Monday, November 13, 2006 - 2:15 PM
119-8
Soil Charcoal--a Potential Humification Catalyst.
Humification of organic carbon in soil is believed to involve both abiotic and enzymatically driven processes. Phenol oxidase enzymes catalyze the oxidation of phenolic and related compounds to form quinones, which then react readily with amines to form melanin-type compounds that are more resistant to microbial degradation. Opposing this forward humification process is the breakdown and eventual oxidation of soil carbon through a combination of oxidative and hydrolytic processes, involving both enzymatic and abiotic pathways. Net humification thus involves enhancing the right type and amount of oxidation while minimizing competing degradative processes. Much of our work has focused on identifying practical ways of stabilizing phenol oxidase enzymes to enhance their longevity and total activity in soils. We (and others) have noted that the presence of Fe and Mn oxide minerals favors the activity of tyrosinase (a phenol oxidase), as do alkaline pH conditions and microporous matrix materials. Experiments involving tyrosinase with several alkaline fly ashes, in the presence and absence of a carbonate-rich soil, however, demonstrated that another variable, charcoal, may be very important to the forward humification process. The tyrosinase-promoting effect of charcoal likely stems from its high ion exchange capacity, extensive hydrophobic surfaces, and microporosity, all of which combine to concentrate organic reactants and the enzyme at the charcoal/water interface. We are now expanding our experiments to include the impact of charcoal on the degradative processes involving hydrolase enzymes in order to determine whether charcoal indeed promotes net humification.
Recorded presentation