Rhizobiome diversity and its impact on drought resistance in dominant prairie grass big bluestem Andropogon gerardii

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Kaitlyn Ward, Abigail Kamke, Shiva Thapa, Qinghong Ran, Soumyadev Sarkar, Lauren Anderson, Loretta Johnson and Sonny T.M. Lee, Biology, Kansas State University, Manhattan, KS, Matthew Galliart, Division of Biology, Kansas State University, Manhattan, KS

Background/Question/Methods
Understanding drought resistance mechanisms in plants are critical, as the negative effects of climate change become more apparent. Gaining insights into the interactions between plants and the associated rhizosphere microbiome are vital to enhance plant host resilience under continuing threats of climate change. In this study, we focused on Andropogon gerardii – an ecologically dominant tallgrass of the Great Plains with a wide distribution from western Kansas to Illinois. This study took advantage of a ten year long reciprocal garden experiment, where the seeds of native wet, mesic and dry ecotypes of A. gerardii had been reciprocally planted from western KS (rainfall 500 mm) to Illinois (1200 mm). We examined the microbiomes of these ecotypes grown in the western most site in Kansas, Colby, as a surrogate for the dry conditions expected in the future. Our overall goal was to gain insights into plant-host-microbiota associated with drought resiliency. We collected and extracted root associated microbiome from a total of 95 A. gerardii ecotypes, and sequenced the samples on the Illumina MiSeq. We used Qiime2 to profile the rhizobiome 16S rRNA and ITS1 amplicons to determine the rhizosphere’s bacterial and fungal compositional differences among the A. gerardii ecotypes.

Results/Conclusions
Our results showed that host’s ecotype had an influence on the bacterial community. Bacterial composition in wet and mesic ecotypes were more similar to each other, congruent with strong plant phenotypic similarities, as compared to the dry ecotype. We also noticed that there was a high degree of dissimilarity in the bacterial community within the dry ecotype samples. Furthermore, we found Streptomycetaceae were of higher relative abundance in the dry ecotype as compared to the other two ecotypes suggesting that Streptomycetaceae might be more resilient in precipitation-limited soils. Bacterial members from Sphingomonas were highly abundant in all ecotypes, indicating the potential of Sphingomonas to play a role in plant host drought resistance. We did not find any significant differences among the rhizosphere mycobiome. The dominant fungi among the ecotypes were members of Ascomycota, which are important drivers in the carbon and nitrogen cycling in arid ecosystems. This study enabled us to take the first step in identifying the core microbiome that may enhance drought resistance in plant hosts. Identifying the functional role of these bacterial/fungal populations and their interaction with the plant host is crucial to enhance the growth of a dominant grass in the face of climate change.