PHYSIOLOGICAL MODELS FOR SCALING PLOT MEASUREMENTS OF CO<sub>2</sub>FLUX ACROSS AN ARCTIC TUNDRA LANDSCAPE
Bibliographic record
Abstract
Regional estimates of arctic ecosystem CO2 exchange are required because of the large soil carbon stocks located in arctic regions, the potentially large global-scale feedbacks associated with climate-change-induced alterations in arctic ecosystem C sequestration, and the substantial small-scale (1–10 m2) heterogeneity of arctic vegetation and hydrology. Because the majority of CO2 flux data for arctic ecosystems are derived from plot-scale studies, a scaling routine that can provide reliable estimates of regional CO2 flux is required. This study combined data collected from chamber measurements of CO2 exchange, meteorology, hydrology, and surface reflectance with simple physiological models to quantify the diurnal and seasonal dynamics of whole-ecosystem respiration (R), gross primary production (GPP), and net CO2 exchange (F) of wet- and moist-sedge tundra ecosystems of arctic Alaska. Diurnal fluctuations in R were expressed as exponential functions of air temperature, whereas diurnal fluctuations in GPP were described as hyperbolic functions of diurnal photosynthetic photon flux density (PPFD). Daily integrated rates of R were expressed as an exponential function of average daily water table depth and temperature, whereas daily fluctuations in GPP were described as a hyperbolic function of average daily PPFD and a sigmoidal function of the normalized difference vegetation index (NDVI) calculated from satellite imagery. These models described, on average, 75–97% of the variance in diurnal R and GPP, and 78–95% of the variance in total daily R and GPP. Model results suggest that diurnal F can be reliably predicted from meteorology (radiation and temperature), but over seasonal time scales, information on hydrology and phenology is required to constrain the response of GPP and R to variations in temperature and radiation. Using these physiological relationships and information about the spatial variance in surface features across the landscape, measurements of CO2 exchange in 0.5-m2 plots were extrapolated to the hectare scale. Compared to direct measurements of hectare-scale F made using eddy covariance, the scaled estimate of seasonally integrated F was within 20% of the observed value. With a minimum of input data, these models allowed plot measurements of arctic ecosystem CO2 exchange to be confidently scaled in space and time.
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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) | 0.005 | 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".