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

Abstract

Prescribed burns were carried out in mountain shrub and grassland communities in the montane zone of the Rocky Mountains in Colorado. Nitrogen mineralization rate was increased 1 year after the burn in both communities. This increase persisted for 1 year in the grassland and for 2 years in the shrub community. Total mineralized soil-N was greater in the burned than unburned areas of both communities during the first growing season after fire. An acetylene reduction assay for nitrogenase activity showed depressed activity 1 year after the burn. We suggest that elevated inorganic N levels caused the reduction in nitrogenase activity.