Alleviation of Saline–Alkaline Stress in Alfalfa by a Consortium of Plant-Growth-Promoting Rhizobacteria

Soil salinization critically threatens global agricultural productivity by impairing plant growth and soil fertility. This study investigated the potential of a consortium, comprising <i>Acinetobacter calcoaceticus</i> DP25, <i>Staphylococcus epidermidis</i> DP28, and <i>Enterobacter hormaechei</i> DP29, to enhance the saline-alkali tolerance of alfalfa and improve soil properties. The experiments comprised five germination treatments (saline control, each strain alone, consortium) and three pot treatments (non-saline control, saline control, consortium). Under saline-alkali stress, co-inoculation with the consortium significantly (<i>p</i> < 0.05) increased alfalfa seed germination rates, emergence rates, and biomass (shoot and root dry weight), while promoting root development. Physiological analyses revealed that the bacterial consortium mitigated stress-induced damage by enhancing photosynthetic efficiency, chlorophyll content, and antioxidant enzyme activities (superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)), while decreasing malondialdehyde (MDA) levels. Moreover, the inoculant improved osmoprotectant accumulation (soluble sugars, soluble proteins, and proline) and modulated soil properties by reducing pH and electrical conductivity (EC), while elevating nutrient availability and soil enzyme activities. Correlation and principal component analyses (PCA) confirmed strong associations among improved plant growth, physiological traits, and soil health. These findings demonstrate that the bacterial consortium effectively alleviates saline-alkali stress in alfalfa by improving soil health, offering a sustainable strategy for ecological restoration and improving agricultural productivity in saline-alkali regions.