Do competition and herbivory alter the internal nitrogen dynamics of birch saplings?

Authors

  • J. Millett,

    Corresponding author
    1. The Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, UK;
    2. Department of Plant and Soil Sciences, School of Biological Sciences, University of Aberdeen, Aberdeen AB24 3UU, UK;
    3. Present address: Department of Geography, Deanery of Science and Social Sciences, Liverpool Hope University, Hope Park, Liverpool L16 9JD, UK
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  • P. Millard,

    1. The Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, UK;
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  • A. J. Hester,

    1. The Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, UK;
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  • A. J. S. McDonald

    1. Department of Plant and Soil Sciences, School of Biological Sciences, University of Aberdeen, Aberdeen AB24 3UU, UK;
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Author for correspondence: Jon Millett Tel: +44 (0)151 291 2174 Fax: +44 (0)151 291 3100 Email: milletj@hope.ac.uk

Summary

  • • Deciduous trees recycle nitrogen within their tissues. The aim of this study was to test the hypothesis that reductions in plant growth, caused by competition and herbivory, reduce the sink strength for N during autumn nutrient withdrawal, and reduce the storage capacity and hence the amount of N remobilized in the following spring.
  • • We used 15N-labelled fertilizer to quantify N uptake, leaf N withdrawal and remobilization. Betula pubescens saplings were grown with either Molinia caerulea or Calluna vulgaris, and subjected to simulated browsing damage.
  • • Competition reduced B. pubescens leaf N withdrawal and remobilization, with C. vulgaris having a greater effect than M. caerulea. However, simulated browsing had no significant effect on sapling N dynamics. The patterns of leaf N withdrawal and remobilization closely followed sapling dry mass.
  • • We conclude that the effect of competition on sapling mass reduces their N-storage capacity. This reduces sink strength for leaf N withdrawal and the source strength for remobilized N. The ability of saplings to compensate for browsing damage removed any potential effect of browsing on N dynamics.

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