Properties of the techno-humus systems at a former cooking plant site drives the diversity of fungal and bacterial soil communities

Technosols are characterized by wide vertical and horizontal heterogeneity, and understanding their pedological and ecological functioning remains a challenge. In forest ecosystems, soil microbiological communities in the humipedon are depicted as relevant functional indicators; however, their relevance for Technosol humipedon is still to be investigated. Our study aimed to clarify the factors that shape the microbial community of previously described Techno-humus systems by investigating the bacterial and fungal community on a former coking plant. We compared three soils (a Cambisol and two Technosols) with physical and chemical heterogeneity that resulted in different vegetation, humus forms, and edaphic faunal communities. The bacterial communities were mainly adapted to the scale of the soil horizon (organic or technogenic), while the fungal communities were adapted to each of the three stations with a lesser influence of the soil horizon. The technogenic horizon hosted a lower microbial diversity (fungal and bacterial), and the bacterial community was richer in oligotrophs. The proportion of saprophytes, ectomycorrhizal, and arbuscular mycorrhizal fungi varied depending on the station for each fungal community. Among the soil parameters, the EDTA-extractable Zn in the soil horizons was more correlated to the structure of the bacterial communities than the fungal communities, while, conversely, Cd contamination had impacted fungal diversity more than bacterial diversity. Our results revealed that interactions between fungi and trees have persisted on Technosols, shaping the fungal communities, at least partially, while bacterial diversity was more changed by the highly heterogeneous soil horizons studied. • Cd contamination had impacted fungal diversity more than bacterial diversity. • Zn in the soil horizons was more correlated to the structure of the bacterial communities. • Vegetation cover is an important driver especially for fungal diversity. • Bacterial community adapts at the scale of the horizon, less based on forest station. • Fungal community adapts at the scale of forest station, less based on the horizon.