Simple three-pool model accurately describes patterns of long-term litter decomposition in diverse climates

Authors

  • E. CAROL ADAIR,

    1. Department of Ecology, Evolution, and Behavior, University of Minnesota, Saint Paul, 1987 Upper Buford Circle, MN 55108, USA,
    2. Department of Forest Resources, University of Minnesota, Saint Paul, MN 55108, USA,
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  • WILLIAM J. PARTON,

    1. Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523, USA,
    2. Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO 80523, USA,
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  • STEVEN J. DEL GROSSO,

    1. Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523, USA,
    2. Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO 80523, USA,
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  • WHENDEE L. SILVER,

    1. Ecosystem Sciences Division, Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA, USA,
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  • MARK E. HARMON,

    1. Department of Forest Sciences, Oregon State University, Corvallis, OR 97331, USA,
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  • SONIA A. HALL,

    1. The Nature Conservancy, North Central Washington Field Office, Wenatchee, WA 98801, USA,
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  • INGRID C. BURKE,

    1. Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO 80523, USA,
    2. Department of Forest, Rangeland, and Watershed Stewardship, Colorado State University, Fort Collins, CO 80523, USA,
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  • STEPHEN C. HART

    1. School of Forestry, Northern Arizona University, PO Box 15018, Flagstaff, AZ 86011-5018, USA
    2. Merriam-Powell Center for Environmental Research, Northern Arizona University, PO Box 15018, Flagstaff, AZ 86011-5018, USA
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E. Carol Adair, Department of Ecology, Evolution, and Behaviour, University of Minnesota, 1987 Upper Buford Circle, MN 55108, USA, fax +1 612 624 6777, e-mail: adair016@umn.edu

Abstract

As atmospheric CO2 increases, ecosystem carbon sequestration will largely depend on how global changes in climate will alter the balance between net primary production and decomposition. The response of primary production to climatic change has been examined using well-validated mechanistic models, but the same is not true for decomposition, a primary source of atmospheric CO2. We used the Long-term Intersite Decomposition Experiment Team (LIDET) dataset and model-selection techniques to choose and parameterize a model that describes global patterns of litter decomposition. Mass loss was best represented by a three-pool negative exponential model, with a rapidly decomposing labile pool, an intermediate pool representing cellulose, and a recalcitrant pool. The initial litter lignin/nitrogen ratio defined the size of labile and intermediate pools. Lignin content determined the size of the recalcitrant pool. The decomposition rate of all pools was modified by climate, but the intermediate pool's decomposition rate was also controlled by relative amounts of litter cellulose and lignin (indicative of lignin-encrusted cellulose). The effect of climate on decomposition was best represented by a composite variable that multiplied a water-stress function by the Lloyd and Taylor variable Q10 temperature function. Although our model explained nearly 70% of the variation in LIDET data, we observed systematic deviations from model predictions. Below- and aboveground material decomposed at notably different rates, depending on the decomposition stage. Decomposition in certain ecosystem-specific environmental conditions was not well represented by our model; this included roots in very wet and cold soils, and aboveground litter in N-rich and arid sites. Despite these limitations, our model may still be extremely useful for global modeling efforts, because it accurately (R2=0.6804) described general patterns of long-term global decomposition for a wide array of litter types, using relatively minimal climatic and litter quality data.

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