Gigasporaceae versus Glomeraceae (phylum Glomeromycota): A biogeographic tale of dominance in maritime sand dunes

Community composition of arbuscular mycorrhizal fungi (AMF) is influenced by host, soil chemistry, and climatic conditions at the local and regional scale, but little is known about factors shaping community composition on a global scale. In this study, the pattern of dominance by families in Glomeromycota in maritime sand dunes worldwide was examined to test the hypothesis that soil pH is a major factor shaping AMF community structure. We analyzed 38 publications from the literature containing data on soil chemistry and species composition and calculated relative species richness (RSR) for each of the families Gigasporaceae, Glomeraceae, and Acaulosporaceae. Regression and multivariate analyses were performed to determine the relationship and association of RSR of families with soil pH, temperature and precipitation and biogeographical realms. Of the 119 AMF species found in sand dunes, members of Gigasporaceae and Glomeraceae dominated in all studies. In Nearctic dunes, Gigasporaceae and Glomeraceae co-dominated fungal communities while Gigasporaceae dominated in Neotropical dunes and Glomeraceae dominated Palearctic and Oriental/Sino-Japanese realms. Overall, the proportion of species in Gigasporaceae was above 40% in soil pH < 6.5 while the proportion of those in Glomeraceae exceeded 40% in soil pH > 6.5. Soil pH was negatively correlated with RSR of Gigasporaceae but positively correlated with RSR of Glomeraceae. Thirteen species were detected in at least four biogeographical realms and are considered cosmopolitan. Redundancy analysis evidenced soil pH and one Moran's spatial variable as significant predictors of Glomeromycota family composition. Moran's I correlograms showed positive spatial autocorrelation only at distances < 2000 km for soil pH and family composition. We conclude that soil pH was a major factor influencing the dominance of Gigasporaceae and Glomeraceae in sand dunes worldwide, and the proportional dominance of each family was distinct amongst biogeographical realms.