Translocation of 15N indicates nitrogen recycling in the mat-forming lichen Cladonia portentosa

Authors

  • C. J. Ellis,

    1. School of Biology, University of Nottingham, University Park, Nottingham NG7 2RD, UK;
    2. Present address: Royal Botanic Garden Edinburgh, 20A Inverleith Row, Edinburgh EH3 5LR, UK
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  • P. D. Crittenden,

    Corresponding author
    1. School of Biology, University of Nottingham, University Park, Nottingham NG7 2RD, UK;
      Author for correspondence:P. D. Crittenden Tel: +44 115 9513211 Fax: +44 115 9513251 Email: pdc@nottingham.ac.uk
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  • C. M. Scrimgeour,

    1. Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, UK;
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  • C. J. Ashcroft

    1. School of Biology, University of Nottingham, University Park, Nottingham NG7 2RD, UK;
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Author for correspondence:P. D. Crittenden Tel: +44 115 9513211 Fax: +44 115 9513251 Email: pdc@nottingham.ac.uk

Summary

  • • Nitrogen translocation was measured in Cladonia portentosa during 2 yr growth in Scottish heathland. Translocation was predicted to occur if N is resorbed from senescent basal tissue and recycled within the thallus.
  • • 15N was introduced into either the lower (TU thalli) or upper (TD thalli) 25 mm of 50-mm-long thalli as 15N-NH4+, 15N-NO3 or 15N-glycine. Labelled thalli were placed within intact lichen cushions, either upright (TU) or inverted (TD). Vertical distribution of label was quantified immediately following labelling and after 1 and 2 yr.
  • • Independently of the form of introduced label, 15N migrated upwards in TU thalli, with new growth being a strong sink. Sink regions for 15N during year 1 (including new growth) became sources of 15N translocated to new growth in year 2. Upward migration into inverted bases was minimal in TD thalli, but was again marked in new growth that developed from inverted apices.
  • • Relocation of N to regions of growth could facilitate internal N recycling, a process postulated to explain the ecological success of mat-forming lichens.

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