1 Negative feedback may exist between plant species and their biotic soil communities. Two co-occurring native tallgrass species (Andropogon gerardii, a perennial grass, and Chamaecrista fasciculata, an annual legume) were reciprocally transplanted into pots containing soil from areas dominated by one of the species. Half of the soil derived from each area was microwaved to reduce soil fungi, resulting in four different ‘soil types’.
2 Chamaecrista fasciculata plants were smaller when grown in their native soil vs. that from under A. gerardii, but were unaffected by microwaving (i.e. fungal reduction). Andropogon gerardii plants were shorter with fewer inflorescences in non-microwaved soil, with the poorest growth occurring in non-microwaved C. fasciculata soil.
3 Fungi were isolated from roots of A. gerardii growing in the different soil types. We tested whether the fungi found differed between the four soil types and whether any species characteristic of C. fasciculata soil were responsible for the poor growth of A. gerardii in this medium.
4 Fungi unique to the non-microwaved C. fasciculata soil type reduced tillering and caused an early reduction in growth of A. gerardii. These effects were partially ameliorated when potentially mycoparasitic fungi associated with A. gerardii were also included. By the end of the experiment, both fungal treatments increased above-ground biomass but greatly reduced below-ground biomass of A. gerardii compared with controls, suggesting that the exposure to potential fungal pathogens from C. fasciculata soil altered biomass allocation within plants.
5 There was no evidence of negative feedback between the prairie species and their own soils. However, fungi associated with Chamaecrista fasciculata were detrimental to A. gerardii, one of the dominant perennials in the surrounding area, and may facilitate the annual’s long-term persistence. Arbuscular mycorrhizae did not ameliorate the pathogenic effects of these fungi as there was little colonization of A. gerardii roots in C. fasciculata soil.