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## Summary

The article provides an overview of the nitrogen cycle representation in the Community Land Model (CLM) version 5.0. The key points are:

**Overview of Nitrogen Cycling in CLM**
- CLM represents both the relatively rapid cycling of nitrogen within the plant-litter-soil organic matter system, as well as the coupling of the internal nitrogen cycle to external sources and sinks.
- Inputs of new mineral nitrogen come from atmospheric deposition and biological nitrogen fixation. Losses occur through nitrification, denitrification, leaching, and losses in fire.
- The balance between these sources and sinks determines the total ecosystem nitrogen stocks.

**Representation of Inorganic N Transformations**
- CLM5.0 represents inorganic nitrogen transformations based on the Century N-gas model.
- This includes separate ammonium (NH4+) and nitrate (NO3-) pools, with environmentally controlled nitrification and denitrification rates.

The summary covers the key points about the nitrogen cycle representation in the CLM5.0 model, including the internal cycling processes as well as the coupling to external sources and sinks that determine the overall nitrogen stocks in the ecosystem.