Light-dependent maintenance of hydraulic function in mangrove branches: do xylary chloroplasts play a role in embolism repair?

Authors

  • N. Schmitz,

    1. Laboratory for Plant Biology and Nature Management, Vrije Universiteit Brussel, 1050 Brussels, Belgium
    2. Royal Museum for Central Africa, Laboratory for Wood Biology and Xylarium, Leuvensesteenweg 13, 3080 Tervuren, Belgium
    3. Plant Science Division, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia
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  • J. J. G. Egerton,

    1. Plant Science Division, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia
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  • C. E. Lovelock,

    1. The School of Biological Science, The University of Queensland, Brisbane, Qld 4072, Australia
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  • M. C. Ball

    1. Plant Science Division, Research School of Biology, The Australian National University, Canberra, ACT 0200, Australia
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Author for correspondence:
Nele Schmitz
Tel: +32 2 629 34 14
Email: nschmitz@vub.ac.be

Summary

  • To clarify the role of branch photosynthesis in tree functioning, the presence and function of chloroplasts in branch xylem tissue were studied in a diverse range of mangrove species growing in Australia.
  • The presence of xylary chloroplasts was observed via chlorophyll fluorescence of transverse sections. Paired, attached branches were selected to study the effects of covering branches with aluminium foil on the gas exchange characteristics of leaves and the hydraulic conductivity of branches.
  • Xylary chloroplasts occurred in all species, but were differently distributed among living cell types in the xylem. Covering stems altered the gas exchange characteristics of leaves, such that water-use efficiency was greater in exposed leaves of covered than of uncovered branches.
  • Leaf-specific hydraulic conductivity of stems was lower in covered than in uncovered branches, implicating stem photosynthesis in the maintenance of hydraulic function. Given their proximity to xylem vessels, we suggest that xylary chloroplasts may play a role in light-dependent repair of embolized xylem vessels.

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