Compared water deficit response of two Populus x euramericana clones, Luisa Avanzo and Dorskamp

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The drought response of two Populus x euramericana clones cv Dorskamp and Luisa Avanzo was investigated using pot- ted cuttings growing in a greenhouse. The cv Dorskamp clone is known to be more tolerant than Luisa Avanzo under field condi- tions. Watering was withheld and several parameters followed during the onset of drought. The relation between predawn leaf wat er potential (Ψ wp ) and soil water content differed between clones: (i) Ψ wp tended to decline when soil water content decreased below a threshold of 0.11 v/v and 0.13 v/v for Dorskamp and Luisa Avanzo, respectively; and (ii) Ψ wp of stressed cuttings reached -3.5 MPa and -2.5 MPa for Dorskamp and Luisa Avanzo, respectively. Under well watered conditions, Luisa Avanzo had greater relative rates of increase in number of leaves and leaf growth than in Dorskamp. In response to water stress, the relative rates of increase i n num- ber of leaves and leaf growth did not significantly differ between the two clones for similar Ψ wp values. Thus, the growth advantage of Luisa Avanzo observed under control condition appeared counterbalanced by its higher susceptibility to water stress. Our res ults corroborated field observations on mature trees. drought / leaf area / Populus x euramericana / predawn water potential / soil water content