Microbial Activities and Gross Nitrogen Transformation Unaffected by Ten‐Year Nitrogen and Sulfur Addition
Bibliographic record
Abstract
Core Ideas Ten years of N and S deposition did not change microbial and enzyme activities. N and S deposition did not affect gross N transformation rates. Gross N mineralization rates were greater than gross nitrification rates. Gross NO 3 –immobilization rates were greater than gross nitrification rates. Studied soils were still N limited after ten years of N and S deposition. Oil sands mining in northern Alberta, Canada, emits large amounts of NO x and SO 2 to the atmosphere, which will eventually return to the surrounding forest ecosystems. This study was conducted to determine changes in microbial and enzyme activities, and gross nitrogen transformation rates in a boreal forest soil in response to 10 yr (2006–2015) of elevated levels of nitrogen (N) and sulfur (S) addition. The experiment had a two (0 vs. 30 kg N h –1 yr –1 , as NH 4 NO 3 ) × two (0 vs. 30 kg S ha –1 yr –1 , as Na 2 SO 4 ) factorial design with three blocks. A laboratory incubation experiment was conducted using forest floor and the mineral soil (0–15 cm). Ten years of elevated N and S additions did not affect soil chemical (pH, total C, total N and available N concentrations) and microbiological properties (microbial biomass C and N, soil respiration rate, and enzyme activities related to C and N cycling) and gross N transformation rates. Gross N mineralization (0.54–0.62 and 36–49 mg N kg –1 d –1 for mineral soil and forest floor, respectively) and gross NH 4 + immobilization (0.39–0.57 and 10–19 mg N kg –1 d –1 , respectively) rates were tightly coupled in both soil layers. Gross NO 3 ‐ immobilization rates (20–32 mg N kg –1 d –1 ) were significantly greater than gross nitrification rates (9–20 mg N kg –1 d –1 ) in the forest floor. Our results suggest that the studied boreal forest soil was resilient or resistant to 10 yr of N and S addition and the studied soils were still N limited. Given the current N and S emission and deposition rates in northern Alberta, the risk for N and S deposition to significantly affect gross N transformation rates is low for the studied forest ecosystem.
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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 | 0.000 | 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 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".