Assistant Professor Williams College, United States
Autotrophic and heterotrophic organisms require stoichiometrically balanced carbon and nutrient resource ratios, the demand for which links organismal and ecosystem-level biogeochemical cycles. In soils, the relative availability of carbon and nitrogen (N) resources also defines the strength of competition for ammonium between autotrophic nitrifiers and heterotrophic decomposers, which may influence the coupled dynamics between N mineralization to nitrification. Here, we assembled data from the publicly available US Long Term Ecological Research (LTER) data archive to evaluate the influence of soil C concentration on the relationship between net nitrification and net N mineralization. Using existing LTER data allowed us to explore the influence of soil C on coupled N transformations across ecosystems and climatic regimes. We hypothesized that soil C availability constrains the fraction of mineralized nitrogen that is ultimately nitrified beyond local or climatic drivers, contributing to reduced rates of nitrification in soils with high C concentration.
We found that soil C availability constrains the fraction of mineralized N that is ultimately nitrified across the continental gradient, contributing to reduced rates of nitrification in soils with high C concentrations. While mean annual temperature (MAT) and mean annual precipitation (MAP) each independently influence N mineralization, when considered together with soil C as potential drivers, the interaction between soil C and N mineralization most strongly explained variation in the N mineralization – nitrification relationship across ecosystems and climates. As nitrate is a highly mobile ion that easily leaches to aquatic ecosystems or denitrifies into the greenhouse gas N2O, understanding the connection between soil C concentration and soil N transformations is important for managing potential ecosystem N losses and representing biogeochemical constraints on soil greenhouse gas emissions.