Seed priming-induced modulation of photosynthesis and root system architecture in faba bean under controlled conditions

Priming is a water-based method that partially hydrates seeds to activate the early germination process. Faba bean (Vicia faba L.) seeds typically take 7–14 days to germinate under normal conditions. Delayed germination may reduce faba bean plant establishment and potential yield. A greenhouse pot experiment evaluated the effects of seed priming treatments on photosynthetic traits and root architecture of four faba bean varieties (Windsor, Purple Negreta, Big Organic, and Midnight). Seeds were primed with water (hydropriming), NaCl (osmopriming), bulk ZnO, and nano-ZnO. Results revealed significant variation among varieties and priming treatments for morphological, physiological, and root-related traits. Midnight demonstrated the lowest growth and delayed flowering. Windsor and Purple Negreta exhibited higher shoot biomass and branching. Nano-ZnO significantly enhanced plant height and shoot dry matter, whereas NaCl priming increased root biomass and branching. Gas exchange parameters, including net photosynthesis rate (Pn), transpiration rate (E), and water use efficiency (WUE), were positively influenced by seed priming across growth stages. Water priming notably enhanced Pn and WUE, particularly in the Windsor variety. Chlorophyll content (SPAD) increased under seed priming, especially at the flowering stage. Specific root length decreased under priming, with NaCl resulting in the lowest values. Application of nano-ZnO reduced the number of roots by 11% while increasing root depth by 8% compared to the control. Overall, seed priming may enhance growth, photosynthesis, and root development of faba beans under controlled conditions regardless of seed size.