Impact of drought and salinity on olive water status and physiological performance in an arid climate

Effects of drought and salinity on water status, growth and physiological activity of olive can be temporary or permanent and may impact olive production sustainability, especially in southern Mediterranean areas. Tunisia has a Mediterranean climate with high temperatures and low summer rainfall. Thus water stress problems are likely to be more severe for cultivated olive trees. In addition, the reduction in the availability of good quality irrigation water will increase the use of saline water. Olive trees are able to tolerate low soil water availability and quality and develop physiological adaptations to cope with water and salt stress. However, these adaptation strategies are limited and permanent damages can be observed. The permanent effects caused to olive leaves due to drought, and the capacity of irrigation with saline water to avoid these impacts is not well known. The aim of this work was to compare olive leaves performance after a severe drought with, and without, irrigation and to assess recovering capacities after a rainy period. Moreover, irrigation water quality effects were also evaluated. The results showed that, photosynthetic rate was very low for rainfed plants, during drought, as compared to irrigated ones. After re-watering, rainfed trees photosynthetic rate was only 55% of that of trees irrigated with fresh water. Irrigation with saline water (EC = 7.5 dS m(-1)) reduced drought impact by increasing photosynthesis by 55% but remained lower than that of fresh water by 23%. Thus olive leaves were unable to recover their whole photosynthetic capacity after being exposed to severe water or salt stress. Furthermore, young leaves had the same photosynthetic capacity at the beginning. This indicated that olive leaves lost permanently half of their photosynthetic activity during to drought without irrigation. The use of saline water reduced this gap to 23% as compared to fresh water.