THE BIOLOGY OF MYCORRHIZA IN THE ERICACEAE .18. CHITIN DEGRADATION BYHYMENOSCYPHUS-ERICAE AND TRANSFER OF CHITIN-NITROGEN TO THE HOST-PLANT

In acid mor-humus soils of heathland ecosystems fungi are a significan t part of the soil biomass. In these organic soils chitin and hyphal w all hexosamines are major potential sources of nitrogen (N). The abili ty of the ericoid mycorrhizal fungus Hymenoscyphus ericae (Read) Korf & Kernan to degrade purified chitin and the hexosamines, N-acetylgluco samine, glucosamine and galactosamine when supplied as sole sources of N, was investigated in aseptic liquid culture. The fungus grew rapidl y on all the organic N sources, producing the largest dry weight incre ase when supplied with galactosamine and similar yields on the other n itrogenous sources. Mycelial N contents of fungus grown on the hexosam ines reflected the dry weight yields with the fungus grown on galactos amine having the highest N content. After 20 d only trace quantities o f N-acetylglucosamine and glucosamine were present in culture filtrate , and 15% of the galactosamine remained at the final harvest. Plants o f Vaccimium macrocarpon Ait. and Calluna vulgaris (L.) Hull were grown aseptically in the mycorrhizal or nonmycorrhizal condition on agar me dia containing chitin or a hexosamine and compared with yields and N c ontents in the absence of an N source. It was revealed that significan t quantities of N were transferred to the host in the mycorrhizal cond ition that led to enhanced growth rates. The highest yields of V. macr ocarpon were observed with N-acetylglucosamine, with the other hexosam ines giving yields slightly below that on chitin. The yields were refl ected in the calculation of the percentage of available substrate pres ent in the plant; up to 40% of the N-acetylglucosamine was present in the plants after 40 d.