THE INFLUENCE OF IAA, CARBOHYDRATE AND MINERAL CONCENTRATION IN HOST TISSUE ON ECTOMYCORRHIZAL DEVELOPMENT ON PINUS-SYLVESTRIS L IN RELATION TO NUTRIENT SUPPLY

Concentrations of indole-3-acetic acid (IAA) in lateral roots, fungal biomass (ergosterol) in lateral roots and extramatrical mycelium, and carbohydrates and minerals in shoots were measured in mycorrhizal and nonmycorrhizal Pinus sylvestris L. seedlings supplied with different a mounts of N and P. IAA concentrations in lateral roots of mycorrhizal seedlings were the same or lower than those in control seedlings. The concentrations of IAA in mycorrhizal root tips of Laccaria bicolor-ino culated seedlings were 40% lower than those in lateral roots. IAA conc entrations in lateral roots of L. bicolor-inoculated seedlings were po sitively related to N supply. A rise in N supply reduced the developme nt of extramatrical mycelium of L. bicolor and the fungal biomass in l ateral roots of Hebeloma crustuliniforme-inoculated seedlings. High N supply reduced concentrations of starch, Ca and Mg in shoots but incre ased those of glucose and fructose. P had no effect on fungal growth o r on concentrations of IAA. Fungal growth was negatively correlated wi th levels of soluble carbohydrates in shoots, shoot concentrations of N, P and K, relative growth rate and the shoot:root ratio of the seedl ings. Starch, Mg and Ca concentrations in the shoot were positively co rrelated with fungal growth. No support was found for the hypothesis t hat IAA is important in regulating mycorrhizal colonization.