Growth and ectomycorrhiza formation of container-grown red oak seedlings as a function of nitrogen fertilization and inoculum type of Laccariabicolor

Abstract

Containerized red oak (Quercusrubra L.) seedlings were inoculated at the time of sowing with Laccariabicolor (Maire) Orton using two methods to compare the efficiency of two inoculum types: a mycelial suspension (Ecot-Sol®101) produced by Rhizotec Laboratories Inc. and calcium alginate beads containing this mycelial suspension. Red oak seedlings were also grown for 19 weeks in a peat moss – vermiculite substrate under three levels of N fertilization (100, 120, and 140 mg/seedling per season) to determine the N level that maximizes the ectomycorrhizae formation and growth of seedlings. After 19 weeks in the greenhouse, seedlings inoculated with liquid inoculum had significantly more mycorrhizae than both those inoculated with beads and controls, regardless of the N level. For any of the N levels, liquid-inoculated seedlings had significantly lower shoot height, root-collar diameter, and dry weights (shoot, root, and total) than both those inoculated with beads and the controls, whereas there were no significant differences for any growth parameters between the bead and control treatments. For the three inoculum treatments, root and total dry weights of seedlings fertilized with 100 mg N were significantly lower than those of seedlings that received both 120 and 140 mg N, whereas shoot height, root-collar diameter, and shoot:root ratio of seedlings did not differ significantly between any of the three N levels. After 19 weeks, seedlings inoculated with liquid inoculum had significantly greater N and P concentrations (%) and contents (mg/seedling) than those inoculated with beads only at the 140 mg N level. Analyses show that seedling concentrations of 1.2% N and 0.1% P and substrate fertility of 25 ppm N and 30 ppm P would be appropriate to maintain the ectomycorrhizal association Q. rubra – L. bicolor.