Competition, nutrient reduction and the competitive neighbourhood of a bunchgrass

Schizachyrium scoparium is often the dominant species on unproductive, N-poor, sandy soils in Minnesota. Removal of all neighbouring plant biomass within a 2 m radius of individual S. scoparium bunches resulted in a 3.8-fold increase in the biomass of bunches and demonstrated that the neighbouring plants had been reducing the level of extractable ammonium plus nitrate by 3.9-fold. This suggests that there may be strong competition in this unproductive habitat. The mechanism of competition may be nutrient consumption. Schizachyrium scoparium significantly reduced nitrate and ammonium levels within a 60-75 cm radius around individual plants, with the magnitude of reduction decreasing with distance from an individual. The neighbourhood from which a S. scoparium bunch obtains nitrogen thus had an area of 1-1.5 m² and may include hundreds of other individual plants. -Author