Multi-Level Environmental Filtering Governs Soil N2O Fluxes: A Quantitative Hierarchical Framework for Two Key Microbial Production Pathways

Terrestrial soils represent a dominant source of atmospheric nitrous oxide (N2O), with emissions governed by complex interactions among various biotic, abiotic and microbial drivers. A dataset (n = 275 study sites/plots) that integrates field and laboratory measurements of soil N2O emissions with corresponding environmental drivers was compiled from the peer-reviewed literature. A quantitative hierarchical framework was refined to clarify the interactions among these drivers and their regulatory effects, which are mediated through a three-level mechanistic pathway. At the primary level, environmental drivers (e.g., air temperature, precipitation, site location) act as foundational constraints on soil physical properties (e.g., soil temperature, moisture regime, texture). At the secondary level, the soil’s physical properties create the conditions for soil microbes through influencing chemical properties. At the tertiary level, soil chemical drivers (e.g., the contents of soil organic carbon, nitrogen, ammonium and nitrate; carbon-to-nitrogen ratio) exert direct influences on the N2O flux through modulating the soil’s biotic conditions, affecting microbe community composition and the metabolic activities of microbes. However, these regulatory effects only function when the previous abiotic conditions fall within permissive thresholds. The framework also demonstrates the interactions among biotic and abiotic drivers. This study highlights that future studies should pay greater attention to soil-type- or ecosystem-specific abiotic thresholds and quantify their interactions to improve the simulations of soil N2O fluxes to the atmosphere at either regional or global scales.