ИСТИНА

The changes of composition and activity of fungal community under soil passage through digestive tract of earthworms Aporrectodea caliginosa and clarification of their mechanisms were investigated. The comparative study was done on the samples of soddy-podzolic soils, digestive tract and cast of A. caliginosa. Fungal composition was investigated by plate method. Species was identified according cultural-morphological characteristics and molecular-genetic method. Physiological state of fungi was assessed by analysis of dynamics of colonies formation on medium, metabolic activity - by Biolog approach with antibiotics for separation fungal from total microbial activity, biomass - by luminescent microscopy. Germination and vitality of spores and mycelial fragments of species were estimated in the midgut liquid of A. caliginosa. The fungal growth, N transformation and water stability of cast aggregates were studied in the incubation experiments with cycloheximide. Fungal biomass is lower in the gut and the fresh casts A. caliginosa than the soil. It increases several times after few days of incubation of the casts. During further incubation (for 2 weeks) structure of microbial biomass (pools and ratio of fungi and bacteria) becomes close to the soil. Fungal populations have longer lag-phase period and lower indexes of probability of propagation in the gut than in the soil. Sharp activation of fungi occurs after short-term incubation of the cast. Decline of metabolic activity of fungi in the digestive tract and increase in the cast was established. Fungal diversity decreases in the gut and the cast compared to the soil. Species survived in the digestive tract and developing in fresh cast were established. Germination of spores of majority of fungi was inhibited after incubation in digestive liquid of earthworms and increase only single species. Decrease of spores germination and death of mycelial fragments of some fungi was detected under short-term (1-2 min) impact of the digestive liquid. Activities of immobilization, ammonification, nitrification and denitrification in the fresh casts were higher than in the soil, N2-fixation - lower. Fungal immobilization of N in the casts is significant mechanism of the decline N losses from soil in the form of nitrous oxide. The inhibition of fungal growth by cyclohemide decrease of water stability of cast aggregates on 15-20%.