title: Thermal limits of leaf metabolism across biomes.
abstract: High-temperature tolerance in plants is important in a warming world, with extreme heat waves predicted to increase in frequency and duration, potentially leading to lethal heating of leaves. Global patterns of high-temperature tolerance are documented in animals, but generally not in plants, limiting our ability to assess risks associated with climate warming. To assess whether there are global patterns in high-temperature tolerance of leaf metabolism, we quantified Tcrit(high temperature where minimal chlorophyll a fluorescence rises rapidly and thus photosystem II is disrupted) and Tmax(temperature where leaf respiration in darkness is maximal, beyond which respiratory function rapidly declines) in upper canopy leaves of 218 plant species spanning seven biomes. Mean site-based Tcritvalues ranged from 41.5 °C in the Alaskan arctic to 50.8 °C in lowland tropical rainforests of Peruvian Amazon. For Tmax, the equivalent values were 51.0 and 60.6 °C in the Arctic and Amazon, respectively. Tcritand Tmaxfollowed similar biogeographic patterns, increasing linearly (˜8 °C) from polar to equatorial regions. Such increases in high-temperature tolerance are much less than expected based on the 20 °C span in high-temperature extremes across the globe. Moreover, with only modest high-temperature tolerance despite high summer temperature extremes, species in mid-latitude (~20-50°) regions have the narrowest thermal safety margins in upper canopy leaves; these regions are at the greatest risk of damage due to extreme heat-wave events, especially under conditions when leaf temperatures are further elevated by a lack of transpirational cooling. Using predicted heat-wave events for 2050 and accounting for possible thermal acclimation of Tcritand Tmax, we also found that these safety margins could shrink in a warmer world, as rising temperatures are likely to exceed thermal tolerance limits. Thus, increasing numbers of species in many biomes may be at risk as heat-wave events become more severe with climate change.
authors: Division of Plant Sciences, Research School of Biology, The Australian National University, Building 46, Canberra, ACT, 2601, Australia.|Department of Animal and Plant Sciences, University of Sheffield, Alfred Denny Building, Western Bank, Sheffield, S10 2TN, UK.
authors: Odhran S
authors: OS
authors: O'sullivan
authors: Division of Plant Sciences, Research School of Biology, The Australian National University, Building 46, Canberra, ACT, 2601, Australia.|The Ecosystems Center, Marine Biological Laboratory, Woods Hole, MA, 02544, USA.
authors: Mary A
authors: MA
authors: Heskel
authors: Hawkesbury Institute for the Environment, Western Sydney University, Penrith, NSW, 2751, Australia.|Department of Forest Resources, University of Minnesota, 1530 Cleveland Avenue North, St. Paul, MN, 55108, USA.
authors: Peter B
authors: PB
authors: Reich
authors: Hawkesbury Institute for the Environment, Western Sydney University, Penrith, NSW, 2751, Australia.
authors: Mark G
authors: MG
authors: Tjoelker
authors: Division of Plant Sciences, Research School of Biology, The Australian National University, Building 46, Canberra, ACT, 2601, Australia.|Faculty of Agriculture, University of Peradeniya, Peradeniya, 20400, Sri Lanka.
authors: Lasantha K
authors: LK
authors: Weerasinghe
authors: Division of Plant Sciences, Research School of Biology, The Australian National University, Building 46, Canberra, ACT, 2601, Australia.
authors: Aurore
authors: A
authors: Penillard
authors: Division of Plant Sciences, Research School of Biology, The Australian National University, Building 46, Canberra, ACT, 2601, Australia.|ARC Centre of Excellence in Plant Energy Biology, Research School of Biology, The Australian National University, Building 134, Canberra, ACT, 2601, Australia.
authors: Lingling
authors: L
authors: Zhu
authors: Division of Plant Sciences, Research School of Biology, The Australian National University, Building 46, Canberra, ACT, 2601, Australia.
authors: John J G
authors: JJ
authors: Egerton
authors: Division of Plant Sciences, Research School of Biology, The Australian National University, Building 46, Canberra, ACT, 2601, Australia.
authors: Keith J
authors: KJ
authors: Bloomfield
authors: Division of Plant Sciences, Research School of Biology, The Australian National University, Building 46, Canberra, ACT, 2601, Australia.|Hawkesbury Institute for the Environment, Western Sydney University, Penrith, NSW, 2751, Australia.
authors: Danielle
authors: D
authors: Creek
authors: Division of Plant Sciences, Research School of Biology, The Australian National University, Building 46, Canberra, ACT, 2601, Australia.|ARC Centre of Excellence in Plant Energy Biology, Research School of Biology, The Australian National University, Building 134, Canberra, ACT, 2601, Australia.
authors: Nur H A
authors: NH
authors: Bahar
authors: Department of Earth and Environment Sciences, Columbia University, Palisades, NY, 10964, USA.
authors: Kevin L
authors: KL
authors: Griffin
authors: Umeå Plant Science Centre, Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, Umeå, SE-901 84, Sweden.
authors: Vaughan
authors: V
authors: Hurry
authors: Division of Plant Sciences, Research School of Biology, The Australian National University, Building 46, Canberra, ACT, 2601, Australia.|School of Geosciences, University of Edinburgh, Edinburgh, EH9 3FF, UK.
authors: Patrick
authors: P
authors: Meir
authors: Centre for Integrative Ecology, School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand.
authors: Matthew H
authors: MH
authors: Turnbull
authors: Division of Plant Sciences, Research School of Biology, The Australian National University, Building 46, Canberra, ACT, 2601, Australia.|ARC Centre of Excellence in Plant Energy Biology, Research School of Biology, The Australian National University, Building 134, Canberra, ACT, 2601, Australia.
authors: Owen K
authors: OK
authors: Atkin
mesh_terms: D000064:Acclimatization; D000818:Animals; D001110:Arctic Regions; D002734:Chlorophyll; D000077194:Chlorophyll A; D057231:Climate Change; D018515:Plant Leaves / Q000378:metabolism*; D013696:Temperature
chemical_list: D002734:Chlorophyll; D000077194:Chlorophyll A
keywords: 
  T
  crit
  ; 
  T
  max
  ; heat waves; high-temperature tolerance; latitudinal patterns; photosynthesis; respiration; temperature extremes