Production of hydroxyl radicals following water-level drawdown in peatlands: A new induction mechanism for enhancing laccase activity in carbon cycling

The hydroxyl radical (center dot OH) is the most powerful reactive oxygen species that plays a critical role in the fate of redox-active substances. Peatlands are carbon-rich ecosystems with highly reduced substances and ubiquitous redox interfaces. However, little is known about the production of center dot OH during the reoxidation of peatlands under waterlogged conditions. Here, we conduct a set of reoxidation experiments using waterlogged peat soil dominated by various vegetation species and monitored center dot OH production. The results show that the cumulative concentrations of center dot OH produced within 24 h upon oxygenation of waterlogged peat samples are 307-840 mmol g(-1). The main factors affecting the production of center dot OH include an acidic environment, abundant reduced dissolved organic matter and Fe(II). In addition, center dot OH production enhances laccase activity (the largest class of phenol oxidases in the soil) by 7.7% similar to 20.4% and increases soil respiration by 3.17% similar to 23.67% during the reoxidation of the waterlogged peat samples. In addition, the simulation experiments confirm that center dot OH can promote laccase activity directly by serving as an electron acceptor and indirectly by oxidizing substrates. Both mechanisms are greater than the effect of oxygen (O-2) alone on laccase activity. Our results indicate a new induction mechanism for enhancing laccase activity by center dot OH when subjected to anoxic-oxic interface fluctuations, which is particularly important for carbon cycling in peatlands because it can break the decomposition latch and can further promote soil organic carbon mineralization.

Automated summary

The study found that under oxygenation of waterlogged peat samples for 24 hours, the cumulative concentrations of hydroxyl radical (center dot OH) produced ranged from 307-840 mmol g(-1). Factors affecting center dot OH production include an acidic environment, abundant reduced dissolved organic matter, and Fe(II). Additionally, the production of center dot OH enhanced laccase activity (the largest class of phenol oxidases in the soil) by 7.7% to 20.4% and increased soil respiration by 3.17% to 23.67% during the reoxidation of waterlogged peat samples.