Soil Nutrient and Greenhouse Gas Cycles in Managed Mixed Deciduous Ontario Forests: The Role of Elevated Atmospheric Nitrogen Deposition and Nutrient and Biochar Amendments
Bibliographic record
Abstract
Canada’s temperate forests are experiencing an environmental disturbance in the form of atmospheric nitrogen deposition arising from fossil fuel burning and agricultural practices. Nitrogen, a major nutrient required for plants and soil microorganisms, is normally in short supply in temperate forest ecosystems. However, when soil nitrogen is in excess, various negative impacts can result such as nutrient leaching, increased nitrous oxide emissions and disturbances to carbon cycling, including reduced soil methane uptake. Research has revealed a shift from nitrogen to phosphorus limitation in forests in central Ontario where chronic nitrogen deposition rates are high, and introducing soil amendments might have the potential to mitigate these negative effects. Before management strategies can be devised, it is important to characterize the degree of nitrogen excess, and how soil nutrient cycling and fluxes of greenhouse gases are being influenced, which may offset carbon gains from increased primary productivity. In an assessment of ambient soil characteristics representing natural topographic heterogeneity at Haliburton Forest, high inorganic nitrogen pools did not result in elevated nitrous oxide effluxes in upland soils, though hot spots and hot moments of nitrous oxide efflux occurred in wet depression areas where ammonium concentrations and moisture were high. Rapid methane efflux was also observed including what appear to be the highest rates in forest systems reported to date. A reduction in longer- (>5 year) and shorter-term (0-3 year) inorganic nitrogen pools in upland phosphorous-amended sites does support that the forest is phosphorous limited, however, there was no evidence of increased nitrous oxide emissions, even in nitrogen-amended sites that would be expected under nitrogen saturated conditions. Phosphorous limitation may be ameliorated by amending soils with biochar, which resulted in increased soil phosphorus, pH, and cation retention. The results of this research reveal that soils in temperate forests in Ontario are at a stage of nitrogen excess relative to ecosystem demands, but do not appear to have reached nitrogen saturation. However, with elevated exchangeable nitrogen pools and increasing nitrogen deposition, denitrification and methanogenic potentials, particularly under predicted increasing moisture regimes, may substantially impact and offset the overall carbon sink at this forest.
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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 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 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 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".