The combination of a complex non-microbial biostimulant and an arbuscular mycorrhizal fungi increases yield under salt stress in lettuce and tomato by enhancing energy metabolism

Soil salinization limits horticultural productivity and is expected to increase under climate change. Biostimulants, including arbuscular mycorrhizal fungi (AMF) and non-microbial products derived from natural extracts, are used to improve stress tolerance, but the effects and mechanisms of their combined application remain insufficiently characterized under real cultivation conditions. This study evaluated the AMF Rhizophagus irregularis strain RI6E6, the non-microbial biostimulant Calbio, a combination of four plant-, yeast-, and algae-based extracts developed in our laboratory, and their combined application in lettuce ( Lactuca sativa L.) and tomato ( Solanum lycopersicum L.) grown under control and salt-stress conditions. Both crops were analyzed within the same experimental framework. Physiological, biochemical, metabolomic, and gene expression responses were assessed. Under salt stress, the combined treatment increased yield by 27.8% in tomato and 32.3% in lettuce relative to stressed controls and was more effective than individual applications. Co-application increased photosynthetic pigment content, enhanced carbon metabolism, and increased gibberellin levels in both crops. These responses correlated with improved energetic status and stress tolerance. Crop-specific responses included increased sodium extrusion in lettuce and increased vacuolar sodium sequestration in tomato. In conclusion, the combined application of AMF and Calbio improves yield under salt stress through shared metabolic activation and species-specific responses. These results support integrated microbial–non-microbial biostimulant strategies for improving horticultural performance in saline environments.