Gas exchange and water relations of young apricot plants under drought conditions

Abstract

Potted 1·5-year-old apricot plants (Prunus armeniaca L.), growing under polycarbonate glasshouse conditions with a cooling system, were subjected to two successive water stress/recovery periods until pre-dawn leaf water potential (Ψ_pd) reached values between −2·0 and −2·5 MPa, during summer 1996. Control plants were irrigated daily to maintain the soil matric potential at c. −20 kPa. Water stress limited plant growth and induced a significant reduction in leaf area, caused by mature leaf abscission. The parallel behaviour of leaf turgor potential and epinasty in stressed plants indicated that these movements are turgor-dependent. Osmotic adjustments of 0·27 and 0·60 MPa were observed at the end of the first and second stress period, respectively. Relative apoplastic water content (RWC_a) values were high, ranging from 27 to 42%, and were not affected by water stress. The rapid decrease in leaf conductance (g_l) from the beginning of the stress periods, together with the delay in stomatal reopening after rewatering the plants, indicated that stomatal behaviour was not a simple passive response to water deficits. Net photosynthesis decreased only at the end of both stress periods and recovered quickly. These observations indicate that leaf productivity may be affected only slightly by short-term water stress. The results indicate that drought resistance in apricot is based mainly on avoidance mechanisms, such as stomatal control, epinasty and limitation of transpiration by reducing leaf area. However, some tolerance characteristics, including osmotic adjustment, high RWC _a and low leaf osmotic potential at turgor loss point (Ψ_tlp) values were observed.