Strong host and environment modulation of rhizosphere-to-endosphere
colonisation in the pan-palaeotropical keystone grass species, Themeda
triandra
Abstract
Soil microbiota can colonise plant roots via a two-step selection
process, which involves the recruitment of microbiota first from bulk
soil into plant rhizospheres, then into root endospheres. This process
is poorly understood in all but a few model species, which is surprising
given its fundamental role in plant and soil ecology. Here we examined
the microbial assembly processes across the rhizospheres and root
endospheres in eight natural populations of the pan-palaeotropical C4
grass, Themeda triandra, in southern Australia. We assessed whether root
endosphere colonisation patterns aligned with the two step-selection
process. We also assessed the degree to which the assembly patterns of
these rhizospheres and endospheres were influenced by deterministic
processes. We show that two-step selection was the dominant recruitment
dynamic across these natural T. triandra populations, and present clear
evidence that host plants influenced microbial assembly via
deterministic pressures that produced strong convergence of endospheres.
Both endospheres and rhizospheres were influenced by local environmental
filtering, including aridity. Our study improves our understanding of
assembly processes of root endospheres, which is central to plant-soil
interactions yet poorly understood in non-model species. We show that
endospheres of native populations of a widely distributed, keystone
grass (T. triandra) were strongly shaped by the host plant and displayed
patterns consistent with the two-step selection process. These findings
raise intriguing questions about the functions of this ‘core’ microbial
endosphere, but our limited understanding of their ecology hinders our
ability to harness these important relationships to, for example,
improve plant propagation and revegetation practices.