Pronounced differences in diurnal variation of carbon isotope composition of leaf respired CO₂ among functional groups

Abstract

Summary 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‰) 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.

Diel variations in the carbon isotope composition of respired CO<sub>2</sub> and associated carbon sources: a review of dynamics and mechanisms

“…At the ecosystem level, an additional factor is the fact that respiration of leaves is strongly inhibited in the light but may exhibit a marked increase with very positive δ 13 C res (LEDR) at the beginning of the dark period (Barbour et al, 2011). A maximum peak in δ 13 C res after sunset (duration of 60-100 min) was correlated with the light intensity on the prevailing day, showing higher 13 C enrichment during sunny compared to cloudy days (Barbour et al, 2011), thus confirming the patterns observed in leaves (Prater et al, 2006;Priault et al, 2009). Indeed, markedly 13 C-enriched CO 2 has been measured in tree crowns at night .…”

Disentangling drought-induced variation in ecosystem and soil respiration using stable carbon isotopes

“…This intramolecular heterogeneity of 13 C results in an 'apparent fractionation' during dark respiration depending on the balance between pyruvate dehydrogenase and Krebs cycle metabolic reactions due to the deviation of C to secondary metabolism Ghashghaie et al 2003;Werner et al 2007b;Priault et al 2009). The observed depletion in foliage d 13 C res with drought ( Fig.…”

“…Changes in either the magnitude of component fluxes or their isotope composition (d 13 C res ) may drive the observed variations in the isotopic signature of d 13 C R . Substantial temporal variations in isotopic composition of CO 2 respired by leaves (e.g., Hymus et al 2005;Mortazavi et al 2005;Kodama et al 2008;Werner et al 2007bWerner et al , 2009Priault et al 2009;Sun et al 2009), roots (e.g., Klumpp et al 2005), and soils (e.g., McDowell et al 2004a;Ekblad et al 2005;Kodama et al 2008) have been observed. Variability in photosynthetic discrimination is thought to largely determine the isotopic composition of plant as well as soil and even R eco (e.g., Ekblad and Högberg 2001;Bowling et al 2002;Mortazavi et al 2005;Werner et al 2006).…”

“…Another reason for the variation in d 13 C res and d 13 C R might be temporal changes in C supply by assimilation that could bring about changes in the utilization of different respiratory substrates (e.g., old vs. new C; Nogués et al 2006). Additionally, there is now evidence for substantial metabolic fractionation in the dark respiratory pathways of leaves (e.g., Rossmann et al 1991;Gleixner and Schmidt 1997;Tcherkez et al 2003;Ghashghaie et al 2003;Mortazavi et al 2006;Werner et al 2007bWerner et al , 2009Barbour and Hanson 2009;Priault et al 2009) and during C transport and allocation to stem and roots (Gleixner and Schmidt 1997;Tcherkez et al 2004;Brandes et al 2006;Gessler et al 2009a;Cernusak et al 2009). Thus, apart from the differential climatic dependencies that bring about changes in magnitude and isotope composition of plant, soil and root respiration fluxes, metabolic processes occurring in each of these components will also have isotope effects which may influence d 13 C R .…”

Carbon allocation and carbon isotope fluxes in the plant-soil-atmosphere continuum: a review

“…Partitioning acetyl-CoA to fatty acid synthesis and TCA leads to an overall higher contribution of PDH than TCA activity to total CO 2 efflux, which may explain the often-observed 13 C-enrichment of CO 2 efflux compared to respiratory substrate . Imbalances between TCA and PDH may also account for diel changes in δ 13 C of plant respiration (Kodama et al, 2008;Priault et al, 2009;Kodama et al, 2011). In addition, fractionation by PDH and TCA cycle enzymes may further change the isotopic signature of respired CO 2 (Tcherkez and Farquhar, 2005).…”