The impact of C:N and of internal and external nitrogen on plant residues (corn leaves) decomposition was studied in a series of long-term laboratory incubation experiments: without nitrogen addition (internal organic and inorganic N), with KNO3 and NH4NO3 addition (external N). Mineralization rates of the labile and the recalcitrant carbon pools were estimated by fitting 365-day cumulative CO2 losses by double-pool exponential decay function. It has been shown that decrease of C:N leads to stimulated mineralization at the early stages of decomposition (first 20 days of incubation). The value of C:N affects the k(1) parameter of the double exponential decay model of plant residues. The decomposition constant of the labile carbon pool directly depends on C:N in the C:N range from 22 to 62, but decreases under the stress of high doses of internal (C:N = 22) and external (C:N = 10) nitrogen. The internal organic nitrogen affected the decay constant (k(1)) of the labile pool only. KNO3 as an external N form influenced the size (A(1)) and k(1) value of the labile pool. NH4NO3 affected all the parameters of the double exponential decay including constant (k(2)) of the recalcitrant pool, and also resulted in intensive transformation of plant residues (humification index alkyl/O-alkyl increased from 0.33 to 0.51). Thus, mineralization and humification of plant residues depends on C:N ratio, origin and form of available nitrogen. The internal nitrogen in plants and the external nitrogen (KNO3 and NH4NO3) affect in the same direction, but the effect of external nitrogen is more pronounced than of internal, and of ammonium nitrogen is more than that of nitrate nitrogen.

Global warming can lead to a significant transformation of the structure of terrestrial ecosystems and changes in the mode of functioning of their components. In this connection, studies of soil respiration, particularly of the biological activity of soils under forest exposed to warm impact of flaring flare are of scientific and practical interests. A long-term experimental plot was established in a lichen pine forest on the Albic Podzols (Arenic) (Khanty-Mansi Autonomous Area-Yugra). Sampling and measurements were carried out in the areas at the distances of 70, 90, and 130 m from the flare with the strong, moderate, and weak heating effects, respectively. In the zone of the maximum heating effect, the soil temperature was by 1.3°C higher, and the rate of CO 2 emission from the surface in situ was greater by 18% compared to the zone with weak impact of the flare. Along with increasing CO 2 emissions, organic matter accumulated due to increasing the stable pool. The parameters of the microbial biomass, basal respiration, and the input of labile organic matter pool increased with the distance from the flare.

RUSSIAN JOURNAL OF FOREST SCIENCE. 2017, No. 2, pp. 128-139 THE CONTRIBUTION OF NITROGEN TO MINERALIZATION AND HUMIFICATION OF FOREST LITTER IN SIMULATION STUDY A. A. Larionova 1 , A. K. Kvitkina 1 , S. S. Bykhovets 1 , V. O. Lopes-de-Gerenyu 1 , Y. G. Kolyagin 2 , V. V. Kaganov 3 1 Institute of Physicochemical and Biological Problems of Soil Sciences, Russian Academy of Sciences Institutskaya st., 2, Pushchino, Moscow Oblast, 142290, Russia E-mail: larionova_al@rambler.ru 2 Faculty of Chemistry, Lomonosov Moscow State University Leninskie gory, 1, bldg.3, Moscow, 119991, Russia 3 Center for Forest Ecology and Productivity of the Russian Academy of Sciences Profsoyuznaya st., 84/32, bldg. 14, Moscow, 117997, Russia Received 16 June 2016 We carried out long-term incubations to study the contribution of endogenous and exogenous nitrogen to decomposition of various fractions of forest litter, sampled in linden, pine and aspen mixed forest in Prioksko-Terrasny Nature Reserve. Based on C:N ratio signatures (including endogenous nitrogen) the following sequence was found: mortmass of cyanobacteria Nostoсcommunae (C:N ratio 9), deciduous litter (C:N ratio 32), pine needles litter (C:N ratio 66), pine bark litter (C:N ratio 84), coarse woody debris of linden (C:N ratio 206), coarse woody debris of pine (C:N ratio 510). To find the effect of exogenous nitrogen we applied NH 4 NO 3 to the litters until the prescribed C:N ratio in the range of 5 to 204 has been reached. Mineralization was assessed by CO 2 emission intensity. Humification was measured by changes in the share of structural fragments in organic matter of litter from solid-state 13 C NMR. We found logarithmic relationship between the rate of carbon mineralization and initial C:N ratio in litter, having maximum at C:N ratio of 22. Mineral nitrogen treatment increased the intensity of mineralization of the litter fractions poor in nitrogen (C:N ratio exceeding 66) and inhibited CO 2 emission from decomposition of litter with high nitrogen content (C:N ratio from 9 to 32). During the litter decomposition the Alkyl/O-Alkyl ratio increased. It corresponds to the level of humification of plant matter in soils. Additional nitrogen treatment has stimulated humification, especially during pine needles decomposition. Thus we found the effect of endogenous and mineral nitrogen on both mineralization and humification of forest litter. Acknowledgements: This study was financially supported by the Russian foundation for basic research (14-04-01738, 14-04-01884). Keywords: forest litter, plant debris decomposition, C:N ratio, mineralization, humification, mineral nitrogen. 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Carreiro M.M., Sinsabaugh R.L., Repert D.A., Parkhurst D.F., Microbial enzyme shifts explain litter decay responses to simulated nitrogen deposition, Ecology , 2000, Vol. 81, No. 9, pp. 2359-2365. Chernogaeva G.M., Peshkov Y.V., Kotlyakova M.G., Smirnov V.D., Obzor sostoyaniya i zagryazneniya okruzhayushchei sredy v Rossiiskoi Federatsii za 2013 god (Review of environmental conditions and pollution in the Russian Federation in 2013), Moscow: Rosgidromet, 2014, 228 p. Dijkstra F.A., Hobbie S.E., Knops J.M.H., Reich P.B., Nitrogen deposition and plant species interact to influence soil carbon stabilization, Ecology letters , 2004, Vol. 7, No. 12, pp. 1192-1198. Goldman E., Green L.H., Practical handbook of microbiology , Boca Raton: CRC Press, 2015, 1055 p. Gruber N., Galloway N., An Earth-system perspective of the global nitrogen cycle, Nature , 2008, Vol. 451, No. 7176, pp. 293-296. Hobbie S.E., Eddy W.C., Buyarski C.R., Adair E.C., Ogdahl M.L., Weisenhorn P., Response of decomposing litter and its microbial community to multiple forms of nitrogen enrichment, Ecological monographs , 2012, Vol. 82, No. 3, pp. 389-405. Knorr M., Frey S.D., Curtis P.S., Nitrogen additions and litter decomposition: a meta-analysis, Ecology , 2005, Vol. 86, No. 12, pp. 3252-3257. Kogel-Knabner I., The macromolecular organic composition of plant and microbial residues as inputs to soil organic matter, Soil biology and biochemistry , 2002, Vol. 34, No. 2, pp. 139-162. Larionova A.A., Zolotareva B.N., Kolyagin Y.G., Kvitkina A.K., Kaganov V.V., Kudeyarov V.N., Composition of structural fragments and the mineralization rate of organic matter in zonal soils, Eurasian soil science , 2015, Vol. 48, No. 10, pp. 1110-1119. Leppanen S.M., Salemaa M., Smolander A., Makipaa R., Tiirola M., Nitrogen fixation and methanotrophy in forest mosses along a N deposition gradient, Environmental and experimental botany , 2013, Vol. 90, pp. 62-69. Orlov D.S., Biryukova O.N., Sukhanova N.I., Organicheskoe veshchestvo pochv Rossiiskoi Federatsii (Organic matter in soils of the Russian Federation), Moscow: Nauka, 1996, 253 p. Pestriakov V.K., Kovsh N.V., Popov A.I., Chukov S.N., Modelirovanie transformatsii organicheskikh veshchestv v laboratornom eksperimente (Organic substances transformation modelling in a laboratory experiment), Pochvovedenie , 1990, No. 3, pp. 30-41. Prescott C.E., Litter decomposition: what controls it and how can we alter it to sequester more carbon in forest soils? , Biogeochemistry , 2010, Vol. 101, No. 1, pp. 133-149. Preston C.M., Nault J.R., Trofymow J.A., Chemical changes during 6 years of decomposition of 11 litters in some Canadian forest sites. 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K., Gitarskii M.L., Emissiya dioksida ugleroda ot razlozheniya valezha v yuzhnotaezhnom el'nike (The Emission of Carbon from the Decomposition of Woody Debris in the Southern Taiga Spruce Forest), Lesovedenie , 2012, No. 5, pp. 44-49. Semenov V.M., Ivannikova L.A., Kuznetsova T.V., Semenova N.A., The role of plant biomass in the formation of the active pool of soil organic matter, Eurasian soil science , 2004, Vol. 37, No. 11, pp. 1196-1204. Sutton M.A., Howar C.M., Erisman J.W., Billen G., Bleeker A., Grennfelt P., Van Grinsven H., Grizzetti B., The European nitrogen assessment: sources, effects and policy perspectives , New York: Cambridge University Press, 2011, 664 p. Umarov M.M., Kurakov A.V., Stepanov A.L., Mikrobiologicheskaya transformatsiya azota v pochve (Microbial transformation of nitrogen in soils), Moscow: GEOS, 2007, 137 p. 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The mineralization and humification of leaf litter collected in a mixed forest of the Prioksko-Terrasny Reserve depending on temperature (2, 12, and 22°C) and moisture (15, 30, 70, 100, and 150% of water holding capacity ( WHC)) has been studied in long-term incubation experiments. Mineralization is the most sensitive to temperature changes at the early stage of decomposition; the Q 10 value at the beginning of the experiment (1.5–2.7) is higher than at the later decomposition stages (0.3–1.3). Carbon losses usually exceed nitrogen losses during decomposition. Intensive nitrogen losses are observed only at the high temperature and moisture of litter (22°C and 100% WHC). Humification determined from the accumulation of humic substances in the end of incubation decreases from 34 to 9% with increasing moisture and temperature. The degree of humification C HA /C FA is maximum (1.14) at 12°C and 15% WHC; therefore, these temperature and moisture conditions are considered optimal for humification. Humification calculated from the limit value of litter mineralization is almost independent of temperature, but it significantly decreases from 70 to 3% with increasing moisture. A possible reason for the difference between the humification values measured by two methods is the conservation of a significant part of hemicelluloses, cellulose, and lignin during the transformation of litter and the formation of a complex of humic substances with plant residues, where HSs fulfill a protectoral role and decrease the decomposition rate of plant biopolymers.

The genetic transformation of trees by wood modification genes for the improvement of forest plantations results in shifts in plant litter quality. These alterations in plant chemistry lead to changes in decomposition rates, thus affecting the carbon and nitrogen cycling in ecosystems and nutrient availability for plants. To assess the environmental impacts of transgenic trees, we studied the decomposition of plant litter from aspen plants (Populus tremula L.) transformed with the xyloglucanase gene from Penicillium canescens. Mass, carbon and nitrogen losses in the leaves, stems and roots of greenhouse-grown plants were evaluated during incubation in laboratory microcosms. After 12 months of the decomposition experiment, leaves, stems, and roots lost on average 51%, 46%, and 37% of initial mass, respectively. Decomposition of the transgenic stems was not different from wild-type aspen, but we observed significant differences for the leaves (only at the end of the experiment) and the roots (at the early stage). These differences may be related to the nitrogen content and the C/N ratio in the initial samples. Since the litter decomposability determines the availability of nutrients, such alterations should be taken into consideration when cultivating transgenic trees.

Drying-rewetting and freezing-thawing can drastically alter P availability in soil. We studied how these weather events affect microbial immobilisation/mobilisation of P on the four soil types from a climatic gradient with increasing annual mean temperatures and a progressive decrease in precipitation: Podzol, Phaeozem, Chernozem and Kastanozem. Soils were exposed to (1) optimal moisture and temperature, (2) drying-rewetting and (3) freezing-thawing. Soils were treated with a 33P spike immediately after rewetting or thawing to simulate P pulse. Thereafter, P immobilisation by soil microorganisms was estimated by direct fumigation and anion exchange membrane techniques. To ensure correct estimation of microbial P (Pmic), the conversion factors kP were determined individually for each soil by 33P labelling with the correction for 33P sorption and 31P–33P isotopic exchange. The membrane extraction minimised both sorption and isotopic exchange of P released with both sorption and isotopic exchange coefficients close to 0.9 irrespectively of the soil. Specific kP varied from 0.19 to 0.38. Pmic values followed the pattern freezing-thawing < drying-rewetting < optimal conditions, varying from 2.0 to 36.6 mg P kg−1. Intensive microbial immobilisation of 33P after rewetting (up to 41 %) demonstrated a conversion of dissolved P to Pmic potentially available for plant nutrition. Remarkably, no detectable microbial immobilisation of 33P was found in the freezing-thawing treatment. In contrast to drying, freezing decreased total Pmic by up to 7.5 times. Values of membrane-extractable 33P increased in the order drying-rewetting < control < freezing-thawing, and up to 77 % of added 33P was recovered in dissolved P forms after thawing, indicating the potential risk of P leaching after freezing-thawing events.

В образцах агрочерноземов и агросерых почв выделяли различные по устойчивости пулы углерода в составе почвенного органического вещества. С этой целью использовали комбинацию естественного варьирования изотопного состава углерода при смене С3–С4 растительности с другими методами: биокинетическим, грануло-денсиметрическим и методом химического фракционирования – термического гидролиза с 6 М HCl. Наиболее устойчивые пулы с минимальным содержанием нового углерода идентифицировали с помощью гранулометрического и химического фракционирования. Содержание углерода тонких фракций было примерно равно количеству углерода негидролизуемого остатка. В агрочерноземах и агросерых почвах размер этого пула составил 65 и 48% С орг соответственно. Комбинация биокинетического подхода с гранулометрическим фракционированием или гидролизом 6 М HCl позволила оценить размер среднеустойчивого пула углерода в составе органического вещества со временем обновления от нескольких лет до нескольких десятилетий. Пул органического вещества с такой оборачиваемостью обычно идентифицируют по варьированию обогащения 13 при смене С3–С4 растительности. В агрочерноземе и агросерой почве размер среднеустойчивого пула составил 35 и 46% Сорг соответственно. Для замены изотопной индикации на неизотопный метод определения, который позволит существенно расширить изучение стабильного и среднеустойчивого пулов органического вещества в географическом аспекте, необходимо провести сравнительный анализ результатов гранулометрического и химического фракционирования органического вещества для всех почв России.

Предлагаемый проф. А.В. Смагиным [2014] пункт 4 для правил ведения дискуссии совершенно невыполним по ряду очевидных причин. ...

Carbon pools of different stabilities have been separated from the soil organic matter of agrochernozem and agrogray soil samples. The work has been based on the studies of the natural abundance of the carbon isotope composition by C3-C4 transition using the biokinetic, size-density, and chemical fractionation (6 M HCl hydrolysis) methods. The most stable pools with the minimum content of new carbon have been identified by particle-size and chemical fractionation. The content of carbon in the fine fractions has been found to be close to that in the nonhydrolyzable residue. This pool makes up 65 and 48% of C org in the agrochernozems and agrogray soils, respectively. The combination of the biokinetic approach with particle-size fractionation or 6 M HCl hydrolysis has allowed assessing the size of the medium-stable organic carbon pool with a turnover time of several years to several decades. The organic matter pool with this turnover rate is usually identified from the variation in the 13 C abundance by C3-C4 transition. In the agrochernozems and agrogray soils, the medium-stable carbon pool makes up 35 and 46% of C org , respectively. The isotope indication may be replaced by a nonisotope method to significantly expand the study of the inert and mediumstable organic matter pools in the geographical aspect, but this requires a comparative analysis of particle-size and chemical fractionation data for all Russian soils.

В образцах агрочерноземов и агросерых почв выделяли различные по устойчивости пулы углерода в составе почвенного органического вещества. С этой целью использовали комбинацию естественного варьирования изотопного состава углерода при смене С3–С4 растительности с другими методами: биокинетическим, грануло-денсиметрическим и методом химического фракционирования – термического гидролиза с 6 М HCl. Наиболее устойчивые пулы с минимальным содержанием нового углерода идентифицировали с помощью гранулометрического и химического фракционирования. Содержание углерода тонких фракций было примерно равно количеству углерода негидролизуемого остатка. В агрочерноземах и агросерых почвах размер этого пула составил 65 и 48% С орг соответственно. Комбинация биокинетического подхода с гранулометрическим фракционированием или гидролизом 6 М HCl позволила оценить размер среднеустойчивого пула углерода в составе органического вещества со временем обновления от нескольких лет до нескольких десятилетий. Пул органического вещества с такой оборачиваемостью обычно идентифицируют по варьированию обогащения 13 при смене С3–С4 растительности. В агрочерноземе и агросерой почве размер среднеустойчивого пула составил 35 и 46% Сорг соответственно. Для замены изотопной индикации на неизотопный метод определения, который позволит существенно расширить изучение стабильного и среднеустойчивого пулов органического вещества в географическом аспекте, необходимо провести сравнительный анализ результатов гранулометрического и химического фракционирования органического вещества для всех почв России.

Comparative analysis of the climatic characteristics and the recalcitrance against decomposition of organic matter in the zonal soil series of European Russia, from peat surface-gley tundra soil to brown semidesert soil, has assessed the relationships between the period of biological activity, the content of chemically stable functional groups, and the mineralization of humus. The stability of organic matter has been determined from the ratio of functional groups using the solid-state 13C NMR spectroscopy of soil samples and the direct measurements of organic matter mineralization from CO2 emission. A statistically significant correlation has been found between the period of biological activity and the humification indices: the CHA/CFA ratio, the aromaticity, and the alkyl/O-alkyl ratio in organic matter. The closest correlation has been observed between the period of biological activity and the alkyl/O-alkyl ratio; therefore, this parameter can be an important indicator of the soil humus status. A poor correlation between the mineralization rate and the content of chemically stable functional groups in soil organic matter has been revealed for the studied soil series. At the same time, the lowest rate of carbon mineralization has been observed in southern chernozem characterized by the maximum content of aromatic groups (21% Corg) and surface-gley peat tundra soil, where an extremely high content of unsubstituted CH2 and CH3 alkyl groups (41% Corg) has been noted.

An hypothesis about the different temperature dependences of the decomposition of the labile and stable organic carbon pools has been tested using an agrochernozem sampled from an experimental plot of 42-year-old continuous corn in Voronezh oblast. The partitioning of the CO 2 loss during the decomposition of the labile and stable soil organic matter (SOM) at 2, 12, and 22°C in a long-term incubation experiment was performed using the method of 13 C natural abundance by C3–C4 transition. On the basis of the determined decomposition constants, the SOM pools have been arranged in an order according to their increasing stability: plant residues < new (C4) SOM < old (C3) SOM. The tested hypothesis has been found valid only for a limited temperature interval. The temperature coefficient Q 10 increases in the stability order from 1.2 to 4.3 in the interval of 12–22°C. At low temperatures (2–12°C), the values of Q 10 insignificantly vary among the SOM pools and lie in the range of 2.2–2.8. Along with the decomposition constants of the SOM, the new-to-old carbon ratio in the CO 2 efflux from the soil and the magnitude of the negative priming effect for the old SOM caused by the input of new organic matter depend on the temperature. In the soil under continuous corn fertilized with NPK, the increased decomposition of C3 SOM is observed compared to the unfertilized control; the temperature dependences of the SOM decomposition are similar in both agrochernozem treatments.