Responses of growth and quality of Glycyrrhiza uralensis to salt-alkali-tolerant microbial inoculant via the remodeling of rhizosphere microenvironments in moderate and severe saline-alkali soils

Abstract

Glycyrrhiza uralensis is an ecologically and economically important medicinal species for saline-alkali land restoration in arid northwest China. Nevertheless, excessive soil salinity, alkalinity and nutrient deficiency substantially restrict its growth and degrade medicinal quality. Microbial inoculation serves as a promising strategy to alleviate salt-alkali stress, yet the field stability and rhizosphere regulatory mechanisms of inoculants under diverse cultivation regimes remain poorly understood, limiting their field application. Building on our prior strain screening and preliminary field validation, this study utilized a composite inoculant containing Pseudomonas silesiensis , Arthrobacter sp. GCG3 and Rhizobium sp. DG1, and investigated its effects on G. uralensis growth, bioactive metabolites, rhizosphere soil properties and microbial communities under three field viable cultivation scenarios (direct seeding and seedling transplanting in moderately saline-alkali soil, seedling transplanting in severely saline-alkali soil) with respective tailored fertilization, planting densities and inoculation schedules. The results revealed that under all scenarios, the inoculation induced an increasing trend in the root dry weight and bioactive compound accumulation, with markedly higher dry root weight in seedling transplanting scenarios (101.68%, moderately saline-alkali soil; 53.96%, severely saline-alkali soil, P  < 0.05). Glycyrrhizic acid contents per plant rose by 57.32, 106.11 and 6.56%, while those of liquiritin rose by 42.50, 177.24 and 42.34%, respectively. The inoculant barely altered rhizosphere pH and soluble salt contents, yet universally regulated rhizosphere nutrient pools, which were reflected in a uniform reduction of nitrate nitrogen and scenario-specific shifts in other available nutrients as well as soil organic matter. High-throughput sequencing verified that this inoculant could reshape the rhizosphere microbial community structure of G. uralensis ; across all scenarios, the relative abundance of pathogenic Fusarium significantly decreased, and indigenous beneficial bacteria and fungi were enriched. This inoculant exhibited stable growth-promoting effects across all cultivation regimes. The combined application of microbial inoculation and seedling transplanting is therefore recommended for large-scale and high-quality cultivation of G. uralensis in moderately saline-alkali soils of arid northwestern China, as this integrated practice maximizes plant growth, medicinal compound accumulation, and rhizosphere microenvironment optimization.