Soil moisture, N, P, and forest cover effects on N fixation in alders in the southern boreal forest
Bibliographic record
Abstract
Abstract Outside of tropical and arid regions, plant productivity is limited by the availability of soil N. Ironically, these are the regions where N‐fixing plants are restricted to early successional habitats. The energy cost of N fixation has been used to explain the paucity of N‐fixing plants in late‐successional ecosystems, and models predict reduced light and increased soil N availability will reduce N‐fixing plant success. The lack of success of N‐fixing plants has also been explained by their greater need for some elements, especially phosphorus. We examined the effect of N and P fertilizer over four years on N fixation in Alnus alnobetula spp. crispa in a mature Pinus banksiana forest in the southern boreal forest, and an adjacent site where wildfire had removed the tree canopy. We also monitored N fixation throughout two growing seasons examined the effect of artificial shading on photosynthesis. The addition of N or P fertilizer resulted in a 60% decrease in plant nodule nitrogenase activity. N fertilizer also reduced the proportion of cells in the root nodules containing N‐fixing vesicles in the forest site. Shrubs in the forest had the highest photosynthetic rate when measured on a leaf mass basis, indicating an increased carbon capture efficiency compared with shrubs in the open. Over the course of two growing seasons, soil temperature had a positive effect on specific nitrogenase activity, and soil in the open site was warmer than soil in the forest in the spring. However, as soil moisture decreased, temperature was a weaker predictor of nitrogenase activity. Although all shrubs consistently acquired most of their N from fixation, shrubs in the forest derived more than shrubs in the open, which were more water limited. Overall, these results show that N‐fixing plants may benefit from being in the understory for improved water balance in this region of the boreal forest. As such, light availability may not be the primary factor limiting the abundance of N‐fixing shrubs.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 teacher head, 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".