Energy content and greenhouse gas emissions across a chronosequence of boreal peatlands

Background/Question/Methods

Effects of climate change are leading to extensive areas of permafrost degradation in interior Alaska, resulting in conditions that lead to wetland formation. These peat – accumulating wetlands are effective at sequestering carbon, however, these wetlands are also a source of potent greenhouse gases, such as methane and nitrous oxide, and thus may be the source of a positive feedback for further climatic warming. Because microbial communities play a large role in the oxidation of soil carbon and the metabolism of nutrients, including with the production of these greenhouse gases, we seek to investigate soil ecosystem energetics across a gradient of wetland ecosystems at varying stages of development in northern wetland ecosystems across a chronosequence of degraded permafrost peatlands. Using the maximum power principal and ecosystem development as theoretical frameworks, we seek to answer the following broad question: Do ecosystems develop to maximize efficiency, or to maximize power output? In order to test for patterns across the chronosequence in terms of ecosystem energy production, we: 1) conducted soil – substrate incubations, 2) extracted and quantified soil ATP as a surrogate for soil system power, 3) and measured soil system efficiencies using soil chemistries and greenhouse gases as metrics of efficiency.

Results/Conclusions

Our incubation experiments show that cumulative aerobic CO₂ production is highest over the course of a seven day incubation in amended soils at the youngest site and decreases with the age of the site (80 000 µg CO₂ g^-1 dry soil in youngest site vs. 49 000 µg CO₂ g^-1 dry soil in intermediate site vs. 24 000 µg CO₂ g^-1 dry soil in youngest site). Cumulative anaerobic CH₄ and N₂O production in amended soils was similar at the youngest and oldest site (0.00173 µg CH₄ g^-1 dry soil, 0.84 µg N₂O g^-1 dry soil and 0.253 µg CH₄ g^-1 dry soil, -0.0209 µg N₂O g^-1 dry soil, respectively), but much greater in the intermediate site (461µg CH₄ g^-1 dry soil, 0.286 µg N₂O g^-1 dry soil) In contrast, we observed the highest rates of ATP production and consumption at the oldest site. Response to glucose amendment was variable for peak ATP production across the chronosequence, with the highest amount of peak ATP production occurring at the oldest site without amendment (7.5 µg ATP g^-1 dry soil h^-1).