Influence of Saline Drip Irrigation On Root Bio- and Necromass and Specific Root Area of Mature Olive Trees.

Olive (Olea europaea L.) is one of the most economically valuable trees in the Mediterranean countries especially because of its drought and salt tolerance. While roots play a significant role in the salinity tolerance of plants, belowground data are scarce, especially for mature trees. Eleven years-old, drip-irrigated trees of the highly salt tolerant olive variety ‘Barnea’ were examined in the Negev desert, Israel. Three levels of salinity (1.2, 4.2 and 7.5 dS/m) were applied. Salt sensitive ‘Proline’ trees grown under moderate salinity (4.2 dS/m) were examined as comparison. Bio- and necromass of fine and coarse roots and specific root area (SRA) were determined and correlated to water content, salinity, pH and spatial position (distance from the bole, depth) respectively. A tetrazolium test was used to confirm the applied criteria of root sorting into living and death The highest fine root biomasses were found in moist soil patches close to the drip line. Barnea variety possessed a higher root biomass and subsequently a larger absorbing root surface area than Proline variety under moderate salt stress. Furthermore, fine root biomass of Barnea variety was still considerably high under severe salinity (7.5 dS/m). Fine root bio/necromass ratio of Barnea and Proline varieties decreased under severe and moderate saline irrigation respectively. Specific root area was coupled to soil pH and soil depth. The ability of Barnea variety to possess an significantly increased bio/necromass ratio under moderate salinity and to sustain a relatively high root biomass under severe salinity (7.5 dS/m) are likely to contribute to the high salt tolerance of this variety. Influences of soil parameters on root biomass, bio/necromass ratios and morphology and consequences on water uptake and carbon investment are discussed.