Effect of a constructed technosol on the microbial functional diversity in an urban afforestation site

The rising expansion of urban environments worldwide highlights the need to develop nature-based solutions. These technologies support the development of green urban areas, mitigate environmental and health risks, and allow the recovery of degraded soils. In this study, the effect of a constructed urban technosol on the soil microbial functional diversity was investigated through metagenomics in a site located in the city of Turin (Northern Italy, Europe) and compared with control soil plots. The effectiveness of the nature-based solution, which included soil amendment with compost and microbial inoculum, was monitored three years after the deployment and related to soil physico-chemical features and vegetation assembly. The microbial functional diversity thriving in the technosol was profoundly different compared to the surrounding control soil and applied amendments - compost and microbial inoculum - seems to have largely contributed to the microbiota assembly and functioning. The constructed technosol showed lower nitrification and increased denitrification, but increased prokaryotic diversity. This indicated that a tailored design of technosols, including taxonomic and functional diversity of their microbial communities, can have an impact on soil properties that in turn can greatly influence plant growth and health in urban afforestation interventions. • A soil metagenomic analysis was performed on a constructed technosol in an urban park. • Changes in assembly and functioning of the constructed technosol microbiota emerged. • Soil communities were shaped by compost and microbial inocula application. • Traces of the inoculated microbial consortia were found after three years.