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Soil pH and Nitrogen Influence Pisolithus Ectomycorrhizal Development and Growth of Loblolly Pine Seedlings

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Five families of loblolly pine were grown from April to February in fumigated soil at pH 4.8, 5.8, and 6.8. All microplots received vegetative inoculum of Pisolithus tinctorius (Pt) and three, six, or nine applications of NH4NO3 at 50 kg N/ha/application through August, which totaled 150, 300, or 450 kg N/ha. Vegetative inoculum of Pt buried in soil lost significant viability after 54 days at soil pH 6.8. Inoculum viability declined in all treatments after 81 days, but it was only a little over a third as viable at pH 6.8 as at lower pH levels. Up to three applications of NH4NO3 at 50 kg N/ha each did not affect inoculum viability. The five test families of loblolly pine reacted similarly to soil treatments. Seedling heights, root-collar diameters, and top dry weights were more affected by soil pH than by application of N. As soil pH increased, seedling growth decreased. Dry weight of roots, total length of lateral roots, and number of short roots were not significantly influenced by either soil treatment. Total Pt ectomycorrhizal ratings (combining number of mycorrhizae and proportion of different morphological types) were about one-fourth as much at pH 6.8 as in more acid soil conditions. Applications of NH4NO3 resulting in soil concentrations of NO3-N ranging from 60 to 120 kg/ha and NH4-N ranging from 90 to 130 kg/ha at pH 4.8 and 5.8 were associated with the most abundant Pt ectomycorrhizal development. Increased N applications increased Pt development at pH 5.8 and 6.8. Calcium equivalent treatments, using CaSO4 at similar Ca concentrations, suggested seedling response was due to soil pH and not Ca concentrations. For. Sci. 36(2):224-245.

Keywords: NH4-N; NO3-N; Pinus taeda; Pisolithus tinctorius; ectomycorrhizal measurements; fertilizer; inoculum viability; nursery; root growth measurements

Document Type: Journal Article

Affiliations: Institute Director and Chief Plant Pathologist, Institute for Mycorrhizal Research and Development, USDA Forest Service, Southeastern Forest Experiment Station, Athens, GA

Publication date: June 1, 1990

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