Ideas and perspectives: Nitrite turnover controls nitrogen fate across redox gradients

Abstract

Reactive nitrogen fate in natural systems remains difficult to predict because pathway partitioning occurs at the stage of nitrite turnover, where rapid and tightly coupled production and consumption processes obscure the underlying fluxes. Concentration-based assessments emphasize the dominant pools-nitrate and ammonium-while pathway divergence is determined at the stage of nitrite turnover, independently of pool size. Nitrite is the principal dissolved inorganic intermediate linking the oxidative and reductive branches of the nitrogen cycle and the obligatory precursor to all downstream dissolved and gaseous products. Because nitrite rarely accumulates, it has often been treated as a transient intermediate of limited interpretive value. This apparent invisibility reflects rapid, tightly coupled turnover and does not indicate functional insignificance. Its low and frequently undetectable concentration is the kinetic signature of this central position rather than evidence against it: rapid coupled turnover sustains high gross flux at near-zero standing concentration. Nitrogen retention, recycling and losses to the atmosphere are determined during nitrite turnover, where competing pathways partition fluxes according to kinetic and environmental constraints. Observed concentrations integrate formation and consumption into a net signal that masks opposing fluxes when internal cycling is rapid. Coupled δ15N–δ18O measurements of nitrite constrain simultaneous production and consumption and differentiate biological from abiotic pathways. Partial oxygen isotope exchange with water increases the diagnostic primacy of δ15N in resolving hidden turnover. However, its low concentration in natural environments can pose some challenges for analysis, requiring more sensitive approaches. Centering nitrogen-cycle interpretation on nitrite dynamics and isotopic expression across redox gradients from oxic soils to oxygen minimum zones, provides a mechanistic basis for predicting nitrogen budgets, N2O emissions, and ecosystem sensitivity to increasing redox variability under climate change and land-use intensification.