edu.ucar.opensky::articles:22665 UCAR/NCAR - Library OpenSky Support PO Box 3000 Boulder CO 80307-3000 opensky@ucar.edu http://opensky.ucar.edu/ homepage pointOfContact 2025-12-25T15:30:00.129296 ISO 19115-2 Geographic Information - Metadata - Part 2: Extensions for Imagery and Gridded Data ISO 19115-2:2009(E) https://n2t.org/ark:/85065/d7vt1w60 https://doi.org/10.5281/zenodo.2772160 https Related Software #1 susancheng/15N-data: Second release of 15N data for Cheng et al. submitted to Biogeosciences Decadal fates and impacts of nitrogen additions on temperate forest carbon storage: a data–model comparison 2019-07-16T00:00:00Z publication https://n2t.org/ark:/85065/d7vt1w60 https://doi.org/10.5194/bg-16-2771-2019 Cheng, S. J. author Hess, P. G. author Wieder, William author Thomas, R. Q. author Nadelhoffer, K. J. author Vira, J. author Lombardozzi, Danica author Gundersen, P. author Fernandez, I. J. author Schleppi, P. author Gruselle, M. author Moldan, F. author Goodale, C. L. author UCAR/NCAR - Library publisher To accurately capture the impacts of nitrogen (N) on the land carbon (C) sink in Earth system models, model responses to both N limitation and ecosystem N additions (e.g., from atmospheric N deposition and fertilizer) need to be evaluated. The response of the land C sink to N additions depends on the fate of these additions: that is, how much of the added N is lost from the ecosystem through N loss pathways or recovered and used to increase C storage in plants and soils. Here, we evaluate the C-N dynamics of the latest version of a global land model, the Community Land Model version 5 (CLM5), and how they vary when ecosystems have large N inputs and losses (i.e., an open N cycle) or small N inputs and losses (i.e., a closed N cycle). This comparison allows us to identify potential improvements to CLM5 that would apply to simulated N cycles along the open-to-closed spectrum. We also compare the short- (<3 years) and longer-term (5-17 years) N fates in CLM5 against observations from 13 long-term N-15 tracer addition experiments at eight temperate forest sites. Simulations using both open and closed N cycles overestimated plant N recovery following N additions. In particular, the model configuration with a closed N cycle simulated that plants acquired more than twice the amount of added N recovered in N-15 tracer studies on short timescales (CLM5: 46 +/- 12 %; observations: 18 +/- 12 %; mean across sites +/- 1 standard deviation) and almost twice as much on longer timescales (CLM5: 23 +/- 6 %; observations: 13 +/- 5 %). Soil N recoveries in simulations with closed N cycles were closer to observations in the short term (CLM5: 40 +/- 10 %; observations: 54 +/- 22 %) but smaller than observations in the long term (CLM5: 59 +/- 15 %; observations: 69 +/- 18 %). Simulations with open N cycles estimated similar patterns in plant and soil N recovery, except that soil N recovery was also smaller than observations in the short term. In both open and closed sets of simulations, soil N recoveries in CLM5 occurred from the cycling of N through plants rather than through direct immobilization in the soil, as is often indicated by tracer studies. Although CLM5 greatly overestimated plant N recovery, the simulated increase in C stocks to recovered N was not much larger than estimated by observations, largely because the model's assumed C: N ratio for wood was nearly half that suggested by measurements at the field sites. Overall, results suggest that simulating accurate ecosystem responses to changes in N additions requires increasing soil competition for N relative to plants and examining model assumptions of C : N stoichiometry, which should also improve model estimates of other terrestrial C-N processes and interactions. UCAR/NCAR - Library OpenSky Support PO Box 3000 Boulder CO 80307-3000 opensky@ucar.edu http://opensky.ucar.edu/ homepage pointOfContact PDF Text theme Resource Type 2016-01-01T00:00:00Z publication Copyright author(s). This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License. None eng geoscientificInformation