Ecosystem feedbacks from subarctic wetlands: vegetative and atmospheric CO2 controls on greenhouse gas emissions

Other literature type English OPEN
Bridgman, Matthew J. ; Lomax, Barry H. ; Sjogersten, Sofie (2016)

Wetland vegetation provide strong controls on greenhouse gas fluxes but impacts of elevated atmospheric carbon dioxide (CO<sub>2</sub>) levels on greenhouse gas emissions from wetlands are poorly understood. This study aims to investigate if elevated atmospheric CO<sub>2</sub> enhance methane (CH<sub>4</sub>) emissions from subarctic wetlands and to determine if responses are comparable or species specific within the Cyperaceae, an important group of artic wetland plants. To achieve this we carried out a combined field and laboratory investigation to measure of CO<sub>2</sub> and CH<sub>4</sub> fluxes. The wetland was a CH<sub>4</sub> source with comparable fluxes from areas with and without vegetation and across the different sedge communities. In contrast, the net ecosystem exchange of CO<sub>2</sub> differed with sedge species. Within the laboratory experiment plants grown at double ambient (800 ppm) CO<sub>2</sub>, total biomass of <i>Eriophorum vaginatum</i> and <i>Carex brunnescens</i> increased, whereas the total biomass of <i>E. angustifolium</i> and <i>C. acuta</i> decreased, compared to the control (400 ppm CO<sub>2</sub>). These changes in biomass were associated with corresponding changes in CH<sub>4</sub> flux. <i>E. vaginatum</i> and <i>C. brunnescens</i> mesocosms produced more CH<sub>4</sub> when grown in 800 ppm atmospheric CO<sub>2</sub> when compared to 400 ppm CO<sub>2</sub> with <i>E. angustifolium</i> and <i>C. acuta</i> producing less. Additionally, redox potential and carbon substrate availability in the pore water differed among the plant treatments and in response to the elevated CO<sub>2</sub> treatment. Together, this suggests species specific controls of CH<sub>4</sub> emissions in response to elevated CO<sub>2</sub>, which facilitate differential plant growth responses and modification of the rhizosphere environments. Our study highlights species composition as an important control of greenhouse gas feedbacks in a CO<sub>2</sub> rich future, which need to be considered in models aiming to predict how ecosystems respond to climate change.
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