Role of niche restrictions and dispersal in the composition of arbuscular mycorrhizal fungal communities

1 Metacommunity and neutral theory have reinvigorated the study of 'niches' and have emphasized the importance of understanding the influences of competition, abiotic factors and regional spatial processes in shaping communities. 2 We conducted a field survey to examine the effects of soil characteristics and distance on arbuscular mycorrhizal (AM) fungal communities of maize (Zea mays) in sand and clay soils. To address whether the field distributions of AM fungal species represented their fundamental or realized niches, we grew representative species of the two dominant genera, Glomus and Gigaspora, alone or together on Sorghum bicolor plants in sand, clay or a sand/clay mixture in the glasshouse. 3 In the field, soil characteristics and spatial structure accounted for significant proportions of the variation in community composition among sites, suggesting that both environmental variables and dispersal were important factors shaping AM fungal communities. 4 AM fungi in the family Glomeraceae occurred predominately in clay soils, whereas AM fungi in the family Gigasporaceae dominated in sand soils. Niche space of Glomeraceae was further partitioned by levels of soil organic carbon and nitrogen. 5 In the glasshouse, root colonization by Glomus was high in all three soils when grown in the absence of Gigaspora, indicating a broad fundamental niche. Root colonization by Gigaspora was negatively correlated with percentage clay when grown in the absence of Glomus, consistent with the low abundance of this family in clay soils in the field. When grown together, spore production of both Glomus and Gigaspora was significantly reduced only in the sand soil, indicating that competition could limit niches of both families in certain soil environments. 6 Our results suggest that AM fungal distributions are the product of environment, interspecific competition and regional spatial dynamics, emphasizing the importance of using a metacommunity perspective in community ecology.