title: Two tropical conifers show strong growth and water-use efficiency responses to altered CO2 concentration.
abstract: Conifers dominated wet lowland tropical forests 100 million years ago (MYA). With a few exceptions in the Podocarpaceae and Araucariaceae, conifers are now absent from this biome. This shift to angiosperm dominance also coincided with a large decline in atmospheric CO2concentration (ca). We compared growth and physiological performance of two lowland tropical angiosperms and conifers at calevels representing pre-industrial (280 ppm), ambient (400 ppm) and Eocene (800 ppm) conditions to explore how differences in caaffect the growth and water-use efficiency (WUE) of seedlings from these groups.
  
  
  
  Two conifers (Araucaria heterophylla and Podocarpus guatemalensis) and two angiosperm trees (Tabebuia rosea and Chrysophyllum cainito) were grown in climate-controlled glasshouses in Panama. Growth, photosynthetic rates, nutrient uptake, and nutrient use and water-use efficiencies were measured.
  
  
  
  Podocarpus seedlings showed a stronger (66 %) increase in relative growth rate with increasing carelative to Araucaria (19 %) and the angiosperms (no growth enhancement). The response of Podocarpus is consistent with expectations for species with conservative growth traits and low mesophyll diffusion conductance. While previous work has shown limited stomatal response of conifers to ca, we found that the two conifers had significantly greater increases in leaf and whole-plant WUE than the angiosperms, reflecting increased photosynthetic rate and reduced stomatal conductance. Foliar nitrogen isotope ratios (δ15N) and soil nitrate concentrations indicated a preference in Podocarpus for ammonium over nitrate, which may impact nitrogen uptake relative to nitrate assimilators under high caSIGNIFICANCE: Podocarps colonized tropical forests after angiosperms achieved dominance and are now restricted to infertile soils. Although limited to a single species, our data suggest that higher camay have been favourable for podocarp colonization of tropical South America 60 MYA, while plasticity in photosynthetic capacity and WUE may help account for their continued persistence under large changes in casince the Eocene.
authors: Department of Plant Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Republic of Panama dallingj@life.illinois.edu.
authors: James W
authors: JW
authors: Dalling
authors: College of Science and Engineering, James Cook University, Cairns, Queensland 4870, Australia.
authors: Lucas A
authors: LA
authors: Cernusak
authors: Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Republic of Panama.
authors: Klaus
authors: K
authors: Winter
authors: Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Republic of Panama.
authors: Jorge
authors: J
authors: Aranda
authors: Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Republic of Panama.
authors: Milton
authors: M
authors: Garcia
authors: Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Republic of Panama.
authors: Aurelio
authors: A
authors: Virgo
authors: College of Science and Engineering, James Cook University, Cairns, Queensland 4870, Australia.
authors: Alexander W
authors: AW
authors: Cheesman
authors: School of Earth, Energy and Environmental Sciences, Stanford University, Stanford, CA 94305, USA.
authors: Andres
authors: A
authors: Baresch
authors: Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Republic of Panama.
authors: Carlos
authors: C
authors: Jaramillo
authors: Smithsonian Tropical Research Institute, Apartado 0843-03092, Balboa, Ancon, Republic of Panama.
authors: Benjamin L
authors: BL
authors: Turner
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D029632:Sapotaceae / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D036226:Seedlings / Q000254:growth & development; D029663:Tabebuia / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D064028:Tracheophyta / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D014329:Tropical Climate; D014867:Water / Q000378:metabolism
chemical_list: D014867:Water; D002245:Carbon Dioxide
keywords: Araucaria heterophylla; Chrysophyllum cainito; Podocarpus guatemalensis; Tabebuia rosea; angiosperm dominance; elevated CO2; nitrate assimilation; relative growth rate; tropical conifer; water-use efficiency