Changing sources of soil respiration with time since fire in a boreal forest
Bibliographic record
Abstract
Abstract Radiocarbon signatures (Δ 14 C) of carbon dioxide (CO 2 ) provide a measure of the age of C being decomposed by microbes or respired by living plants. Over a 2‐year period, we measured Δ 14 C of soil respiration and soil CO 2 in boreal forest sites in Canada, which varied primarily in the amount of time since the last stand‐replacing fire. Comparing bulk respiration Δ 14 C with Δ 14 C of CO 2 evolved in incubations of heterotrophic (decomposing organic horizons) and autotrophic (root and moss) components allowed us to estimate the relative contributions of O horizon decomposition vs. plant sources. Although soil respiration fluxes did not vary greatly, differences in Δ 14 C of respired CO 2 indicated marked variation in respiration sources in space and time. The 14 C signature of respired CO 2 respired from O horizon decomposition depended on the age of C substrates. These varied with time since fire, but consistently had Δ 14 C greater (averaging ∼120‰) than autotrophic respiration. The Δ 14 C of autotrophically respired CO 2 in young stands equaled those expected for recent photosynthetic products (70‰ in 2003, 64‰ in 2004). CO 2 respired by black spruce roots in stands >40 years old had Δ 14 C up to 30‰ higher than recent photosynthates, indicating a significant contribution of C stored at least several years in plants. Decomposition of O horizon organic matter made up 20% or less of soil respiration in the younger (<40 years since fire) stands, increasing to ∼50% in mature stands. This is a minimum for total heterotrophic contribution, since mineral soil CO 2 had Δ 14 C close to or less than those we have assigned to autotrophic respiration. Decomposition of old organic matter in mineral soils clearly contributed to soil respiration in younger stands in 2003, a very dry year, when Δ 14 C of soil respiration in younger successional stands dropped below those of the atmospheric 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".