Taxonomic shifts in arbuscular mycorrhizal fungal communities with shade and soil nitrogen across conventionally managed and organic coffee agroecosystems.

The composition of arbuscular mycorrhizal fungal (AMF) communities should reflect not only responses to host and soil environments, but also differences in functional roles and costs vs. benefits among arbuscular mycorrhizal fungi. The coffee agroecosystem allows exploration of the effects of both light and soil fertility on AMF communities, because of the variation in shade and soil nutrients farmers generate through field management. We used high-throughput ITS2 sequencing to characterize the AMF communities of coffee roots in 25 fields in Costa Rica that ranged from organic management with high shade and no chemical fertilizers to conventionally managed fields with minimal shade and high N fertilization, and examined relationships between AMF communities and soil and shade parameters with partial correlations, NMDS, PERMANOVA, and partial least squares analysis. Gigasporaceae and Acaulosporaceae dominated coffee AMF communities in terms of relative abundance and richness, respectively. Gigasporaceae richness was greatest in conventionally managed fields, while Glomeraceae richness was greatest in organic fields. While total AMF richness and root colonization did not differ between organic and conventionally managed fields, AMF community composition did; these differences were correlated with soil nitrate and shade. OTUs differing in relative abundance between conventionally managed and organic fields segregated into four groups: Gigasporaceae associated with high light and nitrate availability, Acaulosporaceae with high light and low nitrate availability, Acaulosporaceae and a single relative of Rhizophagus fasciculatus with shade and low nitrate availability, and Claroideoglomus/Glomus with conventionally managed fields but uncorrelated with shade and soil variables. The association of closely related taxa with similar shade and light availabilities is consistent with phylogenetic trait conservatism in AM fungi.