Synthetic microbial communities mediate maize growth and soil microecology under saline-alkali stress

Soil salinization results in soil degradation and a decline in productivity. Synthetic microbial communities (SynComs) perform more stably than single strains, providing a new approach for saline-alkali soil improvement. Two synthetic communities SynCom1 and SynCom2 were assembled from plant rhizosphere salt-tolerant isolates via antagonism and co-culture assays. Six treatments were established to test SynCom inoculation effects. A represented non-sterilized soil added with SynCom1; B represented non-sterilized soil added with SynCom2, C represented non-sterilized soil supplemented with LB medium as control; D represented sterilized soil added with SynCom1; E represented sterilized soil added with SynCom2; F represents sterilized soil supplemented with LB medium as control. This design was used to distinguish the respective effects of SynComs, indigenous soil microorganisms and fermentation medium. SynComs enhanced the growth of maize plants, and decrease soil pH and electrical conductivity. Specifically, SynCom1 increased the activities of soil urease, alkaline phosphatase, and dehydrogenase under unsterilized environment (P < 0.05). The absolute quantification of 16 S RNA revealed that both agents caused an increase of absolute bacterial abundance in sterilized soil, compared to unsterilized soil. Notably, SynCom2 led to an increase in the beneficial genera including Streptomyces and Micromonospora. In unsterilized soil, the co-occurrence network of SynCom1 exhibited the highest complexity. However, in sterilized soil, the network inoculated with SynCom2 showed greater stability than that with SynCom1. Functional prediction revealed that SynCom1 mainly participated in basal energy metabolism, while SynCom2 activated secondary metabolism in non-sterilized soils. In sterilized soils, the two communities were enriched in colonization adaptation and nutrient metabolism functions, respectively. Our study provides a practical basis for the improvement of saline-alkali soils using SynComs.