Climate controls on C<sub>3</sub>vs. C<sub>4</sub>productivity in North American grasslands from carbon isotope composition of soil organic matter
Bibliographic record
Abstract
Abstract We analyzed the δ 13 C of soil organic matter (SOM) and fine roots from 55 native grassland sites widely distributed across the US and Canadian Great Plains to examine the relative production of C 3 vs. C 4 plants (hereafter %C 4 ) at the continental scale. Our climate vs. %C 4 results agreed well with North American field studies on %C 4 , but showed bias with respect to %C 4 from a US vegetation database ( statsgo ) and weak agreement with a physiologically based prediction that depends on crossover temperature. Although monthly average temperatures have been used in many studies to predict %C 4 , our analysis shows that high temperatures are better predictors of %C 4 . In particular, we found that July climate (average of daily high temperature and month's total rainfall) predicted %C 4 better than other months, seasons or annual averages, suggesting that the outcome of competition between C 3 and C 4 plants in North American grasslands was particularly sensitive to climate during this narrow window of time. Root δ 13 C increased about 1‰ between the A and B horizon, suggesting that C 4 roots become relatively more common than C 3 roots with depth. These differences in depth distribution likely contribute to the isotopic enrichment with depth in SOM where both C 3 and C 4 grasses are present.
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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) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| 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".