The incidence of ectomycorrhizae by Pisolithus tinctorius on Quercus rubra seedlings fertilized with sodium nitrate and ammonium chloride

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Virginia Polytechnic Institute and State University

Quercus rubra seedlings were subjected to five treatment factors in a factorial design replicated ten times in a randomized complete block design. The factors included: (1) Pisolithus tinctorius inoculated seedlings or non-inoculated seedlings; (2) nitrogen fertilizer supplied as sodium nitrate or as ammonium chloride; (3) fertilization at 15 days or at 40 days after planting of seed; (4) rates of nitrogen applied at 0.0, 0.0133, 0.0266, or 0.0532 g N per seedling; and (5) the seedlings grown for 60, 100, or 140 days.

All 960 seedlings were grown in a peatmoss/vermiculite medium in one-liter containers in a greenhouse and fertilized at the time of planting with a nutrient solution excluding nitrogen. Growing medium moisture was maintained between 0.3 and 1.0 bars matric suction throughout the growing periods. Details are given with regards to inoculum synthesis, seed planting, care for seedlings, fertilization and media nutrient status, and data collection procedures.

Ectomycorrhiza formation was observed as early as 18 days after planting. All inoculated seedlings (480) were ectomycorrhizal with P. tinctorius. Ectomycorrhizae other than those characteristically produced by P. tinctorius were not observed and all non-inoculated seedlings (480) were free of ectomycorrhizae. Ectomycorrhiza formation was enhanced with late nitrogen applications; however, infection was low on unfertilized seedlings. Mycorrhizal seedlings generally had less basal area, total seedling weight, root weight, leaf phosphorus weight, and leaf phosphorus percent than non-mycorrhizal seedlings. Mycorrhizal seedlings also had decreased leaf areas and green leaf area percents than non-mycorrhizal seedlings.

Total seedling weight was enhanced with early applications of nitrogen fertilizer. Non-mycorrhizal seedlings fertilized with ammonium chloride generally had greater basal area, total seedling weight, and root weight than non-mycorrhizal seedlings fertilized with sodium nitrate. The probable effects of P. tinctorius in enhancing leaf damage and reducing seedling growth and leaf phosphorus contents are discussed. Several specific fertilization treatments are recommended for the production of large and healthy mycorrhizal and non-mycorrhizal northern red oak seedlings.