Nitrogen deposition impacts on the amount and stability of soil organic matter in an alpine meadow ecosystem depend on the form and rate of applied nitrogen
Bibliographic record
Abstract
Summary The effects of atmospheric nitrogen (N) deposition on carbon (C) sequestration in terrestrial ecosystems are controversial. Therefore, it is important to evaluate accurately the effects of applied N levels and forms on the amount and stability of soil organic carbon ( SOC ) in terrestrial ecosystems. In this study, a multi‐form, small‐input N addition experiment was conducted at the Haibei Alpine Meadow Ecosystem Research Station from 2007 to 2011. Three N fertilizers, NH 4 Cl , ( NH 4 ) 2 SO 4 and KNO 3 , were applied at four rates: 0, 10, 20 and 40 kg N ha −1 year −1 . One hundred and eight soil samples were collected at 10‐cm intervals to a depth of 30 cm in 2011. Contents and δ 13 C values of bulk SOC were measured, as well as three particle‐size fractions: macroparticulate organic C ( MacroPOC , > 250 µm), microparticulate organic C ( MicroPOC , 53–250 µm) and mineral‐associated organic C ( MAOC , < 53 µm). The results show that 5 years of N addition changed SOC contents, δ 13 C values of the bulk soils and various particle‐size fractions in the surface 10‐cm layer, and that they were dependent on the amounts and forms of N application. Ammonium‐N addition had more significant effects on SOC content than nitrate‐N addition. For the entire soil profile, small additions of N increased SOC stock by 4.5% (0.43 kg C m −2 ), while medium and large inputs of N decreased SOC stock by 5.4% (0.52 kg C m −2 ) and 8.8% (0.85 kg C m −2 ), respectively. The critical load of N deposition appears to be about 20 kg N ha −1 year −1 . The newly formed C in the small‐input N treatment remained mostly in the > 250 µm soil MacroPOC , and the C lost in the medium or large N treatments was from the > 53 µm POC fraction. Five years of ammonium‐N addition increased significantly the surface soil POC : MAOC ratio and increased the instability of soil organic matter ( SOM ). These results suggest that exogenous N input within the critical load level will benefit C sequestration in the alpine meadow soils on the Qinghai–Tibetan Plateau over the short term.
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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) | 0.000 | 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".