Physiological responses to abiotic stress.

Olive (Olea europaea L.) trees are widespread in Mediterranean agroecosystems and are now extensively cultivated in different warm-temperate regions of the world such as North and South America, Australia, New Zealand, and South Africa, and even in the monsoon systems of China and India. In the Mediterranean area, the biological and agronomical success of this species is due to its adaptability to the Mediterranean climatic conditions: mild, wet winters with temperatures that drop below 10 °C but rarely below 0 °C and warm, dry summers. When weather conditions become more extreme (drought, high, or low temperatures) or soil conditions are not optimal for olive growth (salinity, low oxygen, nutrient deficiencies), the plant can be subjected to abiotic stresses, which may have negative effects on its physiology. The damages derived from stresses caused by environmental constrains are often not immediately recognized in olive orchards, since plants are largely grown in non-specialized planting systems that are managed with limited cultural practices. However, due to the renewed interest in extra-virgin olive oil for its beneficial health effects, olive cultivation has now been modified from traditional low-density and low-input to high-density and high-input growing systems. Information on the effect of abiotic stresses on trees under the new cultivation systems is scarce due to the wide differences in management practices, environmental conditions and the increase in the use of selected varieties. Under these new conditions, the abiotic factors and their related stresses might have a strong impact on both yield and quality. In this chapter, we focus on physiological responses of olive trees to drought, salinity, and temperature stress. The reader can refer to the existing literature for other abiotic stresses.