Large quantities of organic matter are stored in frozen soils (permafrost) within the Qinghai-Tibetan Plateau (QTP). The most of QTP regions in particular have experienced significant warming and wetting over the past 50 years, and this warming trend is projected to intensify in the future. Such climate change will likely alter the soil freeze-thaw pattern in permafrost active layer and toward significant greenhouse gas nitrous oxide (N2O) release. However, the interaction effect of warming and altered soil moisture on N2O emission during freezing and thawing is unclear. Here, we used simulation experiments to test how changes in N2O flux relate to different thawing temperatures (T-5-5 degrees C, T-10-10 degrees C, and T-20-20 degrees C) and soil volumetric water contents (VWCs, W-15-15%, W-30-30%, and W-45-45%) under 165 F-T cycles in topsoil (0-20 cm) of an alpine meadow with discontinuous permafrost in the QTP. First, in contrast to the prevailing view, soil moisture but not thawing temperature dominated the large N2O pulses during F-T events. The maximum emissions, 1,123.16-5,849.54 mu g m(-2) h(-1), appeared in the range of soil VWC from 17% to 38%. However, the mean N2O fluxes had no significant difference between different thawing temperatures when soil was dry or waterlogged. Second, in medium soil moisture, low thawing temperature is more able to promote soil N2O emission than high temperature. For example, the peak value (5,849.54 mu g m(-2) h(-1)) and cumulative emissions (366.6 mg m(-2)) of (WT5)-T-30 treatment were five times and two to four times higher than (WT10)-T-30 and (WT20)-T-30, respectively. Third, during long-term freeze-thaw cycles, the patterns of cumulative N2O emissions were related to soil moisture. treatments; on the contrary, the cumulative emissions of W-45 treatments slowly increased until more than 80 cycles. Finally, long-term freeze-thaw cycles could improve nitrogen availability, prolong N2O release time, and increase N2O cumulative emission in permafrost active layer. Particularly, the high emission was concentrated in the first 27 and 48 cycles in W-15 and W-30, respectively. Overall, our study highlighted that large emissions of N2O in F-T events tend to occur in medium moisture soil at lower thawing temperature; the increased number of F-T cycles may enhance N2O emission and nitrogen mineralization in permafrost active layer.

Large amounts of organic carbon are stored in Arctic permafrost environments, and microbial activity can potentially mineralize this carbon into methane, a potent greenhouse gas. In this study, we assessed the methane budget, the bacterial methane oxidation (MOX) and the underlying environmental controls of arctic lake systems, which represent substantial sources of methane. Five lake systems located on Samoylov Island (Lena Delta, Siberia) and the connected river sites were analyzed using radiotracers to estimate the MOX rates, and molecular biology methods to characterize the abundance and the community composition of methane-oxidizing bacteria (MOB). In contrast to the river, the lake systems had high variation in the methane concentrations, the abundance and composition of the MOB communities, and consequently, the MOX rates. The highest methane concentrations and the highest MOX rates were detected in the lake outlets and in a lake complex in a flood plain area. Though, in all aquatic systems, we detected both, Type I and II MOB, in lake systems, we observed a higher diversity including MOB, typical of the soil environments. The inoculation of soil MOB into the aquatic systems, resulting from permafrost thawing, might be an additional factor controlling the MOB community composition and potentially methanotrophic capacity.Lake systems on Samoylov Island (Lena Delta) in contrast to the Lena River showed high variation in the methane concentration, the abundance and composition of MOB communities and consequently methane oxidation rates.Lake systems on Samoylov Island (Lena Delta) in contrast to the Lena River showed high variation in the methane concentration, the abundance and composition of MOB communities and consequently methane oxidation rates.

Localized permafrost disturbances such as active layer detachments (ALDs) are increasing in frequency and severity across the Canadian Arctic impacting terrestrial ecosystem functioning. However, the contribution of permafrost disturbance-carbon feedbacks to the carbon (C) balance of Arctic ecosystems is poorly understood. Here, we explore the short-term impact of active layer detachments (ALDs) on carbon dioxide (CO2) exchange in a High Arctic semi-desert ecosystem by comparing midday C exchange between undisturbed areas, moderately disturbed areas (intact islands of vegetation within an ALD), and highly disturbed areas (non-vegetated areas due to ALD). Midday C exchange was measured using a static chamber method between June 23 and August 8 during the 2009 and 2010 growing seasons. Results show that areas of high disturbance had significantly reduced gross ecosystem exchange and ecosystem respiration (R (E)) compared to control and moderately disturbed areas. Moderately disturbed areas showed significantly enhanced net ecosystem exchange compared to areas of high disturbance, but were not significantly different from control areas. Disturbance did not significantly impact soil thermal, physical or chemical properties. According to average midday fluxes, ALDs as a whole (moderately disturbed areas: -1.942 mu mol m(-2) s(-1)+ highly disturbed areas: 2.969 mu mol m(-2) s(-1)) were a small CO2 source of 1.027 mu mol m(-2) s(-1) which did not differ significantly from average midday fluxes in control areas 1.219 mu mol m(-2) s(-1). The findings of this study provide evidence that the short-term impacts of ALDs on midday, net C exchange and soil properties in a High Arctic semi-desert are minimal.