Document: BRU-3-59-65

The effects of elevated CO₂ on nitrogen cycling in a scrub oak ecosystem: An integrated study using a long-term ¹⁵N tracer.

HUNGATE, B.A.* ¹, P.DIJKSTRA ², G.HYMUS ², J.A.LANGLEY ¹, D.W.JOHNSON ³ and B.G.DRAKE ²

Northern Arizona University, Flagstaff, AZ 86011 USA ¹
Smithsonian Environmental Research Center, USA ²
Desert Research Institute, USA ³

Abstract:
We previously reported that elevated CO₂ increased nitrogen (N) fixation and decreased soil N mineralization in a scrub-oak ecosystem, changes in the N cycle that represent positive and negative feedbacks (respectively) to increased plant growth. These results reflect a general problem in our current understanding of the effects of elevated CO₂ on N cycling, where past short-term studies have identified a broad suite of possible changes in N cycling in response to elevated CO₂, but have been less useful in assessing integrative effects, for example, whether net feedbacks to plant growth are positive or negative. To address this, we began a long-term ¹⁵N labeling experiment in the Florida scrub-oak system in June of 1998. Results to date show a sustained increase in N fixation and above-ground N uptake in response to elevated CO₂, with little change in microbial ¹⁵N content. These results suggest that changes in nitrogen cycling may represent a positive feedback to plant growth in response to elevated CO₂.

Keywords: elevated CO2, N cycling, 15N

This abstract is being presented at: 8:45 AM in session:
Oral Session #40: Elevated CO₂ In Forest Systems.