Abstract
Plant fitness is maximized in a complex soil environment when root growth patterns respond to cues in the soil. Two cues that have been studied but are not fully understood are nutrient patches and roots of neighbors. The objectives of this study were to test for species differences in root responses to neighbors, determine the effects of neighbors on root responses to nutrients, and to evaluate how those responses influence competitive interactions and community structure. These objectives were addressed in two greenhouse experiments manipulating soil resource distributions and the presence and identity of competing neighbors. There were no consistent patterns of root foraging responses across our species. Foraging extent was significantly affected by soil treatment for some species but not all. Of the species affected, both had high growth rates that may be resource limited with a neighbor present. Soil heterogeneity had strong effects on our measures of community structure. Removal of Plantago did result in changes to community composition, not because Plantago foraged precisely, but because it had high growth rates and thick roots that allowed it to quickly dominate the community. This study highlights the importance of nutrient heterogeneity and neighbors on grassland community structure. Understanding mechanisms of below ground community interactions will help us better predict community-level responses to environmental changes.