Short-term measurements of carbon isotope discrimination in several C4 species

摘要: Carbon isotope discrimination (Δ) and leaf gas-exchange were measured simultaneously for a number of C4 species. Linear relationships found between A the ratio intercellular to ambient partial pressures CO2, pI/pa. These data used estimate fraction CO2 released by C4-acid decarboxylation in bundle sheath, which subsequently leaks out mesophyll. We define this as leakiness system it is also measure extent phosphoenolpyruvate (PEP) carboxylations exceed ribulose 1,5-bisphosphate (RuBP) carboxylations. For Sorghum bicolor Amaranthus edulis, was estimated at 0.2 constant over wide range irradiances (between 480 1600 μmol quanta m-2 s-1), 30 350 μbar) temperatures (from 21oC 34oC). At less than 240 s-1, appeared increase. dicotyledonous monocotyledonous species, various C4-decarboxylation types, 0.2. Contrary expectation, amongst 11 species examined, those with suberised lamellae did not show lower values without lamellae. one NAD-ME PCK monocot, estimates significantly higher 0.30 0.25, respectively. Long-term (assessed from carbon composition dry matter) correlate well these short- term measures discrimination. suggest that may be due differences fractionations occurring after photosynthesis.