title: A water availability gradient reveals the deficit level required to affect traits in potted juvenile Eucalyptus globulus.
abstract: Drought leading to soil water deficit can have severe impacts on plants. Water deficit may lead to plant water stress and affect growth and chemical traits. Plant secondary metabolite (PSM) responses to water deficit vary between compounds and studies, with inconsistent reports of changes to PSM concentrations even within a single species. This disparity may result from experimental water deficit variation among studies, and so multiple water deficit treatments are used to fully assess PSM responses in a single species.
  
  
  
  Juvenile Eucalyptus globulus were grown for 8 weeks at one of ten water deficit levels based on evapotranspiration from control plants (100 %). Treatments ranged from 90 % of control evapotranspiration (mild water deficit) to 0 % of control evapotranspiration (severe water deficit) in 10 % steps. Plant biomass, foliar abscisic acid (ABA) levels, Ψ leaf , leaf C/N, selected terpenes and phenolics were quantified to assess responses to each level of water deficit relative to a control.
  
  
  
  Withholding ≥30 % water resulted in higher foliar ABA levels and withholding ≥40 % water reduced leaf water content. Ψ leaf became more negative when ≥60 % water was withheld. Plant biomass was lower when ≥80 % water was withheld, and no water for 8 weeks (0 % water) resulted in plant death. The total oil concentration was lower and C/N was higher in dead and desiccated juvenile E. globulus leaves (0 % water). Concentrations of individual phenolic and terpene compounds, along with condensed tannin and total phenolic concentrations, remained stable regardless of water deficit or plant stress level.
  
  
  
  These juvenile E. globulus became stressed with a moderate reduction in available water, and yet the persistent concentrations of most PSMs in highly stressed or dead plants suggests no PSM re-metabolization and continued ecological roles of foliar PSMs during drought.
authors.affiliation: School of Biological Sciences, University of Tasmania, Private Bag 55, Hobart, TAS 7001, Australia.
authors.forename: Adam B
authors.initials: AB
authors.lastname: McKiernan
authors.affiliation: School of Biological Sciences, University of Tasmania, Private Bag 55, Hobart, TAS 7001, Australia.|ARC Training Centre for Forest Value, University of Tasmania, Private Bag 55, Hobart, TAS 7001, Australia.
authors.forename: Brad M
authors.initials: BM
authors.lastname: Potts
authors.affiliation: School of Biological Sciences, University of Tasmania, Private Bag 55, Hobart, TAS 7001, Australia.
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Hovenden
authors.affiliation: School of Biological Sciences, University of Tasmania, Private Bag 55, Hobart, TAS 7001, Australia.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Brodribb
authors.affiliation: Central Science Laboratory, University of Tasmania, Private Bag 74, Hobart, TAS 7001, Australia.
authors.forename: Noel W
authors.initials: NW
authors.lastname: Davies
authors.affiliation: Central Science Laboratory, University of Tasmania, Private Bag 74, Hobart, TAS 7001, Australia.
authors.forename: Thomas
authors.initials: T
authors.lastname: Rodemann
authors.affiliation: School of Biological Sciences, University of Tasmania, Private Bag 55, Hobart, TAS 7001, Australia.
authors.forename: Scott A M
authors.initials: SAM
authors.lastname: McAdam
authors.affiliation: School of Biological Sciences, University of Tasmania, Private Bag 55, Hobart, TAS 7001, Australia.
authors.forename: Julianne M
authors.initials: JM
authors.lastname: O'Reilly-Wapstra
mesh_terms: D003890:Desiccation; D055864:Droughts; D005052:Eucalyptus / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism; D018526:Plant Transpiration; D014867:Water / Q000378:metabolism*
chemical_list: D014867:Water
keywords: Eucalyptus globulus; PSM; abscisic acid; drought; macrocarpal; phenolic; secondary metabolite; tannin; terpene; water potential; water stress