The Study of Different Water Regimes on Photosynthetic Performance and Leaf Water Status of Pistachio Trees (Pistacia vera L.)

Water deficiency is one of the most important environmental stresses that limit plant growth and crop production. Measurement of chlorophyll fluorescence parameters is considered as an important indicator to evaluate the photosynthetic apparatus. In the present study, the effects of regulated water deficit, investigated in four waterregimes in pistachio orchard with 12yearold trees of Akbari cultivar (Pistacia vera cv. Akbari). The water regime treatments included 20, 15.6, 10.4, and 6 % of field capacity (FC) equivalent and irrigation intervals of 4, 12, 18 and 24 days. Chlorophyll fluorescence indices of photosystem 2 (PSII), photosynthetic pigments, and leaf water status parameters were studied. Drought stress inhibited PSII activity and induced alterations in thylakoid proteins. The results showed significant effects on effective quantum yield of PSII (ΦPII), maximum quantum efficiency of PSII (Fv/Fm), electron transport rate (ETR), quantum yield baseline (F0/Fm), nonphotochemical quenching (NPQ), and photoinhibition (PIHN) rate. Such changes may be due to either degradation of photosynthesis apparatus function or photoinhibition process. From the results of the present study, it can be concluded that exposure of pistachio trees (P. vera cv. Akbari) to an interval of 18days (T18) may not significantly affected the parameters measured. This means that with an increase in irrigation intervals to 16days, compared to the traditional interval (varies from 8 to 10days), soil may be able to provide enough moisture for the pistachio trees to complete metabolic activities.