Microbial C-availability and organic matter decomposition in urban soils of megapolis depend on functional zoning

Urbanization has various strong effects on soil processes. Despite an increasing number of studies focused on soil carbon (C) distribution and stocks within cities, the C and nutrient availability to microorganisms and their capacity to decompose organic matter remain nearly unknown. The factors responsible for these processes in megacities are characterized by a very high spatial heterogeneity and therefore, their effects should be investigated as related to specific environmental conditions – common for urban functional zones. This study focuses on the examination of the texture, C, available phosphorus (AP) and potassium (AK), mineral nitrogen, pH, and heavy metals (HMs) contents considering microbial C-availability (ratio of microbial biomass to C) and organic matter decomposition (BR) in soils of Moscow megapolis. The sampling sites were referred to recreational, residential and industrial zones. In the industrial and residential zones, the pH, AK, AP, and HMs were increased compared to recreational. Concurrently, the microbial С-availability and BR were much less in these zones. The high pH and AP content had negative effects on the BR for all soils. Soil segregation into groups (C-poor and C-rich, light texture and heavy texture) reduced heterogeneity and showed the additional patterns. In C-poor soils, the AP effect on BR was confirmed, but not of pH. The AK and Cu contents had negative effects on C-availability for C-poor and light soils, respectively. We conclude that careful control of the soil phosphorus and potassium contents as well as texture is necessary for planning the soil construction in megacities to consider their optimal functioning.