The bryophyte rhizoid-sphere microbiome responds to water deficit.

The roots of vascular plants are colonised by a multitude of microbes, which play an important role in plant health and stress resilience. Drought stress in particular is devastating for crop yield and causes major shifts in the rhizosphere microbial communities. However, the microbiome associated to the rhizoids (hereafter termed rhizoid-sphere) of the nonvascular bryophytes remains largely unexplored. Here, we use amplicon sequencing to explore the rhizoid-sphere microbiome of three bryophyte species under drought and well-watered conditions. Comparing rhizoid-sphere microbial communities associated with the two liverworts Marchantia polymorpha and Marchantia paleacea and the moss Physcomitrium patens showed characteristic differences in composition between host species and both conserved and unique changes under drought. At phylum level, these changes were similar to changes in the rhizosphere of angiosperms under drought. Furthermore, we observed strong differences in rhizoid-sphere colonisation between bryophyte species for taxa known for nitrogen fixation and plant growth promotion. Interestingly, M. polymorpha prioritised the growth of belowground organs under osmotic stress, as is the case for angiosperms under drought. Taken together, our results show interesting parallels between bryophytes and angiosperms in the relation with their rhizo(id-)sphere, suggesting evolutionary conservation among land plants in their response to drought stress.