OSMOTIC ADJUSTMENT IN SESSILE OAK SEEDLINGS IN RESPONSE TO DROUGHT

Three-year-old sessile oak seedlings were submitted to drought develop ed at two different rates (0.050 and 0.013 MPa . day(-1)). Drought was controlled by combining levels of irrigation and grass competition. A t the end of summer, predawn leaf water potential reached values of -2 .3 and -0.8 M Pa in the rapid and slow rates of drought development, r espectively, and leaf osmotic potential at full turgor reached values of -2.0 and -1.5 MPa, for the same treatments. For both treatments, le af water potential and leaf osmotic potential were linearly and positi vely correlated. The rapid rate of drought development resulted in a g reater degree of osmotic adjustment (0.45 versus 0.34 MPa . MPa-1).