Measurements of the chitin content of the rooting horizons of a
mor-humus heathland soil, indicate that
chitin can contain in excess of 20% of the total nitrogen in the litter
horizon and 30% in the fermentation (F)
horizon. Much of this chitin-nitrogen is thought to be contained in the
mycelial walls of soil fungi.
Experiments were therefore designed to test the hypothesis that such
of N could be rendered accessible
to the ericaceous plants by their fungal endophytes. Mycelium of the ericoid
endophyte Hymenoscyphus ericae
(Read) Korf & Kernan and of the ectomycorrhizal fungus Suillus
bovinus (Fr.) O. Krantze were grown in liquid
culture before being killed and added either in the intact condition, or
after fractionation, as sole sources of N to
sterile media upon which were grown H. ericae in pure culture,
or mycorrhizal and non-mycorrhizal plants of
Vaccinium macrocarpon Ait. and Calluna vulgaris L.
The abilities of the test organisms to utilize the nitrogen
contained in the intact mycelial necromass, or in its fractions, were
assessed by determining their yields and
nitrogen concentrations of their tissues.
It was revealed that H. ericae was able to produce
significantly higher yield when grown on intact fungal
necromass than when provided with equivalent concentrations of N in the
form of ammonium. Its yields on
mycelial fractions were lower, but still significantly greater than those
obtained in the controls lacking N.
Significantly greater yields and N contents were also found in the
ericaceous plants grown with these nitrogenous
substrates in the mycorrhizal condition. Without H. ericae
they had no access to the substrates. The possible
ecological implications of these results are discussed.