Physiology, agronomic traits, and transcriptome jointly revealed the radiation toxicity effect and response mechanism of carbon ion beam irradiation on soybean.

Exposure of plant seedlings to acute ionizing radiation can induce developmental toxicity, yet the toxic effects and response mechanisms to carbon ion beam (CIB) radiation remain poorly understood. In this study, three-day-old soybean seedlings were exposed to 0, 5, 10, and 15 Gy of CIB radiation. The toxicity and response mechanism of soybeans to CIB radiation were examined using physiology, agronomic traits, and transcriptome analysis. Physiological results demonstrated dose-dependent reductions in seedling growth and survival rate compared to the control check, with growth parameters (seedling height and first compound leaf area) decreasing by 45.95 % and 41.75 %, respectively, and survival rate dropping to 44.44 % at 15 Gy, while fertility showed low sensitivity to radiation. At 15 Gy, photosynthetic pigment contents decreased by 21.28 % -34.28 %, accompanied by aberrant Photosystem II functional traits indicative of photosystem compensation, though photosynthetic efficiency was compromised. A subtle but nonsignificant hormesis effect was observed in chlorophyll content and fluorescence parameters at 5 Gy. Agronomic trait analysis revealed that 15 Gy CIB radiation significantly increased the number of mainstem nodes while profoundly inhibiting bottom pod height and branch number. Reproductive structures exhibited a notable increase in seed width, with no significant differences in other parameters compared to the control check. Transcriptomic analysis identified plant hormone signal transduction pathways, ubiquinone and other terpenoid-quinone biosynthesis, and photosynthesis-antenna proteins as key regulators of soybean responses to CIB irradiation. A multi-scale response mechanism is proposed to decipher the molecular-physiological trade-offs induced by CIB, offering a comprehensive understanding of the complex interplay between molecular and physiological responses. This study elucidates the toxic effects and response mechanisms of acute high-dose CIB irradiation for soybean seedlings, providing theoretical insights for the safe agricultural application of radiation technologies.