Does nitrogen deposition lead to a weaker or stronger carbon sink in nutrient-poor peatlands?
Bibliographic record
Abstract
Atmospheric nitrogen (N) deposition is increasing owing to fossil fuel burning and agriculture. In nutrient limited peatland ecosystems, the excess of reactive N has been found to increase vascular plant growth, but decrease Sphagnum growth. Higher vascular plant abundance and higher nutrient content alter decomposability of plant litter. These changes are likely to affect net imbalance of production and decomposition and thus carbon (C) accumulation in peatlands, which store about a third of global soil C. We studied whether the vegetation feedbacks of N deposition lead to stronger or weaker C sink in nutrient-poor peatlands. We investigated vegetation and ecosystem CO2 exchange at two of the longest-running nutrient addition experiments on peatlands, Mer Bleue Bog, Canada and Degerö Stormyr poor fen, Sweden that have been fertilized with NH4NO3 (2-15 times ambient annual wet deposition) for 12-23 years. Gross photosynthesis, ecosystem respiration and net CO2 exchange were measured weekly during June-August using chambers. To examine vegetation changes with increasing N influx, we determined the peak growing season aboveground biomass and coverage of vascular plants using the point intercept method. After 12-23 years of nutrient addition, the two sites revealed contrasting patterns: At Mer Bleue the highest nutrient additions were associated with up to 3-fold net CO2 uptake potential than in the control, whereas N addition treatments at Degerö Stormyr showed close to zero net CO2 uptake potential, only 0.3 fold compared to the control. The stronger C sink potential at Mer Bleue was mainly due to up to 50% increase in the gross photosynthesis and a diminished C sink potential at Degerö Stormyr due to down to 40 % lower gross photosynthesis. Ecosystem respiration showed similar trends at both peatlands: the rates were unaltered or increased to a lesser extent under N load. At both sites, the vegetation structure had changed remarkably. Most of the N addition treatments showed an increase of up to 90% in total vascular aboveground plant abundance and a concomitant loss of Sphagnum. At Mer Bleue along with the decrease in Sphagnum cover, the plots under highest N additions had become wetter, counterbalancing the impact of dry summer conditions in the study year whereas at Degerö Stormyr long term treatments did not alter wetness of the site. Thus, the contrasting C sink responses to long term N load may be explained by the type of vegetation and the water table depth. Shrubs were strong competitors at the dry Mer Bleue Bog while sedges had gained in abundance under N load at the wetter Degerö Stormyr. Our bog-fen comparison emphasizes the value of the long-term experiments in examining the ecosystem response of peatlands to N deposition, possible nonlinear responses and whether the key feedback mechanisms to ecosystem C sink potential differ in two main types of peatlands.
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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".