Hidden complexity: exploring the biogeography of dune grass root fungi with next generation sequencing

Abstract

The biogeography of cryptic fungal communities in natural systems is poorly understood, as are the causal factors underlying biogeographic variation. I used next generation sequencing (NGS) to determine the fungal communities associated with the roots of coastal dune grasses. Their biogeography was examined at global, regional, and local spatial scales, to seek evidence of dispersal limitation and environmental filtering. The impact of host plant species on these communities was also considered. The SSU DNA region was used to profile arbuscular mycorrhizal fungal (AMF) communities occupying Spinifex sericeus roots at a New Zealand dune. Then, the impact of host species identity on community composition, and community turnover among samples was explored using Ammophila arenaria and Leymus mollis roots from a Californian dune. The utility of the LSU, ITS and SSU regions for profiling fungal communities was also compared. Root samples were then collected from A. arenaria in multiple dunes in three regions – the United Kingdom, where it is native, and Australia and New Zealand where it is invasive. Heterogeneity in fungal community composition within dunes, among dunes within regions and among regions was examined. Roots were also collected from the native grasses Leymus arenarius (United Kingdom), and Spinifex sericeus (Australasia), to further examine the impact of host plant species identity. Fungal communities varied among regions and some lineages were restricted to single dunes. However dominant lineages were shared, suggesting dispersal limitation is not an important control over fungal community composition. Community differences correlated with changes in temperature, pH and nitrogen. Richness was highest in A. arenaria in its invasive range. Differences in community composition were also seen within regions although again dominant taxa were widely dispersed. High beta diversity among samples within dunes reveals extensive sampling is needed to capture fungal communities. The impact of host identity on fungal community composition was context dependent. The SSU region captured a more phylogenetically diverse AMF community than the other gene regions, and recovered AMF from more samples. The utility of the ITS region for whole community profiling was shown. A phylogenetically and functionally diverse community was present in dune grass roots, comprised of both previously sequenced fungi and unidentifiable lineages. Potentially pathogenic fungi were dominant.