Root exudates are key drivers of rhizosphere microbial assembly, yet their effects across coexisting plant species with different functional roles remain unclear. We examined the effects of root exudates from five desert steppe species in Inner Mongolia: one constructive species, two dominant species, and two accompanying species. Exudates were collected hydroponically and applied to bulk soil in a three-week incubation experiment. Microbial communities were analyzed using high-throughput sequencing, functional prediction, and co-occurrence network analysis. Exudate addition significantly altered bacterial community composition, reducing bacterial richness, while fungal communities showed weaker responses. Exudates from constructive and dominant species enriched Actinobacteria, including Rubrobacter, Arthrobacter, and Solirubrobacter, and increased functional groups linked to chemoheterotrophy and nitrogen transformation. In contrast, exudates from accompanying species induced distinct microbial assemblages without promoting Actinobacteria dominance. Exudate addition also increased bacterial network complexity, suggesting enhanced microbial interactions. Soil pH decreased and available nitrogen and phosphorus increased, strongly correlating with bacterial community shifts. Overall, root exudates mediate species-specific microbial assembly and functional reorganization in desert steppe soils, driven mainly by plant functional roles rather than taxonomic relatedness. This study provides new insights into how plant-derived substrates regulate microbial communities and nutrient cycling in arid ecosystems.
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