Pronounced differences in diurnal variation of carbon isotope composition of leaf respired CO₂ among functional groups
Priault, Pierrick | Wegener, Frederik | Werner, Christiane
The first broad species survey of diurnal variation in carbon (C) isotope signatures of leaf dark-respired CO₂ (δ¹³Cres) is presented here and functional differences and diurnal dynamics are linked to fractionation in different respiratory pathways, based on ¹³C-labelling experiments. δ¹³Cres was analysed with a rapid in-tube incubation technique in 16 species. A large diurnal increase in δ¹³Cres (4-8[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 δ¹³Cres 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 δ¹³Cres 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 δ¹³Cres pattern may provide information for C allocation in plants.
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