Na-salicylate and S-methylmethionine modulate stress-responsive ionomic and metabolomic pathways in Szarvasi-1 energy grass

• NaSA and SMM improved photosynthetic performance under drought conditions • NaSA and SMM treatments modulated antioxidant enzymes in contrasting ways • NaSA and SMM increased K:Na ratio supporting drought resilience • SMM enhanced lignin and phenolic pathways during drought • NaSA induced broad metabolic reprogramming detected by metabolomics Drought is a major constraint on agricultural productivity and developing sustainable strategies to enhance crop resilience is critical under climate change. This study investigated the effects of foliar-applied sodium salicylate (NaSA) and S-methylmethionine (SMM) on the physiology, metabolism, and ion homeostasis of Szarvasi-1 energy grass ( Thinopyrum obtusiflorum cv. Szarvasi-1 ) under field drought conditions. Treatments were applied in small- and large-scale field experiments over two consecutive years characterized by varying drought intensities. Neither NaSA nor SMM significantly altered biomass accumulation, leaf water content, or chlorophyll levels. However, both treatments improved photosynthetic performance, particularly in small-scale experiments, enhancing CO₂ assimilation, transpiration, and photosystem II efficiency. Enzyme assays revealed that NaSA and SMM modulated the antioxidant defence system by increasing superoxide dismutase, peroxidase, and glutathione reductase activities, while catalase and ascorbate peroxidase activities decreased. Elemental analysis showed treatment-dependent adjustments in potassium and sodium levels, resulting in elevated K:Na ratios, which support osmotic regulation under drought. Metabolomic profiling indicated that SMM predominantly enhanced lignin and phenolic biosynthesis and sugar-mediated osmotic adjustment, whereas NaSA triggered broader metabolic reprogramming, including amino acid metabolism, secondary metabolites, and photorespiratory pathways. Principal component analysis confirmed distinct metabolic responses to each biostimulant, highlighting complementary strategies for drought adaptation. Overall, SMM and NaSA improve physiological and biochemical drought tolerance in Szarvasi-1, providing insights for the use of natural biostimulants to enhance stress resilience in biomass crops.