CHITIN AND ERGOSTEROL COMBINED TO MEASURE TOTAL AND LIVING FUNGAL BIOMASS IN ECTOMYCORRHIZAS

We have studied the chitin and ergosterol contents of ectomycorrhizal roots in three sets of experiments to evaluate them as indicators of f ungal biomass. The first set of experiments showed that ageing had a m arked effect on ergosterol concentrations. The ergosterol content of 7 -month-old, brown, shrunken Pinus sylvestris L.-Paxillus involutus (Fr .) Fr. mycorrhizas was found to be only 10% of that found in white, tu rgid, 1- or 4-month-old specimens. This supports the hypothesis that t he compound is a good indicator of living fungal biomass. Ageing had a lesser effect on chitin concentrations since the chitin levels found in 7-month-old mycorrhizas were still 60% of the levels found in 1- an d 4-month-old specimens. Consequently, the chitin:ergosterol ratio inc reased from about 14 to 19 in 1- and 4-month-old mycorrhizas respectiv ely to about 110 in 7-month-old mycorrhizas. In the second set of expe riments, we found that variation in plant growth had no effect on the chitin:ergosterol ratio in whole root systems of either Alnus incana ( L.) Moench or Pinus sylvestris mycorrhizal with Paxillus involutus. In the third set of experiments, we found a constant relationship betwee n the two marker concentrations in 10-month-old root systems of Pinus sylvestris, regardless of fungal species involved, using Paxillus invo lutus, Piloderma croceum Erikss. & Hjorts and Suillus variegatus (Fr.) O. Kuntze as test organisms. Taken together, the results of this stud y suggest that both chitin and ergosterol give reliable, but different , relative measures of fungal biomass in mycorrhizal roots. Furthermor e, we demonstrate that, in combination, the two chemical markers can b e used to estimate both total and living fungal biomass (derived from the chitin:ergosterol ratio).