The decomposition and mineralization of various plant residues (oak and aspen leaves, pine needles, small branches and thin roots of trees, aboveground biomass and roots of meadow grasses, aboveground biomass and roots of clover, and straw and roots of barley) were investigated in the laboratory experiments by quantitative measurement of produced C–CO 2 . The plant residues were mixed with vermiculite or gray forest soil (Greyzemic Phaeozems Albic) and incubated under constant temperature and moisture conditions. After a year of incubation, 25–67% of C org in plant residues were mineralized. Oak leaves, aboveground mass of meadow grasses, and aboveground mass and roots of clover were characterized by a three-pool structure of organic matter with moderate (0.1 > k 1 > 0.01 day –1 ), slow (0.01 > k 2 > 0.001 day –1 ), and very slow ( k 3 < 0.001 day –1 ) mineralization rates, while the other types of plant residues had only a two-pool structure with slow and very slow mineralization rates. An opposite relationship between the decomposition rate and the C : N ratio in the plant residues was found. Poorly decomposable types of plant residues were the main source for particulate organic matter (C POM ) in the soil, while highly decomposable types were the main source for microbial biomass (C mic ). The content of potentially mineralizable organic matter in the soil with plant residues correlated positively with C POM and with C mic .

Рассматриваются полимерная и супрамолекулярная модели гуминовых веществ (ГВ). Отмечается, что в природных объектах ГВ могут находиться одновременно в виде макромолекулярных полимеров и супрамолекулярно организованных мономеров, макромолекулярные полимеры ГВ способны обладать некоторыми свойствами супраструктур или объединяться в агрегаты, а между мономерами супрамолекул возможно образование ковалентных связей. Минеральные частицы почвы выступают катализатором химических реакций между индивидуальными соединениями, сорбентом биомолекул и поверхностью для самосборки ГВ. Допускается, что такие физико-химические процессы и явления в почве, как цементация, обугливание, инкрустация, окклюзия, седиментация, сорбция, коагуляция, флокуляция, инкапсуляция, комплексация, интеркаляция, защемление в микропорах макроорганического, взвешенного и растворимого органического вещества могут быть в совокупности не менее значимой причиной его стабилизации, чем взаимодействия между биомолекулами с образованием ГВ.

Polymeric and supramolecular models of humic substances (HSs) are considered. It has been noted that the HSs in natural objects can simultaneously occur in the forms of macromolecular polymers and supramolecularly organized monomers; macromolecular polymers of HSs can have some properties of suprastructures or be associated into aggregates, and covalent bonds can be formed between the monomers of supramolecules. Mineral particles of soil act as catalysts in chemical reactions between individual compounds, sorbents of biomolecules, and a surface for self-assembling HSs. It is supposed that the combination of such physicochemical processes and phenomena in soil as cementation, charring, incrustation, occlusion, sedimentation, sorption, coagulation, flocculation, encapsulation, complexation, and intercalation, as well as the entrapment of macroorganic, particulate, and soluble organic substances in micropores, can be as important for the stabilization of organic matter as the interactions between biomolecules with the formation of HSs.

The daily dynamics of the number of copiotrophic and oligotrophic bacteria (in colony-forming units) and CO 2 emissions from cultivated soils after short- and long-term disturbances were studied for 25–27 days in a microfield experiment. The relationship of the wavelike fluctuations of the bacterial number and CO 2 emission with the succession of the soil microbial community was determined by the polymerase chain reaction method—denaturing gradient gel electrophoresis (PCR-DGGE). Short-term disturbances involved the application of organic or mineral fertilizers, pesticides, and plant residues to the soils of different plots. The long-term effect was a result of using biological and intensive farming systems for three years. The short-term disturbances resulted in increased peaks of the bacterial number, the significance of which was confirmed by harmonics analysis. The daily dynamics of the structure of the soil microbial community, which was studied for 27 days by the DGGE method, also had an oscillatory pattern. Statistical processing of the data (principal components analysis, harmonics and cross-correlation analyses) has revealed significant fluctuations in the structure of microbial communities coinciding with those of the bacterial populations. The structure of the microbial community changed within each peak of the dynamics of the bacterial number (but not from peak to peak), pointing to the cyclical character of the short-term succession. The long-term effects resulted in a less intense response of the microbiota—a lower rate of CO 2 emission from the soil cultivated according to the organic farming system.

The mineralization rate of the organic matter (OM) in the aggregate fractions of a gray forest soil separated by repeated sieving through sieves with different mesh sizes was assessed. The samples of the soil aggregate fractions were incubated for 141 days under constant temperature and moisture, and the C-CO 2 emission rate was measured. The mineralizable OM pool in the aggregates of <0.25, 1–0.25, and 3–1 mm in size from the soil under a forest contained easily (C 1 , k 1 > 0.1 days −1 ), moderately (C 2 , k 2 > 0.01 days −1 ), and difficultly (C 3 , k 3 > 0.001 days −1 ) mineralized compounds; the C 1 and C 2 components were present in the coarser aggregates. In the arable soil, the C 1 , C 2 , and C 3 OM components were separated in the aggregates of <0.25 and 1–0.25 mm; the C 1 and C 3 were separated in the aggregates of 3–1 and 5–3 mm; and the C 1 and C 2 were separated in the coarsest (10–5 mm) aggregates. The highest content of potentially mineralized OM (C 0 ) occurred in the aggregates of 1–0.25 and 3–1 mm, but the size of the mineralizable OM pool was more dependent on the portion of the aggregate fraction in the soil than on the absolute C 0 content in the fraction. It was shown that the decrease in the share of coarse structural aggregates is accompanied by a depletion of potentially mineralized OM in the arable soil, and the formation of coarse aggregates is an important condition of the soil carbon sequestration.

The effect of three levels of soil moistening on the organic matter mineralization was assessed for three arable soils and wheat straw in the course of a 150-day-long incubation experiment. It was found that the intensity of the organic matter mineralization increased in parallel to soil moistening in the podzolized chernozem and dark-chestnut soil and remained stable in the gray forest soil, which was explained by the low content of easily mineralizable fractions of active organic matter in the latter soil. The mineralization of wheat straw depended on the soil moistening rather than on soil properties.

The susceptibility of soil organic matter (SOM) to mineralization decreases in the following sequence of zonal soils: tundra soil > soddy-podzolic soil > gray forest soil > chestnut soil > dark chestnut soil > chernozem. The content of potentially mineralizable organic matter in the plowed soils is 1.9–3.9 times lower than that in their virgin analogues. The highest soil carbon sequestration capacity (SCSC) is typical of the leached chernozems, and the lowest SCSC is typical of the tundra soil. Taking into account the real soil temperatures and the duration of the warm season, the SCSC values decrease in the following sequence: leached chernozem > dark chestnut soil > chestnut soil ≥ tundra soil > gray forest soil > soddy-podzolic soil. Arable soils are characterized by higher SCSC values in comparison with their virgin analogues.

In three laboratory experiments with gray forest soils, the rates of mineralization of the bacterial mass, green oat mass, and cellulose applied in increasing doses were determined based on the measurement of the C-CO2 emission. The substances applied were used as biological indicators of the mineralizable organic matter pool in the gray forest soils.

In incubation experiments, the soil supply with carbon of mineralizable (Cmin), potentially mineralizable (Cpm), and active (Cac) organic matter, and of microbial mass (Cmb) in natural and agricultural ecosystems of Moscow region (gray forest soil) and Catalonia (Xerochrept) was assessed based on the measurements of the C-CO2 emission. In the gray forest soil, the Cpm and Cac contents decreased in the following sequence of ecosystems: forest > meadow > unfertilized agrocenosis; in the Xerochrept, forest > pasture > scrub > agrocenoses with organic fertilizer > unfertilized agrocenosis. A method for measurement of the Cmb according to the C-CO2 emission during an 11-to 14-day incubation of previously dried soils is proposed.

Seasonal fluctuations in the methane fluxes in the soil–atmosphere system were determined for gray forest soils of Central Russia. Consumption of atmospheric methane was found to exceed methane emission in gray forest soils under forest and in the agrocenosis. The average annual rates of atmospheric methane consumption by the soil under forest and in the agrocenosis were 0.026 and 0.008 mg C-CH 4 /(m 2 h), respectively. The annual rate of atmospheric methane oxidation in the gray forest soils of Moscow oblast was estimated to be 0.68 kton. Seasonal fluctuations in the methane oxidation activity were due to changes in the hydrothermal conditions and in the reserves of readily decomposable organic matter and mineral nitrogen, as well as to changes in the activity of methane oxidizers.

The decomposition of plant material with a C : N ratio of 9 to 99 in gray forest soil was studied by measuring the emission Of C-CO2 and the content of microbial biomass in the soil. Phytomass carbon was rapidly involved in the soil metabolism; it was assimilated and mineralized by microorganisms. The C : N ratio in the phytomass reliably characterized its mineralizing capacity only at the early decomposition stage. It was shown that rapidly (k(1) > 0.2 days(-1)) and slowly (k(2) > 0.02 days(-1)) decomposable and stable (k(3) > 0.002 days(-1)) compounds of plant and microbial biomass form the active pool of soil organic matter composed of readily, moderately, and hard-to-mineralize mineralizable components with mineralization constants higher than 0.1, 0.01, and 0.001 days(-1) and cycle times of lower than 10 days, 3 months, and 2.7 years, respectively.