1. Temperature sensitivity of frozen peatland soils organic matter decomposition (North-Western Siberia, Nadym site, Russia) Tarkhov M. (1) (tarkhov.mo@gmail.com), Matyshak G. (1), Yakushev A. (1), Ogneva O. (1), Bobrik A. (1) Department of Soil Science, Lomonosov Moscow State University, Russia INTRODUCTION Peatlands are expected to play a major role in nearest predictable climate changes due to storing of approximately 1/3 of the total soil carbon content (Bu Zhaojun 2011 and oth.) In this case special focus must be adressed for several types of peatlands, located in Russian Federation, as long as they contribute up to 40% of the Global Carbon stock in peatlands (Yu 2012). Based on generally held opinion today it's a common knowledge that peatlands may cause an increase in air temperature when effluxing greenhouse gases (Dorrepaal 2009). At the same time a number of studies revealed the peatlands possibility for decreasing air temperature by consuming CO2 during peat accumulation processes (Keller 2004). And so far there's no final confidence about any of these scenarios: which of them pretend to be dominant and why? Finally, this experimental study tries to answer the first following question, associated with the above-mentioned topic: what will happen with peatlands, especially in Northern areas, if the temperature of their functioning will steadily increase? In other words, what's about their temperature sensitivity? That's why the purpose of our study was to estimate the response of frozen peatland soils organic matter to increase in the temperature of their functioning. Area of research (exp. site) A growth of soil’s average annual temperature, predicted by the mid of XXI century (°С) 1 1 Permafrost reaction to climate warming. 2008 (www.permafrost.su) MATERIALS Soil samples were collected in "northern" bog peatland ecosystem in forest-tundra (Russia, Tyumen region, Nadym site, 65˚78 ̒ 26 ̋, A). The discontinuous permafrost conditions and a high spatial landscapes heterogeneity caused the uniqueness of our research site. As for possible climate change processes at Nadym site the consequent temperature increase up to 1.4 °С in deep layers (10 m) was recently noticed (Goncharova 2015) The "southern" soil samples with identical morphological and chemical properties were taken in southern taiga (Russia, Moscow region, Chashnikovo site, 56˚37 ̒ 23 ̋, B) and represented as a Control. To summarize, the study objects were frozen/unfrozen (control) weakly and medium decomposed moss peat samples. METHODS We performed our experiments in laboratory conditions. Soil samples taken in the field were transported to laboratory and stored in the incubator (4 °С) until the start of experiments. Field moisture levels were maintained. To study the frozen peatland soils temperature sensitivity we chose 3 different methods related to soil microbial biomass activity: CO2 efflux, Basal respiration (BR), Enzyme activity (EA). Additionally due to frozen peatland soils appropriate data insufficiency we estimated the influence of different water holding capacity levels (WHC, %) on BR rates. CO2 efflux was analyzed using soil mesocosms* (C) by a non-steady-state flow-through chamber system (Reth 2005). BR rate was measured by Ananyeva’s (2008) Anderson/Domsch modified method. Enzyme activity was determined by fluorescein diacetate (FDA) hydrolisis method (Adam 2001, Yakushev 2009). Establishing the different WHC levels was prepared by Rey (2005). RESULTS & DISCUSSION *C Our mesocosm application including a non-steady-state flow- through chamber system for CO2 efflux measuring Sample Soil layer Field moisture, % Perma- frost Average air annual temp., °С Summer СО2 efflux, mg/m 2 *per h. Forest- tundra O1 0-15 cm 747 From 60 cm 0.6*66* South. taiga O1 0-15 cm 651No7.1**190** Tab.1 Large differences in studied soils functioning conditions * Goncharova 2014, ** Smagin 2005 Sample Soil layer Ash content, % pH H 2 0 Total org. carbon, % Dissolved org. carbon, mg/g oven dry soil Forest- tundra O1 0-15 cm 9.93.940.72.9 South. taiga O1 0-15 cm 8.23.945.22.2 Tab.2 General properties of studied soils WHC analysis Prior to main experiments we decided to analyze the possible influence of WHC level on soil microbial biomass activity (BR rate). We performed this due to relatively high moisture content of our frozen peatland soils (pleas look at table 1) and because of this aspect insufficient literature coverage (Chang 2012). Finally, we wanted to make sure that for nearly arctic soils microbial biomass activity the considered optimal water content is 60-80% of their WHC (Mikan 2002) Design: We preincubated soil samples (O1 and O2 layers) at 25 °С within 4 days and then incubated them at the same temperature 25 °С for 1 day as it was recommended since Anderson/Domsch (1978) and then modified by Pell (2006) and Ananyeva (2008). Result: For O1 layer we found no relations between WHC level and the BR rate. Contrasting to this the O2 layer revealed the maximum BR rate response in 40-80 % WHC range, correspondingly to several authors (Mikan 2002, Smith 2005, Wang 2010 and oth.). Taking into account this result, in further experiments we were working without any manipulations with moisture content as it was approximately 50% of their WHC: so that ‘s OK for our samples. CO2 efflux measurements Design: Firstly an estimation of peatland soils response to temperature increase was studied by Sequential method (Hamdi 2013). Soil mesocosms CO2 efflux value response to sequential increase in temperature from 4 to 31 °C during 40 days was carried out (n=2). Measurements were taken after raising the temperature up to 3 °C and for each step lasted for 3 days. We maintained the initial filed moisture levels in our mesocosms throughout the experiment. BR rate measurements Design: We chose the Equal-time method (Hamdi 2013) for BR rate measurements. Gently homogenized soil samples were initially preiuncubated at 5 or 25 °С for 3 days to normalize the respiration rates. After the preincubation period the incubation procedure lasting for 1 day was prepared at the same temperatures 5/25 °С. During all the manipulations we maintained the constant field moisture levels in our samples. Results referred to 1 g of absolutely dry weight soil mass. Enzyme activity measurements Design: A FDA hydrolisis method to measure the enzyme (esters) activity was applied. We prepared the standard solutions in 50-ml flasks, containing 1 g of fresh studied soils, 10ml of distillate water and a required FDA-acetone 100 µl proportion. We shook the flasks and incubated the solutions for 4 days to let the FDA hyrdolisis reaction fully comply. On the 4th day we centrifugated our samples and measured the filtrates at 490 nm on a spectrophotometer. Exp. site Control site Lomonosov MSU, Soil Science Department Our team In discussion And working hard! B Bog peatland ecosystem landscape in southern-taiga and a typical soil… A Bog peatland ecosystem landscape in forest-tundra and a typical soil… C1 C2 Our first results showed the similar general chemical properties for studied soils (tab. 2), however soils functioning conditions differ a lot (tab. 1). We supposed this fact to be one of the key factors causing the contrasting results for forest-tundra and southern-taiga peatland soils in our laboratory experiments. Result: For 2 studied soils we found the positive feedback of CO2 efflux values to sequential temperature increase. However we noticed the CO2 efflux values of forest-tundra samples being 3 times lower in comparison with southern taiga on average: the maximal difference was at 16-22 °С range. Result: Accordingly to CO2 efflux values we found the positive response of all studied soils BR rates to temperature rise. Nevertheless, the forest-tundra samples rate was 4,5 times lower as compared with southern-taiga samples on average. Result: Enzyme activity results are in line with our previous results (CO2 efflux, BR rate) showing the lower forest- tundra samples reaction at each experimental temperature. In total the forest-tundra samples EA was 2,5 times lower if compare to southern-taiga samples on average.