Comparison of soil organic carbon and nitrogen dynamics between urban impervious surfaces and vegetation

Impervious surfaces (IS) are widespread globally due to increasing urbanization, and relatively static carbon (C) and nitrogen (N) processes are usually expected in these soils. However, an understanding of how soil organic carbon (SOC) and soil organic nitrogen (SON) dynamics under IS in comparison with urban vegetation is still lacking. Here we used soil fractionation and stable isotopic analysis to examine C and N dynamics in IS soils and soils that were vegetated for 20-30 years in Guangzhou and Shenzhen, China. Soil samples from bare land (CK) and other land uses (grass, forest, and IS) were split into different chemical fractions. The C and N content, C:N ratio, delta C-13, delta N-15, C and N recalcitrant indices (RIC, RIN), and mean residence time (MRT) were analyzed. The results showed that soil C and N stocks increased in the first (20 years) as reflected in the enhanced labile (LP) and recalcitrant C pools (RP), but then stabilized or decreased after 30 years with the IS ages in both cities. IS had a lower SOC decomposition rate and thus resulted in 5-10-times longer MRT (259-465 years) than that in vegetated soils (39-55 years). The study showed that IS caused remarkable changes in soil C and N pools and turnover rates compared with vegetated lands. Our results are potentially useful for better understanding, predicting, and managing soil C dynamics under urbanization.