¹³C isotopic fractionation during biodegradation of agricultural wastes

Abstract

Significant differences in δ¹³C signatures occur within and between plant tissues and their constituent biochemical entities, and also within and between heterotrophic bacteria and fungi and their metabolic products. Furthermore, ¹³C isotopic fractionation occurs during the biodegradation of organic molecules as seen in the substrate, respired CO₂ and the microbial biomass, which could be related to substrate composition and/or microbial metabolism. The ¹³C isotopic fractionation observed during the decomposition of a single defined C substrate appears to be due to the intra-molecular heterogeneity in ¹³C in the substrate and to ¹³C isotopic fractionation during microbial metabolism. Very limited data suggest that the latter may be quantitatively more important than the former. Studies with defined fungi in culture media have highlighted the complexities associated with the interpretation of the observed patterns of ¹³C isotopic fractionation when a single defined C source is added to the culture medium which itself contains one or more C sources. Techniques involving ¹³C enrichment or paired treatments involving an equivalent C₃- and C₄-derived substrate have been devised to overcome the problem of background C in the culture medium and ¹³C isotopic fractionation during metabolism. Studies with complex substrates have shown an initial ¹³C depletion phase in respired CO₂ followed by a ¹³C enrichment phase which may or may not be followed by another ¹³C depletion phase. Basic studies involving an integrated approach are required to gain a new insight into ¹³C isotopic fractionation during organic residue decomposition, by simultaneous measurements of δ¹³C in all C moieties. New analytical tools to measure real-time changes in δ¹³CO₂ and the intra-molecular δ¹³C distribution within plant biochemical entities offer new opportunities for unravelling the complex interactions between substrate and microbial metabolism with respect to ¹³C isotopic fractionation during biodegradation.

Keywords:

• agricultural waste
• artificial media
• biodegradation
• biogeochemistry
• carbon-13
• crop residues
• defined compounds
• isotopic fractionation
• white rot fungi

Acknowledgements

The senior author thanks EMBRAPA-Solos as the host institution and the University of Melbourne for assistance with travel expenses.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The senior author thanks the Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ) for a visiting scientist fellowship (Pesquisador Visitante N^o. 101.466/2014).