Impact of Warming on Greenhouse Gas Production and Microbial Diversity in Anoxic Peat From a Sphagnum-Dominated Bog (Grand Rapids, Minnesota, United States)

Abstract

Climate warming is predicted to increase heterotrophic metabolism in northern peatland soils leading to enhanced greenhouse gas emissions. However, the specific relationships between temperature and the greenhouse gas producing microbial communities are poorly understood. Thus, in this study, the temperature dependence of carbon dioxide (CO₂) and methane (CH₄) production rates along with abundance and composition of microbial communities were investigated in peat from a Sphagnum-dominated peatland, S1 bog (Minnesota, United States). Whereas CH₄ production rates increased with temperature up to 30°C, CO₂ production did not, resulting in a lower CO₂:CH₄ ratio with increasing temperature. CO₂ production showed both psychrophilic and mesophilic maxima at 4 and 20°C, respectively, and appears to be mediated by two anaerobic microbial communities, one that operates under psychrophilic conditions that predominate for much of the year, and another that is more active under warmer conditions during the growing season. In incubations at 10°C above the ambient range, members of the Clostridiaceae and hydrogenotrophic methanogens of the Methanobacteriaceae dominated. Moreover, a significant negative correlation between temperature and microbial diversity was observed. Results indicate that the potential consequences of warming surface peat in northern peatlands include a large stimulation in CH₄ production and a significant loss of microbial diversity.

Keywords: climate change; methanogenesis; microbial community; microbial diversity; peatlands.

FIGURE 1

The temperature dependence of (A) CO₂ maximum potential production rates; (B) CH₄ maximum potential production rates; (C) bacterial 16S rRNA gene copy numbers; and (D) archaeal 16S rRNA gene copy numbers in anaerobic incubations of surface peat collected from the S1 bog in northern Minnesota. Microbial 16S rRNA gene copy numbers were determined in samples collected after 4 weeks of incubation by qPCR with bacterial or archaeal primers. The error bars show the standard deviation for each temperature treatments (n = 3).

FIGURE 2

(A) Linear regression of the square root of the CH₄ production rate as a function of incubation temperature. (B) Temperature dependence of the ratio of CO₂ produced to CH₄ produced after 4 weeks of anaerobic incubation at different temperatures. The shaded area shows 95% confidence intervals. The error bars show the standard deviation for each temperature treatments (n = 3).

FIGURE 3

Beta diversity of microbial communities as a function of temperature after 4 weeks of anaerobic incubation. The plot represents a principal coordinates analysis (PCoA) of microbial community compositions based on Bray–Curtis distance matrices calculated after cumulative sum scaling (CSS) normalization of the final data.

FIGURE 4

Temperature dependence of alpha diversity of peat microbial communities after 4 weeks of anaerobic incubation determined by (A) richness as an abundance of ASVs and (B) Faith’s phylogenetic diversity (PD). The graph represents a linear regression between alpha diversity indices and incubation temperature. The shaded area shows 95% confidence intervals.

FIGURE 5

Microbial taxonomic composition as a function of temperature after 4 weeks of anaerobic incubation. (A) Relative abundance of the most abundant bacterial phyla. (B) Relative abundance of known groups of methanogens within the Euryarchaeota, and (C) relative abundance of genera affiliated with Clostridiales having similar abundance profile with methane production rates. The relative abundance of the sequences assigned to a given taxonomic level was calculated for each of the biological replicate, and the average value was then used to represent the relative abundance of each temperature treatment. The treatment “Pre” on the (A) and “-2” on the (B,C) is a microbial community of the unincubated peat samples. The error bars show the standard deviation of relative abundance for each temperature treatments (n = 4).