Document: ERI-3-38-20

Belowground bullies? Root competition and nutrient foraging as an indication of interspecific competition.

O'BRIEN, E.E.* ¹, J.S.BROWN ¹ and M.GERSANI ²

University of Illinois at Chicago, Chicago, IL 60607 USA ¹
Ben Gurion University of the Negev, Beer-Sheva 84105, Israel ²

Abstract:
Root allocation by plants provides a method to quantify foraging effort in response to soil nutrient patches. A plant should reduce root growth (density) in response to either reduced nutrient availability or increased competition from the roots of others. Previous work with domesticated species strongly supports our centrally-planned model of habitat selection which predicts that total root density will be higher when two plants compete than when the plants do not interact. At the evolutionary stable strategy the plants engage in a "tragedy of the commons." This response should also provide insight into interspecific interactions. Competition between two species creates an asymmetric form of intraspecific competition thus expanding the range of potential outcomes and responses at the evolutionary stable strategy. For tallgrass prairie plants, potential outcomes include intense over-proliferation of roots, microspatial partitioning, and the ghost of competition past. We grew pairs of both split-root Gaillardia (annual sp.) and Rudbeckia amplexicaulis in three pots with the central one shared by both plants. To remove the effect of competition, the middle pot was replaced with two pots whose combined volume equaled that of the middle pot in the other pairs. Our results support the centrally planned model of habitat selection and suggest that the degree of over-proliferation in these plants is species-specific. In inter-specific competition, an asymmetrical game, the allocation patterns of the two plants reflects each plant's competitive ability with the more successful competitor claiming a greater proportion of the middle pot. This experimental approach lets the plants, through their allocation of roots, indicate the directions and strengths of interspecific competition.

Keywords: interspecific plant competition, belowground plant competition

This abstract is being presented at: 3:30 PM in session:
ROOT PROCESSES