Activation Energy of Extracellular Enzymes in Soils from Different Biomes

Enzyme dynamics are being incorporated into soil carbon cycling models and accurate representation of enzyme kinetics is an important step in predicting belowground nutrient dynamics. A scarce number of studies have measured activation energy (E_a) in soils and fewer studies have measured E_a in arctic and tropical soils, or in subsurface soils. We determined the E_a for four typical lignocellulose degrading enzymes in the A and B horizons of seven soils covering six different soil orders. We also elucidated which soil properties predicted any measurable differences in E_a. β-glucosidase, cellobiohydrolase, phenol oxidase and peroxidase activities were measured at five temperatures, 4, 21, 30, 40, and 60°C. E_a was calculated using the Arrhenius equation. β-glucosidase and cellobiohydrolase E_a values for both A and B horizons in this study were similar to previously reported values, however we could not make a direct comparison for B horizon soils because of the lack of data. There was no consistent relationship between hydrolase enzyme E_a and the environmental variables we measured. Phenol oxidase was the only enzyme that had a consistent positive relationship between E_a and pH in both horizons. The E_a in the arctic and subarctic zones for peroxidase was lower than the hydrolases and phenol oxidase values, indicating peroxidase may be a rate limited enzyme in environments under warming conditions. By including these six soil types we have increased the number of soil oxidative enzyme E_a values reported in the literature by 50%. This study is a step towards better quantifying enzyme kinetics in different climate zones.