Abstract
Utilizing plant growth-promoting rhizobacteria (PGPR) offers a sustainable solution for enhancing root nutrient uptake, stimulating plant growth, and increasing crop resilience, while reducing the need for fertilizers. This study aimed to investigate the combined effects of bacterial inoculants and different nutrient availability levels on cucumber plant development and nutrient accumulation. Seedlings were hydroponically grown in a completely randomized 4 × 3 factorial experimental design, which included four PGPR treatments (Azospirillum brasilense (AB), Ewingella americana (AS4), Pantoea agglomerans (AS8), and an uninoculated (Control) and three levels of nutrient availability (1X, 0.5X, and 0.1X) in the hydroponic solution, mimicking three different levels of crop fertilization. The results revealed that PGPR inoculants, fertilization levels, and their interaction had significant effects on several plant growth parameters. Notably, AS4 and AS8 significantly improved root and shoot traits, especially under the half-strength nutrient solution (0.5X), leading to biomass accumulation comparable to or even exceeding that observed under full-strength fertilization (1X). Under severe nutrient limitation (0.1X), PGPR inoculation partially alleviated growth restrictions, with A. brasilense notably enhancing shoot biomass and foliar N content, and AS4 slightly improving root development and micronutrient uptake. Ionomic and clustering analyses revealed that PGPR effects were both nutrient-specific and strain-dependent, reflecting complex interactions between bacterial activity and plant nutritional state. These findings suggest that targeted inoculation with AS4 and AS8 can enhance plant development under reduced fertilization, supporting more sustainable agricultural practices.