The influence of the moisture content on the CO2 emission from peat soils of palsa mires in the discontinuous permafrost area was studied in the north of Western Siberia (Nadym region). The CO2 flux was measured in Histic Cryosols of permafrost peatlands (palsas) and Fibric Histosols of surrounding bog using the closed chamber method for four years at the peak of the growing season (August). Despite a significant difference in the soil moisture (34.8 +/- 13.2 and 56.2 +/- 2.1% on average), no significant difference in the CO2 emission from these ecosystems was found in any of the observation years; the rates of emission averaged 199.1 +/- 90.1 and 182.1 +/- 85.1 mg CO2 m(-2) x h(-1), respectively. Experimental wetting or drying (with a twofold difference in the moisture content) of peat soils at the two sites via their transplantation to a different position showed no significant effect on the CO2 emission even three years after the beginning of the experiment. The absence of significant differences in the CO2 flux between the two different ecosystems was explained by the presence of permafrost and the influence of many multidirectional factors mitigating changes in the CO2 production by soils. An increased CO2 emission from the peat soils of bogs was possible due to the additional contribution of the methanotrophic barrier and the lateral runoff of dissolved CO2 over the permafrost table from the palsa toward the surrounding bog. The absence of response of the CO2 emission to a significant change in the soil moisture content may be indicative of a wide optimum of this characteristic for the microbiological activity of peat soils in the studied region. The obtained data suggest that, while studying CO2 fluxes in cryogenic soils of hydromorphic landscapes, it is necessary to take into account not only biogenic sources, but also other factors, often of a physical nature, affecting the balance of CO2 fluxes and CO2 emission from soils.

Cryosols in tundra ecosystems contain large stocks of organic carbon as peat and as organic cryoturbated layers. Increased organic mater decomposition rate in those Arctic soils due to increasing soil temperatures and to permafrost thawing can lead to the release of greenhouse gases, thus potentially creating a positive feedback on global warming. Instrumentation was installed on permafrost terrain in Salluit (Nunavik, Canada; 62 degrees 14'N, 75 degrees 38'W) to monitor respiration of two Cryosols under both natural and experimental warmed conditions and to simultaneously monitor the soil solution composition in the active layer throughout a thawing season. Two experimental sites under tussock tundra vegetation were set up: one is on a Histic Cryosol (H site) in a polygonal peatland; the other one is on a Turbic Cryosol reductaquic (T site) on post-glacial marine clays. At each site an open top chamber was installed from mid-July to the end of August 2010 to warm the soil surface. Thermistors and soil moisture probes were installed both in natural (N), or non-modified, surface thermal conditions and in warmed (W) stations, i.e. under an open top chamber. At each station, ecosystem respiration (ER) was measured three times per day every second day with an opaque closed chamber linked to a portable IRGA. Soil solutions were also sampled every alternate day at 10, 20 and 30 cm depths and analysed for dissolved organic C (DOC), total dissolved nitrogen (TON) and major elements. The experimental warming thickened the active layer in the Histic soil while it did not in the Turbic soil. In natural conditions, average ER at the HN station (1.27 +/- 0.32 mu mol CO2 m(-2) s(-1)) was lower than at the TN station (1.96 +/- 0.41 mu mol CO2 m(-2) s(-1)). A soil surface warming of 2.4 degrees C lead to a similar to 64% increase in ER at the HW station. At the TW station a similar to 2.1 degrees C increase induced an average ER increase of similar to 48%. Temperature sensitivity of ER, expressed by a Q(10) of 2.7 in the Histic soil and 3.9 in the Turbic Cryosol in natural conditions, decreased with increasing temperatures. There was no difference in soil solution composition between the N and W conditions for a given site. Mean DOC and TDN contents were higher at the H site. The H site soil solutions were more acidic and poorer in major solutes than the T ones, except for NO. The induced warming increased CO2 fluxes in both soils; this impact was however more striking in the Histic Cryosol even if ER was lower than in the Turbic Cryosol. In the Histic Cryosol, the thickening of the active layer would made available for decomposition new organic matter that was previously frozen into permafrost; due to acidic conditions, CO2 would be directly emitted to atmosphere. In contrast, the smaller increase in ER in the Turbic Cryosol may indicate the lack of organic matter input and carbon stabilization because of cold, non-acidic and more concentrated soil solutions; at this site warming mainly stimulates plant-derived respiration without decomposing a newly available carbon pool. (C) 2013 Elsevier Ltd. All rights reserved.