title: High-resolution temperature responses of leaf respiration in snow gum (Eucalyptus pauciflora) reveal high-temperature limits to respiratory function.
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 R-T 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 Q10 -T 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.
authors.affiliation: Division of Plant Sciences, Research School of Biology, The Australian National University, Canberra, Australian Capital Territory 0200, Australia.
authors.forename: Odhran S
authors.initials: OS
authors.lastname: O'Sullivan
authors.affiliation: Division of Plant Sciences, Research School of Biology, The Australian National University, Canberra, Australian Capital Territory, 0200, Australia.|Faculty of Agriculture, University of Peradeniya, Peradeniya, 20400, Sri Lanka.
authors.forename: K W Lasantha K
authors.initials: KW
authors.lastname: Weerasinghe
authors.affiliation: Division of Plant Sciences, Research School of Biology, The Australian National University, Canberra, Australian Capital Territory, 0200, Australia.
authors.forename: John R
authors.initials: JR
authors.lastname: Evans
authors.affiliation: Division of Plant Sciences, Research School of Biology, The Australian National University, Canberra, Australian Capital Territory, 0200, Australia.
authors.forename: John J G
authors.initials: JJ
authors.lastname: Egerton
authors.affiliation: Hawkesbury Institute for the Environment, University of Western Sydney, Richmond, New South Wales, 2751, Australia.
authors.forename: Mark G
authors.initials: MG
authors.lastname: Tjoelker
authors.affiliation: Division of Plant Sciences, Research School of Biology, The Australian National University, Canberra, Australian Capital Territory, 0200, Australia.
authors.forename: Owen K
authors.initials: OK
authors.lastname: Atkin
mesh_terms: D000465:Algorithms; D019069:Cell Respiration; D005052:Eucalyptus / Q000166:cytology / Q000502:physiology*; D006813:Humidity; D008954:Models, Biological; D018515:Plant Leaves / Q000166:cytology / Q000502:physiology; D013696:Temperature
keywords: Arrhenius; Q10; acclimation; heat stress; leaves; respiration