Diurnal Patterns of Photosynthesis and Water Relations for Four Orchard-Grown Pomegranate ( Prunica GranatumL.) Cultivars

Abstract

Long-term drought, coupled with tighter regulations on limited water resources have caused growers to seek drought tolerant cultivars of common tree crops in California. Yet information on pomegranate physiology is lacking, even though it is grown throughout the world in various climates. The purpose of this research was to determine the effect of time of day and cultivar on pomegranate photosynthesis and water relations, and calculate values for water-use efficiency, defined as photosynthetic carbon gain divided by water lost during transpiration. The study utilized four field-grown cultivars in their fourth year of growth (‘Eversweet,’ ‘Haku Botan,’ ‘Parfianka,’ and ‘Wonderful’), in Riverside, California. Variables analyzed included photosynthesis, stomatal conductance, transpiration, instantaneous water-use efficiency, intrinsic water-use efficiency, and pre-dawn and midday water potential. Differences were detected for time of day, with higher rates of assimilation, transpiration, and stomatal conductance in morning. Intrinsic water-use efficiency was higher in the afternoon compared to the morning. There were also differences among cultivars for stomatal conductance and transpiration during the morning but not during the afternoon, with ‘Eversweet’ having significantly lower rates of stomatal conductance and transpiration than ‘Parfianka’: other cultivars were intermediate. These results further our understanding of how pomegranate cultivars function on a physiological level during different times of the day, and suggest that efficiency of production can be improved through cultivar selection.