Labile carbon input substantially increases priming effect in urban greenspace soils

Urban greenspace soils can store equal amount of carbon, or even more, compared to agricultural and forest soils, and play an important role in carbon sequestration. Despite its importance, the patterns and drivers of the priming effect-a key and complex process in soil organic matter decomposition-in urban ecosystems remain poorly understood. Here, we sampled soils in urban lawns, suburban lawns, and forests, and conducted a 30-day microcosm incubation with ¹³C-labelled glucose and nitrogen additions to explore whether and how the intensity of soil organic matter priming effect differs between urbanized and forest ecosystems. We found that lawn soils in urban (7.01 mg C g^-1 SOC) and suburban (5.86) areas had a significantly higher intensity of priming effect than forest soils (1.34), with further enhancement observed in urban lawn soils through simulated nitrogen deposition. Moreover, the alpha diversity of soil bacteria and fungi was found to play a crucial role in modulating the priming effect, exhibiting a positive correlation with its intensity. These findings advance our understanding of the potential mechanisms behind the soil priming effect in urban greenspaces, providing crucial insights for predicting soil carbon stocks and environmental impacts of urban development.