第五章 同位素示踪方法.pptVIP

第三章 同位素示踪技术 (Isotope Tracer Method and Technology ) 2. 实证——Case Study Mapping Spatial Variability in Marsh Redox Conditions Using Biomass Stable Isotopic Compositions Carol Kendall, Steven Silva, Daniel Steinitz, Erika Wise, Cecily Chang? (USGS, Menlo Park CA);? Jerry Stober, Phyllis Meyer? (USEPA, Athens GA) Photosynthesis and carbon cycling: Terrestrial plants fix atmospheric CO2 by two main photosynthetic reaction pathways: the Calvin-Benson, or C3, and the Hatch-Slack, or C4. C3 plants convert atmospheric CO2 to a phosphoglycerate compound with three C atoms while C4 plants convert CO2 to dicarboxylic acid, a four-C compound. Carbon isotopes are strongly fractionated by photosynthesis and the C3 and C4 processes involve different isotopic fractionation, with the result that C4 plants have higher delta13C values ranging from -17o/oo to -9o/oo with a mean of -13o/oo relative to PDB, while C3 plants show delta values ranging from -32o/oo to -20o/oo with an average value of -27o/oo. Most terrestrial plants are C3, all forest communities and most temperate zone plant communities of all kinds being dominated by C3 plants. The native plant populations of North America and Europe are almost exclusively C3. Over 80% of crop plants are C3. C4 plants are characteristically found in hot, arid environments: a selective advantage of C4 photosynthesis is more efficient use of water. Some crops of immense importance are C4 plants: maize, sorghum, millet, and sugar cane. The 13C value is a standard method for distinguishing the C3 and C4 plant groups and is used by plant physiologists to determine drought resistance in C3 plants, as well as to breed for improvement in this increasingly vital characteristic. * * 1. 基本原理 Table 1. Estimates of quasi-natural sources of lead, cadmium and mercury in the EMEP domain 样品被高温燃烧，成为CO2, N2, SO2，然后进入质谱仪。 采取重轻同位素比。 一般误差在：±0.1 to 0.2‰, or 0.5 ‰(S). 基本公式： 2.1 碳同位素示踪及其应用 The distribution of ?13C values for water, sediments a