Stomatal behavior of olive cv. Zard under drought stress conditions

The rate of photosynthesis and water saving are dependent on opening and closing of stomata. This opening and closing depends on some factors such as light, temperature, humidity and water availability. Under draught conditions, most plants close their stomata in order to prevent water loss and resistance against the stress. On the other hand, for photosynthesis, plants should take CO2 through stomata and when stomata are closed, this function is prevented; hence, it results in loss of photosynthesis. This research was conducted at the Agriculture Faculty of Tehran University in Iran, to study the stomatal behavior of olive plants under drought stress for better orchard management. Drought was applied by irrigation intervals of 6 days on potted olive trees and the resistance of stomata was measured by porometer type AP4 at 1.5 hours intervals from 8 a.m. until 6 p.m. Control plants were irrigated daily. Control plants had the minimal stomatal resistance at 9:30-11:00 AM at average temperature of 23-25 degrees C and relative humidity of 35-40% and at 15:30-17:00 PM with average temperature of 30-35 degrees C and relative humidity of 30-35%. At 18,00 PM with average temperature of 35-40 degrees C and relative humidity of 30-35% they had the highest stomatal resistance. However, plants under stress opened their stomata just at the first hours of the morning and then the resistance increased indicating a decrease in stomata opening during the rest of the day. Plants under drought stress, after the second irrigation, opened their stomata for a longer period (reduced stomatal resistance) indicating an adoption to higher water use efficiency for photosynthesis. After two cycles of stress, at the third cycle, plants opened their stomata in the morning and in the afternoon at a higher rate than after the second cycle. These observations indicate a possible reason for tolerance of olive trees to drought conditions, which usually occurs at dry farming.