Effects of ammonium and nitrate on mycorrhizal infection of Norway spruce seedlings under controlled conditions

Abstract Seedlings of Picea abies inoculated with Lactarius rufus or L. theiogalus were grown in a sterile sand culture system with flowing nutrient solution. NO 3 − at 2.7 mM applied over a 90 or 120 days period had no significant effect on the degree of infection and total numbers of mycorrhizae per seedling, whereas NH 4 + at 1.5 mM or 2.7 mM had a significant negative effect on mycorrhizal development.