Fine-root respiration in a loblolly pine (Pinus taeda L.) forest exposed to elevated CO2 and N fertilization

Authors

  • JOHN E. DRAKE,

    1. Program in Ecology, Evolution, and Conservation Biology,
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  • PAUL C. STOY,

    1. School of GeoSciences, Department of Atmospheric and Environmental Science, University of Edinburgh, Edinburgh EH9 3JN, UK and
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  • ROBERT B. JACKSON,

    1. Department of Biology and Nicholas School of the Environment and Earth Sciences, Duke University, Durham, NC 27708, USA
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  • EVAN H. DeLUCIA

    Corresponding author
    1. Program in Ecology, Evolution, and Conservation Biology,
    2. Department of Plant Biology and
    3. Institute of Genomic Biology, University of Illinois at Urbana – Champaign, Urbana, IL 61801, USA,
      E. H. DeLucia. Fax: +217 244 7246; e-mail: delucia@uiuc.edu
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E. H. DeLucia. Fax: +217 244 7246; e-mail: delucia@uiuc.edu

ABSTRACT

Forest ecosystems release large amounts of carbon to the atmosphere from fine-root respiration (Rr), but the control of this flux and its temperature sensitivity (Q10) are poorly understood. We attempted to: (1) identify the factors limiting this flux using additions of glucose and an electron transport uncoupler (carbonyl cyanide m-chlorophenylhydrazone); and (2) improve yearly estimates of Rr by directly measuring its Q10in situ using temperature-controlled cuvettes buried around intact, attached roots. The proximal limits of Rr of loblolly pine (Pinus taeda L.) trees exposed to free-air CO2 enrichment (FACE) and N fertilization were seasonally variable; enzyme capacity limited Rr in the winter, and a combination of substrate supply and adenylate availability limited Rr in summer months. The limiting factors of Rr were not affected by elevated CO2 or N fertilization. Elevated CO2 increased annual stand-level Rr by 34% whereas the combination of elevated CO2 and N fertilization reduced Rr by 40%. Measurements of in situ Rr with high temporal resolution detected diel patterns that were correlated with canopy photosynthesis with a lag of 1 d or less as measured by eddy covariance, indicating a dynamic link between canopy photosynthesis and root respiration. These results suggest that Rr is coupled to daily canopy photosynthesis and increases with carbon allocation below ground.

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