Stress-adapted bacterial synthetic community enhances drought resilience and recovery in alfalfa

Abstract Drought is a major constraint to the productivity of forage crops, including alfalfa ( Medicago sativa ), a protein-rich livestock feed grown worldwide. While plant-associated bacteria can promote growth in plants, their ability to enhance resilience in drought stress and the efficacy of a multi-strain synthetic community (SynCom) remain underexplored. In this study, we have validated the plant growth properties of five ( Bacillus sp. G3 and G12, Acinetobacter sp. G13, Plantibacter flavus M251 and M259) plant-associated bacteria and investigated the effects of this SynCom inoculation on alfalfa grown using non-sterilized field soil under controlled growth chamber conditions at two time points (Drought, Recovery). Severe drought significantly ( p  < 0.05) reduced shoot length, biomass, and photosystem II efficiency, but SynCom inoculation mitigated these effects by enhancing shoot growth, chlorophyll recovery, and photosynthetic performance. Below-ground, SynCom treatment increased root biomass, surface area, and diameter, and promoted root nodule formation while the nematode population declined during the recovery phase. These benefits likely resulted from strains’ ability to produce phytohormones, solubilize phosphorus, and tolerate abiotic stress. Unlike most SynCom studies conducted in sterilized substrates, using the local field soil captured realistic interactions among plants, soil microbiota, and nematodes, adding ecological relevance. Overall, our findings provide evidence that targeted SynCom inoculation can improve alfalfa plant resilience and recovery under drought, offering a promising and sustainable strategy for forage production in drought-prone regions.