High-resolution temperature responses of leaf respiration in snow gum (Eucalyptus pauciflora) reveal high-temperature limits to respiratory function

Authors

  • ODHRAN S. O'SULLIVAN,

    1. Division of Plant Sciences, Research School of Biology, The Australian National University, Canberra, Australian Capital Territory, Australia
    Search for more papers by this author
  • K. W. LASANTHA K. WEERASINGHE,

    1. Division of Plant Sciences, Research School of Biology, The Australian National University, Canberra, Australian Capital Territory, Australia
    2. Faculty of Agriculture, University of Peradeniya, Peradeniya, Sri Lanka
    Search for more papers by this author
  • JOHN R. EVANS,

    1. Division of Plant Sciences, Research School of Biology, The Australian National University, Canberra, Australian Capital Territory, Australia
    Search for more papers by this author
  • JOHN J. G. EGERTON,

    1. Division of Plant Sciences, Research School of Biology, The Australian National University, Canberra, Australian Capital Territory, Australia
    Search for more papers by this author
  • MARK G. TJOELKER,

    1. Hawkesbury Institute for the Environment, University of Western Sydney, Richmond, New South Wales, Australia
    Search for more papers by this author
  • OWEN K. ATKIN

    Corresponding author
    • Division of Plant Sciences, Research School of Biology, The Australian National University, Canberra, Australian Capital Territory, Australia
    Search for more papers by this author

  • Dedication in memoriam: In a study assessing factors controlling the tree growth of the natural timberline in SE Australia, 40 years ago, Professor Ralph O. Slatyer planted snow gum (Eucalyptus pauciflora) saplings at several altitudes. These trees continue to grow to this day and form the basis of our current study. We dedicate this paper to the memory of Professor Slatyer who passed away on 26 July 2012.

Correspondence: O. Atkin. Fax: +61 2 61255095; e-mail: owen.atkin@anu.edu.au

Abstract

We tested whether snow gum (Eucalyptus pauciflora) trees growing in thermally contrasting environments exhibit generalizable temperature (T) response functions of leaf respiration (R) and fluorescence (Fo). Measurements were made on pot-grown saplings and field-grown trees (growing between 1380 and 2110 m a.s.l.). Using a continuous, high-resolution protocol, we quantified T response curves of R and Fo – these data were used to identify an algorithm for modelling RT curves at subcritical T's and establish variations in heat tolerance. For the latter, we quantified Tmax [T where R is maximal] and Tcrit [T where Fo rises rapidly]. Tmax ranged from 51 to 57 °C, varying with season (e.g. winter > summer). Tcrit ranged from 41 to 49 °C in summer and from 58 to 63 °C in winter. Thus, surprisingly, leaf energy metabolism was more heat-tolerant in trees experiencing ice-encasement in winter than warmer conditions in summer. A polynomial model fitted to log-transformed R data provided the best description of the T-sensitivity of R (between 10 and 45 °C); using these model fits, we found that the negative slope of the Q10T relationship was greater in winter than in summer. Collectively, our results (1) highlight high-T limits of energy metabolism in E. pauciflora and (2) provide a framework for improving representation of T-responses of leaf R in predictive models.

Ancillary