Biochar Reduces Apparent Soil Enzyme Activities.

Recently, biochar has received attention as a potential agent of enhanced soil carbon sequestration.  However, it is a highly bioactive compound with a high capacity for sorption of biomolecules.  In preliminary research for an incubation of soil with 1% biochar (wt%), we observed a significant decrease (75%)  in the enzyme activity measured in biochar-amended soils when compared with soils free of biochar.  In vitro experiments were therefore initiated to determine whether the biochar was inhibiting the enzyme activity or altering the model substrate.  Purified beta-glucosidase was reacted with biochar then filtered, as was the model substrate p-nitrophenyl-beta-D-glucoside.  The biochar-exposed enzyme showed no decrease in activity when assayed with fresh substrate.  However, the activity of both fresh and biochar-exposed beta-glucosidase was significantly diminished when assayed with biochar-exposed p-nitrophenyl-beta-D-glucoside, suggesting that the biochar chemically altered or blocked the binding site of the substrate. When biochar was added directly to the tube in which fresh beta-glucosidase and fresh p-nitrophenyl-beta-D-glucoside were reacting, no decrease in activity was measured, indicating that the binding affinity of this non-biochar exposed enzyme and substrate pair was rapid, and unperturbed by the biochar.  Further research is needed into the effects of biochar on other enzyme-substrate pairs in order to determine the implications of decreased apparent soil enzyme activities on the overall health of the soil biochemical system.