Variation in CO2 and CH4 Fluxes Among Land Cover Types in Heterogeneous Arctic Tundra in Northeastern Siberia.

Arctic tundra is facing unprecedented warming, resulting in shifts in the vegetation, thaw regimes, and potentially in the ecosystem-atmosphere exchange of carbon (C). The estimates of regional carbon dioxide (CO₂) and methane (CH₄) budgets, however, are highly uncertain. We measured CO₂ and CH₄ fluxes, vegetation composition and leaf area index (LAI), thaw depth, and soil wetness in Tiksi (71° N, 128° E), a heterogeneous site located within the prostrate dwarf-shrub tundra zone in northeastern Siberia. Using the closed chamber method, we determined net ecosystem exchange (NEE) of CO₂, dark ecosystem respiration (ER), ecosystem gross photosynthesis (Pg), and CH₄ fluxes during the growing season. We applied a previously developed high-spatial-resolution land-cover map over an m area of 35.8 km². Among the land-cover types varying from barrens to dwarf-shrub tundra and tundra wetlands, the light-saturated NEE and Pg scaled with the LAI of vascular plants. Thus, the graminoid-dominated tundra wetlands, with high LAI and the deepest thaw depth, had the highest light-saturated NEE and Pg (up to -21 (uptake) and 28 mmol m^-2 h^-1, respectively) and were disproportionately important for the summertime CO₂ sequestration on a landscape scale. Dry tundra, including the dwarf-shrub-dominated vegetation and only sparsely vegetated lichen tundra, had only small CO₂ exchange rates. While tundra wetlands were sources of CH₄, lichen tundra, including bare ground habitats, consumed atmospheric CH₄ at a substantial rate. On a landscape scale, the consumption by lichen tundra and barrens could offset ca. 10% of the CH₄ emissions. We acknowledge the uncertainty involved in spatial extrapolations due to a small number of replicates per land-cover type. This study, however, highlights the need for distinguishing different land-cover types including the dry tundra habitats to account for their consumption of the atmospheric CH₄ when estimating tundra C-exchange on a larger spatial scale. [ABSTRACT FROM AUTHOR]