Changes in δ¹³C of dark respired CO₂ and organic matter of different organs during early ontogeny in peanut plants

Abstract

Carbon isotope composition in respired CO₂ and organic matter of individual organs were measured on peanut seedlings during early ontogeny in order to compare fractionation during heterotrophic growth and transition to autotrophy in a species with lipid seed reserves with earlier results obtained on beans. Despite a high lipid content in peanut seeds (48 %) compared with bean seeds (1.5 %), the isotope composition of leaf- and root-respired CO₂ as well as its changes during ontogeny were similar to already published data on bean seedlings: leaf-respired CO₂ became ¹³C-enriched reaching −21.5 ‰, while root-respired CO₂ became ¹³C-depleted reaching around −31 ‰ at the four-leaf stage. The opposite respiratory fractionation in leaves vs. roots already reported for C₃ herbs was thus confirmed for peanuts. However, contrarily to beans, the peanut cotyledon-respired CO₂ was markedly ¹³C-enriched, and its ¹³C-depletion was noted from the two-leaf stage onwards only. Carbohydrate amounts being very low in peanut seeds, this cannot be attributed solely to their use as respiratory substrate. The potential role of isotope fractionation during glyoxylate cycle and/or gluconeogenesis on the ¹³C-enriched cotyledon-respired CO₂ is discussed.

Keywords:

• carbon-13
• cotyledons
• isotope ecology
• leaves vs. roots
• ontogeny
• peanut
• plant respiration
• respired CO₂

Acknowledgements

The authors are grateful to the Laboratoire d'Ecologie, Systématique et Evolution (ESE, CNRS-UMR 8079) at the University of Paris-Sud (Orsay) for financial support for isotope analyses, the platform ‘Métabolisme-Métabolome’ of the IFR87 (Orsay) for technical assistance for isotope analyses of water-soluble fraction, and the Laboratoire de Biogéochimie et Ecologie des Milieux Continentaux (BIOEMCO, INRA, Thiverval-Grignon) for providing both plant culture and IRMS facilities as well as for technical assistance for isotope analyses of respired CO₂ and bulk OM.

Disclosure statement

No potential conflict of interest was reported by the authors.