Diurnal Variation in Water Potential Components and Stomatal Resistance of Irrigated Peach Seedlings1

Peach [Prunus persica, (L.) Batsch] seedling growing in irrigated soil showed strong diurnal variations in totalwater potential, turgor potential, and stomatal resistance. A significant positive correlation existed between turgor potential and total water potential while osmotic potential remained fairly constant. There appeared to be no rapid, diurnal osmotic adjustment to maintain constant turgor, although there may have been some slight, long-term osmotic adjustment over the 2-week experimental period. When turgor approached zero, a depression of osmotic potential due to water loss through transpiration maintained turgor above zero. Stomatal resistance remained low throughout the day, even though total water potential dropped below –16 bars and turgor potential was below 2 bars. Stomatal resistance was negatively correlated with irradiance level but not with turgor potential.