Seasonal Dynamics of Microbial Biomass in Soddy-Podzolic Soil

— The seasonal dynamics of the structure of microbial biomass in a soddy-podzolic soil under fallow was assessed using luminescent microscopy. Samples from three soil horizons (P, 5‒15 cm, BEL, 30‒40 cm, and BT2, 50‒60 cm) were sampled monthly from March, 2017 to February, 2018, in the territory of Eldigino experimental station (Moscow oblast). In addition to microbial biomass measurement, soil temperature and moisture were recorded. The microbial biomass at all sampling times was dominated by fungi (up to 93%). Minimal microbial population and biomass were observed in the period from November to March. The biomass of prokaryotes increased twofold in May, the maximal values were observed in August and September. The length of actinomycete mycelium was maximal in July and August, when the soil water content was the lowest. Maximal fungal biomass was observed in July and September. Seasonal changes of microbial biomass were most pronounced in the upper soil horizon P, while they were more even in the BEL and BT horizons. Using regression analysis, we revealed a significant effect of temperature and sampling depth on the fungal and prokaryotic biomass. The results indicate substantial seasonal variations in biomass of soil microbiota, which should be taken into account when comparing soils sampled at different seasons.