SEASONAL ECTOMYCORRHIZAL FUNGAL BIOMASS DEVELOPMENT ON LOBLOLLY-PINE (PINUS-TAEDA L) SEEDLINGS

Ergosterol, a membrane sterol found in fungi but not in plants, was us ed to estimate live mycelial biomass in ectomycorrhizae. Loblolly pine (Pinus taeda L.) seeds were sown in April 1993 and grown with standar d nursery culture practices. Correlations between total seedling ergos terol and visual assessment of mycorrhizal colonization were high duri ng July and August but low as ectomycorrhizal development continued in to the growing season. Percentages of mycelial dry weight over lateral roots decreased from 9% in July to 2.5% in November because seedling lateral root dry weight accumulated faster than mycelial dry weight. T otal ergosterol per seedling increased from July through February. As lateral root dry weight ceased to increase during winter months, ectom ycorrhizal mycelia became the major carbohydrate sink of pine seedling s. No distinctive seasonal pattern of soil ergosterol content was obse rved. The impact of ectomycorrhizal fungi on plant carbohydrate source -sink dynamics can be quantitatively estimated with ergosterol analysi s but not with conventional visual determination.