Impact of High and Low Plant Diversity on Nitrogen Mineralization Rates

Native plants are important to the functioning of natural ecosystems in the sagebrush steppe, but they are often replaced by exotic invasive annual grasses, such as Bromus tectorum (cheatgrass) following wildfires. Cheatgrass is successful at invading burnt soils, because wildfire increases soil nitrate and ammonium concentrations, which promotes the growth of cheatgrass more than of native grasses. As a result, invasive annual grasses outcompete native species following a fire, and since they continue to manipulate soil processes to advance their own growth, restoration success is limited. Management strategies for reseeding native species should include strategies that reduce soil ammonium and nitrate concentrations, and this may be accomplished by seeding native species at a higher diversity, since this might increase nitrate and ammonium uptake. With this study we ask how seeding with a more diverse mix of native plant species impacts soil nitrate and ammonium concentrations. To test this, we conducted a field experiment in which 48 plots located in a recently burned sagebrush steppe were seeded with a monoculture or 2, 4, or 8 species. Soil cores from plots of high and low plant diversity were analyzed by nitrogen mineralization. Rates of nitrogen mineralization are expected to be higher in plots with high plant diversity