GROWTH AND ECTOMYCORRHIZA FORMATION OF CONTAINERIZED BLACK SPRUCE SEEDLINGS AS AFFECTED BY NITROGEN-FERTILIZATION, INOCULUM TYPE, AND SYMBIONT

Picea mariana (Mill.)B.S.P. seedlings were grown in containers under three levels of nitrogen fertilization (6, 8.5, and 15 mg/seedling per season). Seedlings were inoculated at sowing with Laccaria bicolor and Hebeloma cylindrosporum, using two methods: mycelial suspension liquid inoculum and peat-vermiculite solid inoculum. Results show that liquid inoculum was as effective as solid inoculum for development of Laccaria bicolor ectomycorrhizae on black spruce seedlings. After 20 weeks in the greenhouse, seedlings fertilized wiht 8.5 mg N and inoculated with L. bicolor had the highest percentage of ectomycorrhizal short roots for both inoculum types, with 59 and 53% for liquid and solid inocula, respectively. These L. bicolor seedlings had significantly more ectomycorrhizae with 8.5 mg N than with 15 mg N. Very few ectomycorrhizae were obtained with Hebeloma cylindrosporum for any of the nitrogen levels or either of the inoculum types. There were no significant differences for any growth parameters except shoot/root ratio between L. bicolor seedlings and the controls, regardless of the N level and inoculum type. For both inoculum types, only shoot height of seedlings differed significantly among the three N levels. Seedlings fertilized with 8.5 mg N had root-collar diameter and dry weights that were not significantly less than those that received 15 mg N for both inoculum types. It is only at the lower level of 6 mg N that seedlings inoculated with liquid L. bicolor inoculum absorbed significantly more N than the controls. Analysis of percent N and P concentration in seedlings with the greatest ectomycorrhizal development and analysis of available N and P in their substrate indicated that tissue concentrations of 1.9% N and 0.2% P and substrate fertility of 40 ppm N and 50 ppm P would be appropriate to maintain the ectomycorrhizal association Picea mariana - Laccaria bicolor. Salinity in the substrate of control seedlings was generally significantly different between the three N levels during the growing period.