The fungal and bacterial biomass (selective inhibition) and the production of CO2 and N2O by soddy-podzolic soils of postagrogenic biogeocenoses

In the humus horizon of soddy-podzolic soils of postagrogenic cenoses and primary forests, the contributions of the fungi and bacteria were determined by the selective inhibition of the substrate-induced respiration (SIR) by antibiotics; the basal (microbial) respiration and the net-produced nitrous oxide (N2O) were also determined. The procedure of the SIR separation using antibiotics (cycloheximide and streptomycin) into the fungal and bacterial components was optimized. It was shown that the fungi: bacteria ratio was 1.58, 2.04, 1.55, 1.39, 2.09, and 1.86 for the cropland, fallow, and different-aged forests (20, 45, 90, and 450 years), respectively. The fungal and bacterial production of CO2 in the primary forest soil was higher than in the cropland by 6.3 and 11.4 times, respectively. The production of N2O in the soils of the primary and secondary (90-year-old) forests (3 and 7 ng N-N2O/g soil per hour, respectively) was 2–13 times lower than in the postagrogenic cenoses, where low values were also found for the microbial biomass carbon (Cmic), its components (the Cmic-bacteria and Cmic-fungi), and the portion of Cmic in the organic carbon of the soil. A conclusion was drawn about the misbalance of the microbial processes in the overgrown cropland accompanied by the increased production of N2O by the soil during its enrichment with an organic substrate (glucose).