Urbanization and soil type influence prokaryotic, fungal, and metazoan communities in children’s play environments: a pilot study

Outdoor play brings young children into frequent contact with environmental reservoirs that can shape biological exposures, yet the biological composition of urban play environments remains poorly defined. In ENDEMIC-1, we surveyed in a hypothesis-generating pilot investigation 14 children’s play areas in Bielefeld (Germany), spanning daycare, public playgrounds and private gardens across urban-core and peripheral settings. At each sampling location we recorded vegetation and environmental metadata, quantified soil chemistry, and used amplicon sequencing targeting the 16S rRNA, ITS2 and CO1 genetic markers to profile bacteria and archaea, fungi and metazoans, respectively, in soil and sand substrates (n = 24). Across all taxonomic groups examined, substrate type was the dominant driver of community structure: soil versus sand explained 25.1% of variation in prokaryotic (univariate PERMANOVA R² = 0.251, p < 0.001), 12.1% in fungal (R² = 0.121, p < 0.001) and 21.7% in metazoan (R² = 0.217, p < 0.001) β-diversity. Moreover, soil showed higher α-diversity than sand for fungi (observed richness q = 0.044; Effective Number of Species (ENS) q < 0.001), metazoans (observed richness q < 0.001), and for prokaryotes ENS (q = 0.018). Urbanization was associated with bacterial and archaeal (R² = 0.076, p = 0.038) and fungal community structure (R² = 0.065, p = 0.014), with fungal composition remaining significant in multivariate models (R² = 0.043, p = 0.040). Concordance among taxonomic groups: was evident: α-diversity correlated between prokaryotes–metazoans (richness, ρ = 0.514, q = 0.007), fungi–metazoans (richness, ρ = 0.480, q = 0.026) and prokaryotes–fungi (ENS, ρ = 0.467, q = 0.020), and β-diversity concordance was supported by Procrustes tests (prokaryotes–fungi p < 0.001; prokaryotes–metazoans p = 0.005; fungi–metazoans p < 0.001). Together, these data show that small-scale substrate choices (soil versus sand) and urban context measurably structure the biotic communities of children’s play environments, parameters that may modulate everyday environmental biological exposures during early life.