Ecological Microenvironment Response of Rhizosphere Soil Microbial Communities to Varying Soil Amendments: Insights from Diversity, Stability, and Multi-Functionality

Continuous cropping obstacles (CCOs) severely disrupt the soil physical structure, nutrient cycling, and microbial community balance, leading to decreased crop productivity. However, the effects of soil amendment interventions on bacterial, fungal, and archaeal communities in foxtail millet (Setaria italica (L.) P. Beauvois.) systems are not well comprehended. Selected physical, chemical, biological soil amendment and crop rotations were evaluated for their effects on rhizosphere soil microbial diversity, composition, network characteristics, community assembly processes, niche breadth, and multi-functionality. High-throughput sequencing of 16S rRNA and ITS regions demonstrated that earthworm castings significantly enhanced archaeal Chao1, Shannon diversity, and multi-functionality. Meanwhile, Bacillus mucilaginosus enhanced fungal diversity, and B. subtilis promoted bacterial network complexity. In continuous cropping soil alone, microbial communities exhibited low diversity and were predominantly governed by ecological drift. In contrast, soil amendment treatments shifted assembly toward deterministic processes, including homogeneous and heterogeneous selection. However, the analysis demonstrated greater complexity and niche width in bacterial communities than in fungal or archaeal communities, with keystone modules driven by Actinomycetota, Ascomycota, and Halobacteriota. Structural equation modeling indicated that soil physicochemical properties directly mediated rhizosphere soil microbial alpha diversity, which in turn positively influenced multi-functionality. Overall, organic amendments and microbial inoculants were associated with increases in microbial diversity, network stability, and functionality in this pot experiment, suggesting that such practices may help mitigate CCOs and sustainably improve foxtail millet productivity in dryland agricultural systems.