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Soil salinization is considered a serious agricultural problem that affects the growth and yield of plants in the world. Poly-γ-glutamic acid (γ-PGA) can adsorb cations and increase plant salt tolerance. However, the role of γ-PGA-producing bacteria in regulating plant salt stress response and the involved mechanisms remain unknown. This study characterized the effects of plant growth-promoting and γ-PGA-producing strain Bacillus amyloliquefaciens W25 on the growth and salt stress response in lettuce, and the microbial composition and structure in rhizosphere soil. This strain tolerated up to 8% NaCl and showed K solubilization and γ-PGA production in salt setress. Strain W25 significantly decreased the concentration of water-soluble Na+ in solution and the Na+ high storing capability of γ-PGA produced by strain W25 was 27.48 mg g−1. Inoculation with strain W25 could improve lettuce biomass production by decreasing the plant Na/K and Na/Ca ratios, improving the plant antioxidant levels, and regulating the plant IAA level. Strain W25 inoculation enhanced soil quality by reducing soil exchangeable sodium percentage, and increasing available K and P and soil enzyme activities. Furthermore, inoculation with strain W25 not only increased the diversities but also changed the compositions of bacterial and fungal communities in the lettuce rhizosphere soils. The abundances of beneficial soil bacteria, such as Pseudomonas , Massilia , and Bacillus , were enhanced, which showed significantly positive correlations with the biomass of lettuce. While the abundances of plant pathogenic fungal genera like Fusarium and Cephaliophora were decreased in strain W25 inoculated rhizosphere soils. This study showed the great potential of γ-PGA-producing PGPB for the enhancement of plant growth in salt-affected soil. [Display omitted] • Bacillus amyloliquefaciens W25 showed K solubilization and γ-PGA production. • Strain W25 promoted plant growth and salt tolerance. • Strain W25 decreased plant Na/K and Na/Ca ratios and regulated the plant IAA level. • Strain W25 improved the rhizosphere soil quality. • Strain W25 increased beneficial bacteria and decreased plant pathogenic fungi. [ABSTRACT FROM AUTHOR]

Super austenitic stainless steel (SASS) is widely used in extreme environments due to its excellent corrosion resistance and mechanical properties, and a feature of this grade is its relatively high nitrogen content. As valuable tools to study the solidification process and phase transformation, high temperature confocal microscopy (HTCM) and thermal analysis methods, such as differential thermal analysis (DTA) and differential scanning calorimetry (DSC), have been widely reported in the investigation of SASS. However, the inherent limitations of these two techniques make it difficult to explain the complex solidification behaviors of SASS, which involves multiple phases. Here, a unique design of HTCM-DTA was employed to investigate the nucleation and subsequent phase transformation of SASS. This in-house build apparatus enables contemporaneous in-situ observation of the surface and thermal analysis of the bulk thermal events. Using the novel HTCM-DTA device, we systematically revealed the four solidification modes of SASS and analyzed them in detail through thermodynamic arguments and multiple sets of experimental data under different conditions: (a) bimodal solidification with solid-state phase transformation, (b) bimodal solidification with liquid-state phase transformation, (c) pseudo-bimodal solidification, and (d) unimodal solidification. By comparing with the findings of earlier studies, the limitation of spatiotemporal separation employing HTCM and thermal analysis methods was pointed out. The results suggest that both the shielding gas and the time of retaining in the liquid state affect the N content in the melt, leading to a change of the primary nucleation phase. The cooling rate not only affects the undercooling and microstructure but also the transformation stage of δ-ferrite to γ-austenite, and when the phase transformation occurs in the liquid state it is usually accompanied by recalescence. These insights contribute understanding required for adjusting the continuous casting process of high nitrogen alloys. • In-situ observations on surface and thermal analysis of the bulk in parallel. • Solidification mode and phase transformation highly depend on shielding gas. • Four different solidification modes of S31254 were found and analyzed in detail. • The recalescence phenomenon was observed and analyzed frame by frame. • C.R. and t L influence the solidification behavior. [ABSTRACT FROM AUTHOR]