PARENT SESSION
Oral Session #35: Carbon and Nitrogen Cycling.
Presiding: D. Rothstein
Tuesday, August 6. 8:00 AM to 11:30 AM. Palo Verde Room, Radisson.

Effects of elevated CO₂ on nitrate leaching and denitrification in herbaceous ecosystems.

Leadley, Paul^*,1, Barnard, Romain¹, Barthes, Laure¹, ¹ Laboratory of Ecology, Evolution and Systematics, Orsay, France

ABSTRACT- Nitrogen availability often strongly limits plant productivity and soil carbon storage in temperate ecosystems; therefore, it is essential that we develop a better understanding of the effects of climate change on neglected aspects of nitrogen cycling such as nitrification, denitrification, and nitrate leaching. We have examined the effects of elevated CO₂ on these processes in herbaceous mesocosms planted with Holcus lanatus, Festuca rubra, and/or Rumex acetosa. We find that soil nitrate concentrations and nitrate leaching are always significantly lower at elevated CO₂. The reduction in nitrate concentrations appears to be primarily related to increased plant uptake capacity and microbial N immobilization. However, nitrification increased and denitrification decreased at elevated CO₂, both of which would tend to increase nitrate concentrations. Comparisons with other studies suggest that decreased soil nitrate concentrations and nitrate leaching are a common response to elevated CO₂, but the mechanisms that led to these changes vary greatly. Of particular importance is the highly variable response of denitrification, because this compromises our ability to predict the effects of CO₂ on N₂O release in terrestrial ecosystems.

KEY WORDS: Nitrification, Nitrate , Leaching, Denitrification