Bioinoculant substitution enhances rhizosphere soil quality and maize growth by modulating microbial communities and host gene expression in alkaline soils.

The application of plant growth-promoting bacteria (PGPB) as bioinoculants is widely recognized for improving crop yields and soil fertility. However, the precise mechanisms underlying their impact on rhizosphere soil quality and crop productivity remain insufficiently understood. This study elucidates how a solid bioinoculant, comprising Bacillus velezensis FZB42 and attapulgite clay, enhances rhizosphere soil quality and maize (Zea mays) growth in nutrient-deficient alkaline calcareous soils. Pot experiments reveal that bioinoculant application promotes extensive root colonization under nitrogen-deficient conditions, with significantly higher colonization rates observed in the half-nitrogen (HN) and zero-nitrogen (ZN) treatments compared to full-nitrogen conditions. Notably, bioinoculant application in ZN and HN significantly increases phosphorus availability and soil quality in the rhizosphere. Furthermore, maize growth parameters, including plant height, stem diameter, and kernel yield, are markedly enhanced, with optimal biomass accumulation achieved under HN conditions. High-throughput sequencing of rhizosphere microbiomes uncovers significant shifts in microbial community composition, with enrichment of key taxa involved in nutrient cycling and plant-microbe interactions. Transcriptomic analysis of maize tissues demonstrates the upregulation of genes associated with nutrient transport, photosynthesis, fatty acid biosynthesis, and kernel development, with a pronounced enrichment in metabolic pathways linked to growth and productivity. Structural equation modeling indicates that increased microbial diversity and gene expression collectively account for 69 % of the variance in the soil quality index and 45 % of the variance in maize yield. These findings provide critical mechanistic insights into the role of solid bioinoculant in enhancing soil fertility and crop performance, highlighting their potential as a sustainable agricultural strategy for improving productivity in low-fertility alkaline soils.