Top-down is bottom-up:: Does predation in the rhizosphere regulate aboveground dynamics?

We explore two aspects of how predation within the rhizosphere influences nutrient availability, plant productivity, and aboveground community dynamics. First, plant roots and soil microbes have a long history of interaction that is centered on the reciprocal acquisition of carbon by microbes and nitrogen by plants. Predators within the rhizosphere alter these interactions in ways that benefit plants but also influence the dynamics of other species within ecosystems and processes that are important to ecosystem function and stability. These same predators regulate their prey in a traditional "top-down" manner but in doing so alter the release of nutrients that may limit plant productivity and thereby affect plant growth in a "bottom-up" fashion as well. Second, much attention has been given to the importance of specific interactions, or, as presented within this series, genes and/or gene products as critical control points. We suggest that control should be viewed within the framework of interactivity. The interdependence between the aboveground and belowground realms can be explained in terms of the patterning of trophic interactions within the rhizosphere and the influence of these interactions on the supply of nutrients and rates of nutrient uptake by plants. While specific interactions may be important, it is the patterning of these interactions into assemblages of species that share similar growth rates and habitats that is the salient feature of the rhizosphere that confers stability, affects nutrient retention, and regulates aboveground and belowground dynamics.