Traits related to other ecological processes.
An individual plant's ability to compete below ground is likely to be determined not only by traits internal to that individual, but will also include traits related to how a plant uses, and is used by, other species. For example, grazing by ungulates can stimulate root growth (Frank et al. 2002
), and root characteristics vary widely as a function of root order (Pregitzer et al. 2002
). As a result, grazing may alter below-ground competitive ability through changes in root architecture and other related root properties. As different plant species respond differently to grazing (Diaz et al. 2001
), grazing could cause increased interspecific variation in below-ground competitive ability of the species within a community. Such indirect effects on below-ground competition may also involve plant–fungal interactions. Interspecific variation in mycorrhizal associations, along with the potential for resource sharing of interconnected individuals, can alter diversity (Hartnett & Wilson 1999
), potentially through altered competitive hierarchies. Additionally, recent work indicates that mycorrhizas can enhance the competitive ability of an invasive species (Marler et al. 1999
). There are numerous other ecological processes that are likely to influence a plant's ability to compete for soil resources. Although a better understanding of plant competition is dependent upon a more active exploration of the functional ecology of roots, it is equally important that this work be brought to the field to allow for the determination of the potential strengths of these indirect effects on competition below-ground.