Soil salinization critically threatens global agricultural productivity by impairing plant growth and soil fertility. This study investigated the potential of a consortium, comprising Acinetobacter calcoaceticus DP25, Staphylococcus epidermidis DP28, and Enterobacter hormaechei 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 (p < 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.

Drought stress is one of the major impediments to plant growth. Plant growth-promoting rhizobacteria (PGPR) can mitigate moisture stress in plants by increasing the ability of plant nutrient uptake and transport. In this study, we investigated the root phenotype, mineral nutrients (in leaves, roots, and soil), soil pH, water saturation deficit (WSD), free water content (FWC), and bound water content (BWC) of leaves of two alfalfa varieties, ‘Galalxie Max’ (drought-tolerant) and ‘Saidi 7’ (drought-sensitive), in the presence or absence of Bacillus amyloliquefaciens QST713 under drought stress conditions. The results showed that water stress negatively affected both cultivar root morphology (total root length, average diameter, total surface area, and volume) and the contents of K and Fe in leaves, roots, and soil. It also reduced the Mn and Zn contents in the soil while increasing the content of Na in the leaves and soil. Additionally, alfalfa plants under drought stress exhibited higher levels of soil pH, WSD, and BWC but lower contents of FWC and ratios of BWC/FWC in the leaves of both cultivars. However, QST713 application significantly enhanced the total root length, average root diameter, and the contents of K and Fe in alfalfa leaves, roots, and soil, as well as the BWC/FWC ratio in leaves under drought stress conditions. A significant reduction in the Na content was detected in QST713-treated alfalfa leaves and soil under drought stress. Furthermore, QST713 application noticeably decreased soil pH and WSD. The current findings showed that QST713 enhanced the water stress tolerance of alfalfa plants by ameliorating root morphology, reducing soil pH, and improving the BWC/FWC ratio, consequently promoting the accumulation of mineral nutrients (mainly K and Fe). Overall, Bacillus amyloliquefaciens QST713 can serve as a potential green fertilizer in sustainable agriculture to improve soil nutrients and enhance plant production under increasing drought conditions.

Speed breeding technology has been used as a promising approach to accelerate plant breeding cycles and enhance agricultural productivity. However, systematic research on optimizing speed breeding conditions for alfalfa (Medicago sativa L.) in controlled plant factory environments remains limited. This study aimed to optimize light intensity, nutrient solution formulations, and photoperiod conditions for alfalfa speed breeding in plant factories equipped with full-spectrum LEDs, and to validate the applicability of these conditions across cultivars with different fall dormancy levels. Results demonstrated that a light intensity of 250 μmol·m⁻²·s⁻¹ significantly enhanced photosynthetic parameters, antioxidant enzyme activities, and biomass accumulation while minimizing malondialdehyde (MDA). The 75% concentration of the Japanese garden-test formula (JGTF) outperformed the Hoagland solution in promoting growth and photosynthetic pigment synthesis. An extended photoperiod (22 h/d) substantially accelerated growth and shortened flowering time. Under optimized conditions (250 μmol·m⁻²·s⁻¹ light intensity, 22 h/d photoperiod, and 75% Japanese Garden Test Formula), alfalfa cultivars reached initial flowering in approximately 37 days, regardless of fall dormancy level. This study establishes an effective speed breeding protocol for alfalfa, and the optimized conditions demonstrate broad applicability across cultivars with varying fall dormancy characteristics, providing a valuable foundation for accelerated alfalfa breeding programs and contributing to enhanced forage crop development efficiency.

Background: Lespedeza davurica is an important perennial leguminous shrub endemic to China’s Loess Plateau, and it plays a crucial role in ecosystem restoration and soil erosion control. However, phosphorus deficiency and environmental stresses limit its growth potential and ecological function. Methods: In the present study, the interaction between Acinetobacter calcoaceticus DP25, a phosphate-solubilizing rhizobacterium isolated from L. davurica rhizosphere, and L. davurica was investigated. We performed biochemical analyses of leaves from L. davurica planted in saline–alkali soil to monitor antioxidant defense systems and stress-related metabolites, and conducted a combination of transcriptomics and metabolomics approaches to elucidate the bacteria-mediated enhancement of growth and stress tolerance in L. davurica. Results: DP25 inoculation substantially enhanced L. davurica growth performance, increasing plant height by 47.68%, biomass production by 102.54–132.42%, and root architecture parameters by 62.68–78.79% (p < 0.0001). Catalase activity, a key antioxidant enzyme, showed a marked increase of 41.53% (p < 0.001), while malondialdehyde and free proline contents decreased by 18.13% and 19.33%, respectively (p < 0.05). Transcriptomic analysis revealed 263 differentially expressed genes, with enrichment in carotenoid biosynthesis, ABC transporters, and pentose and glucuronate interconversion pathways. Metabolomic profiling identified 246 differentially accumulated metabolites, highlighting enhanced secondary metabolite production and stress response mechanisms. Integration of multi-omics data revealed 19 co-regulated pathways involved in growth promotion and stress tolerance. Conclusions: A. calcoaceticus DP25 enhances L. davurica growth through coordinated regulation of metabolic pathways involved in photosynthesis, antioxidant defense, and secondary metabolite biosynthesis. These findings provide molecular insights into beneficial plant–microbe interactions and support the development of sustainable strategies for ecosystem restoration in degraded environments.

Soil salinity severely impairs plant growth, and polyamines such as spermidine (Spd) are known to bolster stress tolerance by acting as osmoprotectants and signaling molecules. Using TiO₂ enrichment, iTRAQ quantification, and bioinformatics analysis, we identified 870 proteins and 157 differentially phosphorylated proteins. Functional annotation showed that salt stress activated key components of the Salt Overly Sensitive pathway, particularly serine threonine kinases (SOS2) and Ca²⁺ binding sensors (SOS3). Among thirty-six SOS-associated kinases detected, eight SOS2 isoforms, four MAPKs, and two SOS3 homologs were significantly upregulated by NaCl, and Spd further increased the phosphorylation of six SOS2 proteins and one SOS3 protein under salt stress, with no detectable effect on SOS1. qRT PCR revealed enhanced expression of MAPKs and calcium-dependent protein kinases, suggesting a phosphorylation-centered model in which Spd amplifies Ca²⁺-mediated SOS signaling and reinforces ion homeostasis through coordinated transcriptional priming and post-translational control. Additional, proteins involved in protein synthesis and turnover (ribosomal subunits, translation initiation factors, ubiquitin–proteasome components), DNA replication and transcription, and RNA processing showed differential expression under salt or Spd treatment. Central metabolic pathways were reprogrammed, involving glycolysis, the TCA cycle, the pentose phosphate pathway, as well as ammonium transporters and amino acid biosynthetic enzymes. These findings indicate that exogenous Spd regulated phosphorylation-mediated networks involving the SOS signaling pathway, protein homeostasis, and metabolism, thereby enhancing cucumber salt tolerance.

Soil acidification from excessive nitrogen and potassium fertilization in protected cucumber systems impairs calcium uptake, triggering physiological calcium deficiency and reducing yield. We investigated whether the plant growth-promoting rhizobacterium Bacillus amyloliquefaciens QST713 could mitigate low-calcium stress in cucumber (‘Jinyou No. 4’). Under controlled nutrient solution irrigation (4, 0.4, and 0 mmol/L Ca²⁺, with or without B. amyloliquefaciens QST713), low-calcium conditions suppressed growth, reduced ion uptake capacity, photosynthetic pigment content, gas exchange (Pn, Gs, Tr), PSII efficiency (ΦPSII, ETR), and decreased carbohydrate (starch, sucrose) accumulation, while disrupting nitrogen balance (decreases in NO₃⁻-N, soluble protein, and amino acids; increase in NH₄⁺-N) and inhibiting key N-assimilation enzymes (NR, GS, GOGAT, GDH). Inoculation with B. amyloliquefaciens QST713 reversed these effects: it enhanced ion acquisition, chlorophyll content, and photosynthetic performance; restored carbohydrate reserves; promoted NO₃⁻ uptake and NH₄⁺ assimilation; and upregulated N-metabolizing enzyme activities. Principal component analysis confirmed strong coupling among growth, photosynthesis, and C-N metabolism. In summary, low-calcium stress markedly inhibited cucumber growth, suppressed photosynthetic activity, and reduced the levels of carbon and nitrogen metabolism. Application of B. amyloliquefaciens QST713 effectively alleviated the physiological damage caused by low-calcium stress, enhancing photosynthetic performance and thereby accelerating the synthesis and turnover of carbon- and nitrogen-containing metabolites. These effects collectively improved cucumber tolerance to low-calcium conditions and promoted plant growth and development. This study provides a preliminary theoretical basis for further exploration of the stress-resistance capacity of B. amyloliquefaciens.