13 Jul 2021
 | 13 Jul 2021
Status: this preprint is currently under review for the journal BG.

The impacts of model structure, parameter uncertainty and experimental design on Earth system model simulations of litter bag decomposition experiments

Daniel M. Ricciuto, Xiaojuan Yang, Dali Wang, and Peter E. Thornton

Abstract. Accurate Earth system model simulations of the terrestrial carbon cycle and its feedbacks to climate critically depend on algorithms representing the decomposition of litter and soil organic matter. Litter bag studies, in which specific types of plant litter are subject to varying environmental conditions in the field and decomposition is measured, serve as valuable benchmarks for model performance. Here we test the Energy Exascale Earth System land model (ELM), which has two different structural representations of decomposition, using observations from the Long-term Intersite Decomposition Experiment (LIDET) over six different biomes and six different leaf litter types. We find that seasonal patterns in soil conditions and nutrient availability have large effects on decomposition rates, and that it is critical to include this in the simulation design. Despite widely differing base decomposition rates between the two different model structures, the models produce similar temporal patterns of decomposition when nitrogen is limiting. Both models overpredict the fraction of original nitrogen present as a function of carbon remaining when using default parameterizations. A parameter sensitivity analysis indicates strong dependence of model outputs on nitrogen limitation, carbon use efficiency and decomposition rates. A large spread in model predictions when considering an ensemble of possible parameter combinations strongly suggests parameter uncertainty may be more influential than model structural uncertainty, and that new measurement and modelling approaches may be necessary to constrain these uncertainties.

Daniel M. Ricciuto et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-163', Anonymous Referee #1, 10 Aug 2021
    • AC1: 'Reply on RC1', Daniel Ricciuto, 15 Mar 2022
  • RC2: 'Comment on bg-2021-163', Anonymous Referee #2, 02 Sep 2021
    • AC2: 'Reply on RC2', Daniel Ricciuto, 15 Mar 2022

Daniel M. Ricciuto et al.

Daniel M. Ricciuto et al.


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Short summary
This paper uses a novel approach to quantify the impacts of the choice of decomposition model on carbon and nitrogen cycling. We compare the models to experimental data that examined litter decomposition over five different biomes. Despite widely differing assumptions, the models produce similar patterns of decomposition when nutrients are limiting. This differs from past analyses that did not consider the impacts of changing environmental conditions or nutrients.