Improvement of rhizosphere—rhizoplane—endosphere bacterial network on salt tolerance of maize after biological enhancement of earthworm and mycorrhizal fungi

Salt stress is one of the most important abiotic stresses that restrict crop growth. Plant root-related microorganisms are important in moderating abiotic stress in plants. In this study, changes in microbial community composition in the different ecological niches of maize roots were studied to evaluate whether earthworms and mycorrhizal fungi could improve the salt tolerance of maize.

This experiment was a 2 × 2 factorial design representing all the combinations of arbuscular mycorrhizal (AM) fungi (2.5 g/kg) with earthworms (10/pot) in saline soil. After culture, rhizosphere, rhizoplane and endosphere bacteria of maize were collected, and community assembly was analyzed and co-occurrence network was constructed.

The regulating effect of earthworm-arbuscular mycorrhiza fungi (AMF) on bacterial community gradually decreased along the rhizosphere-rhizoplane-endosphere continuum. Earthworms and AMF are able to regulate key species in bacterial co-occurrence networks, thereby influencing the composition and function of the microbiome. Members of Rhizobiaceae and Gemmatimonadaceae, as key species, potentially regulate rhizosphere bacterial communities with earthworms and AMF. On the rhizoplane, AMF may specifically enriched bacterial communities with functions related to plant P absorption and maintenance of plant K-Na ratio, thereby maintaining plant nutrient homeostasis.

Soil nitrate nitrogen content, plant K-Na ratio and root abscisic acid content were correlated with a large number of microbial network modules, and had potential causal relationship with rhizosphere, rhizoplane and endosphere bacterial community changes, which played an important role in the biomass accumulation of maize seedlings in saline soil. These results will provide a theoretical basis for the study of soil root-microbe interactions.