Document: JAM-3-38-3

Interactions between root and shoot competition vary among species and with fertilization.

CAHILL, JR., J.F.*

University of Alberta, Edmonton, Alberta, T6G 2E9, Canada ¹

Abstract:
Understanding how competition varies with productivity is essential to differentiate among alternative models of community organization. Recent work has demonstrated that root and shoot competition interact to affect plant growth, and attempts to explain shifts in competition along gradients based upon additive interactions between competitive forms fail to capture the dynamics of competition which actually occur. Root and shoot competition were separated using exclusion tubes and tiebacks in a successional community. Individuals of four species (Abutilon theophrasti, Amaranthus retroflexus, Rumex crispus, and Plantago lanceolata) were grown at two levels of fertilization in four competition treatments (full, aboveground, belowground, none). In contrast to predictions from current models, but in agreement with other experimental studies, there was no change in the strengths of root, shoot, or total competition with an increase in productivity. Despite no effect of fertilization on the strength of competition, the interaction between root and shoot competition varied as a function of species identity and fertilization. For some species the combined effects of root and shoot competition were less than that predicted assuming no interaction, with some species switching from an additive to a negative interaction with fertilization. If root-shoot interactions are common in natural systems, then simply measuring the strength of one form of competition in no way provides any information about its overall importance to plant growth.

Keywords: plant competition, root-shoot interactions, old-field, non-additive effects, productivity gradient, negative interactions, community organization

This abstract is being presented at: 11:45 AM in session:
Oral Session #72: Plant Competition.