Inhibitory effects of drought induced acidification on phenol oxidase activities in Sphagnum-dominated peatland

Extracellular phenol oxidases play an important role in the soil carbon cycle. How phenol oxidase activity in peatlands will respond to increased aeration induced by water-table drawdown or droughts if global warming continues remains unclear. We investigated the short-term effects of drought induced acidification on phenol oxidase activities of a Sphagnum-dominated peatland in central China. The results indicated a significant acidification induced by drought, with a decline in the average pH value from 5.67 +/- A 0.08 under waterlogging to 4.84 +/- A 0.08 in droughted peat. In addition, drought-treated peat had a lower average value of phenol oxidase activities compared to the waterlogging-treated peat (mean values of 0.1404 +/- A 0.0305 and 0.2623 +/- A 0.0324 mu mol diqc min(-1) g(-1), respectively). The decreased phenol oxidase activities were mainly attributed to the acidification induced by drought. However, the declines in phenol oxidase activity did not lead to the reduction of the degradation in the deeper peat. Under drought conditions, a considerable part of the adsorbed phenolics, consisting primarily of high molecular-weight organic substances with phenolic groups, were further degraded into smaller-sized or lower molecular weight hydrophilic fractions in the vicinity of the water table. Our results highlight the important role of the water table position in peat decomposition processes. Even with lower activities of phenol oxidase, the decomposition processes were able to effectively keep on going as long as there was sufficient supply of water, oxygen and nutrients.