Microbial Processes and Nutrient Transformation in Soils: Nitrogen Fixation, Nitrification–Denitrification, Phosphate Solubilization, and Organic Matter Decomposition

Abstract Soil microorganisms regulate the transformation, retention, and loss of nutrients through a suite of tightly coupled biochemical processes that underpin ecosystem productivity and sustainability. Among these processes, biological nitrogen fixation, nitrification, denitrification, phosphate solubilization, and organic matter decomposition are central to soil fertility, greenhouse gas dynamics, and plant nutrition. This narrative review synthesizes current knowledge on microbial nutrient transformation pathways, emphasizing the organisms involved, biochemical mechanisms, environmental controls, and ecosystem implications. Drawing on peer-reviewed literature indexed in Google Scholar, the review highlights how microbial functional diversity mediates nutrient availability and loss, how land management and climate change alter these processes, and how emerging tools are improving our ability to quantify microbial contributions to soil functioning. The review concludes by identifying key knowledge gaps and implications for sustainable and climate-smart land management. Keywords: soil microbiology, nitrogen fixation, nitrification, denitrification, phosphate solubilization, decomposition, nutrient cycling