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IntroductionStable isotope ratios are an increasingly popular tool for biological research. Isotopes are nuclides that vary in the number of neutrons that they contain and thus their atomic mass. Because isotopes of the same element have different masses, they are preferentially taken-up or left behind by physical, chemical and biological processes. Stable isotopes in plant material have been used to investigate water use efficiency and water sources, as well as the temperature and precipitation of a plant's environment. However, isotopic ratios in plants reflect a series of events, and not simply the one of interest for a given study. Therefore researchers must be aware of all of the factors that may be reflected in their results. In these pages, we summarize the abiotic and biotic factors that determine the relative ratios of oxygen and hydrogen isotopes in plants and their environment.
Notation and StandardsIsotopic values are reported in a standard notation as delta: d sample = (R sample / R standard -1) x 1000 Where R represents the ratio of the heavy to light isotope. Delta values are then expressed as per mil (‰). The reference standard for both hydrogen and oxygen is the isotopic ratio of Vienna Standard Mean Ocean Water (VSMOW) and Vienna PeeDee Belemnite (VPDB) for carbonates, silicates and OH minerals: d2H (VSMOW) = 155.95±0.08*10-6
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| Hydrogen | 1H 99.985% |
| 2H 0.015% | |
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Oxygen
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16O 99.759% |
| 17O 0.037% | |
| 18O 0.204% |
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Ashley
Ballantyne 919-684-5245 |
Jessica Hardesty 919-680-3734 |