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Growth of Eastern Cottonwoods (Populus deltoides) in elevated [CO2] stimulates stand-level respiration and rhizodeposition of carbohydrates, accelerates soil nutrient depletion, yet stimulates above- and belowground biomass production

Authors

  • Greg Barron-Gafford,

    1. Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85719, USA,
    2. Biosphere 2 Laboratory, Columbia University, Oracle, AZ 85621, USA,
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  • Dean Martens,

    1. Southwest Watershed Research Center, U.S. Department of Agriculture, Agricultural Research Service, Tucson, AZ 85719, USA,
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  • Katie Grieve,

    1. Biosphere 2 Laboratory, Columbia University, Oracle, AZ 85621, USA,
    2. Quantitative Ecology and Resource Management, University of Washington, Seattle, WA 98195, USA,
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  • Karl Biel,

    1. Biosphere 2 Laboratory, Columbia University, Oracle, AZ 85621, USA,
    2. Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino, Moscow Region 142290, Russia,
    3. Center for the Investigation of Food and Development, Hermosillo, Sonora, Mexico,
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  • Valery Kudeyarov,

    1. Institute of Basic Biological Problems, Russian Academy of Sciences, Pushchino, Moscow Region 142290, Russia,
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  • Jean E. T. McLain,

    1. Southwest Watershed Research Center, U.S. Department of Agriculture, Agricultural Research Service, Tucson, AZ 85719, USA,
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  • David Lipson,

    1. Department of Biology, San Diego State University, San Diego CA 92182-4614, USA,
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  • Ramesh Murthy

    1. Department of Earth and Environmental Sciences, Lamont-Doherty Earth Observatory, Biosphere 2 Laboratory, Columbia University, Oracle, AZ 85621, USA
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Greg A. Barron-Gafford, Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85719, USA. e-mail: gregbg@email.arizona.edu

Abstract

We took advantage of the distinctive system-level measurement capabilities of the Biosphere 2 Laboratory (B2L) to examine the effects of prolonged exposure to elevated [CO2] on carbon flux dynamics, above- and belowground biomass changes, and soil carbon and nutrient capital in plantation forest stands over 4 years. Annually coppiced stands of eastern cottonwoods (Populus deltoides) were grown under ambient (400 ppm) and two levels of elevated (800 and 1200 ppm) atmospheric [CO2] in carbon and N-replete soils of the Intensive Forestry Mesocosm in the B2L. The large semiclosed space of B2L uniquely enabled precise CO2 exchange measurements at the near ecosystem scale. Highly controllable climatic conditions within B2L also allowed for reproducible examination of CO2 exchange under different scales in space and time. Elevated [CO2] significantly stimulated whole-system maximum net CO2 influx by an average of 21% and 83% in years 3 and 4 of the experiment. Over the 4-year experiment, cumulative belowground, foliar, and total aboveground biomass increased in both elevated [CO2] treatments. After 2 years of growth at elevated [CO2], early season stand respiration was decoupled from CO2 influx aboveground, presumably because of accelerated fine root production from stored carbohydrates in the coppiced system prior to canopy development and to the increased soil carbohydrate status under elevated [CO2] treatments. Soil respiration was stimulated by elevated [CO2] whether measured at the system level in the undisturbed soil block, by soil collars in situ, or by substrate-induced respiration in vitro. Elevated [CO2] accelerated depletion of soil nutrients, phosphorus, calcium and potassium, after 3 years of growth, litter removal, and coppicing, especially in the upper soil profile, although total N showed no change. Enhancement of above- and belowground biomass production by elevated [CO2] accelerated carbon cycling through the coppiced system and did not sequester additional carbon in the soil.

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