Abstract: The intricate relationships between plants and their rhizobacteria are crucial for plant success, yet our understanding of these associations, particularly in diverse alpine natural grasslands, remains limited. Here, we investigated two widespread grass genera (Stipa Linn and Poa Linn) and their core rhizobacteria across a vast 2,161 km transects on the Qinghai–Tibetan Plateau. Compared to Stipa L., which has a broader niche breadth, Poa L. displays higher above- and below-ground biomass. This characteristic reflects a more resource-conservative and stable growth strategy, consistent with traits commonly observed in K-strategists. However, Poa's core rhizobacteria (5,458 species, 9.51% of total ASVs) were enriched with here r-strategists, while Stipa's (5,193 species, 9.05% of total ASVs) were dominated by K-strategists. These findings highlight contrasting life-history strategies between grasses and their associated core rhizobacteria. Notably, only 633 core rhizobacteria overlapped between these two grasses. Functionally, Poa's r-strategists microbiota likely prioritizes rapid resource acquisition for high biomass production, while Stipa's K-strategist-dominated community might enhance stress tolerance in their resource-limited habitat. The observed pattern of life-history differences between grasses and rhizosphere microbes supports plant survival in alpine ecosystems. Our study advances understanding of rhizosphere ecology and its importance for ecosystem health in the natural environments.

Key words: core rhizobacteria, dominant grass, functional predictions, r/K selection theory, Qinghai–Tibetan Plateau region