NITROGEN TRANSLOCATION BETWEEN ALNUS-GLUTINOSA (L) GAERTN SEEDLINGS INOCULATED WITH FRANKIA SP AND PINUS-CONTORTA DOUG EX-LOUD SEEDLINGS CONNECTED BY A COMMON ECTOMYCORRHIZAL MYCELIUM

Uptake and translocation of nitrogen was studied in laboratory microco sms consisting of Alnus glutinosa (L.) Gaertn., Frankia sp., Paxillus involutus (Fr.) Fr. and Pinus contorta Dougl. ex Loud. P. involutus wa s shown to form a fully functional ectomycorrhizal association with al der as well as pine, and the seedlings thus became interconnected by a common mycelium. When microcosms were exposed to N-15(2) gas, interpl ant translocation of N-15 was observed in two out of three experiments . N-15(2) was fixed by Frankia and translocated to all other parts of the system. In the two experiments in which interplant translocation o ccurred, between 5 and 15 % of the N-15 recovered was found in the pin e seedlings. Within seven days, fixed N2 was incorporated into amino a cids in the Frankia nodules, translocated to both the A. glutinosa and P. contorta seedlings and incorporated into macromolecules. In alder seedlings, citrulline and ornithine were the free amino acids that had both the highest N-15 enrichment levels and concentrations. In pine, glutamine and citrulline had the highest N-15 concentrations, and glut amine had the highest level of N-15 enrichment. N-15 enrichment levels were greatest in the nodules, at between 5.5 and 29 % in the differen t amino acids and 12 % in the macromolecular fraction. Enrichment leve ls decreased with increasing distance from the nodules. The uptake and translocation of N-15 applied as (NH4Cl)-N-15 to the mycelium was als o studied. N-15 was incorporated into amino acids in the mycelium and translocated further in this form. Generally, free amino acids had hig h N-15 enrichment levels in the mycelium, decreasing along the translo cation pathway. Citrulline and glutamine were the amino acids with hig hest N-15 concentrations in all parts of the system. N-15 was also fou nd in the macromolecular fraction.