Effects of Direct and Indirect Cold Plasma Treatments on Barley (Hordeum vulgare L.) Seed Germination and Seedling Growth

This study presents a comparative evaluation of direct and indirect cold plasma treatments on seed germination and seedling growth of barley (Hordeum vulgare L. cv. Sahra). Direct treatments was performed using low-pressure nitrogen glow discharge under ion-dominant (P1) and electron-dominant (P2) conditions, while indirect treatments employed plasma-activated water (PAW) generated via atmospheric-pressure dielectric barrier discharge (DBD) in deionized (PAW1) and tap water (PAW2). Germination rate, seedling vigor index, and early growth parameters were assessed under controlled conditions. The ion-dominant plasma treatment (P1) showed the highest germination rate (93.3%) and seedling vigor index (7082.0), outperforming PAW1 (79.7%), PAW2 (73.3%), and control (72.0%). In contrast, electron-dominant treatment (P2) reduced germination (60.3%), demonstrating the crucial role of plasma species composition in biological responses. The enhanced efficacy of PAW was associated with its physicochemical properties, particularly a reduced pH (3.42) and increased conductivity (174 µS/cm for PAW1, 1281 µS/cm for PAW2), which may facilitate the stabilization of reactive nitrogen species and improve seed coat permeability. Optical emission spectroscopy and water contact angle measurements supported plasma-induced surface hydrophilization and the presence of excited nitrogen species under ion-dominant conditions. These findings establish ion-dominant nitrogen cold plasma as an effective, chemical-free seed priming strategy and emphasize the importance of plasma regime control in optimizing sustainable agricultural applications.