Interactions between phenolic compounds present in dry olive residues and the arbuscular mycorrhizal symbiosis

The use of “alpeorujo” (dry olive residue) has been proposed as an organic amendment in order to enhance soil structure and to increase C storage in soils. The aim of this work is to study how aqueous alpeorujo (ADOR) extracts bioremediated with white-rot fungi and three representative phenolic acids present in this extract (protocatechuic, vanillic and caffeic acid) affect the growth of the arbuscular mychorrhizal fungus Rhizophagus custos in monoxenic culture. Our results show that ADOR decreased mycorrhization parameters; however, this negative effect ceased after ADOR bioremediation. Although protocatechuic and vanillic acids have drastic negative effects at high concentrations, these phenols enhance mycorrhization processes at low concentrations and caffeic acid negatively affects symbiosis at low concentrations. Finally, the capacity of root biomass to dissipate individual phenols was also estimated, in which mycorrhized roots improve phenol dissipation in the growth medium in the presence of different phenols. This study highlights the important role played by arbuscular mycorrhiza in protecting plants from phytotoxicity.This study was carried out thanks to financial support from the Ministry of Economy and Competitiveness (MINECO) within the framework of project AGL2012-32873. R. Reina gratefully acknowledges the support provided by the JAE-Pre Program which is co-financed by CSIC and the European Social Fund. E. Aranda thanks the Ministry of Economy and Competitiveness (MINECO) and FEDER funds for co-funding the Ramón y Cajal contract (RYC-2013-12481).Peer reviewe