PARENT SESSION
Thursday, August 10, 1:30-5:00 pm
COS 102 - Arid ecosystem ecology
L-14, Lobby Level, Cook Convention Center
Presiders: J Fehmi
The role of water, nutrients, and temperature in regulating NO and NH3 efflux from Mojave Desert soils.
McCalley, Carmody*,1, Sparks, Jed1, 1 Cornell University, Ithaca, NY
ABSTRACT- Gaseous reactive nitrogen compounds produced during terrestrial N cycling play an important role in the atmospheric chemistry defining climate and air quality. Nitric oxide (NO) released during microbial nitrification and denitrification is a precursor to ozone production in the troposphere while ammonia (NH3) volatilized during organic matter decomposition provides a nucleation site for the formation of secondary organic aerosols, influencing cloud generation and global temperature. Field measurements in the Mojave Desert suggest that spatial heterogeneity in nutrients and seasonal changes in temperature and precipitation control NO and NH3 efflux from soils. To elucidate the mechanisms driving field observations, I combined NO and NH3 soil flux measurements with laboratory manipulations of temperature, water, and nutrient conditions using intact soil profiles. At summer temperatures (35°C), soil wetting caused a short, intense pulse of NH3 (3 to 6 nmol m-2 s-1) followed by several days of elevated NO emissions (1.5 to 3 nmol m-2 s-1). Maximum NO efflux at 35°C was 3 times higher than at 17.5°C; however, NH3 emissions were unaffected by temperature. Supplementation of water with NO3- extended the period of high NH3 emissions and caused a 2 to 3 fold increase in NO efflux, while addition of labile carbon reduced N gas emissions. Our study suggests that NH3 efflux responds primarily to addition of water whereas NO efflux is modulated by temperature and nutrient constraints on microbial activity. Addition of labile C appears to stimulate microbial immobilization of N, reducing gaseous N loss, whereas addition of NO3- stimulates NO and NH3 efflux.
Key words: desert, nitrogen cycling, biogeochemistry