Extracellular enzymes (exoenzymes) are the proximate agents in microbial cycling of organic matter, because they catalyze many hydrolytic and oxidative reactions that initiate the decomposition of soil organic matters (SOM). Forms and activities of exoenzymes in soils are regulated by their interaction with soil components (e.g. clay mineral and black carbon), which depends on surface properties and solution chemistry. Pyrogenic carbon is ubiquitous in soils and possesses strong adsorption properties, enabling it to interact with a wide range of molecules in soils, including exoenzymes. In this work, we comparatively studied the impacts of surface properties of biochar derived from pine wood and wheat straw on amyloglucosidase and α-amylase adsorption, and evaluated the impact of surface adsorption on amyloglucosidase activity. Results showed that factors, including feedstocks, pyrolysis temperatures and particulate size have evident impacts on biochar surface properties and thus affected amyloglucosidase and α-amylase adsorption adsorption. Activity of enzyme in the absence and presence of biochar was measured by microcalorimetry, and the results showed that adsorption inhibited the enzyme activity. However, specific activity of the surface-bound enzymes varies between biochar types (and minerals).  Loss of enzyme activity after surface adsorption is possibly caused by: 1) disruption of enzyme structure, and 2) shielding of enzyme active site and reducing its accessibility to substrate, which need further verification. Our results showed the differential impacts of biochar on not only exoenzyme adsorption (and mobility in soils), but also specific activity of the surface-bound enzymes.

Extracellular enzyme activity impacted by surface adsorption: Comparison between black carbon and minerals

ACS Fall 2021

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