Growth and ectomycorrhizal formation of container-grown Douglas-fir seedlings inoculated with Laccariabicolor under four levels of nitrogen fertilization

Container-grown Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seedlings were inoculated at the time of sowing with a Laccariabicolor (Maire) Orton mycelial suspension produced in a fermentor. They were grown in a peat moss–vermiculite substrate under four levels of N fertilization (7.2, 14.4, 21.6, and 28.7 mg/seedling per season (N1, N2, N3, and N4, respectively)) to determine the N level suitable for both ectomycorrhizal development and seedling growth. After 18 weeks in the greenhouse, seedlings inoculated with L. bicolor had 44%, 32%, 44%, and 5% of their short roots mycorrhizal when fertilized with N1, N2, N3, and N4, respectively. Only when they were fertilized with N4 did the L. bicolor seedlings have significantly greater shoot height than the controls. For the other growth parameters, they were not significantly different from control seedlings for any of the N levels. After 18 weeks, regardless of the level of N, seedlings inoculated with L. bicolor had significantly lower N concentrations (...