Ecosystem nutrient competition, plant traits, and advective solution in ALM simulations

Abstract

            Nitrogen (N) and phosphorus (P) dynamics are important controllers of ecosystem carbon exchanges, and therefore on C-climate feedbacks. However, the current representations of these processes in ALM are poorly tested and numerically problematic. Under ACME support, we have begun to address some of these issues. Here, we synthesize results from several recently submitted ACME-supported publications demonstrating that using a new method to represent multi-nutrient and multi-consumer interactions (called ECA; Equilibrium Chemistry Approximation), leaf traits that control photosynthesis, plant root nutrient uptake traits, and improved advective flux calculations leads to improved estimates of global carbon exchanges, N and P partitioning, NO₃^- leaching, and N₂O gas emissions. Global biases in GPP have been reduced by ~60% from the baseline CLM4.5 predictions. The improved ALM accurately captures results from N and P addition experiments, while the baseline CLM4.5 is unable to do so. The partitioning of ecosystem N losses to N₂O and NO₃^- has been dramatically improved compared to observations; these results depend directly on improved representations of nutrient competition and advective fluxes. While much work remains, these model improvements and the benchmark datasets applied represent important steps toward improving the ACME Land Model.