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Estimating age-dependent costs and benefits of roots with contrasting life span: comparing apples and oranges

Authors

  • Tjeerd J. Bouma,

    Corresponding author
    1. Pennsylvania State University, Department of Horticulture, 103 Tyson Building, University Park, Pennsylvania 16802–4200, USA;
    2. Present address: Netherlands Institute of Ecology, PO Box 140, NL–4400 AC Yerseke, The Netherlands
      Author for correspondence: Tjeerd J. Bouma Tel: +31 113 577454 Fax: +31 113 573616 Email:bouma@cemo.nioo.knaw.nl
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  • Ruth D. Yanai,

    1. State University of New York College of Environmental Science and Forestry, Department of Forestry, Syracuse, New York 13210, USA;
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  • Adrienne D. Elkin,

    1. Pennsylvania State University, Department of Horticulture, 103 Tyson Building, University Park, Pennsylvania 16802–4200, USA;
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  • Ulrich Hartmond,

    1. University of Florida, IFAS, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred, FL 33850, USA;
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  • Dora E. Flores-Alva,

    1. Pennsylvania State University, Department of Horticulture, 103 Tyson Building, University Park, Pennsylvania 16802–4200, USA;
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  • David M. Eissenstat

    1. Pennsylvania State University, Department of Horticulture, 103 Tyson Building, University Park, Pennsylvania 16802–4200, USA;
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Author for correspondence: Tjeerd J. Bouma Tel: +31 113 577454 Fax: +31 113 573616 Email:bouma@cemo.nioo.knaw.nl

Summary

  •  The relation between root age and root function is poorly understood, despite its importance to root longevity.
  •  The effect of root age on respiration rates and 32P-uptake kinetics was determined for roots excavated from mature apple and citrus trees (median root life spans of 30 vs 300 d). To evaluate whether root longevity maximizes the efficiency of nutrient capture, daily and lifetime efficiencies were calculated by dividing simulated P-uptake benefits (solute transport model) by age-specific respiration costs.
  •  We found that: respiration rates and P uptake capacity change with root age in a species-specific way; and soil characteristics that determine the rate of nutrient depletion in the rhizosphere are as important as changes in root physiology in determining the age at which a root reaches its maximum efficiency.
  •  Further testing of the efficiency of nutrient capture as a predictor of root life span requires measurement of both soil properties and age-specific physiology of roots including their mycorrhizal fungi.

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