Change of ergosterol content after inorganic N fertilizer application does not affect short-term C and N mineralization patterns in a grassland soil

•Investigation of N fertilizer on microbial biomass and mineralization in grassland.•Effects of root residue presence on mineralization processes were evaluated.•No effects of fertilizer type or level on soil microbial biomass and activity.•The microbial community of the grassland soil has a high level of resistance.•Roots and inorganic fertilizer resulted in relative increase of saprotrophic fungi.