Temporal Nutrient and Microbial Functional Dynamics in a Cattle Manure Composting System Inoculated with Lactobacillus acidophilus

This study presents an observational analysis of the chemical and microbial dynamics of cattle manure compost during maturation in a system inoculated with Lactobacillus acidophilus. Composting samples were collected at D15 and D60 to assess changes in key nutrient parameters and microbial community shifts from the early stage to the composting phase. At D60 in this inoculated composting system, ammonium nitrogen (NH4+-N), potassium (K), phosphorus (P), calcium (Ca), magnesium (Mg), and total nitrogen (T-N) levels were higher than at D15, with NH4+-N measuring 813.01 and 1714.24 mg/kg at D15 and D60, respectively (p < 0.001). Microbial analysis based on 16S rRNA gene sequencing showed that alpha diversity was slightly lower at D60 than at D15, although this difference was not statistically significant; in contrast, the community composition shifted toward a higher relative abundance of Firmicutes and lower relative abundances of Bacteroidetes and Proteobacteria. Mantel correlation analyses indicated strong associations between specific bacterial phyla and manure chemical properties, particularly between Firmicutes and levels of NH4+-N, chloride, and sodium. PICRUSt2-based functional prediction further suggested that mature compost samples had a higher predicted representation of genes associated with nitrogen- and energy-related pathways, including arginine and polyamine biosynthesis and butanoate fermentation. This observational study outlines how nutrient profiles, microbial communities, and PICRUSt2-predicted functional potentials change over time in a composting system amended with L. acidophilus. By documenting these characteristic patterns, our results provide a useful reference for focusing future research on specific nutrient–microbe–function linkages in lactic acid bacteria-amended composting systems, and for interpreting compost maturation in such systems within the context of sustainable agricultural practice.