A Synthetic Community from <i>Campeiostachys nutans</i> Rhizosphere in the Qinghai-Tibet Plateau Endow Alfalfa with the Ability to Resist Drought and Cold

, widely distributed in the Qinghai-Tibet Plateau, possesses notable stress tolerance, yet the exploration of its functional rhizosphere microbes remains limited. In this study, we characterized bacterial variations across rhizosphere surrounding soil, rhizosphere, and endosphere compartments from five grassland types, isolated core strains, and established a synthetic community (SynCom). Results revealed that under PEG-induced drought, SynCom significantly altered alfalfa responses by scavenging reactive oxygen species (ROS), modulating immune gene expression, and synthesizing glutamate metabolites. Additionally, SynCom inoculation conferred cold resistance to alfalfa by enhancing photosynthetic activity, boosting antioxidant enzymes, and producing osmotic adjustment compounds like trehalose. This investigation underscores the capacity of core rhizosphere taxa to enhance stress tolerance, offering novel perspectives for developing microbial inoculants to improve crop productivity under drought and cold stress.