Biological and Environmental Research - Earth and Environmental System Sciences
Earth and Environmental System Modeling

Global evaluation of ELM v1 and the role of the phosphorus cycle and non-structural carbon in the historical terrestrial carbon balance

Tuesday, December 8, 2020 - 10:56
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The importance of carbon (C)-nutrient interactions to the prediction of future C uptake has long been recognized. Many ESMs in CMIP6 (the Coupled Model Intercomparison Project phase 6) are now including nitrogen (N) cycle and C-N interactions. However, only a few models in CMIP6 have developed the capability to include phosphorus (P) cycle processes and C-N-P interactions. The Energy Exascale Earth System Model (E3SM) land model (ELM) version 1 is one of the few that has this capability. Here we provide a comprehensive global scale evaluation of ELM v1. Using the International Land Model Benchmarking (ILAMB) system we show that the implementation of P cycle dynamics is critical to improving model simulated biomass, leaf area index (LAI), and global net C balance. The evaluation of model sensitivity to a step increase of CO2with free-air CO2 enrichment (FACE) observational data suggests that ELM v1 is able to capture the field observed responses for photosynthesis, growth, LAI and vegetation C stocks. The good agreement between model simulations and FACE observations is mainly due to the introduction of a non-structural carbon pool in ELM v1. Model simulations showed that global C sources and sinks are significantly affected by P limitation, as the historical CO2 fertilization effect was reduced by 20% and C emission due to land use and land cover change was 11% lower when P limitation was considered. Our study suggests that introduction of C-N-P coupling and a non-structural carbon pool will likely have substantial consequences for projections of future C uptake.

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