Surface Chemical and Structural Modifications of Barley Seeds Induced by Low-Temperature Oxygen and Nitrogen Plasma Treatments

Low-temperature plasma treatments are increasingly explored to stimulate seed germination and early plant development. In this study, barley seeds were exposed to dielectric barrier discharge (DBD) plasma generated in air with controlled oxygen or nitrogen admixtures to elucidate surface chemical and structural modifications. X-ray photoelectron spectroscopy (XPS) showed a pronounced increase in oxygen-containing functional groups (C–O, C=O, O–C=O) and the emergence of nitrogen functionalities after plasma exposure, indicating oxidative activation and partial surface amination. SEM-EDX analysis revealed slight oxygen enrichment and nitrogen incorporation at the near-surface region, while backscattered electron images confirmed that the plasma treatments did not induce measurable morphological damage. Raman and ATR-FTIR spectra demonstrated that the molecular backbone of polysaccharides and proteins remained intact, although bands associated with –OH and –NH vibrations intensified, confirming increased surface hydrophilicity. Water absorption kinetics, modeled using the Peleg equation, showed that plasma-treated seeds absorbed water more rapidly than untreated controls, evidencing improved wettability and hydration efficiency. Overall, the combined results indicate that plasma exposure primarily induces surface oxidation and mild nitrogen incorporation without compromising seed integrity, thereby enhancing water uptake.