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A CO2-induced enhancement of peatland carbon sequestration

11 May 2022 | Science Notes

From CO2Science: Peatlands play a significant role in the global carbon cycle, particularly with respect to the amount of carbon they store. As net carbon sinks, peatlands are estimated to contain approximately 30% (~550 Pg C) of the Earth’s total terrestrial soil carbon, yet they comprise only a miniscule 3% of Earth’s total land area. In the future, it has been hypothesized that peatlands will become net sources of carbon to the atmosphere, releasing more CO2 (and methane) to the atmosphere if temperatures warm, which warming is projected to stimulate decomposition rates (carbon losses) beyond that expected to be sequestered by warming-induced productivity gains. But are such predictions correct? And what influence might rising atmospheric CO2 have on these processes?

Paper reviewed: Newman, T.R., Wright, N., Wright, B. and Sjögersten, S. 2018. Interacting effects of elevated atmospheric CO2 and hydrology on the growth and carbon sequestration of Sphagnum moss. Wetlands Ecology and Management 26: 763-774.

Hoping to gain some insight into the latter of these matters, Newman et al. (2018) recently conducted an experiment to examine the effects of elevated CO2 on the growth of three Sphagnum moss species (Sphagnum fallax, Sphagnum capillifolium and Sphagnum papillosum). More specifically, the three species were grown under ambient (400 ppm) or elevated (800 ppm) CO2 over a period of 13 weeks in a controlled-environment setting, while also being subjected to one of three water treatment levels (where the water level was filled to either 1, 4 or 7 cm below the peat surface to represent a high, medium and low water level, respectively).

The results of the analysis revealed a positive influence of elevated CO2 on the three Sphagnum species, increasing both their height and dry weight (see Figure 1a). With respect to this latter parameter, elevated CO2 boosted biomass production by 130%, 101% and 43% in S. fallax, S. capillifolium and S. papillosum, respectively.

Newman et al. also report finding a relationship between water level and plant dry weight such that Sphagnum biomass increased as water levels increased. What is more, elevated CO2 positively impacted this relationship (see Figure 1b) such that it boosted dry weights in the 1, 4 and 7 cm water level treatments by 142%, 66% and 19%, respectively.

Finally, the researchers also measured “a consistent three-fold increase of the CO2 sink strength under elevated CO2” after week 9 of their experiment. Consequently, in light of all of the above, Newman et al. say their findings “suggest that in the context of future elevated CO2, all three species of Sphagnum will increase in CO2 assimilation due to increased growth,” adding that “the increase in CO2 uptake found in response to elevated CO2 suggests that the capacity to sequester carbon by Sphagnum dominated peatbogs may increase under future CO2 rich atmospheric conditions.” And that enhanced sequestration of carbon will help act as a natural brake on CO2-induced warming.

Figure 1. Panel a: The dry weight (mean ± SE) response of three Sphagnum moss species after 13 weeks of exposure to normal (400 ppm, green bars) and elevated (800 ppm, blue bars) atmospheric CO2. Panel b: The effect of water level on dry weight (mean ± SE) after the 13 week experimental period. Water levels (in cm) represent the height of water below the surface (e.g., 1 cm = water filled to 1 cm below the surface); bar shading is the same as in Panel a. Source: Newman et al. (2018).

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