Reconciling apparent variability in effects of biochar amendment on soil enzyme activities by assay optimization

Authors: BAILEY, VANESSA - Pacific Northwest National Laboratory; FANSLER, SARAH - Pacific Northwest National Laboratory; Smith, Jeffrey; BOLTON, HARVEY - Pacific Northwest National Laboratory

Submitted to: Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/18/2010
Publication Date: 10/31/2010
Citation: Bailey, V.L., Fansler, S.J., Smith, J.L., Bolton, H. 2010. Reconciling apparent variability in effects of biochar amendment on soil enzyme activities by assay optimization. Soil Biology and Biochemistry. 43(2):296-301. doi:10.1016/j.soilbio.2010.10.014.

Interpretive Summary: Biochar is being promoted as a soil amendment to enhance soil quality; it is also seen as a mechanism of long-term sequestration of carbon. We studied the effects of a biochar made from switchgrass on four soil enzymes (ß- glucosidase, ß-N-acetylglucosaminidase, lipase, and leucine aminopeptidase) to determine if biochar would consistently modify soil biological activities. We found inconsistent results from enzyme assays of char-amended soils which suggested that biochar had variable effects on soil enzyme activities. In an effort understand the varied effects, purified enzymes or substrates were briefly exposed to biochar and then assayed. the exposure of substrate to biochar reduced the apparent activity of the enzymes, suggesting that sorption reactions between substrate and biochar impeded enzyme function. We conclude that the effects of biochar on enzyme activities in soils are highly variable; these effects are likely associated with reactions between biochar and the target substrate. This research will aid scientists in determining the effects of biochar on soil quality and carbon sequestration.

Technical Abstract: We studied the effects of a biochar made from switchgrass on four soil enzymes (ß- glucosidase, ß-N-acetylglucosaminidase, lipase, and leucine aminopeptidase) to determine if biochar would consistently modify soil biological activities. Inconsistent results from enzyme assays of char-amended soils suggested that biochar had variable effects on soil enzyme activities, thus we conducted a second experiment to determine if biochar reacts predictably with either enzyme or substrate in in vitro reactions. Seven days after biochar was added to 3 soils, fluorescence-based assays revealed increased enzyme activities (up to 7-fold for one measure of ß-glucosidase) and some decreased activities (one-fifth of the unamended control for lipase measured in the same soil), compared to non-amended soil. In an effort understand the varied effects, purified enzymes or substrates were briefly exposed to biochar and then assayed. In contrast to the soil assays, except for ß-N-acetylglucosaminidase, the exposure of substrate to biochar reduced the apparent activity of the enzymes, suggesting that sorption reactions between substrate and biochar impeded enzyme function. Our findings indicate that fluorometric assays account for, this sorption better than the colorimetric assays. The activity of purified ß-N acetylglucosaminidase increased 50-75% following biochar exposure, suggesting a chemical enhancement of enzyme function. In some cases, biochar stimulates soil enzyme activities, to a much greater degree than soil assays would indicate, given that substrate reactivity can be impeded by biochar exposure. We conclude that the effects of biochar on enzyme activities in soils are highly variable; these effects are likely associated with reactions between biochar and the target substrate.