Ecological patterns of root nodule diversity in cultivated and wild rooibos populations: a community prediction approach

There is interest in understanding the factors behind the biogeography of
root-associated bacteria due to the joint effects that plant host,
climate, and soil conditions can have on bacterial diversity. For legume
crops with remaining wild populations, this is of even more importance,
because the effects of cropping on undisturbed root-associated bacterial
communities can be addressed. Here, we used a community prediction
approach to describe the diversity of the root nodule bacterial
communities of rooibos (Aspalathus linearis), an endemic legume crop from
South Africa. The goal was to reveal whether patterns of root nodule
community composition in paired cultivated and wild rooibos populations
could be related to geographical distance, plant traits, and plant
population type (i.e. cultivated or uncultivated). We identified a core of
dominant and widespread Mesorhizobium ZOTUs that each defined one of 4
different root nodule community classes. Rooibos cultivation impacted root
nodule bacterial diversity at regional and local scales, while the
geographical origin of the root nodule communities was the strongest
predictor of root nodule community structure. Beyond impacts of
cultivation on root nodule bacterial diversity, this study suggests a
mixture of dispersal limitation and ecological drift regionally, and
selection by different plant populations locally, define the biogeography
of rooibos root nodule bacterial
communities.