Time and amount of supplemental irrigation at different distances from tree trunks influence on morphological characteristics and physiological responses of rainfed fig trees under drought conditions

摘要

This study was carried out to identify the effects of time and amount of supplemental irrigation (SI) at different distances from tree trunks on morphological characteristics and physiological responses of mature rainfed fig trees in Estahban County, Fars Province, Iran. The two-year experiment was conducted in a split-split plot statistical design with four replications. SI treatments consisted of 1) irrigation position treatments in a micro-catchment close to tree trunks, 1-1.1 m from tree trunks inside of canopy, and 2.1-2.2 m from tree trunks outside of canopy 2) irrigation time treatments in early spring and in mid-summer, and 3) irrigation water amount treatments of no supplemental irrigation (control), 1000 liters, and 2000 liters of irrigation water per tree. The results showed a positive effect of SI on some morphological traits of rainfed fig trees. SI increased the leaf gas exchange parameters, including net photosynthesis rate (A(n)), transpiration rate (T-r), and stomatal conductance (g(s)). The highest A(n) and g(s) occurred in leaf water potential (LWP) around -1 MPa and the air temperature of 20 degrees C. The LWP equal to - 2 MPa could be considered as a threshold for stomatal closure of rainfed fig trees, which put this plant among drought-tolerant trees. The higher correlation coefficient between A(n) and g(s) compared with that obtained for A(n) and T-r implied the higher dependence of the A(n) variation on the g(s) than that of T-r. The highest leaf scale water use efficiency for trees irrigated with 2000 liters of water, out of the canopy, indicated higher increase of A(n) compared with T-r after irrigation. Applying SI with 2000 liters of water per tree (200 m(3)ha(-1)), outside of canopy in early spring could improve some of the morphological traits and physiological responses of rainfed fig trees, under drought conditions. However, under water resources limitation, 1000 liters of irrigation water per tree (100 m(3)ha(-1)) could be recommended for rainfed fig orchards.