Abstract
Methane (CH4 ) emissions from northern peatlands are projected to increase due to climate change, primarily because of projected increases in soil temperature. Yet, the rates and temperature responses of the two CH4 emission-related microbial processes (CH4 production by methanogens and oxidation by methanotrophs) are poorly known. Further, peatland sites within a fen-bog gradient are known to differ in the variables that regulate these two mechanisms, yet the interaction between peatland type and temperature lacks quantitative understanding. Here, we investigated potential CH4 production and oxidation rates for 14 peatlands in Finland located between c. 60 and 70°N latitude, representing bogs, poor fens, and rich fens. Potentials were measured at three different temperatures (5, 17.5, and 30℃) using the laboratory incubation method. We linked CH4 production and oxidation patterns to their methanogen and methanotroph abundance, peat properties, and plant functional types. We found that the rich fen-bog gradient-related nutrient availability and methanogen abundance increased the temperature response of CH4 production, with rich fens exhibiting the greatest production potentials. Oxidation potential showed a steeper temperature response than production, which was explained by aerenchymous plant cover, peat water holding capacity, peat nitrogen, and sulfate content. The steeper temperature response of oxidation suggests that, at higher temperatures, CH4 oxidation might balance increased CH4 production. Predicting net CH4 fluxes as an outcome of the two mechanisms is complicated due to their different controls and temperature responses. The lack of correlation between field CH4 fluxes and production/oxidation potentials, and the positive correlation with aerenchymous plants points toward the essential role of CH4 transport for emissions. The scenario of drying peatlands under climate change, which is likely to promote Sphagnum establishment over brown mosses in many places, will potentially reduce the predicted warming-related increase in CH4 emissions by shifting rich fens to Sphagnum-dominated systems.
Highlights
Global estimates have revealed a change in the global methane (CH4) budget in the past decades, an increase in atmospheric CH4 concentrations until the early 2000s, a stabilization period until 2006, and an ongoing new rise afterwards (Dlugokencky et al, 2011; Nisbet et al, 2019; Rigby et al, 2008)
We explored whether CH4 emission patterns in the same study sites could be connected to their CH4 production and oxidation potential rates
Our particular questions were: (1) What are the roles of peat properties and plant functional types in driving CH4 production and oxidation? (2) How does the temperature response vary for CH4 production and oxidation, and for different peatland types?
Summary
Global estimates have revealed a change in the global methane (CH4) budget in the past decades, an increase in atmospheric CH4 concentrations until the early 2000s, a stabilization period until 2006, and an ongoing new rise afterwards (Dlugokencky et al, 2011; Nisbet et al, 2019; Rigby et al, 2008). Several studies have already shown that the activity and community composition of both CH4 producing (methanogens) and CH4 oxidizing (methanotrophs) microbes in peatlands are largely influenced by climate change-related environmental conditions, such as water level and temperature (Larmola et al, 2010; Turetsky et al, 2008; Yrjälä et al, 2011). Despite this knowledge, the direction and magnitude of the responses of CH4 production and oxidation processes to such variables remain poorly understood and can differ greatly, which makes predicting the dynamics of the net CH4 flux in peatlands challenging. Our particular questions were: (1) What are the roles of peat properties and plant functional types in driving CH4 production and oxidation? (2) How does the temperature response vary for CH4 production and oxidation, and for different peatland types?
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