PARENT SESSION
Oral Session #19: Plant Competition. Presiding: N. Slade.
Monday, August 6, 2001. 1:00 PM to 5:15 PM. Hall of Ideas J.

Species specific root allocation patterns in belowground competition.

O'Brien, Erin¹, Brown, Joel¹, ¹

ABSTRACT- We have previously shown how a plant will over-proliferate roots in patches it shares with a conspecific. This result supports our centrally-planned theory of habitat selection which predicts that total root density will be higher when plants compete than when plants do not interact. This generates a 'tragedy of the commons' as an evolutionary stable strategy. We extend the theory and experiments to include interspecific competition, thus expanding the range of potential responses. For our tallgrass prairie annuals, possible outcomes include intense over-proliferation of roots, microspatial partitioning, and the ghost of competition past. Preliminary data suggest that the over-proliferation of roots may also be species specific. We tested for these potential outcomes in a greenhouse experiment. The experimental approach used lets the plants, through their allocation of roots, indicate the directions and strengths of interspecific competition. Our results verify that for some species the responses can be species specific. The larger species, Gaillardia (sp.), did not respond differently to intra- and interspecific roots, while the smaller species, Rudbeckia amplexicaulis, actually grew more roots when competing with Gaillardia than with conspecifics. Rudbeckia appears to view patches occupied by Gaillardia as preferable to those occupied by conspecifics. This illustrates that the study of adaptive behavioral responses, widely used in animal community ecology, can provide insight into community interactions in plants.

KEY WORDS: root allocation, belowground competition, interspecific competition