Diversified Portfolios of Bacterial Communities in Peri-urban Miyawaki Forests and Grassland Shaping Ecosystem Functions and Services

Soil microflora is fundamental to ecosystem functioning, yet their contribution in Miyawaki afforestation, a globally implemented ecological engineering approach, remains poorly characterized. In the present study, we examined the bacterial taxonomic diversity and their functional potential in a peri-urban Miyawaki mini-forest and compared with a nearby grassland the pre-existing ecosystem across dry and wet seasons. The Miyawaki plantation comprised of highly diverse native trees, sub-trees and shrubs spanning evergreen and deciduous varieties, potentiating nitrogen-fixation, diverse litter generation and rooting strategies resulting in pronounced functional heterogeneity. Notably relative to grassland, the Miyawaki forest was intensively managed and supplemented with organic amendments, and supportive irrigation, buffering the seasonal moisture stress. Using 16S rRNA amplicon sequencing of soil eDNA, we characterized seasonal variation in soil bacterial communities in both the systems. The observed soil bacterial community organization in forest as compared to the unmanaged grassland indicates combined influence of vegetation structure, dense canopy cover, continuous litter generation and root exudates. Microbial assemblages in the forest specialised in heterotrophic complex carbon degradation, biofilm formation, exopolysaccharide production and sporulation pathways which suggests adaptive abilities to anoxic microsites and other stressful conditions. In contrast, grassland soils harboured less diversified bacterial communities dominated by phototrophic and oxidative stress adaptation pathways consistent with sun lit, non-irrigated and moisture-variable conditions. Nonetheless, functional divergence in dry season reflects temporal reorganization of microbial communities marking a gradual trend towards soil ecosystem development. Together, these findings establish microbial baseline for Miyawaki forests revealing how tree-dense mini-forests restructure soil bacterial communities relative to grasslands highlighting the value of identifying soil microbial indicators for critically evaluating urban afforestation outcomes over extended time scales to inform sustainable design and policy. Graphical abstract Schematic representation of the study depicting the Miyawaki forest and nearby grassland.