Silicon Nanoparticles Enhance Cold Tolerance in <i>Elymus nutans</i> Seedlings by Regulating Growth, Physiology, and Gene Expression Under Cold Stress

ABSTRACT Cold stress represents one of the primary abiotic stresses affecting forage growth, development, yield, and quality. As a novel agricultural nanomaterial, silicon nanoparticles (SiNPs) demonstrate unique potential in regulating plant stress responses. However, their mechanism of action in forage cold responses remains poorly understood. This study aims to explore the role of SiNPs in the cold tolerance mechanism of Elymus nutans ( E. nutans ) through physiological and transcriptomic analyses. In this study, E. nutans seedlings were subjected to 3 h and 48 h of cold stress, with SiNPs applied to a portion of the samples. After 3 h of cold stress, the proline (Pro) content in seedlings treated with SiNPs increased by 16.38%. After 48 h of cold stress, the superoxide dismutase activity increased by 7.92%, the Chl content increased by 22.74%, and the abscisic acid (ABA) content decreased by 12.83%. Transcriptomic analysis revealed time‐dependent regulatory effects of SiNPs; 3 h cold stress induced photosynthesis‐related gene expression, while 48 h cold stress promoted upregulation of ribosome biosynthesis and amino acid biosynthesis genes. Weighted gene co‐expression network analysis (WGCNA) identified two core modules (skyblue and floralwhite), enriched in photosynthesis, secondary metabolism, and ribosomal pathways, respectively, which were closely associated with cold‐response physiological traits. In conclusion, SiNPs enhance cold tolerance in the QL20‐04 (QL) variety of E. nutans by synergistically regulating photosynthetic protection, ribosomal rebuilding, and amino acid metabolism in a stress duration‐dependent manner. This study provides novel molecular insights for improving cold adaptation in alpine grasslands and optimizing SiNPs applications in cold‐vulnerable agroecosystems.