• carbon isotope discrimination (Δ);
  • drought tolerance;
  • genotypic diversity;
  • hybrid poplars;
  • leaf traits;
  • open field;
  • productivity;
  • water use efficiency (WUE)


  • • 
    We examined the relationships among productivity, water use efficiency (WUE) and drought tolerance in 29 genotypes of Populus × euramericana (Populus deltoides×Populus nigra), and investigated whether some leaf traits could be used as predictors for productivity, WUE and drought tolerance.
  • • 
    At Orléans, France, drought was induced on one field plot by withholding water, while a second plot remained irrigated and was used as a control. Recorded variables included stem traits (e.g. biomass) and leaf structural (e.g. leaf area) and functional traits [e.g. intrinsic water use efficiency (Wi) and carbon isotope discrimination (Δ)].
  • • 
    Productivity and Δ displayed large genotypic variability and were not correlated. Δ scaled negatively with Wi and positively with stomatal conductance under moderate drought, suggesting that the diversity for Δ was mainly driven by stomatal conductance.
  • • 
    Most of the productive genotypes displayed a low level of drought tolerance (i.e. a large reduction of biomass), while the less productive genotypes presented a large range of drought tolerance. The ability to increase WUE in response to water deficit was necessary but not sufficient to explain the genotypic diversity of drought tolerance.