Synergistic regulation of calcium hydroxide and ARC microbial inoculant on rhizosphere microbiota and soil chemical properties during peanut middle growth stages in acidic red soils

To address the high acidity and low fertility of acidic red soils in southern China, this study evaluated the effects of calcium hydroxide (Ca(OH) 2 ) and the Aspergillus -Rhizobia Coupling (ARC) microbial inoculant on rhizosphere microbiota, soil chemical properties, and peanut (Arachis hypogaea L.) yield during the middle growth stage of peanuts (i.e., flowering-pegging and pod-setting stages). Calcium hydroxide modulated the rhizosphere microenvironment by increasing soil pH and exchangeable calcium, thereby enhancing microbial α-diversity, stimulating the metabolic activity of both ARC inoculant strains and native microbiota, and enriching carbon and nitrogen (C-N) cycling-related taxa (e.g., Sphingomonas ), thus elevating soil organic matter and hydrolyzable nitrogen, and ultimately increasing peanut total pod weight per plant. Meanwhile, the ARC inoculant reshaped the rhizosphere microbial community structure without altering α-diversity, specifically enriching phosphorus and potassium (P-K) activation-related taxa (e.g., Paraglomus ), thereby increasing soil available phosphorus and available potassium, and ultimately enhancing peanut total pods per plant. The combined application of these amendments exhibited obvious synergistic effects in the above aspects, with the Ca 50 A 4 treatment (750 kg/ha calcium hydroxide + 60 kg/ha ARC inoculant) achieving the greatest effects. Compared with the control (Ca 0 A 0 , CK), the total pods per plant and total pod weight per plant in the Ca 50 A 4 treatment were significantly increased by 57.14 % and 45.18 %, respectively. Overall, calcium hydroxide improved the rhizosphere microhabitat primarily through chemical regulation, whereas the ARC inoculant acted via direct and community-mediated biological regulation. Their synergistic application provides an efficient and innovative strategy for improving soil quality and enhancing peanut productivity in acidic red soil regions of southern China. • Calcium boosts the soil microenvironment by neutralizing H + and supplementing Ca 2+ . • ARC inoculant activates nutrients by the ecological function of composite strains. • Calcium and ARC inoculant mainly increase the weight and number of pods, respectively. • Combined application of calcium and ARC inoculant is superior to single application. • Middle growth stages of peanuts intrinsically drive the soil amelioration.