Abstract. Arctic tundra ecosystems are currently facing amplified rates of climate
warming. Since these ecosystems store significant amounts of soil organic
carbon, which can be mineralized to carbon dioxide (CO2) and methane
(CH4), rising temperatures may cause increasing greenhouse gas fluxes
to the atmosphere. To understand how net the ecosystem exchange (NEE) of
CO2 will respond to changing climatic and environmental conditions,
it is necessary to understand the individual responses of the processes
contributing to NEE. Therefore, this study aimed to partition NEE at the
soil–plant–atmosphere interface in an arctic tundra ecosystem and to
identify the main environmental drivers of these fluxes. NEE was partitioned
into gross primary productivity (GPP) and ecosystem respiration
(Reco) and further into autotrophic (RA) and
heterotrophic respiration (RH). The study examined CO2 flux
data collected during the growing season in 2015 using closed-chamber
measurements in a polygonal tundra landscape in the Lena River Delta,
northeastern Siberia. To capture the influence of soil hydrology on
CO2 fluxes, measurements were conducted at a water-saturated polygon
center and a well-drained polygon rim. These chamber-measured fluxes were
used to model NEE, GPP, Reco, RH, RA, and net
primary production (NPP) at the pedon scale (1–10 m) and to determine
cumulative growing season fluxes. Here, the response of in situ measured
RA and RH fluxes from permafrost-affected soils of the
polygonal tundra to hydrological conditions have been examined. Although
changes in the water table depth at the polygon center sites did not affect
CO2 fluxes from RH, rising water tables were linked to
reduced CO2 fluxes from RA. Furthermore, this work found
the polygonal tundra in the Lena River Delta to be a net sink for atmospheric
CO2 during the growing season. The NEE at the wet, depressed polygon
center was more than twice that at the drier polygon rim. These differences
between the two sites were caused by higher GPP fluxes due to a higher
vascular plant density and lower Reco fluxes due to oxygen
limitation under water-saturated conditions at the polygon center in
comparison to the rim. Hence, soil hydrological conditions were one of the
key drivers for the different CO2 fluxes across this highly
heterogeneous tundra landscape.