Contrasting biogeography of fungal communities associated with roots versus soils and the role of root morphology in mycobiome assembly in coast redwood, Sequoia sempervirens

As fungal communities generally assemble as roots grow through rhizosphere soil, it is important to understand how geography, climate, and environmental that influence the soil fungal community may also impact fungal community assembly in roots. Further, the heterogeneity of root morphology might also play an important role in fungal community assembly.
The coast redwood (Sequoia sempervirens) is spans substantial geographic, climatic, and environmental gradients throughout its nearly contiguous range and, like many other tree species that associate with symbiotic, root-associated arbuscular mycorrhizal fungi (AMF), coast redwood roots host nodule-like structures that may be important to fungal community assembly in its massive rooting systems.
Leveraging improvements in DNA sequencing, we demonstrate how root-associated communities show more conserved patterns of community composition than do fungal communities in the surrounding soil across geographic, climatic, and environmental gradients. Further, we describe how nodule-like structures (“rhizonodes”) act as domiciles for AMF. In addition, we find numerous ecto- and ericoid mycorrhizal fungi associated with redwood roots, potentially linking redwoods to surrounding trees and shrubs.
These findings highlight the importance of plant specificity in fungal interactions and the potential precision of such selection with important implications for root-mycobiome selection in the face of climatic change.