Evaluation of 11 terrestrial carbon-nitrogen cycle models against observations from two temperate Free-Air CO2 Enrichment studies.
Bottom Line: Nonetheless, many models showed qualitative agreement with observed component processes.The results suggest that improved representation of above-ground-below-ground interactions and better constraints on plant stoichiometry are important for a predictive understanding of eCO2 effects.Improved accuracy of soil organic matter inventories is pivotal to reduce uncertainty in the observed C-N budgets.
Affiliation: Biogeochemical Integration Department, Max Planck Institute for Biogeochemistry, Hans-Knöll-Str. 10, D-07745, Jena, Germany.Show MeSH
Mentions: Elevated CO2 increased NPP in the initial (first) year of the experiments by 25 ± 9% and 25 ± 1% at Duke and ORNL FACE, respectively, according to the measurements (Figs2c,d, 5a,b). Most models simulated an initial (first year) increase in NPP as a result of eCO2 that was close to the observations. Notable exceptions were CABLE and CLM4, which systematically underestimated the initial response at both sites, as well as EALCO and ISAM, which overestimated the response for Duke FACE (Fig.5a,b). Nonetheless, no model simulated the underlying changes in fNup and NUE correctly for both sites. At Duke Forest, according to the measurements, the increase in NPP was associated with a strong increase in fNup. The models generally underestimated the observed increase in fNup and overestimated the increase in NUE. At ORNL, according to the measurements, the initial increase in NPP was associated with nearly equal increases of fNup and NUE (Fig.5). Some models simulated a change in NUE in agreement with the observations (DAYCENT, GDAY, ISAM, LPJ-GUESS, OCN, TECO), but most models had a tendency to underestimate the increase in fNup.
Affiliation: Biogeochemical Integration Department, Max Planck Institute for Biogeochemistry, Hans-Knöll-Str. 10, D-07745, Jena, Germany.