Soil physicochemical traits and environmental context shape the efficacy of a halophyte-derived plant growth-promoting bacterial biofertilizer

PGPB-based biofertilizers offer a sustainable and cost-effective alternative for agriculture; however, their widespread adoption remains limited due to gaps in understanding strain adaptability to the physicochemical variability of soils and the reproducibility of results under field conditions. This study evaluated how soil properties and environmental variability modulate the beneficial effects of a halophytic PGPB inoculum, composed of self-compatible, stress-tolerant strains with multiple growth-promoting traits, on crop productivity. To this end, two experimental approaches were designed in which Beta vulgaris plants were subjected to two inoculation treatments (non-inoculated and inoculated) and grown in two soils with contrasting physicochemical properties, both under controlled greenhouse and field conditions, respectively. Results showed that the bacterial inoculum significantly enhanced . vulgaris growth, physiological performance, and nutritional balance under controlled greenhouse conditions. However, inoculation efficacy was strongly soil-dependent and did not scale linearly from greenhouse to field. In Soil 1, characterized by a sandy texture, low organic matter content, and limited water and nutrients retention, inoculation increased leaf dry matter content by 55% and 91%, respectively. In contrast, plants grown in Soil 2, with finer texture, higher organic matter content, and greater nutrient availability, exhibited a modest increase of 17% following inoculation. Field validation further confirmed this context dependency. While inoculation enhanced plant yield and physiological performance in plants grown in experimental Area 1, no significant benefits were detected in Area 2. In fertile soils like Area 2, optimal nutrient availability and favorable climatic conditions likely reduce plant dependence on microbial related functions, masking inoculation effects. These findings demonstrate that halophytic PGPB inoculum can substantially improves B. vulgaris growth and physiology performance under suboptimal edaphic and climatic conditions, particularly in nutrient-poor, sandy soils, while its benefits are limited in fertile soils with optimal climate, emphasizing the need to consider soil and environmental context for effective biofertilizer use. • PGPR biofertilizer improves Beta vulgaris growth under variable soils. • Inoculation enhances photosynthetic performance and PSII efficiency. • Bacterial inoculation modulates nutrient and ion accumulation. • Soil type strongly modulates the efficacy of bacterial inoculation. • Field responses vary; benefits are higher under suboptimal conditions.