Characteristics of N Mineralization in Urban Soils of Hefei, East China

Abstract

Nitrogen cycling has been poorly characterized in urban ecosystems. An in-situ buried bag incubation technique was used to quantify net rates of N mineralization and nitrification in soils of two urban sites, a street greening belt and a university campus, and a suburban site, a forest park, in Hefei, East China. The average concentration of extractable NO − 3 in the surface soil (0–10 cm) was significantly higher at the urban sites than the suburban park site, whereas extractable NH + 4 concentration was significantly higher at the suburban park site than the urban sites. The forest park soil had greater potential N mineralization (148.1 μg N cm −3) than the soils from the campus (138.3 μg N cm −3)and street (99.8 μg N cm −3). The net mineralization rates varied between 1.63 and 2.69 μg N cm −3 d −1 and net nitrification rates between 0.82 and 1.02 μg N cm −3 d −1 at the suburban forest park site, but the rates varied from 1.27 to 2.41 μg N cm −3 d −1 and from 1.07 to 1.49 μg N cm −3 d −1, respectively, at the urban campus site. Both net mineralization and nitrification rates were lower during dry seasons. Results from regression analysis indicated that net N mineralization was significantly and positively correlated with soil moisture and soil C/N ratio, and was negatively correlated with soil pH. Relative nitrification was, however, significantly and negatively correlated with soil moisture and soil C/N ratio, and was positively correlated with soil pH. Mean relative nitrification was 0.763, indicating the dominance of nitrate cycling relative to ammonium cycling at the urban sites. The urban soils had the great potential for N losses compared to the suburban soils.