Effect of soil nutrient heterogeneity on the symmetry of belowground competition

Size variability in plant populations has been extensively studied and much of this inquiry has focused on the types of competition that are involved in increasing or decreasing size inequality. It is often assumed that competition for light is size-asymmetric, meaning that a plant can potentially dominate a competitive relationship through shading if it is taller than its competitor. The light resources obtained by the taller plant are thus disproportionate to its size. In contrast, competition for soil resources may be more size-symmetric, the amount of soil nutrients obtained seems to be in direct proportion to a plant's size. Most studies examining belowground competition have used homogeneously distributed nutrient resources. Soil homogeneity could make size-asymmetric belowground competition unlikely, but homogeneity is not often found in nature. In this study I use a greenhouse pot experiment utilizing Ipomoea tricolor to examine the hypothesis that size-asymmetric competition for soil nutrients may result when soil resource distribution is spatially heterogeneous. The results did not support the hypothesis of belowground size-asymmetric competition. Differences between experimental treatments and controls were not statistically significant suggesting size-symmetric competition. Implications of these results are discussed.