title: Strong thermal acclimation of photosynthesis in tropical and temperate wet-forest tree species: the importance of altered Rubisco content.
abstract: Understanding of the extent of acclimation of light-saturated net photosynthesis (An) to temperature (T), and associated underlying mechanisms, remains limited. This is a key knowledge gap given the importance of thermal acclimation for plant functioning, both under current and future higher temperatures, limiting the accuracy and realism of Earth system model (ESM) predictions. Given this, we analysed and modelled T-dependent changes in photosynthetic capacity in 10 wet-forest tree species: six from temperate forests and four from tropical forests. Temperate and tropical species were each acclimated to three daytime growth temperatures (Tgrowth): temperate - 15, 20 and 25 °C; tropical - 25, 30 and 35 °C. CO2response curves of Anwere used to model maximal rates of RuBP (ribulose-1,5-bisphosphate) carboxylation (Vcmax) and electron transport (Jmax) at each treatment's respective Tgrowthand at a common measurement T (25 °C). SDS-PAGE gels were used to determine abundance of the CO2-fixing enzyme, Rubisco. Leaf chlorophyll, nitrogen (N) and mass per unit leaf area (LMA) were also determined. For all species and Tgrowth, Anat current atmospheric CO2partial pressure was Rubisco-limited. Across all species, LMA decreased with increasing Tgrowth. Similarly, area-based rates of Vcmaxat a measurement T of 25 °C (Vcmax25) linearly declined with increasing Tgrowth, linked to a concomitant decline in total leaf protein per unit leaf area and Rubisco as a percentage of leaf N. The decline in Rubisco constrained Vcmaxand Anfor leaves developed at higher Tgrowthand resulted in poor predictions of photosynthesis by currently widely used models that do not account for Tgrowth-mediated changes in Rubisco abundance that underpin the thermal acclimation response of photosynthesis in wet-forest tree species. A new model is proposed that accounts for the effect of Tgrowth-mediated declines in Vcmax25on An, complementing current photosynthetic thermal acclimation models that do not account for T sensitivity of Vcmax25.
authors.affiliation: ARC Centre of Excellence in Plant Energy Biology, Research School of Biology, The Australian National University, Building 134, Canberra, ACT, 2601, Australia.
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Scafaro
authors.affiliation: Chengdu Institute of Biology, Chinese Academy of Sciences, No. 9, Section 4, Renmin South Road, Chengdu, Sichuan, 610041, China.|Division of Plant Sciences, Research School of Biology, The Australian National University, Building 46, Canberra, ACT, 2601, Australia.
authors.forename: Shuang
authors.initials: S
authors.lastname: Xiang
authors.affiliation: Division of Plant Sciences, Research School of Biology, The Australian National University, Building 46, Canberra, ACT, 2601, Australia.|ARC Centre of Excellence for Translational Photosynthesis, Research School of Biology, The Australian National University, Building 134, Canberra, ACT, 2601, Australia.
authors.forename: Benedict M
authors.initials: BM
authors.lastname: Long
authors.affiliation: ARC Centre of Excellence in Plant Energy Biology, Research School of Biology, The Australian National University, Building 134, Canberra, ACT, 2601, Australia.
authors.forename: Nur H A
authors.initials: NHA
authors.lastname: Bahar
authors.affiliation: Faculty of Agriculture, University of Peradeniya, 20400, Peradeniya, Sri Lanka.
authors.forename: Lasantha K
authors.initials: LK
authors.lastname: Weerasinghe
authors.affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Penrith, NSW, 2751, Australia.
authors.forename: Danielle
authors.initials: D
authors.lastname: Creek
authors.affiliation: Division of Plant Sciences, Research School of Biology, The Australian National University, Building 46, Canberra, ACT, 2601, Australia.|ARC Centre of Excellence for Translational Photosynthesis, Research School of Biology, The Australian National University, Building 134, Canberra, ACT, 2601, Australia.
authors.forename: John R
authors.initials: JR
authors.lastname: Evans
authors.affiliation: Hawkesbury Institute for the Environment, Western Sydney University, Penrith, NSW, 2751, Australia.|Department of Forest Resources, University of Minnesota, 1540 Cleveland Avenue North, St. Paul, MN, 55108, USA.
authors.forename: Peter B
authors.initials: PB
authors.lastname: Reich
authors.affiliation: ARC Centre of Excellence in Plant Energy Biology, Research School of Biology, The Australian National University, Building 134, Canberra, ACT, 2601, Australia.
authors.forename: Owen K
authors.initials: OK
authors.lastname: Atkin
mesh_terms: D000064:Acclimatization; D002245:Carbon Dioxide; D065928:Forests; D010788:Photosynthesis; D018515:Plant Leaves; D012273:Ribulose-Bisphosphate Carboxylase; D014197:Trees
chemical_list: D002245:Carbon Dioxide; D012273:Ribulose-Bisphosphate Carboxylase
keywords: 
  V
  cmax
  ; Rubisco content; climate modelling; earth system models; photosynthesis; photosynthesis modelling; temperature; thermal acclimation; tropical trees