Persistent high temperature and low precipitation reduce peat carbon accumulation

Bragazza, Luca; Buttler, Alexandre; Robroek, Bjorn J. M.; Albrecht, Remy; Zaccone, Claudio; Jassey, Vincent E. J.; Signarbieux, Constant

doi:10.1111/gcb.13319

Cited by 105 publications

(102 citation statements)

References 78 publications

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“…Increased air temperature (+3.6°C) and associated increased evapotranspiration significantly reduced Sphagnum growth independent of water table in a poor fen in Sweden (Gunnarsson, Granberg, & Nilsson, ). S. fallax productivity decreased by 60% in mesocosms transplanted to a warmer (+5°C) location (Bragazza et al, ). Maximum photosynthesis of several Sphagnum species occurred at 30–35°C, but these observations were made on fully water‐saturated Sphagnum stems in the laboratory (Haraguchi & Yamada, ); most temperate species have photosynthetic optima between 15 and 25°C (He et al, ).…”

Section: Discussionmentioning

confidence: 99%

“…Subsequent measurements at this site showed variable responses of the two species to warming in wet and dry habitats (Buttler et al, ). Peat cores of lawns dominated by Sphagnum fallax that were transplanted to a warmer (+5°C) and drier location exhibited a 50% decline in S. fallax occurrence and the appearance of S. magellanicum after 3 years (Bragazza et al, ). These contrasting results suggest that the hummock‐hollow microtopography has a larger influence on Sphagnum responses to warming than species‐specific traits.…”

Section: Discussionmentioning

confidence: 99%

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Rapid loss of an ecosystem engineer: Sphagnum decline in an experimentally warmed bog

Norby

Childs

Hanson

et al. 2019

Ecology and Evolution

105

154

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Sphagnum mosses are keystone components of peatland ecosystems. They facilitate the accumulation of carbon in peat deposits, but climate change is predicted to expose peatland ecosystem to sustained and unprecedented warming leading to a significant release of carbon to the atmosphere. Sphagnum responses to climate change, and their interaction with other components of the ecosystem, will determine the future trajectory of carbon fluxes in peatlands. We measured the growth and productivity of Sphagnum in an ombrotrophic bog in northern Minnesota, where ten 12.8‐m‐diameter plots were exposed to a range of whole‐ecosystem (air and soil) warming treatments (+0 to +9°C) in ambient or elevated (+500 ppm) CO2. The experiment is unique in its spatial and temporal scale, a focus on response surface analysis encompassing the range of elevated temperature predicted to occur this century, and consideration of an effect of co‐occurring CO2 altering the temperature response surface. In the second year of warming, dry matter increment of Sphagnum increased with modest warming to a maximum at 5°C above ambient and decreased with additional warming. Sphagnum cover declined from close to 100% of the ground area to <50% in the warmest enclosures. After three years of warming, annual Sphagnum productivity declined linearly with increasing temperature (13–29 g C/m2 per °C warming) due to widespread desiccation and loss of Sphagnum. Productivity was less in elevated CO2 enclosures, which we attribute to increased shading by shrubs. Sphagnum desiccation and growth responses were associated with the effects of warming on hydrology. The rapid decline of the Sphagnum community with sustained warming, which appears to be irreversible, can be expected to have many follow‐on consequences to the structure and function of this and similar ecosystems, with significant feedbacks to the global carbon cycle and climate change.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Rapid loss of an ecosystem engineer: Sphagnum decline in an experimentally warmed bog

Norby

Childs

Hanson

et al. 2019

Ecology and Evolution

105

154

View full text Add to dashboard Cite

show abstract

“…High temperature and limited moisture conditions with limited or no permafrost have been generally found to accelerate peat decomposition (Franzén, 2006;Ise et al, 2008;Bragazza et al, 2016). This will also result in the drawdown of water position and dominance of woody shrubs.…”

Section: Discussionmentioning

confidence: 99%

Modelling past, present and future peatland carbon accumulation across the pan-Arctic region

2017

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Abstract. Most northern peatlands developed during the Holocene, sequestering large amounts of carbon in terrestrial ecosystems. However, recent syntheses have highlighted the gaps in our understanding of peatland carbon accumulation. Assessments of the long-term carbon accumulation rate and possible warming-driven changes in these accumulation rates can therefore benefit from process-based modelling studies. We employed an individual-based dynamic global ecosystem model with dynamic peatland and permafrost functionalities and patch-based vegetation dynamics to quantify long-term carbon accumulation rates and to assess the effects of historical and projected climate change on peatland carbon balances across the pan-Arctic region. Our results are broadly consistent with published regional and global carbon accumulation estimates. A majority of modelled peatland sites in Scandinavia, Europe, Russia and central and eastern Canada change from carbon sinks through the Holocene to potential carbon sources in the coming century. In contrast, the carbon sink capacity of modelled sites in Siberia, far eastern Russia, Alaska and western and northern Canada was predicted to increase in the coming century. The greatest changes were evident in eastern Siberia, north-western Canada and in Alaska, where peat production hampered by permafrost and low productivity due the cold climate in these regions in the past was simulated to increase greatly due to warming, a wetter climate and higher CO 2 levels by the year 2100. In contrast, our model predicts that sites that are expected to experience reduced precipitation rates and are currently permafrost free will lose more carbon in the future.

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“…It is striking that DIC concentrations at site 4 were notably lower as compared with other sites. A reasonable explanation is a lower peat quality resulting from repeated peat oxygenation upon water table fluctuations of the reservoir, stimulating microbial decomposition in the presence of deciduous shrubs (Bragazza et al, 2016), which are apparently promoted in closer vicinity to the eutrophic water reservoir. Such an effect of aeration might appear contradictory, as wetter conditions would be expected near the water reservoir.…”

Section: Seasonal Development Of Carbon Fluxesmentioning

confidence: 99%

Differential response of carbon cycling to long-term nutrient input and altered hydrological conditions in a continental Canadian peatland

et al. 2018

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Abstract. Peatlands play an important role in global carbon cycling, but their responses to long-term anthropogenically changed hydrologic conditions and nutrient infiltration are not well known. While experimental manipulation studies, e.g., fertilization or water table manipulations, exist on the plot scale, only few studies have addressed such factors under in situ conditions. Therefore, an ecological gradient from the center to the periphery of a continental Canadian peatland bordering a eutrophic water reservoir, as reflected by increasing nutrient input, enhanced water level fluctuations, and increasing coverage of vascular plants, was used for a case study of carbon cycling along a sequence of four differently altered sites. We monitored carbon dioxide (CO 2 ) and methane (CH 4 ) surface fluxes and dissolved inorganic carbon (DIC) and CH 4 concentrations in peat profiles from April 2014 through September 2015. Moreover, we studied bulk peat and pore-water quality and we applied δ 13 C-CH 4 and δ 13 C-CO 2 stable isotope abundance analyses to examine dominant CH 4 production and emission pathways during the growing season of 2015. We observed differential responses of carbon cycling at the four sites, presumably driven by abundances of plant functional types and vicinity to the reservoir. A shrub-dominated site in close vicinity to the reservoir was a comparably weak sink for CO 2 (in 1.5 years: −1093 ± 794, in 1 year: +135 ± 281 g CO 2 m −2 ; a net release) as compared to two graminoid-moss-dominated sites and a moss-dominated site (in 1.5 years: −1552 to −2260 g CO 2 m −2 , in 1 year: −896 to −1282 g CO 2 m −2 ). Also, the shrub-dominated site featured notably low DIC pore-water concentrations and comparably 13 C-enriched CH 4 (δ 13 C-CH 4 : −57.81 ± 7.03 ‰) and depleted CO 2 (δ 13 C-CO 2 : −15.85 ± 3.61 ‰) in a more decomposed peat, suggesting a higher share of CH 4 oxidation and differences in predominant methanogenic pathways. In comparison to all other sites, the graminoid-mossdominated site in closer vicinity to the reservoir featured a ∼ 30 % higher CH 4 emission (in 1.5 years: +61.4 ± 32, in 1 year: +39.86 ± 16.81 g CH 4 m −2 ). Low δ 13 C-CH 4 signatures (−62.30 ± 5.54 ‰) indicated only low mitigation of CH 4 emissions by methanotrophic activity here. Pathways of methanogenesis and methanotrophy appeared to be related to the vicinity to the water reservoir: the importance of acetoclastic CH 4 production apparently increased toward the reservoir, whereas the importance of CH 4 oxidation increased toward the peatland center. Plant-mediated transport was the prevailing CH 4 emission pathway at all sites even where graminoids were rare. Our study thus illustrates accelerated carbon cycling in a strongly altered peatland with consequences for CO 2 and CH 4 budgets. However, our results suggest that long-term excess nutrient input does not necessarily lead to a loss of the peatland carbon sink function.

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Persistent high temperature and low precipitation reduce peat carbon accumulation

Cited by 105 publications

References 78 publications

Rapid loss of an ecosystem engineer: Sphagnum decline in an experimentally warmed bog

Rapid loss of an ecosystem engineer: Sphagnum decline in an experimentally warmed bog

Modelling past, present and future peatland carbon accumulation across the pan-Arctic region

Differential response of carbon cycling to long-term nutrient input and altered hydrological conditions in a continental Canadian peatland

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