Comparison of the lethal water potential of nine temperate tree species submitted to a prolonged water stress

The threshold of water-stress induced mortality is known to vary with tree species and reflect their ability to withstand an acute drought spell. We exposed potted juvenile trees to a range of water stresses, triggering plant death to evaluate their drying-limits of viability. We relied on 3 hygrophytes (Salix alba, Alnus glutinosa and Populus tremula x Populus alba), 3 mesophytes (Fagus sylvatica, Quercus petreae and Pseudotsuga menziesii) and 3 xerophytes (Quercus ilex, Pinus halepensis and Cedrus atlanitca). We made a census of predawn (Yp) and midday leaf water potential (Ym), and of the evapotranspiration of the potted trees together with stem X-ray microtomography measurement of some of the focus trees at the end of the growing season. The lethal water potential (Ylet) calculated as (Yp - Ym), differed substantially between some of the study species. The Ylet ranged from -1.75 +/- 1.05 MPa (Salix alba) to -6.97 +/- 0.85 MPa (Cedrus atlantica). The results revealed that the threshold of water-stress induced mortality ranged from 5 weeks (Populus tremula x Populus alba ; Salix alba.) to more than 12 weeks (Pseudotsuga menziesii).