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Long- and short-term effects of fire on nitrogen cycling in tallgrass prairie
Authors:Dennis S. Ojima  D. S. Schimel  W. J. Parton  C. E. Owensby
Affiliation:(1) Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, Colorado, 80523;(2) Climate System Modeling Program, NCAR, 1850 Table Mesa Drive, P.O. Box 3000, Boulder, CO, 80303;(3) Department of Range Science, Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, Colorado, 80523;(4) Department of Agronomy, Kansas State University, Manhattan, Kansas 66506, USA
Abstract:Fires in the tallgrass prairie are frequent and significantly alter nutrient cycling processes. We evaluated the short-term changes in plant production and microbial activity due to fire and the long-term consequences of annual burning on soil organic matter (SOM), plant production, and nutrient cycling using a combination of field, laboratory, and modeling studies. In the short-term, fire in the tallgrass prairie enhances microbial activity, increases both above-and belowground plant production, and increases nitrogen use efficiency (NUE). However, repeated annual burning results in greater inputs of lower quality plant residues causing a significant reduction in soil organic N, lower microbial biomass, lower N availability, and higher C:N ratios in SOM. Changes in amount and quality of below-ground inputs increased N immobilization and resulted in no net increases in N availability with burning. This response occurred rapidly (e.g., within two years) and persisted during 50 years of annual burning. Plant production at a long-term burned site was not adversely affected due to shifts in plant NUE and carbon allocation. Modeling results indicate that the tallgrass ecosystem responds to the combined changes in plant resource allocation and NUE. No single factor dominates the impact of fire on tallgrass plant production.
Keywords:carbon  fire  immobilization  mineralization  nitrogen use efficiency  soil organic matter  tallgrass prairie
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