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

(C)hanges in isotopic C-13 signatures Of CO2-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 28degreesC. The CO2 concentration in the jars was periodically determined using an infrared gas analyzer and its isotopic (C-13) 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 CO2 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 CO2-C released was less than 2% of the initial C. Considerable C-13 isotopic fractionation during the degradation of plant tissue and of pure biochemical compounds was revealed as well as progressive shifts in cumulative CO2-C-13 isotopic signatures over time. During the first stages of decomposition, the CO2-C released was usually depleted in C-13 as compared with the initial solid substrate, but with ongoing decomposition the CO2-C evolved became progressively more enriched in C-13. p. chrysosporium usually showed a slightly higher C-13 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 C-13 discrimination during microbial degradation both of simple biochemical compounds and of complex vegetal tissue confirmed not only the existence of significant C-13 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 C-13 even when degrading an isolated simple substrate. Copyright (C) 2003 John Wiley Sons, Ltd.