| Ecological relationships between arbuscular mycorrhizal fungi (AMF) and plant species were explored in midwestern oak savannas, among the rarest and most diverse communities in the central US. A gradient analysis of 63 samples from three savannas spanning light and soil fertility gradients showed that AMF and plant species richness were highly significantly correlated with each other, soil texture, and total N, but only at a point scale, not at a 1-m2 quadrat scale. AMF and plant community composition at all scales were also significantly correlated with each other and the same environmental factors.; A field experiment examined the effects of AMF on plant composition at the sandiest savanna, Upper Tarr Creek (TCU). Thirty pairs of quadrats received fungicide (Benomyl) treatment or control watering each month for two growing seasons. Analysis revealed no treatment effect, suggesting that AMF do not influence plant community composition at TCU in the short term.; Two experiments were conducted in greenhouse microcosms, using plants, AMF, and soil collected largely from TCU. In the first study, four plant species were grown in monocultures or in mixtures in 15 cm pots, under sun and shade, and with five different AMF treatments (two individual AMF species, both species; neither; and addition of unsterilized soil form TCU). All treatments had significant effects, most opposite to expectations. Mycorrhizal plants showed neutral or negative responses to AMF addition, and a non-mycorrhizal species grew largest in competition with AMF-infected plants. The combination of small pots, sandy soil, and long duration of the experiment apparently induced the AMF to act as parasites on susceptible hosts.; In the second greenhouse study, larger (10.8-liter) microcosms were seeded with 11 plant species and subjected to the same light and AMF treatments. Light had a significant effect on plant community composition, but AMF had almost no effect. There were no treatment effects on species evenness. Nevertheless, these results were consistent with those of the field experiment at TCU. These studies indicate that plant and AMF composition are correlated with each other and soil texture/N, but AMF appears to have little or no direct effect on plant composition in sandy savannas. |
