Implementation of nitrogen cycle in the CLASSIC land model
Bibliographic record
Abstract
Abstract. A terrestrial nitrogen (N) cycle model is coupled to the carbon (C) cycle in the framework of the Canadian Land Surface Scheme Including Biogeochemical Cycles (CLASSIC). CLASSIC currently models physical and biogeochemical processes and simulates fluxes of water, energy, and CO2 at the land–atmosphere boundary. CLASSIC is similar to most models and its gross primary productivity increases in response to increasing atmospheric CO2 concentration. In the current model version, a downregulation parameterization emulates the effect of nutrient constraints and scales down potential photosynthesis rates, using a globally constant scalar, as a function of increasing CO2. In the new model when nitrogen (N) and carbon (C) cycles are coupled, cycling of N through the coupled soil–vegetation system facilitates the simulation of leaf N amount and maximum carboxylation capacity (Vcmax) prognostically. An increase in atmospheric CO2 decreases leaf N amount and therefore Vcmax, allowing the simulation of photosynthesis downregulation as a function of N supply. All primary N cycle processes that represent the coupled soil–vegetation system are modelled explicitly. These include biological N fixation; treatment of externally specified N deposition and fertilization application; uptake of N by plants; transfer of N to litter via litterfall; mineralization; immobilization; nitrification; denitrification; ammonia volatilization; leaching; and the gaseous fluxes of NO, N2O, and N2. The interactions between terrestrial C and N cycles are evaluated by perturbing the coupled soil–vegetation system in CLASSIC with one forcing at a time over the 1850–2017 historical period. These forcings include the increase in atmospheric CO2, change in climate, increase in N deposition, and increasing crop area and fertilizer input, over the historical period. An increase in atmospheric CO2 increases the C:N ratio of vegetation; climate warming over the historical period increases N mineralization and leads to a decrease in the vegetation C:N ratio; N deposition also decreases the vegetation C:N ratio. Finally, fertilizer input increases leaching, NH3 volatilization, and gaseous losses of N2, N2O, and NO. These model responses are consistent with conceptual understanding of the coupled C and N cycles. The simulated terrestrial carbon sink over the 1959–2017 period, from the simulation with all forcings, is 2.0 Pg C yr−1 and compares reasonably well with the quasi observation-based estimate from the 2019 Global Carbon Project (2.1 Pg C yr−1). The contribution of increasing CO2, climate change, and N deposition to carbon uptake by land over the historical period (1850–2017) is calculated to be 84 %, 2 %, and 14 %, respectively.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".