The effect of fire, mowing and fertilizer amendment on arbuscular mycorrhizas in tallgrass prairie

Tallgrass prairie sites subjected to 10 y of annual burning, mowing, nitrog en (N) fertilization or phosphorus (P) fertilization and untreated referenc e sites were studied to examine effects of these management practices on ar buscular mycorrhizal (AM) symbiosis. Spring burning of native prairie field plots significantly reduced AM fungal species diversity, while increasing spore abundance. This increase in total spore number was due to a general i ncrease in most of the 17 fungal species present. In general, the managemen t treatments had larger effects on the richness component of diversity than on the evenness of AM species abundances. Burning and mowing had no signif icant effects on AM fungal colonization of roots or extraradical mycorrhiza l hyphae (EMH) development. However, nitrogen fertilization significantly i ncreased root colonization and EMH development, and P amendment decreased E MH development. There was no significant effect of fertilizer amendment on AM spore abundance, fungal species diversity or richness, but N and P ferti lization decreased fungal species evenness. Effects of management practices on AM fungi may be mediated through changes in soil resources or microclim ate or through changes in their host plants. These effects on AM symbiosis and community structure are important because AM fungi strongly influence t he growth, demography, competitive relationships, relative abundances and d iversity of plants in grassland communities.