Responses of Young Almond Trees to Two Drought Periods in the Field

SummaryWater potential, conductance to water vapour diffusion and 14CO2 uptake rate were measured in the field on leaves of young, trickle-irrigated almond trees subjected to drought periods. Treatments imposed were: T. two one-month drying cycles with an interim period of recovery; T2, a single one-month drying cycle; T3, a single 2.5-month drying cycle; and T4, daily irrigation. Midday leaf water potential in T, and T2 trees decreased 0.8 to 1.0 MPa below that of the control, and that of T3 trees was further decreased by about 0.7 MPa. Turgor pressure was partially maintained in the stressed treatments through osmotic adjustment. Osmotic potential at full turgor in leaves of unirrigated trees was about 0.3 MPa lower than in the controls and was the same at the end of both drought cycles. Decreases in osmotic potential were accompanied by increases in dry weight per unit leaf area. Despite partial maintenance of turgor, water stress decreased leaf conductance and 14CO2 uptake. Leaf conductance and 14CO2 ...