CO<sub>2</sub> and CH<sub>4</sub> budgets and global warming potential modifications in <i>Sphagnum</i>-dominated peat mesocosms invaded by <i>Molinia caerulea</i>

Abstract

Plant communities play a key role in regulating greenhouse gas (GHG) emissions in peatland ecosystems and therefore in their ability to act as carbon (C) sinks. However, in response to global change, a shift from Sphagnumdominated to vascular-plant-dominated peatlands may occur, with a potential alteration in their C-sink function. To investigate how the main GHG fluxes (CO 2 and CH 4 ) are affected by a plant community change (shift from dominance of Sphagnum mosses to vascular plants, i.e., Molinia caerulea), a mesocosm experiment was set up. Gross primary production (GPP), ecosystem respiration (ER) and CH 4 emission models were used to estimate the annual C balance and global warming potential under both vegetation covers. While the ER and CH 4 emission models estimated an output of, respectively, 376 ± 108 and 7 ± 4 g C m −2 yr −1 in Sphagnum mesocosms, this reached 1018 ± 362 and 33 ± 8 g C m −2 yr −1 in mesocosms with Sphagnum rubellum and Molinia caerulea. Annual modeled GPP was estimated at −414±122 and −1273±482 g C m −2 yr −1 in Sphagnum and Sphagnum + Molinia plots, respectively, leading to an annual CO 2 and CH 4 budget of −30 g C m −2 yr −1 in Sphagnum plots and of −223 g C m −2 yr −1 in Sphagnum + Molinia ones (i.e., a C sink). Even if CH 4 emissions accounted for a small part of the gaseous C efflux (ca. 3 %), their global warming potential value makes both plant communities have a climate warming effect. The shift of vegetation from Sphagnum mosses to Molinia caerulea seems beneficial for C sequestra-tion at a gaseous level. However, roots and litter of Molinia caerulea could provide substrates for C emissions that were not taken into account in the short measurement period studied here.

Carbon Balance and Spatial Variability of CO2 and CH4 Fluxes in a Sphagnum-Dominated Peatland in a Temperate Climate

“…Moreover, these high water table levels was spatially and temporally similar during the time course of the experiment (2013-2014, two exceptionally wet years), which did not allow to include this factor during the modelling processes. Higher variation of the water table depth could have brought to use equations with this parameters as Luan et al (2015) to explain the GPP or Leroy et al (2019) to model the CO2 and CH4 emissions. Nevertheless, inclusion of environmental parameters have to be considered up to their contribution to the models and to the models parsimony (Baird et al, 2019).…”

“…The observed C flux intensities and losses are often related to the plant community of the peatland. Vascular plants have higher gaseous C fluxes than bryophytes in poor fens (Leroy et al, 2019;Rydin and Jeglum, 2013) and a shift in peatland plant communities, especially those reducing Sphagnum dominance in favor of vascular vegetation, is expected to have significant effects on carbon storage (Dieleman et al, 2015). Now, the site is almost entirely invaded by vascular plants, especially Molinia caerulea in the graminoid strata (Gogo et al, 2011).…”

“…Now, the site is almost entirely invaded by vascular plants, especially Molinia caerulea in the graminoid strata (Gogo et al, 2011). The occurrence of this plant can stimulate the C uptake compared to Sphagnum peatland (Leroy et al, 2019). However it also significantly increase the ER respiration and CH4 emissions through different physiological, phenological, and ecological traits (Gogo et al, 2011;Leroy et al, 2019).…”

“…The occurrence of this plant can stimulate the C uptake compared to Sphagnum peatland (Leroy et al, 2019). However it also significantly increase the ER respiration and CH4 emissions through different physiological, phenological, and ecological traits (Gogo et al, 2011;Leroy et al, 2019). The ratio GPP/ER should be further assessed, especially in the context of interaction between different functional types (D'Angelo, 2015)…”

“…Invasive vegetation can play a major role in CO2 and CH4 emissions by (i) producing litter that is more easily degradable than mosses, (ii) altering the growth of subservient species such as Sphagnum mosses, and/or (iii) allowing more CH4 to be transferred to the atmosphere through the plant aerenchyma (Bubier et al, 2007;Francez and Vasander, 1995;Gogo et al, 2011;Armstrong et al, 2015). The role of the vegetation on the C fluxes are often related to a comparison between different plant community composition (Ward et al, 2013;Noyce et al, 2014); however only a few of them have attempted to integrate vegetation directly in a C balance model (Bortoluzzi et al, 2006;Kandel et al, 2013;Leroy et al, 2019).…”