WATER RELATIONS AND GAS EXCHANGE OF OLIVE TREES: DIURNAL AND SEASONAL PATTERNS OF LEAF WATER POTENTIAL, PHOTOSYNTHESIS AND STOMATAL CONDUCTANCE

Authors:	C. Gimenez, E. Fereres, C. Ruz, F. Orgaz
Keywords:	Olea europaea, gas exchange, CO₂ assimilation, vapour pressure deficit
Abstract: The daily course of leaf photosynthesis, stomatal conductance and water potential was followed in drip-irrigated olive trees, cv. Picual between 1993 and 1995 in Cordoba, southern Spain. The results indicate that leaves fully open stomata early in the morning, when vapour pressure deficit (VPD) is low, showing high assimilation and low transpiration rates. Maximum CO₂ assimilation ranged from 7 to 18 μmol m^-2 s^-1, depending on the time of the year. Some time before noon stomata partially close reducing leaf photosynthesis as well as transpiration. Such closure occurs in all seasons although it is less evident in spring and autumn. While in spring, summer and autumn midday stomatal closure appears to be related mainly to VPD and air temperature, in winter, low soil temperatures effect low leaf water potential (₁) and stomatal closure despite high soil water potential (_s).
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