Soil microedges provide an ecological niche for Desmodium canadense

Within a plant community, variation among species in their abilities to exploit different types of soil patches can promote increased species diversity. However, it also has been suggested that some species may be disproportionately abundant along the edges between soil patches (i.e. soil microedges). We investigated the potential mechanisms whereby microedges can offer distinct ecological niches. Desmodium canadense, a tallgrass prairie species observed anecdotally to be abundant along patch edges, was grown in homogenized sandy loam (low-quality patch), clay loam (high-quality patch), or along the microedge between these two substrates, both in the presence or absence of competitors (Andropogon gerardii and Solidago juncea). Treatment effects on the biomass and root foraging strategies of D. canadense were assessed and compared to the responses of Andropogon gerardii and Solidago juncea. Although D. canadense biomass was highest in the clay loam without competition, with competition D. canadense biomass was highest along the microedge, which was a pattern not observed in A. gerardii or S. juncea. D. canadense also exhibited disproportionate root proliferation along the microedge into the clay loam patch, regardless of competitor presence. Although D. canadense biomass can be limited in both low- and high-quality soil patches, the edges between these patches allow D. canadense to avoid intense aboveground competition yet still access beneficial soil patches through lateral root foraging, thus enabling soil patch microedges to serve as a unique ecological niche.