Absence of significant effect of nitrogen addition on soil respiration in a subtropical Chinese fir plantation
Bibliographic record
Abstract
Chinese fir ( Cunninghamia lanceolata (Lamb.) Hook) is one of the most dominant tree species in southern China. However, the effect of different nitrogen (N) levels on soil respiration in subtropical Chinese fir plantations remains unclear. We studied soil respiration, soil physicochemical properties, and microbial biomass in Chinese fir plantations under four N treatments (control, low-N, moderate-N, and high-N). The results showed that soil respiration under low-N, moderate-N, and high-N treatments increased by 9%, 50%, and 79%, respectively, compared to the control, but the increases did not reach statistical differences. N addition significantly decreased soil microbial biomass and soil pH, and tended to increase soil aluminum ions (Al3+). These results indicated that soil microorganisms are inhibited by enhanced Al3+ content under increased N addition, which therefore reduced the soil microbial biomass. The negative correlation between soil microbial biomass and soil respiration suggests that reductions in soil microbial biomass may inhibit microbial respiration. N addition significantly increased soil ammonium nitrogen, decreased soil moisture, combined with the lower soil microbial biomass in the middle of the growing season compared with in the end of the growing season. This indicated that N addition stimulated plant growth to absorb more nutrients, intensified plant-microbe competition, and may lead to an increase in plant autotrophic respiration, which was higher than the decrease in heterotrophic respiration. Our study highlights that isolating and quantifying the source of soil respiration will be necessary in future studies.
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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".