Using amino-nitrogen pools and fluxes to identify contributions of understory Acacia spp. to overstory Eucalyptus regnans and stand nitrogen uptake in temperate Australia

Authors

  • Sebastian Pfautsch,

    1. Faculty for Agriculture, Food and Natural Resources, University of Sydney, 2006 NSW, Australia
    2. Chair of Tree Physiology, Institute of Forest Botany and Tree Physiology, Albert-Ludwigs University, Georges-Koehler-Allee 53/54, D–79110 Freiburg, Germany
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  • Arthur Gessler,

    1. Core Facility Metabolomics, Centre for System Biology (ZBSA), Albert-Ludwigs University, Habsburgerstrasse 49, D–79104 Freiburg, Germany
    2. Chair of Tree Physiology, Institute of Forest Botany and Tree Physiology, Albert-Ludwigs University, Georges-Koehler-Allee 53/54, D–79110 Freiburg, Germany
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  • Mark A. Adams,

    1. Faculty for Agriculture, Food and Natural Resources, University of Sydney, 2006 NSW, Australia
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  • Heinz Rennenberg

    1. Chair of Tree Physiology, Institute of Forest Botany and Tree Physiology, Albert-Ludwigs University, Georges-Koehler-Allee 53/54, D–79110 Freiburg, Germany
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Author for correspondence:
S. Pfautsch
Tel:+61 3 5321 4309
Email: s.pfautsch@usyd.edu.au

Summary

  • • Amino acid concentration and composition in xylem and phloem sap and in plant tissues are good markers of plant performance and general plant nitrogen (N)-supply. Here, we tested if amino acid pools in Eucalyptus regnans, growing in southeastern Australia were increased by understory acacias in 70-yr-old stands, and if xylem N-transport of temperate Acacia spp. differs from their tropical counterparts.
  • • We analysed amino-N concentrations and composition in foliage, xylem and phloem. In a novel approach we coupled amino-N concentrations of xylem with long-term sap flow measurements to calculate total stand N-transport.
  • • Xylem N-transport of E. regnans is largely based on amino compounds of the glutamate group (more than 90%). By contrast, Acacia spp. transport mainly aspartate group amino acids in xylem (up to 80%). Amino compound diversity and concentration in tissues and xylem and phloem sap were universally greater in acacias compared to eucalypts. Acacias investigated here can be classified as ‘amide transporters’.
  • • We conclude that N-status and growth potential of aging E. regnans forest is not enhanced by a contribution of N from understory acacias, and that xylem N-transport in temperate Acacia spp. differs from acacias located in the tropics.

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