ABOVE- AND BELOW-GROUND RESPONSES TO SOIL MOISTURE DEFICITS IN OLIVE

Abstract

Olive (Olea europaea L.) is characterized by high drought tolerance and adaptability to changing moisture conditions. Root morphological and physiological acclimation is an important component of olive tolerance to drought. The main objective of this experiment was to examine aboveground and belowground growth and physiological responses to drought. Self-rooted olive plants (‘Arbequina’), were grown in splitted rhizoboxes. Plants were exposed either to continuously well watered equally in both halves of the container (WW), continuously deficit irrigated in both halves with 1/3 the quantity of water as the WW treatment (DD), and heterogeneously irrigated with full watering in half the container (Wh) and only partial (1/3) watering in the other side (Dh). Irrigation regimes were maintained for 75 days. Canopy parameters measured were: stem growth rate, photosynthetic activity, stomatal conductance, leaf turgor, osmotic and total water potential and leaf total nonstructural carbohydrate concentration. Root parameters measured were: root respiration, an estimator of metabolic activity and electrolyte leakage, an indicator of root stress. The DD treatment differed significantly from DhWh and WW in all the aboveground parameters showing that drought stress applied to the whole root system was able to reduce plant growth, leaf water potential and leaf gas exchange. Root respiration decreased in the DD treatment and in the dry sector (Dh) of the DhWh treatment. This experiment highlights how roots can respond to drought conditions by reducing metabolism in a localized way. Under low water availability reduction of metabolic activity may contribute to the maintenance of a sustainable costs/benefit ratio. Stress indicators showed higher electrolyte leakage in Dh roots compared to Wh roots, but mainly in fibrous roots older than 38 days. This confirms that olive is a species sensitive to water availability in terms of growth but generally tolerant of water deficits in terms of survival.