The structure and function of the vegetative mycelium of ectomycorrhizal plants

summary The relationships between colonization of fermentation horizon organic matter (FHOM) by an ectomycorrhizal fungus and the activities of enzymes involved in key processes of nitrogen (N) and phosphorus (P) mobilization were investigated. FHOM was collected from a birch forest and placed in transparent observation chambers with (M) or without (NM) plants of Betula pendula Roth, the roots of which were infected by Paxillus involutus (Fr.) Fr. The fungus colonized the FHOM of the M chambers, and after different periods of occupation the activities of protease, polyphenol oxidase, peroxidase and phosphomonoesterase were determined in colonized and uncolonized substrate. Activities of protease and polyphenol oxidase increased in organic matter that had been occupied for 28–50 d, and remained elevated in FHOM that had been occupied for 50–98 d. However, although activity of phosphomonoesterase increased in FHOM that had been colonized for 28–50 d, amounts in FHOM colonized for 50–98 d decreased to below that found in uncolonized material. No difference in peroxidase activity was detected between colonized and uncolonized organic matter. The results are discussed in relation to the role of ectomycorrhizal fungi in nutrient cycling processes in temperate forest ecosystems.