V. N. Kudeyarov

Annual and seasonal CO2 fluxes from Russian southern taiga soils

Annual and seasonal characteristics of CO2 emission from five different ecosystems were studied in situ (Russia, Moscow Region) from November 1997 through October 2000. The annual behaviour of the soil respiration rate is influenced by weather conditions during a particular year. Annual CO2 fluxes from the soils depend on land use of the soils and averaged 684 and 906 g C m−2 from sandy Albeluvisols (sod-podzolic soils) under forest and grassland, respectively. Annual emission from clay Phaeozems (grey forest soils) was lower and ranged from 422 to 660 g C m−2; the order of precedence was arable < grassland < forest. The coefficients of variation for annual CO2 fluxes caused by weather conditions ranged from 18% (forest ecosystem on Phaeozems) to 31% (agroecosystem). The contribution from the cold period (with snow, November—April) to the annual CO2 flux was substantial and averaged 21% and 14% for natural and agricultural ecosystems, respectively. The CO2 fluxes comprised approximately 48–51% in summer, 23–24% in autumn, 18–20% in spring and 7–10% in winter of the total annual carbon dioxide flux.

Updated estimate of carbon balance on Russian territory

The land use system in Russia changed considerably after 1990: 30.2 million ha of croplands were abandoned. Based on the own field investigations that were carried out in abandoned lands of different age (Luvic Phaeozems, deciduous forest zone; Moscow region, 54.50N, 37.37E), it has been shown that after 4.5 yr of abandonment, the former croplands acted as a stable sink of CO2. The net ecosystem production (NEP) in the post-agrogenic ecosystems averaged 245 ) 73g C m-2 yr-1 for the first 15 yr after land use change that corresponds to an estimated 74 ) 22 Tg C yr-1 for the total area of abandoned lands in Russian Federation. Currently, the Russian territory acts as an absolute sink of atmospheric CO2 at a rate about 0.90 Pg C yr-1. Using three different approaches, it was demonstrated that after 1990, the carbon sequestration in Russian soils (0.20 cm layer) has averaged 34 ) 2.2 Tg C yr-1. This soil C forms net biome production (NBP) where carbon lifetime is much longer than in eKyoto forestsf. Thus, the post-agrogenic ecosystems in Russia provide with the additional CO2 sink in NEP and NBP that could annually compensate about 25% of the current fossil fuel emissions in the Russian Federation.

Biomass and respiration activity of soil microorganisms in anthropogenically transformed ecosystems (Moscow region)

In the forest, meadow, arable, and urban ecosystems (recreational, residential, and industrial zones) of Sergiev Posad, Shatura, Serpukhov, and Serebryanye Prudy districts of Moscow region, spatially separated sites (3–5 points per site) have been randomly selected and soil samples have been taken from the 0–10 (plant litter excluded) and 10- to 150-cm layers (a total of 201 samples have been taken). In the samples, the microbial biomass carbon (Cmic), the rate of the basal (microbial) respiration (BR), and the physical parameters (the particle size distribution (PSD), organic carbon (Corg), pH, heavy metals, and nutrients (NPK)) have been determined. High spatial variability has been revealed for Cmic and BR in all the ecosystems and the functional zones of the studied districts, and a clear tendency of a decrease in these parameters has been shown in the arable soils (by 1.4–3.2 times) and the industrial zone (by 1.7–3.3 times) compared to the natural analogues and other corresponding functional zones. It has been shown that the spatial distribution of the microbiological parameters is significantly (p ≤ 0.05) affected by the physicochemical properties of the soil (Cmic by the PSD and PSD × Corg; BR by the pH and pH × NPK; contributions of 40 and 63%, respectively), as well as by the type of ecosystem and the region of study (the contribution of the sum of these factors to the Cmic and BR was 56 and 67%, respectively). A tendency toward the deterioration of the functioning of the microbial community under the anthropogenic transformation of the soil has been shown. The contribution of the urban soils as a potential source of CO2 emission to the atmosphere has been calculated and discussed.

Fungi-to-bacteria ratio in soils of European Russia

The selective inhibition technique by specific antibiotics (streptomycin, cycloheximide) applied to substrate-induced respiration (SIR) measurement was used to test the relative contribution of fungi to bacteria (F/B ratio) to the overall microflora-induced activity in soils of European Russia. Investigated soils covered a wide climatic transect and different ecosystem types including managed vs. natural ecosystems. Before direct comparison among sites, the antibiotic inhibition technique was optimized for soil characteristics. Once the optimal concentration was set, the combined effect of the two antibiotics resulted in average 60% inhibition of SIR. The analyzed sites (in total 47) including various biomes (tundra, middle taiga, southern taiga, subtaiga, dark coniferous forests outside the boreal region, steppe, mountain forests and arable sites), were characterized by a wide range of soil pHw (3.95–7.95), soil organic carbon (0.69–24.08%), soil microbial biomass carbon (149–5028 µg C g−1 soil) and soil basal respiration (0.24–8.28 µg CO2-C g−1 soil h−1). In all the analyzed sites, a predominance of fungal over bacteria activity was observed with F/B ratios always higher than one (4.9 on average). Natural sites were characterized by higher F/B ratios (on average 5.6) compared to agricultural ones (on average 3.5).

Current state of the carbon budget and the capacity of Russian soils for carbon sequestration

The growing population of the Earth is unlikely to stop using traditional energy sources in the foreseeable future, though energy-saving technologies are being actively developed and the use of nontraditional renewable energy sources is expanding. The analysis of the modern state of the global carbon turnover indicates that the greenhouse effect will continue to grow despite serious measures undertaken to reduce the industrial emission of carbon dioxide. The existing hopes to sequester CO2 on a large scale via conversion of various land uses into forest ecosystems are not justified, because forest stands reaching the climax stage stop further accumulation of carbon in the aboveground biomass, so that the carbon balance approaches zero; in mature and overripe forests, it may become negative. The level of the organic matter accumulation in soils also has its limits specified by the soil and climatic characteristics of a given area. The reverse process of the transformation of forest and meadow cenoses into agrocenoses subjected to regular tillage leads to the active mineralization of the soil organic matter with the release of the accumulated organic carbon into the atmosphere. Mature tree stands are highly susceptible to various external impacts, including fires and invasions of pests and diseases. Though the ecological significance of afforestation measures is beyond question, it is important to concentrate efforts on the development of adaptation measures towards changing environmental and climatic conditions, i.e., to develop efficient technologies to protect humans from extreme weather events, to control forest fires, pest invasions, and floods, etc. For Russia, it is important to be prepared for the potential permafrost thawing and, hence, for solving problems of safe construction in the extreme North and in the permafrost zone.

Composition of structural fragments and the mineralization rate of organic matter in zonal soils

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.

Effect of temperature and moisture on the mineralization and humification of leaf litter in a model incubation experiment

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 Q10 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 CHA/CFA 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.

Specific features of determination of the net production of nitrous oxide by soils

The rate of the net nitrous oxide (N2O) production, the content of microbial biomass carbon (Cmic), and its portion in the total soil organic carbon (Corg) were determined in the samples from podzol, soddy-podzolic soils, gray forest soils, chernozems, burozems, and carbolithozems of natural, arable, and fallow ecosystems in Kostroma, Vladimir, Moscow, Kaluga, Voronezh oblasts, and Krasnodar region. The most sustainable N2O production was found in the soils enriched with glucose or its mixture with ammonium sulfate at 22°C upon the preliminary incubation of the soil samples (7 days, 60% of water holding capacity). In the profiles of forest soils, a direct correlation was found between the N2O production and the Cmic content (r = 0.74, p ≤ 0.05, n = 18). In the upper mineral layers (0–10 cm) of soddy-podzolic soils of the cropland, fallow, young, secondary and native forests, the inverse relationship between the N2O production and the Cmic content (r = −0.75, p ≤ 0.05, n = 6) was observed. In a series of the fallowed, cultivated, and forest soils, the net N2O production decreased (239, 69, and 38 ng N2O-N × 10−3/g per h), and the Cmic content and Cmic: Corg ratio increased (181, 569, and 1020 μg C/g; 1.4, 2.6, and 3.0%, respectively) attesting to the increasing N2O flux in the anthropogenically transformed ecosystems. The application of cycloheximide (20–50 mg/g) to the soil lowered the N2O production by 69–99%, which pointed to a significant contribution of fungi to this process. An approach to separate nitrification and denitrification in the soil using low concentrations of acetylene (1.8 Pa) was proposed. The conditions of preparation of the soil samples for sustainable detection of N2O production were specified. It was shown that this process is tightly related to the soil microbial biomass and its fungal component.

Assessing the stability of soil organic matter by fractionation and 13C isotope techniques

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 Corg 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 13C abundance by C3-C4 transition. In the agrochernozems and agrogray soils, the medium-stable carbon pool makes up 35 and 46% of Corg, 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.