Changes in soil phenol oxidase activities due to long-term application of compost and mineral N in a walnut orchard

Results showed that the application of compost significantly increased C and N pools. qCO2 and DHD/Cext data indicated that the biota at 20-40 cm soil depth was more stressed or mainly composed of microorganisms with low substrate utilization efficiency. Phenol oxidase, tyrosinase, and catechol oxidase activities were significantly promoted in the surface layer by compost addition. In contrast, laccase activity showed a large increase in the deeper soil layer when supplied with mineral N, whereas compost addition led to increased activity in the surface layer. These findings suggest that soil phenol oxidases play a part in the determination of soil functionality, but they need to be investigated in greater depth in order to understand the mechanisms regulating their activities.