought was severe. Liquidambar styraciflua, the other major species in the forest, used progressively less water, settling at 25% reduction in sap flux density after 3.5 years under CO2e. Because P. taeda dominated the stand, and severe drought periods were of relatively short duration, the direct impact of CO2e on water savings in the stand was undetectable. Moreover, the forest used progressively more water under CO2e, probably because soil moisture availability progressively increased, probably owing to a reduction in soil evaporation caused by more litter buildup in the CO2e plots. The results suggest that, in this forest, the effect of CO2e on transpiration was greater indirectly through enhanced litter production than directly through reduced stomatal conductance. In forests composed of species more similar to L. styraciflua, water savings from stomatal closure may dominate the response to CO2e.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2002.00513.x
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  • 4
    Electronic Resource
    Electronic Resource
    Modelling night-time ecosystem respiration by a constrained source optimization method (2002)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 8 (2002), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: One of the main challenges to quantifying ecosystem carbon budgets is properly quantifying the magnitude of night-time ecosystem respiration. Inverse Lagrangian dispersion analysis provides a promising approach to addressing such a problem when measured mean CO2 concentration profiles and nocturnal velocity statistics are available. An inverse method, termed ‘Constrained Source Optimization’ or CSO, which couples a localized near-field theory (LNF) of turbulent dispersion to respiratory sources, is developed to estimate seasonal and annual components of ecosystem respiration. A key advantage to the proposed method is that the effects of variable leaf area density on flow statistics are explicitly resolved via higher-order closure principles. In CSO, the source distribution was computed after optimizing key physiological parameters to recover the measured mean concentration profile in a least-square fashion. The proposed method was field-tested using 1 year of 30-min mean CO2 concentration and CO2 flux measurements collected within a 17-year-old (in 1999) even-aged loblolly pine (Pinus taeda L.) stand in central North Carolina. Eddy-covariance flux measurements conditioned on large friction velocity, leaf-level porometry and forest-floor respiration chamber measurements were used to assess the performance of the CSO model. The CSO approach produced reasonable estimates of ecosystem respiration, which permits estimation of ecosystem gross primary production when combined with daytime net ecosystem exchange (NEE) measurements. We employed the CSO approach in modelling annual respiration of above-ground plant components (c. 214 g C m−2 year−1) and forest floor (c. 989 g C m−2 year−1) for estimating gross primary production (c. 1800 g C m−2 year−1) with a NEE of c. 605 g C m−2 year−1 for this pine forest ecosystem. We conclude that the CSO approach can utilise routine CO2 concentration profile measurements to corroborate forest carbon balance estimates from eddy-covariance NEE and chamber-based component flux measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1354-1013.2001.00447.x
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  • 5
    Electronic Resource
    Electronic Resource
    Reduction of forest floor respiration by fertilization on both carbon dioxide-enriched and reference 17-year-old loblolly pine stands (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: Elevated atmospheric carbon dioxide (CO2e) increases soil respiration rates in forest, grassland, agricultural and wetland systems as a result of increased growth, root biomass and enhanced biological activity of soil microorganisms. Less is known about how forest floor fluxes respond to the combined effects of elevated CO2 and nutrient amendments; until now no experiments have been in place with large forest trees to allow even preliminary investigations. We investigated changes in forest floor respiration (Sff) in a Pinus taeda L. plantation fumigated with CO2 by using free-air CO2 enrichment (FACE) technology and given nutrient amendments. The prototype FACE apparatus (FACEp; 707 m2) was constructed in 1993, 10 years after planting, on a moderate fertility site in Duke Forest, North Carolina, USA, enriching the stand to 55 Pa (CO2e). A nearby ambient CO2 (CO2a) plot (117 m2) was designated at the inception of the study as a reference (Ref). Both FACEp and Ref plot were divided in half and urea fertilizer was applied to one half at an annual rate of 11.2 g N m−2 in the spring of 1998, 1999 and 2000. Forest floor respiration was monitored continuously for 220 days – March through November 2000 – by using two Automated Carbon Efflux Systems. Thirty locations (491 cm2 each) were sampled in both FACEp and Ref, about half in each fertility treatment. Forest floor respiration was strongly correlated with soil temperature at 5 cm. Rates of Sff were greater in CO2e relative to CO2a (an enhancement of ∼178 g C m−2) during the measurement period. Application of fertilizer resulted in a statistically significant depression of respiration rates in both the CO2a and CO2e plots (a reduction of ∼186 g C m−2). The results suggest that closed canopy forests on moderate fertility sites cycle back to the atmosphere more assimilated carbon (C) than similar forests on sites of high fertility. We recognize the limitations of this non-replicated study, but its clear results offer strong testable hypotheses for future research in this important area.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2003.00630.x
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  • 6
    Electronic Resource
    Electronic Resource
    Exposure to an enriched CO2 atmosphere alters carbon assimilation and allocation in a pine forest ecosystem (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: We linked a leaf-level CO2 assimilation model with a model that accounts for light attenuation in the canopy and measurements of sap-flux-based canopy conductance into a new canopy conductance-constrained carbon assimilation (4C-A) model. We estimated canopy CO2 uptake (AnC) at the Duke Forest free-air CO2 enrichment (FACE) study. Rates of AnC estimated from the 4C-A model agreed well with leaf gas exchange measurements (Anet) in both CO2 treatments. Under ambient conditions, monthly sums of net CO2 uptake by the canopy (AnC) were 13% higher than estimates based on eddy-covariance and chamber measurements. Annual estimates of AnC were only 3% higher than carbon (C) accumulations and losses estimated from ground-based measurements for the entire stand. The C budget for the Pinus taeda component was well constrained (within 1% of ground-based measurements). Although the closure of the C budget for the broadleaf species was poorer (within 20%), these species are a minor component of the forest. Under elevated CO2, the C used annually for growth, turnover, and respiration balanced only 80% of the AnC. Of the extra 700 g C m−2 a−1 (1999 and 2000 average), 86% is attributable to surface soil CO2 efflux. This suggests that the production and turnover of fine roots was underestimated or that mycorrhizae and rhizodeposition became an increasingly important component of the C balance. Under elevated CO2, net ecosystem production increased by 272 g C m−2 a−1: 44% greater than under ambient CO2. The majority (87%) of this C was sequestered in a moderately long-term C pool in wood, with the remainder in the forest floor–soil subsystem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2486.2003.00662.x
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  • 7
    Electronic Resource
    Electronic Resource
    Leaf and canopy responses to elevated CO2 in a pine forest under free-air CO2 enrichment (1996)
    Springer
    Oecologia 106 (1996), S. 416-416 
    Details
    ISSN: 1432-1939
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00334570
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  • 8
    Electronic Resource
    Electronic Resource
    Leaf and canopy responses to elevated CO2 in a pine forest under free-air CO2 enrichment (1995)
    Springer
    Oecologia 104 (1995), S. 139-146 
    Details
    ISSN: 1432-1939
    Keywords: Elevated CO2 ; Forest ecosystem ; Photosynthesis ; Pinus taeda ; Stomata
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Physiological responses to elevated CO2 at the leaf and canopy-level were studied in an intact pine (Pinus taeda) forest ecosystem exposed to elevated CO2 using a free-air CO2 enrichment (FACE) technique. Normalized canopy water-use of trees exposed to elevated CO2 over an 8-day exposure period was similar to that of trees exposed to current ambient CO2 under sunny conditions. During a portion of the exposure period when sky conditions were cloudy, CO2-exposed trees showed minor (≤7%) but significant reductions in relative sap flux density compared to trees under ambient CO2 conditions. Short-term (minutes) direct stomatal responses to elevated CO2 were also relatively weak (≈5% reduction in stomatal aperture in response to high CO2 concentrations). We observed no evidence of adjustment in stomatal conductance in foliage grown under elevated CO2 for nearly 80 days compared to foliage grown under current ambient CO2, so intrinsic leaf water-use efficiency at elevated CO2 was enhanced primarily by direct responses of photosynthesis to CO2. We did not detect statistical differences in parameters from photosynthetic responses to intercellular CO2 (A net-C i curves) for Pinus taeda foliage grown under elevated CO2 (550 μmol mol−1) for 50–80 days compared to those for foliage grown under current ambient CO2 from similar-sized reference trees nearby. In both cases, leaf net photosynthetic rate at 550 μmol mol−1 CO2 was enhanced by approximately 65% compared to the rate at ambient CO2 (350 μmol mol−1). A similar level of enhancement under elevated CO2 was observed for daily photosynthesis under field conditions on a sunny day. While enhancement of photosynthesis by elevated CO2 during the study period appears to be primarily attributable to direct photosynthetic responses to CO2 in the pine forest, longer-term CO2 responses and feedbacks remain to be evaluated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00328578
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  • 9
    Electronic Resource
    Electronic Resource
    Elevated carbon dioxide does not affect average canopy stomatal conductance of Pinus taeda L. (1998)
    Springer
    Oecologia 117 (1998), S. 47-52 
    Details
    ISSN: 1432-1939
    Keywords: Key wordsPinus taeda ; Stomatal conductance ; Elevated CO2 ; Whole-plant water use
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract While photosynthetic responses of C3 plants to elevated CO2 are fairly well documented, whole-plant water use under such conditions has been less intensively studied. Woody species, in particular, have exhibited highly variable stomatal responses to high CO2 as determined by leaf-level measurements. In this study, sap flux of Pinus taeda L. saplings was periodically monitored during the 4th year of an open-top chamber CO2 fumigation experiment. Water use per unit sapwood area did not differ between treatments. Furthermore, the ratio of leaf area to sapwood area did not change under high CO2, so that average canopy stomatal conductance (on a unit leaf area basis) remained unaffected by the CO2 treatment. Thus, the only effect of high CO2 was to increase whole-plant water use by increasing sapling leaf area and associated conducting sapwood area. Such an effect may not directly translate to forest-level responses as the feedback effects of higher leaf area at the canopy scale cannot be incorporated in a chamber study. These feedbacks include the potential effect of higher leaf area index on rainfall and light interception, both of which may reduce average stomatal conductance in intact forest canopies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050630
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  • 10
    Electronic Resource
    Electronic Resource
    Modelling Vegetation-Atmosphere Co2 Exchange By A Coupled Eulerian-Langrangian Approach (2000)
    Springer
    Boundary layer meteorology 95 (2000), S. 91-122 
    Details
    ISSN: 1573-1472
    Keywords: Canopy turbulence ; Lagrangian stochastic model ; Turbulence closure ; Canopy photosynthesis ; Carbon dioxide ; Radiation attenuation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A Eulerian-Lagrangian canopy microclimate model wasdeveloped with the aim of discerning physical frombiophysical controls of CO2 and H2O fluxes. The model couples radiation attenuation with mass,energy, and momentum exchange at different canopylevels. A unique feature of the model is its abilityto combine higher order Eulerian closure approachesthat compute velocity statistics with Lagrangianscalar dispersion approaches within the canopy volume. Explicit accounting for within-canopy CO2,H2O, and heat storage is resolved by consideringnon-steadiness in mean scalar concentration andtemperature. A seven-day experiment was conducted inAugust 1998 to investigate whether the proposedmodel can reproduce temporal evolution of scalar(CO2, H2O and heat) fluxes, sources andsinks, and concentration profiles within and above auniform 15-year old pine forest. The modelreproduced well the measured depth-averaged canopy surfacetemperature, CO2 and H2O concentrationprofiles within the canopy volume, CO2 storageflux, net radiation above the canopy, and heat andmass fluxes above the canopy, as well as the velocitystatistics near the canopy-atmosphere interface. Implications for scaling measured leaf-levelbiophysical functions to ecosystem scale are alsodiscussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002473906184
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