Net soil carbon input under ambient and elevated CO<sub>2</sub> concentrations: isotopic evidence after 4 years
Bibliographic record
Abstract
Summary Elevation of atmospheric CO2 concentration is predicted to increase net primary production, which could lead to additional C sequestration in terrestrial ecosystems. Soil C input was determined under ambient and Free Atmospheric Carbon dioxide Enrichment (FACE) conditions for Lolium perenne L. and Trifolium repens L. grown for four years in a sandy‐loam soil. The 13C content of the soil organic matter C had been increased by 5‰ compared to the native soil by prior cropping to corn (Zea mays) for > 20 years. Both species received low or high amounts of N fertilizer in separate plots. The total accumulated above‐ground biomass produced by L. perenne during the 4‐year period was strongly dependent on the amount of N fertilizer applied but did not respond to increased CO2. In contrast, the total accumulated above‐ground biomass of T. repens doubled under elevated CO2 but remained independent of N fertilizer rate. The C:N ratio of above‐ground biomass for both species increased under elevated CO2 whereas only the C:N ratio of L. perenne roots increased under elevated CO2. Root biomass of L. perenne doubled under elevated CO2 and again under high N fertilization. Total soil C was unaffected by CO2 treatment but dependent on species. After 4 years and for both crops, the fraction of new C (F‐value) under ambient conditions was higher (P= 0.076) than under FACE conditions: 0.43 vs. 0.38. Soil under L. perenne showed an increase in total soil organic matter whereas N fertilization or elevated CO2 had no effect on total soil organic matter content for both systems. The net amount of C sequestered in 4 years was unaffected by the CO2 concentration (overall average of 8.5 g C kg−1 soil). There was a significant species effect and more new C was sequestered under highly fertilized L. perenne. The amount of new C sequestered in the soil was primarily dependent on plant species and the response of root biomass to CO2 and N fertilization. Therefore, in this FACE study net soil C sequestration was largely depended on how the species responded to N rather than to elevated CO2.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| 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) | 0.001 | 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 source (direct Gemma or distilled Codex), 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".