Discrimination against 13 C during degradation of simple and complex substrates by two white rot fungi

Changes in isotopic 13 C signatures of CO 2 ‐C evolved during decomposition of a sugar (glucose), a fatty acid (palmitic acid), a protein (albumin), a structural biopolymer (lignin) and bulk plant tissue (aerial shoots from Lolium perenne ) were monitored over a period of 76 days. All materials were sterilized and inoculated with either of two different species of white rot fungi, Phanerochaete chrysosporium or Coriolus versicolor , and incubated in sealed bottles at 28°C. The CO 2 concentration in the jars was periodically determined using an infrared gas analyzer and its isotopic ( 13 C) signature was assessed using a trace gas (ANCA TGII) module coupled to an isotope ratio mass spectrometer (IRMS, Europa 20‐20). L. perenne material inoculated with C. versicolor showed the highest C mineralization activity with approximately 70% of total C evolved as CO 2 after 76 days of incubation, followed by glucose. Substrates inoculated with C. versicolor generally decomposed faster than when degraded by P. chrysosporium , except for lignin, where no significant differences between the two fungi types were found and CO 2 ‐C released was less than 2% of the initial C. Considerable 13 C isotopic fractionation during the degradation of plant tissue and of pure biochemical compounds was revealed as well as progressive shifts in cumulative CO 2 ‐ 13 C isotopic signatures over time. During the first stages of decomposition, the CO 2 ‐C released was usually depleted in 13 C as compared with the initial solid substrate, but with ongoing decomposition the CO 2 ‐C evolved became progressively more enriched in 13 C. P. chrysosporium usually showed a slightly higher 13 C fractionation than C. versicolor during the first decomposition phase. At posterior decomposition stages isotopic discrimination was often stronger by C. versicolor . These findings on isotopic 13 C discrimination during microbial degradation both of simple biochemical compounds and of complex vegetal tissue confirmed not only the existence of significant 13 C isotopic fractionation during plant residue decomposition, but also the existence of non‐random isotopic distribution within substrates. They also demonstrated the ability of microorganisms to selectively discriminate against 13 C even when degrading an isolated simple substrate. Copyright © 2003 John Wiley & Sons, Ltd.