## 2.22.2. Overview[¶](#overview "Permalink to this headline")
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In addition to the relatively rapid cycling of nitrogen within the plant – litter – soil organic matter system, CLM also represents several processes which couple the internal nitrogen cycle to external sources and sinks. Inputs of new mineral nitrogen are from atmospheric deposition and biological nitrogen fixation. Losses of mineral nitrogen are due to nitrification, denitrification, leaching, and losses in fire. While the short-term dynamics of nitrogen limitation depend on the behavior of the internal nitrogen cycle, establishment of total ecosystem nitrogen stocks depends on the balance between sources and sinks in the external nitrogen cycle ([Thomas et al. 2015](https://escomp.github.io/ctsm-docs/versions/master/html/tech_note/References/CLM50_Tech_Note_References.html#thomasetal2015)).

As with CLM4.5, CLM5.0 represents inorganic N transformations based on the Century N-gas model; this includes separate NH4+ and NO3\- pools, as well as environmentally controlled nitrification and denitrification rates that is described below.

