The Influence of Prairie and Forest Vegetation on Soil Moisture and Available Nitrogen

Abstract

-Aspen clones have expanded into prairie during the last century at the northern edge of the Great Plains. Soil under aspen has more water and available N than that under adjacent prairie. We used a field experiment to test whether high resource availability in forest soil was attributable to the environment associated with forest vegetation. We collected 80 soil cores from prairie and forest and moved them to either prairie or forest. Neighboring roots were excluded from half the cores. Cores were moved in April and 10 samples were taken from each core in September. Cores from forest had significantly higher moisture and available N than those from prairie. Cores moved from forest to prairie had significantly less moisture than those moved from forest to forest, suggesting that the lower moisture in prairie soils depended partly on the environment associated with prairie vegetation. Available N did not differ between cores moved to prairie and forest. Both water and N were higher in cores with roots excluded, but the magnitude of this difference did not differ between prairie and forest, suggesting that there were no differences between prairie and forest in their abilities to take up these resources. The spatial variability of soil moisture was significantly higher in cores from forest than in those from prairie and tended to be highest in cores with roots present, which was consistent with the idea that uptake enhances resource heterogeneity.