Root growth dynamics of olive (Olea europaea L.) affected by irrigation induced salinity

Irrigated olives are increasingly exposed to conditions of high salinity. Salt tolerance of olives is commonly attributed to ion exclusion. Our objective was to advance understanding of salt stress response of olive roots. Nine levels of root zone salinity originating from either irrigation water salinity or leaching level were applied to bearing olive cv. Barnea trees grown in large weighing-drainage lysimeters. Minirhizotrons were used to measure count, diameter, length and age (color) of roots while analysis of sampled roots and leaves quantified ion uptake and accumulation. Increased exposure to salinity caused reduction in number and length of roots and increased root turnover. The most drastic effects occurred at the first level of salt gradient. Concentration of Na+ and Cl- was 5-10 times greater in root compared to leaf tissue. The K+/Na+ ratio decreased tenfold as root zone salinity increased in both roots and leaves. Restricted ion transport from roots protected aerial tissue from ion toxicity, but at a high cost as root growth decreased and mortality rate increased. We suggest that the ionic component of salt stress is a prevailing force restricting root growth, life span and development in olives.