Effect of cold stress on survival and gas exchanges of olive seedlings (Olea europaea L.)

Cold tolerance is one of the important factors in the distribution of plant species. The aim of this study was to investigate the survival and gas exchange responses of olive (Olea europaea L.) seedlings to low temperature and freezing stress. For this purpose, 144 two-years-old potted seedlings of olive (cultivar yellow) with averaged height of 30 cm were examined as factorial in a completely random design (CRD) with 3 replications. Seedlings were exposed to six temperature levels (+2, -5, -7, -10, -16, and -20° C) for 1 and 3 hours. Gas exchange parameters such as net photosynthesis rate, transpiration, and stomatal conductance were measured for each treatment in three steps: before stress, immediately after stress, and 12 days after stress. Results showed that in each temperature level net photosynthesis rates, stomatal conductance, and transpiration reduced in both 1 and 3 hours chilling and this reduction was higher in seedlings subjected to 3 hours chilling. Olive seedlings exposed to -10, -16 and -20 °C temperatures were dead while in seedlings subjected to -7 °C and higher temperature (under both 1 and 3 hours chilling) gas exchange variables were recovered on day 12 after the stress. In general, this research revealed that olive seedlings (cultivar yellow) are able to tolerate low temperature up to -7°C for 3 hours.