Determination of tolerance to below-zero temperatures in Prosopis juliflora using physiological indices

The occurrence of below-zero temperatures in recent winters in Khuzestan province has caused the freezing of Prosopis juliflora trees. The aim of this study was to determine the sensitivity of this species to freezing under zero temperatures. In this study, a split split plot was used in a completely randomized design with six replications. In order to apply the treatments, the branches of elderly trees and two-year old seedlings were considered as main treatment; below-zero temperatures (-1-, -3, -5 and 7 ° C) as the first sub treatment; and different times (1, 2, 3 and 4 hours) as the second sub-treatment. The amount of electrolyte leakage from the membrane of leaf and stem cells was measured and, based on this, LT50 was calculated. The chlorophyll (II) fluorescence and photosynthesis efficiency of the leaves were measured as indicators for determining the damage to frost. The results showed that there was no significant difference for all traits between branches of the old trees and two-year-old seedlings. The percentage of electrolyte leakage from leaf and stem increased significantly with decreasing temperature. The LT50 occurred at -5 ° C after three hours. At -7 ° C, after the first hour, LT50 occurred in the leaves and after the third hour in the stems. After freezing stress, the Fv/Fm decreased significantly. After two hours at -1°C, Fv/Fm did not change significantly but in three hours Fv/Fm decreased from 0.64 (in control) to about 0.48. It reached to 0.15 after applying four hours at -7°C.