Table 1.
Observed and predicted values of δ18Owl for bulk leaf water
| Plant | Observed δ18Owl, ‰ | Craig–Gordon-predicted δ18Owl, ‰ |
|---|---|---|
| Agropyron desertorum (C3) | 7.7 ± 1.6 | 7.8 |
| Agrostis stolonifera (C3) | 9.2 ± 2.8 | 8.1 |
| Alopecurus pratensis (C3) | 8.3 ± 3.6 | 7.6 |
| Bromus inermis (C3) | 8.2 ± 1.7 | 7.6 |
| Lolium multiflorum (C3) | 8.0 ± 1.2 | 7.8 |
| Andropogon gerardii (C4) | 15.1 ± 3.7 | 8.0 |
| Bouteloua curtipendula (C4) | 12.7 ± 0.3 | 7.6 |
| Eragrostis curvula (C4) | 12.4 ± 4.2 | 8.0 |
| Leptochloa dubia (C4) | 14.2 ± 2.8 | 7.8 |
| Muhlenbergia wrightii (C4) | 9.0 ± 2.6 | 8.1 |
| C3 mean | 8.3 ± 0.5a | 7.8 |
| C4 mean | 12.6 ± 3.2b | 7.8 |
Each value represents a mean of three plants and the associated standard deviation. C3 and C4 means are significantly different at P < 0.01. Predicted δ18Owl values (SMOW scale) are based on a single-water-source Craig–Gordon model. Sample conditions were: δ18Oatm w vapor = −27‰; relative humidity = 35%; air temperature = 25°C; leaf temperatures varied but were not significantly different from the mean of 27°C. Sample conditions for pilot experiment (data in text): δ18Oatm w vapor = −24‰; δ18Osource = −15.6‰; relative humidity = 40%; air temperature = 35°C; leaf temperatures were C3 dicot = 34°C, C3 grass = 35°C, and C4 grass = 37°C.