Urbanization enhances soil nitrogen mineralization mainly by increasing particulate organic nitrogen fractions in urban park greenspaces: A case study in Hangzhou, China

In addition to the direct input of inorganic nitrogen (N), the supply of plant-available N driven by soil organic N mineralization is crucial for the development of urban greenspaces, which are essential components of urban ecosystems. Soil N mineralization may vary with urbanization, but the responses of soil N mineralization to different urbanization intensities remain controversial. In this study, we investigated the responses of urban park soil (planted with trees, shrubs or grasses) N mineralization to different urbanization intensities (low, medium and high) in Hangzhou, China. To further evaluate the relative importance of soil organic N fractions in explaining variations in N mineralization, we analyzed the responses of soil particulate organic N (PON) and mineral-associated organic N (MAON) to different urbanization intensities, as well as their relationships with N mineralization. Our results indicated that soil N mineralization increased with increasing urbanization intensity, likely due to increases in soil organic carbon concentration, clay content, microbial biomass and activity under high urbanization intensity. Notably, compared to soil MAON , the increase in soil PON induced by urbanization was more pronounced, and its relationship with soil N mineralization was stronger. Furthermore, soil N mineralization and its relationships with soil organic N fractions varied substantially among different vegetation types . These findings suggest that researchers and urban planners should evaluate the N supply mineralized from soil organic N fractions, particularly PON fractions, to optimize N and vegetation management strategies in urban greenspaces under different urbanization intensities. • Urbanization increased soil net nitrogen mineralization rates (Nmin). • Soil Nmin under trees presented significantly higher than those under grasses. • Relationships of soil Nmin and organic N fractions varied with vegetation types. • Particulate organic N was more crucial for the increase in soil Nmin.