Synergy effect of peroxidase enzymes and Fenton reactions greatly increase the anaerobic oxidation of soil organic matter

Carolina Merino,Francisco Matus,Karina Godoy,Pablo Cornejo,Yakov Kuzyakov

doi:10.1038/s41598-020-67953-z

Abstract

In temperate rainforest soils of southern Chile (38 °S), there are high rates of soil organic carbon (SOC) mineralization under oxygen (O2) limitation. We study the combined effects of Fenton reactions and the activity of two enzymes manganese peroxidase (MnP) and lignin peroxidase (LiP), which was hypothesised potentiate SOC mineralization under anoxic conditions leading to carbon dioxide (CO2) release. Both mechanisms produce free radicals when competing for SOC oxidation in the absence of microorganisms. We quantify the CO2 release by induced Fenton reactions in combination with MnP and LiP under aerobic and anaerobic conditions (20 °C, 36 h) in temperate rainforest soils. CO2 levels released by Fenton reactions and enzyme activity were eight times higher than those released by Fenton reaction and peroxidase enzymes in individual treatment. Approximately 31% of the CO2 released under aerobic soil incubation was found to be abiotic (sterilized), while 69% was biotic (non-sterilized soils), and respective values of 17% and 83% were recorded under anaerobic conditions. The relative fluorescence intensity clearly shows ·OH radicals production from Fenton reactions. In conclusion, levels of MnP and LiP coupled with Fenton reactions strongly increase SOC mineralization under long periods of O2 limitation in temperate rainforest soils.

Highlights

In temperate rainforest soils of southern Chile (38 °S), there are high rates of soil organic carbon (SOC) mineralization under oxygen (O2) limitation
We hypothesize that Fenton reactions in combination with the activities of ligninolytic enzymes form a complementary mechanism of C O2 release, enhancing the oxidation of SOC under O 2 limitation conditions in the absence of microorganisms
The lowest levels of C mineralization were recorded in sterilized soils under anaerobic incubation. These results are consistent with the consumption of hydrogen peroxide; Anaerobic abiotic, where Fenton reactions are assumed to occur, showed the highest levels of H2O2 consumption while aerobic biotic incubation showed the lowest (Fig. 1D–F)

Summary

Introduction

In temperate rainforest soils of southern Chile (38 °S), there are high rates of soil organic carbon (SOC) mineralization under oxygen (O2) limitation. We study the combined effects of Fenton reactions and the activity of two enzymes manganese peroxidase (MnP) and lignin peroxidase (LiP), which was hypothesised potentiate SOC mineralization under anoxic conditions leading to carbon dioxide (CO2) release Both mechanisms produce free radicals when competing for SOC oxidation in the absence of microorganisms. Fenton reactions in combination with the activity of these enzymes can potentiate SOC mineralization due to the production of free radicals (strong oxidants of SOM) competing for soil organic matter (SOM) oxidation under anoxic conditions This perspective challenges the traditional assumption that the soils of humid temperate rainforests, especially under high levels of precipitation, mineralize slowly due to a high proportion of anaerobic soils microsites. To broaden the scope of our study, we evaluated three soil types differing in Fe content, pH, and parent material origin

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