XVI International Botanical Congess

Previous studies have shown that fertilization with Nitrogen (N) changes the composition of arbuscular mycorrhizal (AM) spore populations and alters the functioning of the symbiosis. We investigated the effects of N fertilization on AM at two semiarid experimental grasslands located in Colorado and New Mexico (Shortgrass Steppe (SSE) and Sevilleta (SEV), respectively). Bouteloua gracilis and Elymus elymoides from SSE and B. gracilis and B.eriopoda from SEV, were used to compare the growth response of local grasses to AM from fertilized and unfertilized areas. AM fungi from unfertilized soils increased dry root and shoot biomass, and chlorophyll content, particularly in species distributed in nutrient limited conditions. The cost:benefit of the mycorrhizal symbiosis is discussed in relation to increasing N deposition.