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.