The organic soil horizons of heathland and temperate forest ecosystems
are characteristically rich in phenolics, which present barriers
to organic N availability to the microflora. The abilities of ectomycorrhizal
(ECM), ericoid mycorrhizal and wood decomposing
saprotrophic fungi to degrade model compounds representing the insoluble
phenolic lignin, and soluble phenolics, which provide
physical and chemical barriers respectively to organic N availability,
were
compared. No clear relationship was found between ability
to degrade lignin and soluble phenolics. The presumptive assays indicated
that
most mycorrhizal fungi have only low abilities to
degrade these compounds relative to the wood decomposing fungi. In general,
ericoid mycorrhizal fungi were capable of greater
phenolic degradation than most ECM species, and degradative ability was
associated with production of phenol-oxidizing enzymes.
In no case was presumptive degradation of lignin or soluble phenolic, or
production of phenol-oxidizing enzymes by mycorrhizal
fungi as great as that of the wood decomposing fungi. In the case of the
ericoid endophyte Hymenoscyphus ericae, phenol-oxidation
was associated with production of an extracellular o-polyphenol
oxidase (tyrosinase) which showed optimal activity at a pH of 5–5·5
and temperature of 30°C. The ecological significance of the results
is discussed.