¹³C/¹²C isotope labelling to study leaf carbon respiration and allocation in twigs of field‐grown beech trees

Abstract

In situ (13)C/(12)C isotopic labelling was conducted in field-grown beech (Fagus sylvatica) twigs to study carbon respiration and allocation. This was achieved with a portable gas-exchange open system coupled to an external chamber. This method allowed us to subject leafy twigs to CO(2) with a constant carbon isotope composition (delta(13)C of -51.2 per thousand) in an open system in the field. The labelling was done during the whole light period at two different dates (in June 2002 and October 2003). The delta(13)C values of respiratory metabolites and CO(2) that is subsequently respired during the night were measured. It was found that night-respired CO(2) is not completely labelled (only ca. 58% and 27% of new carbon is found in respired CO(2) immediately after the labelling in June 2002 and October 2003, respectively) and the labelling level progressively disappeared during the next day. It is concluded that the carbon respired by beech leaves after illumination was supplied by a mixture of carbon sources in which current carbohydrates were not the only contributors. In addition, as has been found in herbaceous plants, isotopic data before labelling showed that carbon isotope discrimination favoring the (13)C isotope occurred during the night respiration of beech leaves.

A continuous labelling approach to recover photosynthetically fixed carbon in plant tissue and rhizosphere organisms of young beech trees (Fagus sylvatica L.) using 13C depleted CO2

“…1). In accordance with other studies (Nogués et al 2006), the obtained results illustrate the distribution and allocation of assimilated carbon within the plant. In leaves, photosynthetically fixed carbon is transformed into sugars and transported to different carbon sinks (twigs, fine roots and coarse roots) via phloem through the plant.…”

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

“…In accordance with our findings, Tcherkez et al (2003) showed that increasing temperatures led to more depleted d 13 C res . Further, old C sources may contribute more than 50% to overall respiration (Nogués et al 2006). When respiratory demand exceeds C input during drought, C from more depleted C sources will be respired, particularly at night when assimilate pools decline, which was probably the case in T. guttata.…”

“…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).…”

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

“…In summary, plant respiratory CO 2 losses are largely, but not exclusively fuelled by recently assimilated C. Temporal changes in substrate use (e.g. Hymus et al, 2005;Nogués et al, 2006) and post-carboxylation isotope fractionation in leaves and heterotrophic tissues can partially uncouple the isotope composition of respired CO 2 from assimilates (see also 2.2), and imprint valuable information in its δ 13 C. However, as measurements in tall stature plants are technically challenging, data on plant respiration and its isotopic composition from field studies, especially from forests, are scarce. Also the emission of biogenic volatile organic compounds (BVOC) can constitute a considerable loss of C from vegetation in the range of a few percent of the current net assimilation rate under non-stress conditions, but can reach or even exceed net assimilation rates under stress conditions, such as drought, and continue even when net assimilation has ceased (e.g., Brüggemann and Schnitzler, 2002), using alternative carbon sources like xylem-transported sugars and breakdown of starch (Loreto and Schnitzler, 2010).…”