Differences between stem and branch xylem water isotope composition in four tropical tree species
Bibliographic record
Abstract
Abstract Stable isotope studies (δ 2 H and δ 18 O) of water within plants are providing new information on water sources, competitive interactions and water use patterns under natural conditions. This is based on the assumption that there is no fractionation at the time of water uptake or during its transport within trees. However, previous studies have found fractionation does occur in water taken up through the roots in halophytic and xerophytic plants. It is unclear how widespread such fractionation is in other species. In this study, we tested this fractionation by comparing stem and branch xylem water isotopes over the period of one day (from 8 am to 5 pm) in four wet tropical rainforest tree species ( Dendrocnide photinophylla , Aphananthe philippinensis , Daphnandra repandula and Mallotus polyadenos ). We found branch water isotope ratios (δ 2 H and δ 18 O) were enriched compared with stem xylem water isotopes. D. photinophylla had a significantly different branch δ 18 O ratio than A. philippinensis , D. repandula and M. polyadenos . In contrast, there were no significant differences in stem xylem δ 18 O among the four observed tree species. We found clear differences in the stable isotope ratios of δ 18 O for stem and branch xylem water for D. photinophylla and D. repandula of upto −0.85% and 0.50%, respectively. Remarkable δ 2 H differences were also found between stem and branch xylem water isotope ratios for A. philippinensis , D. repandula and M. polyadenos , being upto −12.14%, −16.17% and −9.65%, respectively. A dual isotope (δ 2 H–δ 18 O) plot showed branch water values were more enriched than stem xylem water values for D. photinophylla and D. repandula , indicating a clear difference between stem and branch xylem water. This study suggests that δ 2 H and δ 18 O fractionation could be a species‐specific phenomenon in tropical trees, which has important implications for plant water source identification and evapotranspiration partitioning.
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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".