Effect of soil nutrient heterogeneity on the symmetry of belowground competition

Abstract

Size variability in plant populations has been extensively studied andmuch of this inquiry has focused on the types of competition that are involvedin increasing or decreasing size inequality. It is often assumed thatcompetition for light is size-asymmetric, meaning that a plant canpotentially dominate a competitive relationship through shading if it is tallerthan its competitor. The light resources obtained by the taller plant are thusdisproportionate to its size. In contrast, competition for soil resources maybemore size-symmetric, the amount of soil nutrients obtained seems to be indirect proportion to a plant's size. Most studies examining belowgroundcompetition have used homogeneouslydistributed nutrient resources. Soil homogeneity could makesize-asymmetric belowground competition unlikely, but homogeneity is notoften found in nature. In this study I use a greenhouse pot experimentutilizing Ipomoea tricolor to examine the hypothesis thatsize-asymmetric competition for soil nutrients may result when soilresource distribution is spatially heterogeneous. The results did not supportthe hypothesis of belowgroundsize-asymmetric competition. Differences between experimental treatmentsand controls were not statistically significant suggesting size-symmetriccompetition. Implications of these results are discussed.