| 6 | | Nitrogen (N) and phosphorus (P) constraints on carbon (C) and energy exchanges between |
| 7 | | terrestrial biosphere and atmosphere are a major source of uncertainty regarding the drivers |
| 8 | | of the land C sink. In this study, we evaluated the performance of the global version of the |
| 9 | | land surface model ORCHIDEE-CNP (v1.2) which explicitly simulates N and P cycles on |
| 10 | | land, based on a compilation of data from remote-sensing, ground-based measurement |
| 11 | | networks and ecological databases. The sensitivity of gross primary productivity (GPP) to |
| 12 | | increasing CO 2 and water availability in ORCHIDEE-CNP is more realistic in the nutrient- |
| 13 | | enabled model version. However, this model version cannot capture the current land C sink |
| 14 | | in the North Hemisphere (NH), suggesting that either (1) other processes (besides CO 2 |
| 15 | | fertilization) currently not well resolved in global models such as biomass turnover, land |
| 16 | | management, and soil decomposition might play an important role, or (2) that ORCHIDEE-CNP underestimates the ability of ecosystems to circumpass nutrient constraints on biomass |
| 17 | | built up under elevated atmospheric CO 2 concentrations . Components of the N and P budgets |
| 18 | | at biome level are in good agreement with independent estimates, but large-scale patterns in |
| 19 | | ecosystem stoichiometry cannot be reproduced. The analysis of plant use efficiencies of light, |
| 20 | | water, C, N and P and seasonal dynamics reveal issues with respect to canopy processes, |
| 21 | | plant respiration and growth allocation in ORCHIDEE-CNP. We propose ways how to |
| 22 | | address the model biases by refining the canopy light absorption processes, root and leaf |
| 23 | | phenology processes and dynamics of biomass turnover and by better representing soil |
| 24 | | processes related to decomposition, stabilization of soil organic matter and inorganic P |
| 25 | | transformation. |
| | 6 | Nitrogen (N) and phosphorus (P) constraints on carbon (C) and energy exchanges between terrestrial biosphere and atmosphere are a major source of uncertainty regarding the drivers of the land C sink. Sun et al. (2020) evaluated the performance of the global version of the |
| | 7 | land surface model ORCHIDEE-CNP (v1.2) which explicitly simulates N and P cycles on land, based on a compilation of data from remote-sensing, ground-based measurement networks and ecological databases. The sensitivity of gross primary productivity (GPP) to increasing CO2 and water availability in ORCHIDEE-CNP is more realistic in the nutrient-enabled model version. Some model issues were detected and strategies to address them proposed. For more information see Sun et al (2020). |
| | 8 | |
| | 9 | Goll et al (submitted) (SI) showed that the simulated response of above-ground plant production to P fertilization is in line with evidence from a compilation of fertilization experiments. |
| | 10 | |
