Targeted Recruitment of Cross-Kingdom Phosphate-Solubilizing Microbes Drives Asymmetric Rhizosphere Responses Between Solanum rostratum and Cenchrus pauciflorus Benth. in Sandy Habitats

In resource-poor sandy habitats, alien plant co-invasion often triggers intense belowground competition mediated by rhizosphere microorganisms. However, the mechanisms by which these plants overcome nutrient limitations remain unclear. Here, we conducted an eight-month in situ monitoring of single- and co-invasion plots of Solanum rostratum and Cenchrus pauciflorus Benth. in the Horqin Sandy Land. By integrating soil enzyme assays with 16S rRNA and internal transcribed spacer (ITS) amplicon sequencing, we characterized their rhizosphere microbial community assembly. Co-invasion exposed both species to convergent biotic stress, characterized by the significant enrichment of the pathogenic fungi Didymella and Pseudogymnoascus (linear discriminant analysis (LDA) > 4.0). To mitigate these pressures, the dominant competitor, S. rostratum, specifically recruited a cross-kingdom phosphate-solubilizing consortium comprising Bacillus and Penicillium (LDA > 4.0). This targeted recruitment significantly enhanced rhizosphere activities, increasing phosphatase and sucrase to 86.10 U/g and 2.17 U/g, respectively, thereby maintaining available phosphorus at a high level (35.55 mg/kg). Conversely, the subordinate competitor, C. pauciflorus, lost key native stress-resistant bacteria such as Rubrobacter (relative abundance dropping from 5.39% to 3.27%) and failed to recruit effective microbes, leading to the rapid depletion of available phosphorus (dropping to 21.38 mg/kg). Ultimately, under dual nutrient and pathogenic stress, the precise recruitment and functional integration of cross-kingdom phosphate-solubilizing microbes are strongly linked to the divergent belowground competitive outcomes between these co-invading plants.