Buried Surface Horizons in Saskatchewan Croplands Provide Insight into Microbial Soil Carbon Cycling and Development of Persistent Organic Matter
Bibliographic record
Abstract
The accumulation of soil from hillslope erosion in depositional landscape positions can bury the original A horizon soil, leading to a disconnect of C-rich surface soils from surface environments due to burial. The buried C then serves as the primary C for the buried native microbial community. The goal of this thesis was to quantify and characterize the soil organic C (SOC) and examine microbial decomposition of this C in buried surface horizons, decades after burial. Surface (Ah) soils were sampled at 0-10 cm, buried surface (Ahb) soils were identified around 40-50 cm deep, and buried subsoil (Bmb) soils were sampled directly below Ahb soils. Buried surface (Ahb) soils had a SOC content (25.6 mg OC g-1 soil) similar to the corresponding surface (Ah) soil (30.9 mg OC g-1 soil), but greater than Bmb subsoil horizons (8.7 mg OC g-1 soil). Microbial abundance was reduced in Ahb vs. Ah horizons (Total PLFA: Ah = 77.2 nmol g-1 soil, Ahb = 26.8 nmol g-1 soil), however enough viable biomass remained to suggest microbial C cycling was still occurring in Ahb horizons. Over the course of a 100-day controlled incubation experiment, the susceptibility of SOC in Ahb horizons to mineralization to CO2 was 4x lower than corresponding Ah horizons. Carbon mineralization was strongly correlated with mineral-associated organic matter (Rho = -0.67, p < 0.01) in Ah horizons but not in Ahb horizons. Microbial community structure in Ahb horizons was distinct from surface soils, suggesting co-development of the community with increasingly persistent C as decomposition proceeded in the decades after burial. Similar quantities and concentrations of microbial necromass (amino sugars) remained in the Ahb vs. Ah horizon but were strongly correlated with clay only in the Ahb horizons (Rho = 0.77, p < 0.001). Further, microbial communities in Ahb horizons were more thermodynamically efficient at utilizing added glucose than Ah horizons (72 vs. 64 % energy retained) but had a lower calorespirometric ratio under basal metabolism (841 vs 3106 kJ mol-1 CO2-C), suggesting communities are adapted to intense C recycling due to energy limitations of the buried C. This research highlights the co-development of distinct microbial communities with persistent C in buried soils with limited fresh C inputs and examines C persistence in soils after repeated microbial decomposition.
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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 | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 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".