Quantifying the global impact of nitrogen deposition on persistent and vulnerable soil C pools

Soils play a major role in mitigating climate change, as they sequester vast stocks of organic carbon and thereby buffer atmospheric CO2 concentrations. Inorganic nitrogen has been shown to have varying effects on soil C, sometimes promoting soil C buildup yet enhancing C loss in other cases. This contradiction may be a function of how soil C is stored, with C in particulate organic matter (POM) being much more susceptible to microbial decomposition than C in mineral-associated organic matter (MAOM). We have compiled a global dataset of over 200 papers which used a rigorous density fractionation methodology for quantifying stocks of C in POM and MAOM. Preliminary results suggest that inorganic N addition via deposition decreases organic C storage in MAOM, while not affected POM. Further, soil C storage in both pools increased with lower pH, countering our hypothesized negative effect of acidification on microbial activity.