Management matters: homogenized plant–soil linkages constrain carbon cycling in urban green spaces

Urban green spaces (UGSs) have been promoted as nature-based solutions for climate change mitigation and biodiversity conservation. Most UGS planning and studies use vegetation cover as a proxy for soil ecosystem function, yet management practices may alter aboveground-belowground interactions that underpin soil biodiversity and biogeochemical processes, limiting the effectiveness of UGSs in delivering ecosystem services. Here, we trace aboveground-belowground linkages through a comprehensive assessment of plant composition, ground invertebrate communities, soil dissolved organic matter (SDOM), microbial enzyme activities, and surface soil organic matter (SOM) across tree and grass covers in three managed urban parks. We hypothesized that tree cover would enhance soil carbon sequestration through recalcitrant litter inputs and ground invertebrates, while grass cover would foster rapid nutrient cycling with lower SOM through labile litter inputs. Contrary to expectations, SOM was significantly lower under tree cover, accompanied by homogenized ground invertebrate abundance, SDOM composition, and microbial C: N acquisition strategies compared to grass cover. Structural equation modeling revealed that SOM accumulation was not linked to woody inputs but instead to rapid microbial processing of degraded labile inputs mediated by soil moisture. By integrating multiple above- and belowground properties, our study highlights how routine management of leaf litter removal can homogenize plant-soil linkages, regardless of plant traits, and constrain carbon cycling in UGSs. These findings underscore the need for urban landscape design and adaptive management to preserve functional connections from plants through microbial processes to sustain ecosystem multifunctionality.