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

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.

Microbial Community Structure in Ancient European Arctic Peatlands

“…There are many factors inhibiting microbial activity in the peatlands: low temperature, semi-anaerobic and anaerobic conditions, high acidity, lack of mineral nutrients, phenolic compound toxicity, substrate dissociation, enzymes, and microbial cells [ 40 , 41 , 42 ]; however, the significance of individual factors will be different for diverse groups of microorganisms. For fungi development in the peatlands, aeration is an important limiting factor, since most of them are aerobic organisms; therefore, the total number of fungi in the studied peatlands varies from 1.45 × 10 6 ± 4.48 × 10 5 to 1.17 × 10 10 ± 4.40 × 10 8 copies/g of soil, which is significantly lower than the number of bacteria and archaea.…”

Ecological resilience of restored peatlands to climate change

“…Whereas in the tropics, decomposition is slowed down by organic matter recalcitrance as well as high soil moisture condition 18 . In addition to waterlogged conditions, a relatively stable water table is important to limit decomposition and maintain the ecological habitat of peatforming species, such as Sphagnum moss 20 .…”

Back to the Future: Restoring Northern Drained Forested Peatlands for Climate Change Mitigation

“…Due to enhanced decomposition, this phase might be characterized by high dissolved organic matter concentrations (Negassa et al, 2021). Vegetation during this phase is patchy (Hedberg et al, 2012) and growth of mosses such as Sphagnum is likely limited by high water table variability (Kim et al, 2021). Proliferation of wetland associated vascular plants is likely due to nutrient availability, however the specific species will likely be influenced by pH (Kozlov et al, 2016).…”

“…The second phase of restoration is characterized by high water table due to effective water outflow control by years of ditch blocking. However, pore size distribution and bulk density are not expected to be fully recovered (Kreyling et al, 2021), leading to high water table variability and oxic pulses especially in highly degraded peat (Kim et al, 2021). Water table variability might continue to inhibit Sphagnum proliferation and sustain vascular plants, leading to more labile litterfall compared to pristine conditions (Bragazza et al, 2009;Kim et al, 2021).…”

“…However, pore size distribution and bulk density are not expected to be fully recovered (Kreyling et al, 2021), leading to high water table variability and oxic pulses especially in highly degraded peat (Kim et al, 2021). Water table variability might continue to inhibit Sphagnum proliferation and sustain vascular plants, leading to more labile litterfall compared to pristine conditions (Bragazza et al, 2009;Kim et al, 2021). Oxic periods promote the decomposition of recalcitrant peat, thereby increase nutrient content and labile organic substrate availability (Górecki et al, 2021).…”