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 CO 2 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 13 C 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 CO 2 . In contrast, the total accumulated above‐ground biomass of T. repens doubled under elevated CO 2 but remained independent of N fertilizer rate. The C:N ratio of above‐ground biomass for both species increased under elevated CO 2 whereas only the C:N ratio of L. perenne roots increased under elevated CO 2 . Root biomass of L. perenne doubled under elevated CO 2 and again under high N fertilization. Total soil C was unaffected by CO 2 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 CO 2 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 CO 2 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 CO 2 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 CO 2 .
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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".