Lysis of soil microbial cells by CO2 or N2 high pressurization compared with chloroform fumigation

Abstract

Abstract The classical chloroform fumigation-incubation (CFI) and fumigation-extraction (CFE) methods are nowadays among the most used for determining soil microbial biomass, although the chloroform lysing of microbial cells is not always complete. Here, we have tested a physical method, used for sterilizing foods but never in soil, based on N 2 or CO 2 high pressurization (N2HP or CO2HP, respectively) to cause microbial cell lysis. The N 2 HP and CO 2 HP were tested on two soils differing for their organic matter content, one agricultural (AGR) and one forest (FOR), and firstly were compared with the CFI. The CO 2 extra-flush from both soils during 10-d incubation by N 2 HP was lower than that by CFI method, whereas that by CO2HP was greater. Then, the lysis by CO2HP was compared with that by the CFE method by varying CO 2 pressure and duration. The CO2HP, at proper conditions, was more efficient than CFE method to cause the lysis of soil microbial cells. Moreover, both CO 2 pressure value and duration were important in increasing the extractable organic C compared to the CFE. The most successful combination of high CO 2 pressure and duration was 4.13 MPa and 32 h. However, we cannot exclude that CO2HP might have caused the release of soil organic C not ascribable to living organic matter. Further studies using 13 C and/or 15 N-labeled microbial cells should assess the release of abiotic organic C.

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