Understanding drivers of peatland extracellular enzyme activity in the PEATcosm experiment: mixed evidence for enzymic latch hypothesis

© 2015, Springer International Publishing Switzerland. Aims: Our objective was to assess the impacts of water table position and plant functional groups on peatland extracellular enzyme activity (EEA) framed within the context of the enzymic latch hypothesis. Methods: We utilized a full factorial experiment with 2 water table (WT) treatments (high and low) and 3 plant functional groups (PFG: Ericaceae, sedge, Ericaceae and sedge unmanipulated) in twenty-four 1 m3 intact peatland mesocosms. We measured bulk peat and porewater phase oxidative and hydrolytic enzyme activities monthly from June - October 2012. We also measured physical and porewater chemical constituents in tandem to analyze environmental influences on seasonal enzyme activities. Results: No PFG effects on EEA with WT affecting only acid-phosphatase activity in porewater. Strong seasonal dynamics in EEAs overshadowed our manipulations. Analyses indicated phenolic concentrations were influenced by peat redox potential and negatively correlated with phenol oxidase activity as expected from enzymic latch hypothesis. However, no hydrolytic EEA was influenced by total phenolics, but driven largely by seasonal changes in soil temperature and increasing DOC concentrations in porewater. Conclusions: Our results suggest no support for final step in enzymic latch, in which phenolics are posited to regulate hydrolytic EEAs. Mechanisms regulating seasonal influences remain to be elucidated