Soil carbon and nitrogen cycling and ecosystem service in cities

Soil is the foundation of life as well as all ecosystem processes. In urban ecosystems, soils are spatially heterogeneous and temporally dynamic. The spatial heterogeneities of urban soils are both horizontal and vertical (Craul 1985; Forman 2014); vertically, urban soils are often characterized by multiple buried layers, so-called lithologic discontinuity (Craul 1985; Short et al. 1986), while horizontally, they are associated with different land use and land cover, and topographic variations (Band et al. 2005; Pouyat et al. 2006a; Forman 2014). Urban soils are often disturbed and compacted, contain a variety of man-made materials as fill, and have lower levels of soil organic matter (SOM) and high levels of bulk density (BD) that could negatively affect water filtration, aeration, and plant growth (Craul 1985). Urban soils are often contaminated by heavy metals (Pouyat and McDonnell 1991; Yesilonis et al. 2008) and hydrocarbon pollutants and have elevated pH and sometimes very low nutrients (Forman 2014). Yet, dynamic life exists in urban soils and important ecosystem processes affect soil formation and function in cities. The objective of this chapter is to discuss the current understandings of soil carbon (C) dynamics and nitrogen (N) cycling in urban ecosystems, and ecosystem services provided by urban soils.