Successional patterns
Across the common and rare endophyte assemblages of three host tree
species, evidence for deterministic succession was only found for the
rare endophyte communities of one of the three woody host species
(E. crispa ) and in none of the three assemblages of common
endophyte species. Therefore, we find no consistent evidence of
deterministic succession of endophyte communities within individual
hosts across a woody-plant successional gradient. Under a scenario of
deterministic succession, similar directional shifts in fungal endophyte
community composition would have been observed since abiotic
environmental conditions changed fairly consistently with BC size
(Jamison-Daniels et al. , 2021). The lack of consistent
directional changes in endophyte composition with BC size, but
significant effects of the host identity on species composition, suggest
that the effect of the plant host on endophyte composition trumps the
impact that the consistent changes of environmental variables has on
fungal endophyte communities. A large percentage of variation in the
community assembly models remain unexplained, suggesting that unmeasured
or random processes may contribute to the assembly of endophyte
communities (Hubbell, 2001).
The lack of strong evidence for deterministic succession within
endophyte communities does not preclude succession of endophyte
communities of all trees per bush clump. Our study specifically assessed
changes in endophyte composition within single host species across a
tree successional gradient. Because tree composition changed in a
directional manner with BC size (Jamison-Daniels et al. , 2021),
and host identity is an important determinant of endophyte composition
and richness (Liu et al. , 2019; U’Ren et al. , 2019;
Harrison and Griffin, 2020) (Figure 2; Figure 4; Table 1), endophyte
communities of entire BCs (i.e. across different tree species or within
tree genera or families) could show stronger evidence of deterministic
changes in endophyte composition. As a certain suite of tree species are
associated with a specific successional stage in this system
(Jamison-Daniels et al. , 2021), their associated endophyte
communities may also be associated with the associated tree successional
stage. Under this scenario, the succession of endophyte communities
would be driven by changes in host species composition with successional
stage, and not changes in environmental factors with successional stage.