The rhizosphere of Pappostipa frigida as a hotspot of active bacterial communities in the Andean steppe of the Atacama Desert
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Background
The rhizosphere is a resource-rich microenvironment where plants, soil nutrients, and microorganisms interact. In arid and semi-arid regions, this tripartite relationship must withstand long periods of drought followed by brief periods of rainfall. In the present study, we employed a combination of RNA/DNA metabarcoding and shotgun metagenomic sequencing to provide insights into the functional capabilities and activity levels of the bacterial communities present in the bulk soil and rhizosphere samples of Pappostipa frigida , a grass species endemic to the Andean steppe of the Atacama Desert.
Results
The active bacterial community in the rhizosphere of P. frigida exhibited greater diversity and a higher Shannon index than the total bacterial community. In terms of beta diversity, the structures of the total and active communities differed markedly between the BS and the RZ. Furthermore, active bacteria in the RZ showed a stronger correlation with total bacterial populations than those in the BS. This finding is consistent with the low proportion of ASVs derived from RNA extractions detected in the BS. Notably, 64% of these putative inactive bacterial populations were identified as active RZ members and 73% grew in culture media, suggesting they were likely dormant. The bacterial communities of the BS exhibited higher abundances of sporulation genes. In contrast, active bacterial communities in the RZ consistently contained higher abundances of genes associated with halotolerance, siderophore synthesis, and resuscitation-promoting factors.
Conclusions
The results emphasize the importance of the conditions created by plants in recruiting bacterial populations from the soil and provide insights into how the rhizosphere of arid native plants influences the activity and functional traits of soil microorganisms in their natural habitat. Additionally, this study advances our understanding of the mechanisms employed by soil microorganisms to cope with desiccation in natural environments, establishing P. frigida as a model in plant science for studying grass traits and responses to extreme environments.
