PARENT SESSION
Oral Session #82: Urban Ecology.
Presiding: M. Cadenasso
Thursday, August 8. 9:00 AM to 11:30 AM. Grand Ballroom East, Radisson.

Seasonal responses of soils to water and nitrogen along an urban to rural gradient.

KOERNER, BRENDA^*,1, KLOPATEK, JEFFREY¹, ¹ Arizona State University, Tempe, Arizona

ABSTRACT- More than 30% of the world's population lives in arid and semi-arid regions. It is expected that the proportion and total numbers of individuals in these areas will increase, expanding into surrounding natural and agricultural ecosystems. Urban areas present dynamic mesocosms in which to study the effect humans and land-use changes have on urban ecosystem processes. The key question we are asking is: how does urbanization affect the movement of carbon through arid ecosystems? We are evaluating the effects of urbanization on creosote bush (Larrea tridentata) communities along an urban to rural gradient. Water and nitrogen were added to plots in July 2001 and December 2001/Janurary 2002. Soil CO₂ efflux was measured the day of treatment (prior to treatment), day after treatment and 7 days following the treatment using an Infrared Gas Analyzer (IRGA). During July 2001, soil CO₂ efflux was significantly higher in plots that received water and water-nitrogen additions compared to plots receiving nitrogen or no treatment. In winter months, almost no response to any treatment was observed. Water treatment responses were also twice as high under the canopy compared to interspaces. Additionally, soil CO₂ efflux was higher at urban sites than suburban or rural sites. Urbanization appears to increase soil CO₂ efflux in response to summer rains. In contrast, nitrogen deposition only minimally affects soil CO₂ efflux even in the presence of water.

KEY WORDS: urbanization, soil CO₂ efflux, Larrea tridentata, arid ecosystem