Carbon fluxes and nitrogen availability along an urban-rural gradient in a desert ecosystem

Urbanization has increased globally over the past century, and this trend is expected to continue. Much of the new urban expansion is occurring in arid and semi-arid regions of the world. Urbanization impacts ecosystem processes directly through habitat destruction and fragmentation and indirectly through climatic changes and pollution deposition. In the Phoenix, Arizona metropolitan area, urbanization has been shown to increase CO₂ concentrations, nitrogen (N) deposition and nighttime temperatures. We investigated the soil CO₂ efflux and soil carbon (C) dynamics in undisturbed Larrea tridentata communities along an urban – rural gradient in the Central Arizona – Phoenix Long-Term Ecological Research (CAP – LTER). We measured soil respiration rates as well as total N, nitrate and organic C concentrations in soils along the gradient. Total N, nitrate, and organic C were significantly higher in the urban locations compared to both suburban and rural locations under the canopy of L. tridentata and in interplant spaces. Monthly soil respiration measurements were predominately higher at the rural sites both under the canopy and in the interplant spaces. Annual soil respiration was also significantly higher at rural sites compared to urban sites. Urban sites also exhibited no significant difference in soil respiration and total N between the canopy and interplant spaces while the difference was significant at both the rural and suburban sites. Regressions indicate that soil respiration at the urban locations is not as dependent on soil moisture and temperature as outlying rural areas. Although structural differences along the gradient are minimal, the data suggest the functioning of desert ecosystems in an urban setting is altered.