Variability in exchange of CO₂ across 12 northern peatland and tundra sites

Abstract

Many wetland ecosystems such as peatlands and wet tundra hold large amounts of organic carbon (C) in their soils, and are thus important in the terrestrial C cycle. We have synthesized data on the carbon dioxide (CO 2 ) exchange obtained from eddy covariance measurements from 12 wetland sites, covering 1-7 years at each site, across Europe and North America, ranging from ombrotrophic and minerotrophic peatlands to wet tundra ecosystems, spanning temperate to arctic climate zones. The average summertime net ecosystem exchange of CO 2 (NEE) was highly variable between sites. However, all sites with complete annual datasets, seven in total, acted as annual net sinks for atmospheric CO 2 . To evaluate the influence of gross primary production (GPP) and ecosystem respiration (R eco ) on NEE, we first removed the artificial correlation emanating from the method of partitioning NEE into GPP and R eco . After this correction neither R eco (P 5 0.162) nor GPP (P 5 0.110) correlated significantly with NEE on an annual basis. Spatial variation in annual and summertime R eco was associated with growing season period, air temperature, growing degree days, normalized difference vegetation index and vapour pressure deficit. GPP showed weaker correlations with environmental variables as compared with R eco , the exception being leaf area index (LAI), which correlated with both GPP and NEE, but not with R eco . Length of growing season period was found to be the most important variable describing the spatial variation in summertime GPP and R eco ; global warming will thus cause these components to increase. Annual GPP and NEE correlated significantly with LAI and pH, thus, in order to predict wetland C exchange, differences in ecosystem structure such as leaf area and biomass as well as nutritional status must be taken into account.

Soil temperature response to 21st century global warming: the role of and some implications for peat carbon in thawing permafrost soils in North America

“…In particular, climate warming can directly affect C fluxes from peatlands. Ecosystem respiration has been found to increase in response to a 1 • C soil warming in a subarctic bog (Dorrepaal et al, 2009) and to vary depending on seasonal temperature patterns (Lund et al, 2010). Methane emissions are also strongly dependent on soil temperature (Treat et al, 2007;Kettridge and Baird, 2008).…”

Carbon dioxide flux and net primary production of a boreal treed bog: Responses to warming and water-table-lowering simulations of climate change

“…Warm and dry conditions in peatlands can promote CO 2 uptake by enhancing GPP, diminish uptake by limiting moisture (Roulet et al, 2007;Charman et al, 2013) or accelerate CO 2 release by enhancing R (Hanson et al, 2000;Davidson and Janssens, 2006;Lund et al, 2010;Ise et al, 2008;Cai et al, 2010). In a dwarf-shrub pine bog, Pihlatie et al (2010) found that the CO 2 flux peak followed the increase in air and soil temperature closely, being higher (uptake) on warm and lower (emission) on cold days.…”

Seasonal patterns of carbon dioxide and water fluxes in three representative tundra ecosystems in northern Alaska

“…Alternatively, the tundra may have acclimated to temperature changes, and has once again turned back to a sink after acting as a source in the 1980s (Oechel et al 2000). Since climatic factors may vary widely from year to year, there is also a large degree of interannual variability in tundra NEE, gross primary productivity (GPP), and ecosystem respiration (ER) (Kwon et al 2006, Lafleur and Humphreys 2008, Lund et al 2010.…”