Nitrogen Enrichment Enhances Soil Multifunctionality Through Distinct Drivers Across Urban, Suburban, and Rural Forests

The accelerating pace of urban expansion has profoundly reshaped urban–rural ecosystems, altering soil environments and impairing key ecological services. However, the combined impacts of urban expansion and atmospheric nitrogen (N) deposition on soil multifunctionality—the capacity to sustain multiple ecological processes—remain poorly understood. Here, we conducted a six‐year N addition experiment (2018–2024) in urban, suburban, and rural forests. Soil multifunctionality was assessed in 2023 and 2024, corresponding to the fifth and sixth years of N addition. We found significant interactive effects of N addition and forest type on soil multifunctionality. Notably, rural forests exhibited enhanced soil multifunctionality under both low‐N (50 kg N ha −1 year −1 ) and high‐N (100 kg N ha −1 year −1 ) addition, whereas only high‐N addition significantly enhanced soil multifunctionality in urban and suburban forests. Structural equation modeling based on the 2024 dataset revealed distinct regulatory mechanisms across the gradient. In rural forests, N addition enhanced leucine aminopeptidase (LAP) activity, which in turn increased fungal richness and ultimately improved soil multifunctionality. In suburban forests, N addition also mediated soil multifunctionality through LAP activity and fungal richness. Urban forests displayed attenuated microbial diversity‐functionality linkages. Instead, soil multifunctionality was primarily regulated by fine root biomass, which itself was influenced by soil dissolved N content. These findings reveal that elevated N deposition contributes to the enhancement of soil multifunctionality in all forest types, although in rural forests high N addition reduced multifunctionality compared to low N. Our study highlights that soil multifunctionality is primarily regulated by microbial diversity in rural and suburban forests, whereas in urban forests, fine root biomass plays a dominant role, emphasizing the context‐dependent importance of belowground biodiversity and plant–soil interactions. This research reveals how global change drivers jointly regulate soil multifunctionality across urbanization gradients and highlights the importance of considering both microbial and plant contributions for sustaining ecosystem services and the resilience of urban–rural environments under anthropogenic pressures.