Seasonal variation in protein, ergosterol and chitin in five morphotypes of Pinus sylvestris L. ectomycorrhizae in a mature Swedish forest

Pine ectomycorrhizae were collected from bedrock and moraine sites in a mature Pinus sylvestris L. forest in the vicinity of Uppsala, Sweden, on four occasions over the period of a year. Ectomycorrhizae were examined microscopically and five characteristic types ( Piloderma, tuberculate, Lactarius-like, Russula-like and an unidentified pink) were described and used for further biochemical assays. Total protein, ergosterol and chitin extractions were performed in sequence for each sample of distinct mycorrhizal morphotype. Differences between sites (bedrock moss vs moraine) from which the morphotypes originated were small, except for an increase in protein in Piloderma and tuberculate mycorrhizae on moraine sites in July and January. However, there were significant variations in protein and chitin concentrations and in the ergosterol-to-chitin ratio, both between seasons and mycorrhizal types. Protein concentrations were significantly higher in the winter samples for Piloderma, tuberculate and pink mycorrhizae and were at a minimum in the early summer. Chitin concentrations peaked in both early summer and winter for all morphotypes, significantly so for Piloderma and tuberculate mycorrhizae, but remained low during mid-summer and fall. Although the seasonal differences in ergosterol concentrations were small, a significant correlation was found between chitin and ergosterol for Piloderma mycorrhizae. For all morphotypes, the ergosterol-to-chitin ratio varied seasonally from low January values increasing to high values in October, the end of the season of maximum fungal growth. The small seasonal variation in ergosterol and development of the ergosterol-to-chitin ratio suggests that ergosterol remains a better indicator of vital fungal biomass than chitin or other available measures.