The use of alternative electron acceptors in microbial peat decomposition

Abstract

Peat drainage, performed to create usable land, accelerates microbial decomposition of OM, leading to an increase in CO2 emissions from peat as well as land subsidence. While most studies focus on oxic decomposition, anoxic decomposition happening under the water-table is often not considered, leading to a potential underestimation of emission and subsidence rates. Recent studies proposed an “Iron gate theory” model in contrast to the traditional “Enzymic Latch” to explain peat loss regulatory processes. In this study, addition of iron and sulfate on peat originating from two anoxic peat sites in the Netherlands (Assendelft and Rouveen) was performed to evaluate if alternative electron acceptors other than oxygen could be used to decompose peat anoxically. Potential phenol oxidase activity in 15min was measured anoxically via L-DOPA assays. CO2 emission rates from peat in a 48h time period were measured via a respirometer in anoxic conditions. Both basal respiration (BR) and substrate-induced respiration (SIR) rates were measured. The study highlighted an unknown interaction between L-DOPA and ferric iron, which is currently undocumented in soil enzymology literature. This interaction is probable to be causing biases in existing literature on POX activity estimates and peat loss models. CO2 emission rates significantly decreased (n=4, df 3; t= 3.6865; p = 0.0346) with iron addition in Assendelft when a carbon donor (lactate) was added. Sulfate addition in Assendelft instead increased substrate-induced respiration rates. BR and SIR in Rouveen were not affected by addition of both iron and sulfate. Results suggest that sulfate may be used as a TEA in anoxic peat and interactions between iron and sulfate are regulating peat decomposition in anoxic environments.