Seed Priming with Magnesium Nitrate Improves Mineral Nutrition and Early Growth of Bambara Groundnut Under Salinity Stress

Seed priming studies commonly emphasize growth and physiological responses, yet ionomic regulation and tissue-specific nutrient allocation under salinity stress remain poorly explored, particularly in underutilized crops such as Bambara groundnut (Vigna subterranea L.). This study investigated whether Mg(NO3)2 seed priming, previously shown to enhance salt tolerance, is associated with consistent ionomic patterns in contrasting Bambara groundnut genotypes (BGN-14 and BGN-25). Seeds were primed with 0.03% Mg(NO3)2 and grown under control or saline conditions (200 mM NaCl) for five weeks. Shoot and root tissues were analyzed for macro- and micronutrient composition using ICP-OES. In BGN-14, salinity caused a marked reduction in shoot fresh weight (−49.5%, p < 0.05), whereas Mg(NO3)2 priming largely mitigated this effect under salinity (−0.4%, p > 0.05). Root fresh weight declined numerically under salt stress (−70.1%) and primed + salt conditions (−45.5%), but these changes were not statistically significant. Shoot dry weight increased significantly in primed plants (+83.5%, p < 0.05), while salinity reduced SDW (−58.4%); primed + salt plants maintained SDW near control levels (+2.6%). In BGN-25, root biomass was unaffected by treatments, whereas salinity significantly reduced shoot biomass relative to primed plants, with a consistent trend of primed > control > primed + salt > salt. Salinity increased the Na+/K+ ratio, particularly in roots. In BGN-14, the root Na+/K+ ratio increased significantly from 1.07 to 4.49 (p < 0.05), indicating enhanced Na+ accumulation, while shoot ratios increased non-significantly. BGN-25 showed a more moderate increase in shoot ratios and a pronounced rise in root ratios. Principal component analysis revealed distinct nutrient clustering, with Na, Fe, and Al loading strongly under salinity, while Ca, K, Mg, and Cu aligned with improved physiological performance. Although differences between salt and primed + salt treatments were often not statistically significant, several ion ratios and nutrient relationships were numerically enhanced under Mg(NO3)2 priming. This study builds upon earlier physiological findings (where BGN-14 consistently exhibited a stronger positive response to Mg(NO3)2 priming, outperforming BGN-25 under salt stress) and provides exploratory, hypothesis-generating evidence that Mg(NO3)2 priming may contribute to salinity tolerance through coordinated ionomic adjustments, including altered Na+ allocation and improved nutrient balance, rather than complete Na+ exclusion. These findings highlight the relevance of ionomic responses in understanding stress adaptation in underutilized legume crops.