Metagenomic insights into microbial responses to soil amendments and oat cultivar identity in saline-alkali soils.

Host cultivar identity can influence rhizosphere microbiomes, yet its relative importance compared with soil amendment regime in saline-alkali farmland remains insufficiently resolved. Here, we compared how two oat (Avena sativa) cultivars shape soil microbial communities and functions under contrasting amendment regimes. In a field experiment, two oat cultivars, Tianyan 60 (TY60) and Musite (MST), were grown under five treatments: control, bacterial agent, organic manure, silica fume, and their combination. Soil physicochemical properties, enzyme activities, and metagenomic sequencing were used to characterize microbial taxonomic and functional profiles. Amendment regimes strongly altered soil nutrient and enzyme variables, whereas cultivar identity explained more variation than amendment regime in microbial community structure and beta diversity under the tested field conditions. Taxonomically, TY60 showed stronger amendment-associated reassembly, including enrichment of Bacteroidota, Pseudomonadota, and Ascomycota under selected treatments, whereas MST retained a comparatively more stable higher-rank backbone. Network analysis further indicated cultivar-associated differences in microbial community organization. Functionally, organic manure and the combination treatments (MIX3) produced the broadest shifts in C, N, P, and S cycling gene modules, particularly in TY60-associated soils. Null-model analyses showed that stochastic assembly dominated overall, but the dominant stochastic component differed among kingdoms, with bacteria mainly governed by drift, archaea by homogeneous dispersal, and fungi by a more balanced contribution of the drift and homogeneous dispersal. These results indicate that cultivar identity played a stronger role than amendment regime in shaping amendment-associated microbiome and functional shifts in this two-cultivar comparison, highlighting the potential value of combining cultivar choice with organic-microbial inputs to improve rhizosphere multifunctionality in saline-alkali agroecosystems.