Eucalyptus urophylla root-associated fungi can counteract the negative influence of phenolic acid allelochemicals

Root-associated fungi can potentially affect plant allelopathy by degrading or transforming allelochemicals. However, no microorganism has been identified as an allelochemical moderator in Eucalyptus plantations. In this study, three Helotiales sp. (EU03, EU04, and EU05) were isolated from the roots of Eucalyptus urophylla, and all three of the isolated fungi were grown in vitro with mixed phenolic acids (benzoic acid, p-hydroxybenzoic acid, and vanillic acid) as the sole carbon source. EU03 and EU05 can degrade 99% of the p-hydroxybenzoic acid in an inorganic culture medium within 9 days, while EU04 can degrade 100% of the three phenolic acids in potato dextrose broth medium within 7 days. A mixed inoculation with the three isolates can alleviate the allelopathic effects of phenolic acids and E. urophylla litter decomposition on Albizia julibrissin (Fabaceae) nodulation ex situ. The number of nodules on A. julibrissin grown with inoculated fungi plus 50 mg kg−1 or 100 mg kg−1 mixed phenolic acids were 2.17 times and 1.67 times greater than those grown without the inoculation treatments, respectively. These results highlight the role of E. urophylla root associated fungi, which have the potential to moderate the phenolic acid allelopathy caused by E. urophylla. Manipulating root associated fungi is an effective way to alleviate the effects of ecological suppression caused by Eucalyptus allelochemicals.