OSMOTIC ADJUSTMENT IN ASH AND WATER-STRESS SITUATION

This paper shows the existence of an osmotic adjustment in leaves of ash in a water stress situation. During a summer drought the predawn water potential fell to values ns low as -4.2 MPa. Pressure-volume curves demonstrated that osmotic potential at full turgor decreased from - 0.48 to -0.94 MPa (tree 1) and from -0.84 MPa to -1.57 MPa (tree 2) during water stress. This gives an average degree of osmotic adjustment of 0.59 MPa. On the other hand, the forest alluvial ash did not show ally osmotic adjustment since the water stress was compensated by the ground water. In leaves, the percentage of soluble carbon (relative to total carbon) increased when drought started, but the soluble nitrogen level did not change significantly. Together these data suggest the involvement of an osmotic adjustment in which nan-nitrogenous organic compounds could be concerned.