A driver bacterial strain and trait-complementary partners enhance photosynthesis and growth in ryegrass

Background and Aims Forage grasses whose yield is almost entirely leaf-based rely on high canopy photosynthesis and rapid leaf regrowth, yet how they recruit root-associated bacteria to support this aboveground performance remains unclear. Methods Soil samples from ryegrass rhizospheres and bulk soils were analyzed through 16S rRNA sequencing and bacterial isolation, followed by pot and plate experiments to assess the plant growth-promoting effects and interactions of selected strains, along with their transcriptomic responses. Results We identify a small set of root-recruited bacterial strains in wild ryegrass that consistently enhance plant growth and leaf greenness. Each strain individually increased biomass and chlorophyll content, but they differed in plant-beneficial functions such as hormone production and nutrient mobilization. When assembled into single- and multi-strain communities, their effects on plant performance were strong and non-additive: Arthrobacter pascens , the field-dominant rhizosphere strain of wild ryegrass, generated disproportionate gains in growth and chlorophyll, whereas other members acted as complementary helpers that further amplified plant responses in mixtures. Conclusion Our work illustrates how leaf‐dominated crops can harness naturally recruited microbial allies to enhance photosynthetic capacity and leaf production, providing insights for designing microbial inoculants for forage grasses.