Arctic tundra soil depth, more than seasonality, determines active layer bacterial community variation down to the permafrost transition
Bibliographic record
Abstract
Enhanced microbial decomposition of the Arctic’s vast soil carbon pool due to climate warming could result in globally significant CO 2 /CH 4 emissions. Our understanding of tundra soil microbial communities is generally based on studies of either the top surface or the deep frozen permafrost. In contrast, there has been relatively little exploration of bacterial communities and soil biogeochemistry through entire soil depth profiles to the permafrost, and none that has specifically incorporated temporal dynamics with depth as the summer thaw proceeds. Here we report bacterial community composition in 10-cm increments from the surface to the permafrost from late winter through to autumn, at a mesic low Arctic tundra site. Bacterial community composition and phylogenetic diversity varied substantially with soil depth and much less among sampling times. Correlation analysis indicated that the surface organic, subsoil mineral, and permafrost transition soil layers each had distinct community interaction networks. Acidobacteriota- affiliated taxa dominated surface communities but declined significantly with soil depth and increasing pH, while Bacteroidetes taxa relative abundances were also associated with pH, and were largest in the carbon-restricted permafrost transition layer. Thus, patterns in community assembly were primarily associated with depth and correlated with edaphic factors, with relatively little impact of the seasonal changes between frozen and thawed assemblages within each sampling depth interval. Nevertheless, total microbial biomass within each depth interval generally declined during the seasonal transition from frozen to thawed state. Finally, our data indicate that soil pH, which is known to govern tundra microbial community composition horizontally across the surface organic layer at multiple spatial scales, is also an important determinant of vertical differences in bacterial community composition from the surface down to the permafrost. • Soil depth has a greater impact on bacterial community composition than season. • Organic, mineral, and permafrost transition layer soil communities are distinct. • Seasonal thaw generally leads to microbial biomass declines within most soil depths.
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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) | 0.001 | 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 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".