Bacillus cereus G2 Facilitates N Cycle in Soil, Further Improves N Uptake and Assimilation, and Accelerates Proline and Glycine Betaine Metabolisms of Glycyrrhiza uralensis Subjected to Salt Stress

Soil salinity is a severe abiotic stress that reduces crop productivity. Recently, there has been growing interest in the application of microbes, mainly plant-growth-promoting bacteria (PGPB), as inoculants for saline land restoration and plant salinity tolerance. Herein, the effects of the plant endophyte G2 on regulating soil N cycle, plant N uptake and assimilate pathways, proline and glycine betaine biosynthesis, and catabolic pathways were investigated in Glycyrrhiza uralensis exposed to salinity. The results indicated that G2 improved the efficiency of N absorption and assimilation of plants by facilitating soil N cycling. Then, G2 promoted the synthesis substrates of proline and glycine betaine and accelerated its synthesis rate, which increased the relative water content and reduced the electrolyte leakage, eventually protecting the membrane system caused by salt stress in G. uralensis. These findings will provide a new idea from soil to plant systems in a salinity environment.