Urban land use influences microbial functional traits along a management intensity gradient

Under the manicured lawns of city parks and the fertilized turf of football pitches, an invisible ecosystem is being quietly reorganized. A new study from Blois, France, reveals that the intensity with which humans manage urban green spaces acts as a powerful ecological filter, reshaping the functional traits, life strategies and interaction networks of the soil microbes that underpin urban soil health. The findings, published in Frontiers in Microbiomes, suggest that the way cities mow, fertilize and water their green spaces may matter as much for belowground biodiversity as the type of land use itself.

Urbanization is one of the defining land transformations of the modern era. Between 2000 and 2018, more than one million hectares of land were urbanized in Europe, over eight times the area that reverted to agriculture or nature. Urban soils endure simultaneous disturbances, including construction, pollution, trampling and compaction, creating a patchwork of heterogeneous microhabitats. Yet while the effects of urbanization on plants and animals have been studied extensively, the functional consequences for soil microbial communities remain poorly understood, leaving a critical gap in global microbial ecology.

To address this, researchers sampled 135 soils across eight land-use types in Blois, a mid-sized city in central France. The sites ranged from showcase gardens in the historic old town and heavily modified sports fields to parklands, roadsides, residential green spaces, tree-lined paths and unused areas reserved for future development. Each site was assigned a management intensity level from 1 to 4, spanning minimally managed grass mowed once or twice a year to intensively managed turf mowed up to 25 times annually with residue export, watering, scarification and, in the highest category only, fertilizer inputs. Bacterial and fungal communities were characterized using Illumina sequencing, fungal guilds were identified with the FungalTraits database, bacterial taxa were classified by life strategies, enzymatic activities were measured, and co-occurrence networks were constructed.

The results showed that land-use type and management intensity strongly influenced microbial composition, diversity and functioning. Highly managed sites such as gardens and sports fields exhibited lower fungal 18S rRNA gene abundance, higher bacterial 16S rRNA gene copy numbers, reduced diversity and lower nitrogen-related enzyme activities compared to less managed unused areas. Bacterial and fungal richness peaked at the intermediate management intensity, consistent with the intermediate disturbance hypothesis, before declining at the highest level, possibly reflecting soil acidification and nutrient imbalances associated with intensive nitrogen inputs. Sports fields had the lowest fungal richness of any land use, a pattern the authors suggest may stem from fungicide application selectively suppressing non-targeted fungi.

Bacterial life strategies shifted along the management gradient in ways that echo the copiotrophic–oligotrophic continuum. Oligotrophic bacteria, slow-growing taxa adapted to low nutrient availability, were more abundant in unused areas, while copiotrophic Proteobacteria dominated residential soils, likely fueled by heterogeneous organic inputs such as pollutants, pet waste and runoff. Mediation analyses revealed functional consequences of these shifts: copiotrophic Proteobacteria partially mediated the relationship between β-glucosidase activity and soil carbon and nitrogen contents, while oligotrophic Actinobacteria prevalent in unused soils were associated with the decomposition of recalcitrant organic matter and higher carbon-acquisition enzyme ratios.

Fungal communities told a complementary story. Saprotrophic fungi represented the dominant guild in urban areas at 62 percent, followed by plant pathogens at 25 percent. Contrary to expectations based on nitrogen fertilization studies, saprotrophs were not more abundant in fertilized areas; instead, their proportion was higher in less managed soils, likely reflecting greater availability of undecomposed organic materials. Mycorrhizal fungi, unexpectedly, were not more abundant in tree-covered areas than elsewhere. Instead, host-tree identity and symbiotic association type, whether arbuscular or ectomycorrhizal, emerged as stronger determinants of mycorrhizal abundance than land use or soil properties, an insight with direct implications for urban tree planting choices.

Perhaps the most striking findings concerned microbial interaction patterns. Co-occurrence networks constructed from the urban soil communities were consistently less connected than those reported for semi-natural ecosystems such as forests, grasslands and shrublands, indicating more fragmented microbial associations in urban soils. Within the city, unused areas displayed the highest connectivity, with bacterial networks showing large connected components, high clustering coefficients and short average path lengths, while roadsides showed the lowest connectivity. Fungal networks were markedly more interconnected than bacterial ones across all land uses, with positive edge percentages exceeding 97 percent in tree networks.

The authors caution that co-occurrence networks do not provide direct evidence of ecological interactions or resilience, and that network structure is highly sensitive to methodological choices. Still, the reduced connectivity observed in intensively managed sites may indicate shifts in community organization consistent with stronger ecological filtering, potentially reducing functional redundancy and soil ecological resilience. Soil properties, particularly carbon content, nitrogen availability and pH, emerged as primary determinants of microbial richness, diversity and composition, sometimes overshadowing land-use effects, and legacy effects from past land use in this relatively young urban area likely contributed to long-term shifts in microbial communities.

Because all soils were collected during a single season, the dataset does not capture temporal fluctuations driven by temperature, moisture, plant phenology or seasonal management practices, a limitation the authors acknowledge. Future work incorporating repeated seasonal sampling, private gardens, bare soils and engineered soils would help clarify how temporal variability interacts with land use and management intensity to shape microbial communities across the year.

The study’s central message is that management intensity acts as a strong ecological filter shaping microbial functional traits and interaction patterns in urban soils. The reduced connectivity and functional shifts observed in intensively managed sites highlight the need to integrate microbial indicators into urban green-space planning and management. As cities continue to expand and green spaces come under increasing pressure, understanding how microbial communities contribute to nutrient cycling, organic matter decomposition and soil resilience will require moving beyond taxonomic inventories toward functional and interaction-based approaches, ensuring that the invisible ecosystems beneath our feet are not left out of the sustainability conversation.

Subject of Research: Urban soil microbial ecology along a management intensity gradient

Article Title: Urban land use influences microbial functional traits along a management intensity gradient

Article References: Khalfallah, F., Legay, N., Bonthoux, S., Cantarel, A. A. M., Clement, J.-C., Foulquier, A., Joulian, C., Le Roux, X., Richaume, A., Norini, M.-P., & Harris, J. (2026). Urban land use influences microbial functional traits along a management intensity gradient. Frontiers in Microbiomes, 5, Article 1946255. https://doi.org/10.3389/frmbi.2026.1946255

Image Credits: AI Generated

DOI: 10.3389/frmbi.2026.1946255

Keywords: urban soils, microbial communities, management intensity, soil microbiome, co-occurrence networks, urban green spaces, soil enzymes, bacterial life strategies, fungal guilds, urbanization, Urban, land