Urbanization impacts nitrogen cycling and alters the microbial community composition in soils

Many populations around the world are transitioning from rural to urban living, which causes landscape changes and alters the functionality of soil ecosystems. It is unclear how this urbanization disturbs the microbial ecology of soils and how the disruption influences nitrogen cycling. As a test case of this, Xiamen City, China has undergone a rapid urbanization in recent years. In this study, microbial communities in turfgrass soils from urban and suburban areas around Xiamen were compared to communities in agricultural soils from rural areas. Results showed that the activities and abundances of nitrifying and denitrifying guilds significantly varied according to soil types (turfgrass and agricultural soils). High nitrate concentrations in urban soils indicate that the over fertilization of turfgrass soils might lead to increasing N2O emissions, predominantly through nitrification. In addition, the greater abundance of ammonia oxidizing archaea (AOA) compared to ammonia oxidizing bacteria (AOB) in urban turfgrass soils suggests that AOA are chiefly responsible for emitting N2O in urban ecosystems. The overall bacterial community diversity was significantly lower in urban and suburban turfgrass soils compared with rural agricultural soils. Microbial community composition was distinctly grouped along this urbanization gradient (urban, suburban and agricultural), which can in part be attributed to the differences in soil properties. These findings reveal the effects of urbanization on soil microbial communities and their involvement in biogeochemical cycling of nitrogen.