Primary and secondary metabolites from the soil-root interaction in the rhizosphere facilitates extreme water depletion tolerance in olive trees

Water is vital for all living rhizospheric organisms. However, numerous microorganisms have adapted to survive in environments in which water is scarce. Recent evidence has indicated that sugars from root or microbial source is linked with water deficit tolerance of crops. Here we described in olive trees the changes in sugars accumulation in roots, in combination with corresponding changes in microbial and soluble sugar profiles in the rhizosphere under drought conditions. A marked increase in mannitol content occurred in roots of water-stressed plants. Application of drought stress caused a significant increase in the level of microbial trehalose when compared to the control. Trehalose may increase the soil water surface tension, which could facilitate drought tolerance of olive. We showed that complex interactions of root and microbial community in the rhizosphere maintained the relative water content at 60 % under drought conditions and have the potential to regulate the water uptake by olive.