Nitrification and denitrification in the Community Land Model compared to observations at Hubbard Brook Forest

Models of terrestrial system dynamics often include nitrogen (N) cycles to better represent N limitation of terrestrial carbon (C) uptake but simulating the fate of N in ecosystems has proven challenging. Here, key soil N fluxes and flux ratios from the Community Land Model version 5.0 (CLM5.0) are compared to an extensive set of observations from the Hubbard Brook Forest Long-Term Ecological Research (LTER) site in New Hampshire. Simulated fluxes include microbial immobilization and plant uptake, which compete with nitrification and denitrification, respectively, for available soil ammonium (NH4+) and nitrate (NO3-). In its default configuration, CLM5.0 predicts that both plant uptake and immobilization are strongly dominated by NH4+ over NO3-, and that the model ratio of nitrification:denitrification is approximately 1:1. In contrast, Hubbard Brook observations suggest that NO3- plays a more significant role in plant uptake and that nitrification could exceed denitrification by an..., Modifications to CLM5.0 at Hubbard Brook LTER

The Community Land Model version 5.0 (CLM5.0) was modified at a single grid cell corresponding to the Hubbard Brook Experimental Forest, a northern hardwood forest site in the White Mountain National Forest in New Hampshire USA (43°56´N, 71°45´W).  The purpose was to test alternative parameterizations for nitrification and denitrification in CLM5.0.  The CLM5.0 simulations use site-level present day meteorological (from GSWP3 v. 1) and N deposition inputs, created by extracting the single grid cell values from the global gridded forcing data for CLM5.0 [Lawrence et al., 2019].  Atmospheric CO2 concentration (= 367 ppm), land use and N deposition (= 0.7 gN/m2/yr) were fixed at year 2000 conditions throughout the simulations, while meteorological forcings were cycled over 1991-2010.  The plant functional type of the grid cell was prescribed as 100% broadleaf deciduous temperate forest.  Spin-up for each simulation was..., , , # Nitrification and denitrification in the Community Land Model compared to observations at Hubbard Brook Forest

Dataset DOI: [10.5061/dryad.gmsbcc2n2](10.5061/dryad.gmsbcc2n2)

## Description of the data and file structure

All files for this dataset are available through Zenodo at [https://doi.org/10.5281/zenodo.4641366](https://doi.org/10.5281/zenodo.4641366)