CN-model: A dynamic model for the coupled carbon and nitrogen cycles in terrestrial ecosystems

Reducing uncertainty in carbon cycle projections relies on reliable representations of interactions between the carbon and nutrient cycles. Here, we build on a set of principles and hypotheses, funded in established theoretical understanding and supported by empirical evidence, to formulate and implement a dynamic model of carbon-nitrogen cycle (C-N) interactions in terrestrial ecosystems. The model combines a representation of photosynthetic acclimation to the atmospheric environment with implications for canopy and leaf N, a representation of functional balance for modelling C allocation and growth different tissues, and a representation of plant N uptake based on a first principles-informed, simplified description of solute transport in the soil. Here, we provide a comprehensive description of the model and its implementation and demonstrate the stability and functionality of the model for simulating seasonal variations of ecosystem C and N fluxes and pools. This may provide a way forward for representing key ecosystem processes related to C and N cycling based on established theoretical concepts with strong empirical support.