Effect of Sterilization on Mineralization of Straw and Black Carbon

The study was aimed at investigating the role of microorganisms in the degradation of BC (black carbon). CO2 evolution was measured under sterilized and non-sterilized soil using BC and straw amendments. Black carbon and straw were produced from homogenously C labelled roots of barley (Hordeum vulgare) with a specific activity 2.9 MBq g C. Production of BC was implemented at 300 oC for 24 h in a muffle oven, incubated in soil and C in the evolved CO2 was measured after 0.5, 1, 2, 4, 8, 16, 26 and 40 days. BC showed much lower and slow evolution of CO2 than the plant material which refers to high resistance of BC to microbial degradation. The difference between soil respiration in sterilized and non-sterilized soil with plant material was visible from the beginning of the experiment, unlike with BC amendments where differences only occurred after some days. In addition, the CO2 evolution from the plant material proceeded with a lag phase while CO2 evolution from the charcoals showed no lag phase. This indicates that microorganisms are not involved in the initial flush of carbon emitted from the BC. We suggest that an alternative source may be carbonates on the surfaces of the BC, but another abiotic source must also be present perhaps abiotic mineralization of labile BC components