Extracellular phenol oxidase enzymes are a crucial component of the pathways
involved with the breakdown of complex organic matter, and may therefore play an important role in the stability of long-term soil carbon stores. The aim of this PhD was to investigate environmental drivers of change in extracellular phenol oxidase activity in ecosystems with high soil organic-matter content and the implications for soil carbon cycling as a consequence of associated changes in soluble phenolic concentrations.
Water table drawdown in a Scottish cut-over peatland was found to stimulate peat phenol oxidase activity. In contrast, phenol oxidase activity in the surface peat at a Finnish mire complex was found to have been reduced by drainage; the negative correlation between peat phenol oxidase activity and pH found across the mire
complex suggested that pH is a major underlying factor influencing peat phenol
oxidase activity levels, and may have contributed to the fall in peat phenol oxidase activity with drainage. Organic soil phenol oxidase activity and the abundance of dominant fungal species (analysed using ITS-DGGE) were found to be inhibited by low soil moisture during summer drought at a Welsh Calluna heathland; core incubations suggested that extracellular phenol oxidases activity displays a moisture optima. Impeding the drainage of cores from a Welsh riparian wetland was found to result in the dramatic stimulation of peat phenol oxidase activity - potentially driven in part by rising pH - and suggested that under conditions of oxygen limitation alternative redox mediators may facilitate stimulatory responses of extracellular phenol oxidase activity to environmental change. Enhanced nitrogen deposition at a Scottish ombrotrophic bog and a Welsh acidic grassland was found to have no effect upon extracellular phenol oxidase activity, and it may be that adverse ambient conditions and/or pH changes resulting from the nitrogen additions masked or interacted with the phenol oxidase response.
A negative relationship was found between soil concentrations of soluble phenolics and changes in phenol oxidase activity with water-table drawdown at the Finnish site, and a positive relationship with changes in phenol oxidase activity with impeded drainage in the core manipulation and with ambient moisture levels at the Calluna heathland. The opposite direction of the relationship between soluble phenolics and changes in extracellular phenol oxidase activity coinciding with change in soil pH, suggested that the response of extracellular phenol oxidase activity to changes in pH may result in differing directions of change in soluble phenolic concentrations depending on the ecosystem in question.
That extracellular phenol oxidase activity is sensitive to a suite of environmental
variables coinciding with changes in soil concentrations of soluble phenolics,
suggested that the response of extracellular phenol oxidase activity in response to environmental change is likely to have important implications for soil carbon cycling. That changes in extracellular phenol oxidase activity in response to environmental change were found to have divergent implications for soil soluble phenolic concentrations, suggested that the implications of the response of extracellular phenol oxidase activity to environmental change for soil carbon storage and export from soils is more complex than has generally been assumed.