Physiological responses of Laurus azorica and Viburnum rigidum to drought stress: Osmotic adjustment and tissue elasticity

Osmotic adjustment and pressure-volume parameters were studied in leaf tiss ue samples of two woody plants of the Canarian laurel forest during one mon th under drought stress. The osmotic potential at full turgor decreased fro m -2.04 to -3.52 MPa in Laurus azorica (Seub.) France and from -1.91 to -2. 59 MPa in Viburnum rigidum Vent. The osmotic potential at the turgor loss p oint decreased from -2.9 to -3.9 MPa in L. azorica and did not change signi ficantly in V. rigidum (-2.9 to -3 MPa). The maximal bulk modulus of elasti city increased during the water stress period from 20 to 91 MPa and from 12 to 31 MPa in L. azorica and V. rigidum, respectively. Proline contents of L. azorica leaves increased sharply at a water potentia l of -2.6 MPa amounting to final values of approximately 4 mg g(-1) DW. In contrast, proline concentration in V. rigidum did not change although leaf water potential values of -3.5 MPa were reached. Our results indicate signi ficant osmotic adjustment due to drought stress in L. azorica but not in V. rigidum. The particular physiological strategy of each species could expla in their distribution within the laurel forest.