EFFECTS OF LIMING ON THE UPTAKE OF ORGANIC AND INORGANIC NITROGEN BY MYCORRHIZAL (PAXILLUS-INVOLUTUS) AND NONMYCORRHIZAL PINUS-SYLVESTRIS PLANTS

Seedlings of Pinus sylvestris L. were grown in Plexiglas(R) observatio n chambers in limed (CaCO3, pH 5.0 and 5.9) and untreated (pH 4.1) pea t. The seedlings were either colonized by the mycorrhizal fungus Paxil lus involutus (Batsch: Fr.) Fr. Or were non-mycorrhizal. After 18 wk i n the observation chambers, N-15-labelled organic nitrogen, as lyophil ized and ground mycelium of Suillus variegatus (Swartz: Fr.) O. Kuntze , or ammonium, was added to the peat. The plants were harvested after an uptake period of 14 d. Irrespective of the nitrogen form added, lim ing decreased both the content and concentration of N-15 in nonmycorrh izal plants, and, to a lesser extent, those in mycorrhizal plants. In mycorrhizal plants the uptake of N-15 was not correlated with area col onized by the mycorrhizal mycelium. The amount of KCl-extractable N-15 in peat without plants and mycorrhizal fungi decreased with liming. I t is proposed that liming induced chemical or microbial immobilization of the added N-15. This is suggested to be the main reason for the de creased uptake of N-15 in lime treatments.