PARENT SESSION
Oral Session # 80: Urban Ecology II: Soils and Streams.
Presiding: J Ehrenfeld
Thursday, August 7. 1:30 PM to 5:00 PM, SITCC Meeting Room 105.

Soil responses to water and nitrogen additions along an urban to rural gradient.

Koerner, Brenda ^*,1, Klopatek, Jeffrey ¹, ¹ Arizona State University, Tempe, Arizona

ABSTRACT- Over 50% of the world population lives in urban environments, and the proportion of the world population in urban areas is expected to increase. Urban cities present dynamic mesocosms in which to study the effect humans and land-use changes have on urban ecosystem processes. Urbanization can affect temperatures through the heat island affect, precipitation through convection of heat, and nitrogen availability through increased nitrogen deposition. This has led to the question: how do urbanization factors affect the movement of carbon through arid ecosystems? To address this question, we are evaluating the effects of urbanization on the creosote bush community along an urban to rural gradient. Water and nitrogen additions were added to plots during the summer monsoons of 2001 and 2002, and during the winter of 2001. 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. Nitrate and ammonium availability was also determined concurrently with soil CO₂ efflux measurements. During summer additions, soil CO₂ efflux was significantly higher in plots that received water and water-nitrogen additions compared to plots receiving nitrogen or no treatment. During winter treatments, nearly no response to any treatment was seen. Water treatment responses were also twice as high under the canopy compared to interspaces. Additionally, the soil CO₂ efflux was higher at the urban site than at the suburban or rural sites. Nitrogen availability may also help explain differences in soil CO₂ efflux between sites.

Key words: desert , nitrogen, urban ecosystems, soil CO₂ efflux