PUB - Publikationen an der Universität Bielefeld

The first broad species survey of diurnal variation in carbon (C) isotope signatures of leaf dark-respired CO2 (delta C-13(res)) is presented here and functional differences and diurnal dynamics are linked to fractionation in different respiratory pathways, based on C-13-labelling experiments. delta C-13(res) was analysed with a rapid in-tube incubation technique in 16 species. A large diurnal increase in delta C-13(res) (4-8 parts per thousand) occurred in evergreen, slow-growing and aromatic species and correlated significantly with cumulative photosynthesis, whereas no variation occurred in herbaceous, fast-growing plants or temperate trees. The diurnal increase in delta C-13(res) declined almost proportionally to reductions in cumulative light and was reduced in growing compared with mature leaves. Pyruvate positional labelling provided direct evidence that functional groups differ in C allocation between respiratory pathways owing to different metabolic demands for growth, maintenance and secondary metabolism. Diurnal increase in C flux through pyruvate dehydrogenase (for investment in, for example, isoprene or aromatic compounds) combined with consistently low Krebs cycle activity resulted in pronounced increase in delta C-13(res) in evergreen and aromatic species. By contrast, fast growing herbs with high respiratory demand exhibited no diurnal changes since C was fully respired. Hence, diurnal delta C-13(res) pattern may provide information for C allocation in plants. New Phytologist (2009) 181: 400-412doi: 10.1111/j.1469-8137.2008.02665.x.