Fire Effects on Nitrogen Mineralization and Fixation in Mountain Shrub and Grassland Communities

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Abstract
Prescribed burns were carried out in mountain shrub and grassland communities [primarily Agropyron spicata, Stipa comata, Artemisia tridentata and Purshia tridentata] in the montane zone of the Rocky Mountains in Colorado [USA]. N mineralization rate was increased 1 yr after the burn in both communities. This increase persisted for 1 yr in the grassland and for 2 yr in the shrub community. Total mineralized soil-N was greater in the burned than unburned areas of both communities during the 1st growing season after fire. An acetylene reduction assay for nitrogenase activity showed depressed activity 1 yr after the burn. Elevated inorganic N levels apparently caused the reduction in nitrogenase activity.