The ability of several ectomycorrhizal fungi of Pinus cembra to utilize different nitrogen sources was examined. The growth of 30 isolates of eight different species from high-subalpine areas in Austria was estimated on solid media containing 10 different inorganic or organic nitrogen sources. Growth was determined as dry weight yields and as colony size formation. Differences in patterns of growth on nitrogenous substrates were found. All fungi grew well on ammonium. Growth on nitrate generally was poor, except for Paxillus involutus, Rhizopogon spp. and individual isolates of Suillus placidus which grew well and can be termed 'nitrate fungi'. The ability of fungi to grow using single amino acids (asparagine, glycine) and proteins (bovine serum albumin, gliadin) was also examined. Most species grew well on asparagine but growth was more variable on glycine. Some of the isolates tested had limited ability to utilize bovine serum albumin and gliadin; however, other isolates, even of the same species, grew well on these proteins. Considerable intraspecific variation in the ability to use proteins as nitrogen source was found among the isolates tested. Most isolates grew as well on peptone as on ammonium. Although there was considerable intraspecific variability, some patterns of colony development were evident. Certain fungi showed a reciprocal behaviour of growth and formed large colonies with small dry weight yields when grown on nitrate and to some extent on proteins. Exudation of pigments into the agar media was not or only slightly affected by the various nitrogen amendments. The observations suggest that the differences in nitrogen utilization are important ecophysiological markers of ectomycorrhizal fungi. Capabilities to use nitrate, amino acids and proteins may be a better adaptation of species to specific soil types or a prerequisite for selective exploitation of nitrogen sources by individual strains of a given species.
