The integration of nitrogen dynamics into a land surface model. Part 1: model description and site-scale validation

Nitrogen cycling has profound effects on carbon uptake in the terrestrial ecosystem and the response of the biosphere to climate changes. However, nutrient cycling is not taken into account in most land surface models for climate change. In this study, a nitrogen model, based on nitrogen transformation processes and nitrogen fluxes exchange between the atmosphere and terrestrial ecosystem, was incorporated into the Atmosphere–Vegetation Interaction Model (AVIM) to simulate the carbon cycle under nitrogen limitation. This new model, AVIM-CN, was evaluated against site-scale eddy covariance–based measurements of an alpine meadow located at Damxung station from the FLUXNET 2015 dataset. Results showed that the annual mean gross primary production simulated by AVIM-CN (0.7073 gC m−2 d−1) was in better agreement with the corresponding flux data (0.5407 gC m−2 d−1) than the original AVIM (1.1403 gC m−2 d−1) at Damxung station. Similarly, ecosystem respiration was also down-regulated, from 1.7695 gC m−2 d−1 to 1.0572 gC m−2 d−1, after the nitrogen processes were introduced, and the latter was closer to the observed vales (0.8034 gC m−2 d−1). Overall, the new results were more consistent with the daily time series of carbon and energy fluxes of observations compared to the former version without nitrogen dynamics. A model that does not incorporate the limitation effects of nitrogen nutrient availability will probably overestimate carbon fluxes by about 40%.