Urban green infrastructure features influence the type and chemical composition of soil dissolved organic matter

In urban areas, green infrastructure (GI) has been widely developed utilizing different types of engineered soil to enhance ecosystem functions to interact with soil dissolved organic matter (DOM). However, there remains a lack of urban studies that have examined the link between GI features and soil DOM. This study, which was conducted in a typical heavily industrialized and urbanized area (Ningbo City, East China), aimed to characterize the chemical variation and composition of DOM in the engineered soil of four GI types (enhanced tree tips, ETP; street-side infiltration swales, SSIS; vegetated swales, VS; urban forests, UF). The results showed that soil organic carbon varies among the four GI types with significantly lower content in SSIS and ETP compared to VS and UF. Smaller variation was observed in the water-soluble organic carbon (WSOC) content, with UF having significantly higher content than ETP. Three humic-like substances and one protein-like substance were derived using the parallel factor analysis (PARAFAC) model. These fluorescent compositions and their spectral parameters displayed specific distributions among GI features with VS having the highest proportion of humic-like substances (C1) and the lowest proportion of protein-like substances (C4). The distribution of spectral indices indicated terrigenous sources of DOM in these GI engineered soils. Significant positive correlations were found between protein-like substances and the population density and nightlight index, while negative correlations were found between humic-like substances (C1) and these two indices. These results demonstrate significant human disturbance of the chemical composition and characteristics of GI features. Our findings suggest that the overall design and management of GI features have a fundamental influence on soil DOM that is vital for carbon cycling in urban ecosystems.