Water Table Fluctuation in Peatlands Facilitates Fungal Proliferation, Impedes Sphagnum Growth and Accelerates Decomposition

Jinhyun Kim,Chris Freeman,Timothy G. Jones,Sandrine Hogue-Hugron,Zuhair Alqulaiti,Remy Pouliot,Hojeong Kang,Christian Dunn,Line Rochefort

doi:10.3389/feart.2020.579329

Abstract

Northern peatlands are substantial carbon sinks because organic matter in peat is highly stable due to the low rate of decomposition. Waterlogged anaerobic conditions induce accumulation of Sphagnum-derived phenolic compounds that inhibit peat organic matter decomposition, a mechanism referred to as the “enzymic latch”. Recent studies have predicted that the water table in northern peatlands may become unstable. We observed that such unstable water table levels can impede the development of Sphagnum mosses. In this study, we determined the effects of low and high frequency water table fluctuation regimes on Sphagnum growth and peat organic matter decomposition, by conducting a year-long mesocosm experiment. In addition, we conducted a molecular analysis to examine changes in abundance of fungal community which may play a key role in the decomposition of organic matter in peatlands. We found that rapid water table fluctuation inhibited the growth of Sphagnum due to fungal infection but stimulated decomposition of organic matter that may dramatically destabilize peatland carbon storage. Increased pH, induced by the fluctuation, may contribute to the enhanced activity of hydrolases in peat. We demonstrated that the water table fluctuation in peatlands impeded Sphagnum growth and accelerates decomposition due to fungal proliferation. Thus, we suggested that understanding the microbial community in the northern peatlands is essential for elucidating the possible changes in carbon cycle of peatland under the changing world.

Highlights

Northern peatlands are characterized by waterlogged, anaerobic, acidic, phenolic-rich, cool conditions, resulting in the low decomposition rate and high accumulation rate (3–80 g C m−2 y−1) of organic matter as peat (Gorham, 1991; Aerts et al, 1992; Gallego-Sala et al, 2018)
The area of Sphagnum-covered peat was continually reduced by 42–52% during the experiment in the fluctuation treatments compared to the control of more stable water table it was statistically not significant (Figure 2B)
The results showed that both Sphagnum biomass and Sphagnumcovered area were substantially reduced by water fluctuation (Figures 2A,B), suggesting strongly that the water table fluctuation, regardless of whether fluctuations were slow or fast, impeded growth and development of Sphagnum

Summary

Introduction

Northern peatlands are characterized by waterlogged, anaerobic, acidic, phenolic-rich, cool conditions, resulting in the low decomposition rate and high accumulation rate (3–80 g C m−2 y−1) of organic matter as peat (Gorham, 1991; Aerts et al, 1992; Gallego-Sala et al, 2018). If water table is lowered, oxygen becomes available to activate phenol oxidative enzymes, lowering the quantity of phenolic compounds and allowing the decomposition of organic matter. This mechanism is called ‘enzymic latch’ and it is one of the key mechanisms controlling decomposition of organic matter in peatlands (Freeman et al, 2001; Romanowicz et al, 2015; Kang et al, 2018)

Objectives

Methods

Results

Conclusion