Most natural plant communities support a diverse assemblage of arbuscular mycorrhizal fungi (AMF).  These mutualistic fungi have been shown to impact the growth, biomass production, survivorship, and competitiveness of many plant species.  AMF communities have the potential to affect plant community structure and vice versa.  We examined AMF sporulation in a 4.5-ha reconstructed prairie in Eau Claire County, WI.  In the fall of 2003, the site was planted with combinations of native prairie species from each of four functional guilds: C₃ grasses (3 species per plot), C₄ grasses (3 species per plot), legumes (0-8 species per plot) and non-legume forbs (0-16 species per plot).  The various seeding treatments were arranged in a completely randomized design; each treatment was replicated five times.  We hypothesized that diverse plant seeding mixtures would promote AMF diversity.  To further test the interaction between the plant and fungal communities, each plot was subdivided and treated with the fungicide chlorothalonil to suppress AMF (18 mg m^-2 y^-1 in year 1, but less in subsequent years), or ammonium nitrate fertilizer (15 g N m^-2 y^-1).  Replicate soil samples were taken during the summers of 2004, 2006, and 2007 from each subplot.  Spores of AMF were extracted, identified to species, and enumerated.

Results/Conclusions

Plant composition varied significantly among the seeding treatments.  Surprisingly, seeding treatment did not affect fungal diversity and spore abundance.  Ordination analysis over all three sample years revealed a strong impact of time on the AMF community.  Slope and elevation of each plot also had strong influence on the community.  In 2007 (four years after initial treatment), fungal species richness was significantly decreased by both nitrogen and fungicide treatments.  Multivariate analysis of variance revealed significant change in the community due to both nitrogen (Wilks’ lambda, F = 2.518, p = 0.003) and fungicide (Wilks’ lambda, F = 21.208, p < 0.001).  Fungal species richness was weakly (but significantly) correlated with plant productivity (r = 0.37), plant richness (r = 0.28), and plant density (r = 0.29).  Thus, the fungal community mirrored some patterns observed in the plant community, even though initial seeding treatments did not measurably affect the fungal composition.  Perhaps the time scale of this experiment (4 years) was not sufficient for the plant species to alter the fungal composition.  As the plant community becomes more established, it may have more influence on the fungi.