Core species impact plant health by enhancing soil microbial cooperation and network complexity during community coalescence

Soil microbial communities mix and interact, a widespread phenomenon known as community coalescence. However, in the context of different coalescence degrees, the effects and potential applicability of soil mixing on plant disease resistance have not been studied. Here, we mixed soils from two habitats (healthy and diseased soils) at different mixing ratios for watermelon planting. Rhizosphere soils were collected for amplicon sequencing to study the effects of different degrees of bacterial community coalescence on plant growth and disease resistance, as well as on the characteristics, network complexity and stability of rhizosphere microbial communities. Combined with network and cohesion analyses, we found that mixing in more healthy soil reduced the plant disease index and increased biomass by improving the stability and complexity of the network; positive cohesion, reflecting degree of cooperation, was also negatively correlated with the plant disease index. The rhizosphere from healthy soils enriched the core taxa, Nitrospirillum and Singulisphaera. These core taxa were significantly associated with disease suppression and important for regulating the positive cohesion and modularity of the networks. Overall, these findings revealed that the soil bacterial community coalescence enhanced the stability and complexity of the rhizobacterial network, simultaneously core taxa enhanced microbial potential cooperation and network complexity, ultimately enhancing plant health and biomass. Our results provide insights into the understanding of microbial community coalescence as a potentially effective mechanism for improving plant microbial community function and suggest promising new tools for improving plant fitness via mixing soil microbiota.