Uncovering the soil nitrogen cycle from microbial pathways to global sustainability

Abstract

Over the past decade, substantial progress has been made in elucidating nitrogen (N) cycling across multiple dimensions, including quantification of process rates, microbial mechanisms, and sustainable management strategies. Methodological advances, such as ¹⁵N tracing models for separating gross N transformations, robotized continuous-flow incubation systems for real-time gas flux monitoring, and membrane inlet mass spectrometry for sensitive detection of N₂ production, have greatly enhanced the capacity to quantify gross N transformation rates, denitrification losses, and biological N fixation across diverse ecosystems. These tools have substantially improved both the resolution and accuracy of N cycle assessments. Understanding how microbial communities mediate these processes is critical for sustainable N management. Recent discoveries, including complete ammonia oxidation (Comammox), and direct ammonia oxidation (Dirammox), reveal previously unrecognized microbial pathways that reshape our understanding of nitrification–denitrification dynamics, with important implications for optimizing food production and reducing environmental burdens. Integrating these mechanistic insights into cross-scale models, such as coupled human and natural systems (CHANS), and leveraging emerging technologies, including satellite remote sensing and machine learning, enables a high-resolution characterization of N fluxes across spatial and temporal scales. These advances have laid the foundation for innovative management frameworks, such as Integrated Soil–Crop System Management and Nitrogen Credit Systems, which have demonstrated measurable gains in N use efficiency and climate mitigation. Embedding N stewardship within global sustainability agendas and fostering international cooperation are essential for promoting equitable and effective governance of the global N cycle.