Soil Organic Carbon Sequestration Dynamics Under Chronic Nitrogen Deposition in Temperate Deciduous Forest Ecosystems: An Empirical Analysis of Edaphic Microbiome Shifts and Litter Decomposition Rates Along a Deposition Gradient in Central Europe

Abstract

Chronic atmospheric nitrogen (N) deposition constitutes a persistent driver of biogeochemical alteration in temperate deciduous forest soils, yet its cascading effects on edaphic microbial community composition and organic carbon (OC) stabilization pathways remain incompletely resolved. This study quantifies soil organic carbon (SOC) stocks, fungal-to-bacterial biomass ratios, and litter decomposition constants (k) across a replicated N-deposition gradient (5–42 kg N ha⁻¹ yr⁻¹) spanning twelve forest stands in the Rhine–Ruhr and Bohemian Basin regions. Employing phospholipid fatty acid (PLFA) profiling, litterbag incubation assays, and density fractionation of mineral-associated organic matter (MAOM), we demonstrate that elevated N inputs suppress saprotrophic fungal activity by 34–51%, accelerate light-fraction OC mineralization, and ultimately reduce SOC sequestration efficiency by 18–27% relative to low-deposition reference sites. These findings underscore the urgency of integrating reactive N governance into regional carbon accounting frameworks.