Effects of Arbuscular Mycorrhizal Fungi and Clay Minerals on Soil Nitrogen and Phosphorus Availability and Microbial Community Responses

Efficient management of soil nitrogen and phosphorus availability is important for soil fertility and crop productivity, but the field responses of rhizosphere microbial communities to arbuscular mycorrhizal fungi (AMF) and clay-mineral amendments remain unclear. A wheat-field experiment compared four treatments: an untreated control (A), bentonite (B; 39 kg plot−1), sepiolite (C; 39 kg plot−1), and AMF inoculation (E; 2.25 kg inoculum plot−1; 120 spores g−1). Each treatment comprised six 4 × 7.5 m plots. Soil physicochemical properties were evaluated using all six plots, whereas rhizosphere microbial sequencing used three plots per treatment (plots 2, 4, and 6; n = 3). Treatment E showed higher mean alkali-hydrolyzable nitrogen (101.50 vs. 93.33 mg kg−1) and available phosphorus (56.00 vs. 20.98 mg kg−1) than the control, whereas treatment B showed a 32.8% higher mean available potassium. None of the bacterial or AMF alpha-diversity indices differed significantly among treatments. Taxonomic summaries showed descriptive variation among treatments, whereas principal component analysis (PCA) and analysis of similarities (ANOSIM) did not detect significant treatment-level separation of either the bacterial or AMF communities. Shotgun metagenomic annotation, rather than 16S-based functional inference, further showed descriptive differences in nitrogen- and phosphorus-related gene-abundance profiles and functional potential; Pseudomonadota and Actinomycetota accounted for substantial shares of several nutrient-cycling gene categories, while pstB showed comparatively pronounced numerical variation among treatments. These metagenomic profiles represent genetic functional potential and do not demonstrate transcript abundance or metabolic activity. Overall, AMF inoculation and clay-mineral amendments were associated with descriptive differences in nutrient availability, taxonomic profiles, and metagenomic functional potential in alkaline wheat farmland, but significant treatment-level separation of the overall bacterial and AMF communities was not detected.