BELOWGROUND LITTER CONTRIBUTIONS TO NITROGEN CYCLING AT A NORTHERN GRASSLAND–FOREST BOUNDARY
Bibliographic record
Abstract
Forest expansion at the northern edge of the Great Plains is associated with increased availability of soil nitrogen (N). Studies of N dynamics typically focus on aboveground litter production, but in semiarid ecosystems, fine-root production greatly exceeds shoot production. We explored the contribution of root and shoot litter to N cycling in adjacent grassland and aspen (Populus tremuloides) forest at the northern edge of the Great Plains. We used a new approach to measure N inputs from root litter production: we combined root productivity data from minirhizotron images with N content data from several root diameter and color classes. We also measured the production and N content of aboveground litter. The novel contribution of our study comes from the simultaneous measurements of above- and belowground productivity and N input from litter production in adjacent forest and grassland habitats. Aboveground litter production was threefold greater in forest than in grassland (330 vs. 136 g·m−2·yr−1), but fine roots accounted for 80–90% of total litter production. As a result, total production was not significantly different between habitats, and the N contribution from total litter production was surprisingly similar between grassland (16.8 g·m−2·yr−1) and forest (17.1 g·m−2·yr−1). Thus in spite of great differences between habitats in aboveground litter production, N inputs from total litter production cannot explain the higher availability of N in forest soils. However, we found differences between habitats in root litter quality (forest, 1.14% N; grassland, 0.81% N, as well as in the seasonal and vertical distribution of root production. Grassland root production was significantly greater than forest root production in early summer in the top 20 cm of soil. Conversely, forest produced more root length at the end of the growing season in deeper soil layers (>50 cm). These differences may increase available N in forest soils, but this increase is not attributable to differences in total litter production between habitats.
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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) | 0.001 | 0.001 |
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".