Arbuscular mycorrhizal fungi associated with a single agronomic plant host across the landscape: The structure of an assemblage

Arbuscular mycorrhizal (AM) fungi (phylum Glomeromycota) are important components of natural and managed ecosystems. We explored the AM fungal assemblage in a selection of maize fields across a landscape in eastern New York State and characterized their diversity, dominance, and species abundance distribution. In this managed agroecosystem, we could investigate environment-influenced composition and diversity patterns unencumbered by immediate host species effects. We found that AM fungal taxon abundances were distributed lognormally, which suggests that the fungal community structure is shaped in a complex manner by many interacting niche-related factors rather than by only a single factor of disturbance associated with agricultural management. In addition to species abundance distribution, the focal assemblage shared with natural AM fungal communities a pattern of very strong dominance of certain taxa. To quantify this pattern, we developed two new indices “overdominance” and “inequitability”. Contrary to expectations based on observations of natural AM fungal communities, we found that most of the individual field communities were dominated by taxa from within a narrow phylogenetic range. At the landscape scale, we did not find an inverse relationship between the levels of taxonomic richness and phylogenetic relatedness expected in complex communities shaped by competitive exclusion.

► AM fungal communities in maize fields show lognormal species abundance distribution.
► Dominance of top ranked taxon is very pronounced, as in natural systems.
► A new index, “overdominance”, is proposed to characterize the dominance structure.
► No idiosyncrasy or competitive exclusion is apparent.