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Changing Interactions Between Trace Gas Fluxes, Belowground Chemistry, and Plant Traits Across an Arctic Thermokarst Landscape

Journal Article · · Global Change Biology
DOI:https://doi.org/10.1111/gcb.70667· OSTI ID:3018161
Arctic permafrost soils are increasingly subject to thermokarst that is, abrupt ground subsidence caused by thaw. Wetlands can form within these depressions, leading to changes in organic matter decomposition and gas fluxes (CO2, CH4, N2O, NH3). Thermokarst wetlands tend to be dominated by graminoids, while surrounding upland tussock tundra tends to be dominated by mixed communities of shrubs and graminoids. Here, to investigate how thermokarst alters the land-atmosphere exchange of C and N gases in Arctic tundra, we analyzed soil, porewater, above- and belowground biomass, and measured gas fluxes across dominant plant functional types (PFTs) within a lowland thermokarst wetland and adjacent upland tussock tundra. Both locations were overall sinks of CO2, sources of CH4, and sources of both N2O and NH3. We found that thermokarst wetlands emitted enough CH4 to generate a positive radiative forcing in CO2 equivalents (+1.2 μmol m−2 s−1 CO2-eq), counteracting the high CO2 uptake. In contrast, the upland tussock tundra had a net negative radiative forcing (−1.2 μmol m−2 s−1 CO2-eq). Differences in gas flux and soil chemistry between upland and lowland are primarily driven by flooded conditions present in thermokarst wetland. Additionally, root biomass from graminoids across both lowlands and uplands significantly correlated with CH4 fluxes, supporting previous observations of plant-mediated transport of CH4. Graminoid cover was correlated with increases in low molecular weight dissolved organic carbon, possibly associated with root exudates that fuel methanogenesis. Forb cover in the upland tussock tundra was significantly correlated with nine soil chemical variables, indicating that forbs may influence local soil chemistry or conversely, that soil chemistry controls where forbs grow. Overall, our findings indicate the variability in gas fluxes in the upland tussock tundra is partially controlled by PFT cover, while thermokarst wetlands emit enough CH4 to counteract CO2 uptake, with implications for carbon budget changes in Arctic systems.
Research Organization:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Organization:
National Institutes of Health (NIH); National Science Foundation (NSF); USDOE Office of Science (SC), Biological and Environmental Research (BER)
Grant/Contract Number:
AC02-05CH11231; AC02-76SF00515; AC05-00OR22725
Other Award/Contract Number:
2305276
P30GM133894
OSTI ID:
3018161
Journal Information:
Global Change Biology, Journal Name: Global Change Biology Journal Issue: 12 Vol. 31; ISSN 1354-1013; ISSN 1365-2486
Publisher:
WileyCopyright Statement
Country of Publication:
United States
Language:
English

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