Response of CO2 and CH4 emissions from arctic tundra soils to a multifactorial manipulation of water table, temperature, and thaw depth, Alaska, 2014

In this study we tested the response of soil CO2 and CH4 fluxes from 24 cores from drier (high centre polygons and rims) and wetter (low centre polygons and throughs) continuous permafrost tundra ecosystems to a laboratory manipulation of soil temperature (and associated thaw depth), and water table, representing current and future conditions in the Arctic. Similar soil CO2 respiration rates occurred in both drier and wetter sites, suggesting a significant proportion of soil CO2 emissions is occurring via anaerobic respiration under water saturated conditions in these arctic tundra ecosystems. In the absence of vegetation soil CO2 respiration rates decreased sharply within the first seven weeks of the experiment while CH4 emissions remained pretty stable during the entire 26 weeks of the experiment. These patterns suggest that the soil CO2 emission is more related to plant input than the CH4 production and emission. The stable and substantial CH4 emissions observed over the entire course of the experiment are consistent with a temperature limitation more than labile carbon limitation to CH4 production in deeper soil layers and with the presence of a substantial source of labile carbon in these carbon rich soils. The small soil temperature difference (a median difference of 1⁰C (celsius)) and more substantial thaw depth difference (a median difference of 6 cm (centimeters)) between the temperature treatments was associated with a non-significant difference between soil CO2 and CH4 emissions suggesting that temperature and depth of thaw increases reported for these arctic regions have not been responsible for increases in carbon losses. Hydrology remained the major control on CH4 emissions, but these emissions remained low in the drier ecosystem even with a water table at the surface suggesting the absence of a methanogenic microbial community in drier ecosystems.