Nitrogen mobilization from protein-polyphenol complex by ericoid and ectomycorrhizal fungi

Abstract

The horizons of forest and heathland soils in which mycorrhizal roots proliferate typically contain large quantities of polyphenolic materials. These have the potential to bind organic nitrogen in recalcitrant complexes, thereby influencing availability of N to the fungal symbionts. The protein-binding abilities of aqueous extracts of forest soils were examined, and those derived from birch and pine sites were found to bind protein even when present in low concentrations. The effect of polyphenols upon availability of protein to ectomycorrhizal (ECM), ericoid mycorrhizal and wood-decomposing saprophytic fungi was investigated using the soluble polyphenol tannic acid (TA), and protein bovine serum albumin (BSA). While the saprophytic fungi were able to mobilize the precipitate, only three of 18 ECM fungi tested were able to do so. The ericoid mycorrhizal fungi were capable of partial clearance of the precipitate. It was demonstrated that the ericoid mycorrhizal fungi had access to N contained in protein complexed by TA, while ECM fungi did not. The extracellular proteases of ericoid mycorrhizal fungi remained active in the presence of TA, while those of the ECM fungi were inhibited. The ericoid mycorrhizal fungi and several ECM fungi showed abilities to metabolise TA contained in TA-BSA precipitate.