Effects of the soluble polyphenol tannic acid on the activities of ericoid and ectomycorrhizal fungi

Plants with ericoid and ectomycorrhizal (ECM) roots characteristically produce acidic polyphenol-rich residues which accumulate in soil, and may influence the activities of the fungal symbionts directly through toxic effects, or indirectly through effects on nitrogen availability. The ability of fungi representative of these mycorrhizal types to degrade solube polyphenolic materials and, hence, to reduce their nutritional effects was investigated using tannic acid (TA) as a model compound. The ericoid endophyte Hymenoscyphus ericae (Read), Korf and Kernan was able to readily degrade the compound, and as a result, to reduce its ability to bind protein. In contrast, the ECM fungi examined had only limited abilities to degrade TA. The presence of TA induced H. ericae but not the ECM fungi, to produce extracellular polyphenol oxidase. Mycelial yields and the extent of TA degradation by H. ericae were both enhanced by exogenous ammonium.