Leaf gas exchange and water potential responses to drought in nine poplar (Populus spp.) clones with contrasting drought tolerance

The dynamic responses of stomatal conduc-tance (gs) net photosynthesis (A) and leaf water potential (Ψleaf) to a progressive drought were examined in nine poplar clones (Populus spp.) with contrasting drought tolerance from the Canadian Prairies, a region prone to frequent droughts. Plants were grown in a greenhouse and either well-watered or drought preconditioned (5-6 cycles of drought) for 8 weeks. At the end of the last cycle, plants were watered to saturation then progressively dried-down (-1.25 MPa Ψsoil) during which A, gs and Ψleaf were measured. Drought tolerant Okanese reached the lowest combined Ψleaf while sensitive clones (Assiniboine and Imperial) had the highest (-1.6 vs. -1.1 MPa). Steady state gs (measured under well watered conditions) was lower in tolerant (Okanese and Tristis SBC#1) than in sensitive clones. Preconditioning reduced steady state gs in all clones, lowered the threshold Ψleaf for stomatal closure and the minimum Ψleaf in most clones but did not affect the steady state A. Tolerant and some moderately tolerant clones maintained higher A at lower Ψleaf than the other clones. Stomatal closure was gradual in tolerant clones and in moderately tolerant Northwest but rapid in the other clones. Stomata in the sensitive clones closed at the highest Ψleaf, Okanese closed at the lowest. The substantial range in gas exchange and Ψleaf responses observed here represented both drought tolerance and taxonomic (Aegiros or Tacamahaca sections) traits which could play a role in the survival and productivity in environments with limited water or during periods of drought. © Springer-Verlag 2009.