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Grants:"Nutrient cycling in response to forest growth at elevated CO2 (FACE)", NSF, $368,401, 1999 - 2002
Description:We are investigating changes in nitrogen cycling within the loblolly pine forest of the Duke Forest FACE Project. This work aims to provide budgets for the intrasystem cycle of nutrients in the forest, including estimates of plant uptake, plant requirements, nutrient-use efficiency, and nutrient return on an annual basis for the entire ecosystem and for individual species in the forest. Preliminary results (Finzi et al. 2001) indicate no large changes in nutrient-use efficiency within the pine forest, and a large, unexplained internal source of nitrogen to support the growth increment observed during the initial years of fumigation.
Future work in this project will include an 15N-tracer addition study to examine changes in nutrient availability, demand, and competition among uptake processes (e.g., plants vs. microbes) in the FACE forest. These studies will include measurements of soil microbial biomass, gross and net nitrogen mineralization, rhizospheric N cycling, and plant uptake of the applied 15N tracer.
Kirsten Hofmockel has recently completed a study of asymbiotic soil N-fixation in the FACE forest, finding rather low rates and no significant differences in rates between control and fumigated plots of the experiment.