Integrated physiology and multi-omics elucidate photosynthetic adaptation and osmolyte accumulation mechanisms in buffalograss under osmotic stress.

Water deficit threatens global agriculture and ecological construction. Buffalograss (Buchloe dactyloides (Nutt.) Engelm.), a C4 perennial grass native to arid regions, is an ideal model for dissecting drought tolerance mechanisms. In this study, we investigated the physiological responses of buffalograss to PEG-induced osmotic stresses through integrated transcriptomic and metabolomic analyses. The results showed that buffalograss could maintain plant dry weight, chlorophyll content and leaf water use efficiency, simultaneously increase leaf K+ and NO3− accumulation under osmotic stress. After 20% PEG treatment, key metabolites, including amino acids (e.g., aspartate, glutamate and leucine) and other organic acids (e.g., salicylic acid and citrate) were enriched. At the transcriptional level, genes related to chlorophyll biosynthesis (e.g., GluTR, MgCH, POR and DVR) and carbon fixation (e.g., rbcL and PPDK) were coordinately upregulated, implying a proactive reinforcement of photosynthetic capacity to sustain energy supply under water deficit. Several transcripts related to uptake and transport of K+ (e.g., HAK4, KUP6, HAK16 and NHX1) and NO3− (e.g., NPF6;3, NPF2;9, NRT2;1 and NPF8;5) were significantly altered, implying accumulation of K+ and NO3− in leaves may be a strategy for buffalograss to resist drought. In the root, organic acids appear to be the main osmotic regulators. The genes involved in biosynthetic pathways of aspartate (e.g., GOT), glutamate (e.g., ALT), leucine (e.g., BCAT), salicylic acid (e.g., PTAL), citrate (e.g., CS) were significantly induced. This study provides new insights into the drought adaptation mechanisms of buffalograss, emphasizing the roles of sustained photosynthesis, inorganic ion homeostasis and organic acid accumulation.