Measurement of total and extractable enzyme activity from soil and decomposing litter

The total and extractable activities of the enzymes β-glucosidase (bgluc), cellobiosidase (cell), xilanase (xil), chitinase (chit), leucine aminopepditase (leu) and acid phosphomonoesterase (acP) were determined in soil and decomposing litter of miscanthus (Miscanthus x giganteus L.) and black locust (Robinia pseudoacacia L.). The objective was to quantify the enzyme-specific extractability of a desorption-based fluorometric enzyme assay and whether the extractability is affected by soil and litter type. Soil and litter samples were extracted in 2mL eppendorf tubes with glass/ceramic beads and lysozyme solution. Soil suspensions were incubated in a stirring device and aliquotes of the supernatant were dosed in 384-well microplates after centrifugation to determine total activity. The extractable activity was measured on the supernatant taken from incubated suspension. Extractability of soil enzymes (as % of the total activity) was on average as follows: bgluc (3%), cell (11 %), xil (4%), chit (8%), leu (44%) and acP (13%). A significant effect of SOC and FBC/MBC on acP and leu extractability was observed. Extractability of litter enzymes, instead, was on average as follows: bgluc (25%), cell (10 %), xil (19%), chit (16%), leu (31%) and acP (28%). A significantly higher extractability for chit and leu was observed in miscanthus litter (C/N: 71, Lignin/N: 32) compared to black locust litter (C/N: 17, Lignin/N: 6). We also observed that extractability in both litter types increase significantly in bgluc (+405%), xil (+242%), cell (+217%) and acP (+454%) during the late stage of decomposition. This method enabled the quantification of total and extractable activities of several soil/litter hydrolytic enzymes.