Diversification and differentiation of Stipa species shed light on the regional evolutionary history of the eastern Eurasian steppe

Understanding the evolutionary history of the Eurasian steppe is crucial for restoring severely degraded ecosystems and mitigating the impact of future climate change. Stipa species, which demonstrate zonal and extrazonal distribution patterns across the eastern Eurasian steppe, serve as a noteworthy example for elucidating the evolution of this biome. In this paper, we explored the phylogeny of the genus Stipa using transcriptome data, while examined the genetic differentiation, demographic history, and adaptive evolution of S. baicalensis, S. grandis, and S. krylovii using RAD-seq data. We found that from mid-Miocene to early-Pliocene, the Qinghai-Tibet Plateau (QTP) uplift triggered the formation of the Asian monsoon and progressive aridification of Asian interior, fostering Stipa species emergence and out-of-QTP. During the Pleistocene, glacial-interglacial cycles and East Asian monsoon fluctuations led to alternations of cold-dry and warm-wet climate, facilitating the differentiation and migration of these three species across Mongolian Plateau, Loess Plateau, and Central Asia. These climatic oscillations shaped distinct genetic variations among these species in different geographical regions. Furthermore, annual precipitation and total soil nitrogen content were the primary drivers of their adaptive evolution. Noticeably, the evolution of Stipa species exhibits prominent spatio-temporal integration characteristics. Conclusively, we proposed a comprehensive regional evolution framework for plants in the eastern Eurasian steppe. Our research fills gaps in understanding the evolutionary history of the entire Eurasian steppe and the impact of evolutionary processes on contemporary plant distributions, which is vital for assessing steppe vegetation shifts and plant genomic vulnerability under climate change scenarios.