The structure and function of the vegetative mycelium of ectomycorrhizal plants

summary The nutrient mobilizing activities of mycelia of two ectomycorrhizal fungi, Suillus bovinus (Fr.) O. Kuntze and Thelephora terrestris (Ehrh.), were investigated in transparent root observation chambers to which were added discrete weighed samples of organic matter collected from the fermentation horizon of a pine‐forest soil. The mycelia grew from mycorrhizal plants of Pinus sylvestris L. over a homogeneous humified peat and colonized the introduced fermentation horizon organic matter (FHOM). The chronology of intensive mycelial exploitation of the FHOM was followed, and its nutrient status was monitored before and after colonization by the fungal mycelia. The time from initial colonization to early senescence of mycelial patches was c. 40 d. Colonization by S. bovinus reduced concentrations of nitrogen (N), phosphorus (P) and potassium (K.) in FHOM by 23, 22 and 30%, respectively, whereas colonization by T. terrestris led to decreases of N and K of 13 and 21 % respectively, but did not change P concentration. There were increases in calcium and magnesium concentration following colonization by terrestris. Analyses of the inorganic N pool of uncolonized FHOM incubated separately suggested that mineralization rates were inadequate to explain the loss of N from the colonized material. The carbon to nitrogen ratio of material colonized by both fungi increased greatly relative to that in uncolonized material. The significance of these nutrient transfer processes is discussed in relation to element cycling processes in boreal forest ecosystems.