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  • Elevated CO2  (2)
  • 1995-1999  (2)
  • 1
    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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    Paper (German National Licenses)
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  • 2
    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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