I. V. Yevdokimov

Soil respiration and carbon balance of gray forest soils as affected by land use

Abstract Soil respiration was measured by closed chamber and gradient methods in soils under forest, sown meadow and crops. Annual total soil respiration determined with the closed chamber method ranged from 180 to 642 g CO2-C m–2 year–1 and from 145 to 382 g CO2-C m–2 year–1 determined with the CO2 profile method. Soil respiration increased in the order: cropland<sown meadow<forest. The C balance calculated as the difference between net primary production (sink) and respiration of heterotrophs (source) suggested an equilibrium between the input and output of C in the cropland, and sequestration of 135 and 387 g CO2-C m–2 year–1 in the forest and meadow, respectively.

Land-use change and management effects on carbon sequestration in soils of Russia’s South Taiga zone

The impact of land use change and management on soil C sequestration was investigated during the 1980s–1990s on gray forest soils in Pushchino, and on the soddy-podzolic soil in Prioksko-Terrasny Biosphere Reserve, Moscow Region, Russia (54°50ʹN, 37°35ʹE). Mean annual rates of C sequestration after establishment of perennials (layer 0–60 cm) were 63–182 g C m−2 and 22–43 g C m−2 for gray forest and soddy-podzolic soils, respectively. Grassing resulted in higher soil C accumulation than afforestation. Cutting and application of NPK fertilisers increased soil C accumulation, but newly formed soil organic matter was less resistant to decomposition than in unfertilised soil. Preliminary calculations of C sequestration due to abandonment of arable land in Russia since the early 1990s suggest that total C accumulation in soil and the plant biomass could represent about one tenth of industrial CO2 emissions.

Carbon dioxide emissions from agrogray soils under climate changes

The effect of droughts and drying-wetting cycles on the respiration activity of agrogray soils was studied in field and laboratory experiments. The alternation of drought periods and rains during the vegetation season did not increase the annual emission of CO2 from the soils under a sown meadow and an agrocenosis. In laboratory experiments, the wetting of dried soil released 1–1.5% of Corg with a high decomposition constant n × 10−1 day−1 and a very short renewal time (2.1–2.4 days); therefore, an abrupt change in the wetting conditions did not intensify the loss of soil carbon under field conditions.

Experimental Assessment of the Contribution of Plant Root Respiration to the Emission of Carbon Dioxide from the Soil

The contributions of root and microbial respiration to the total emission of CO2 from the surface of gray forest and soddy-podzolic soils were compared under laboratory and field conditions for the purpose of optimizing the field version of the substrate-induced respiration method. The magnification coefficients of respiration upon the addition of saccharose (kmic) were first determined under conditions maximally similar to the natural conditions. For this purpose, soil cleared from roots was put into nylon nets with a mesh size of 40 μm to prevent the penetration of roots into the nets. The nets with soil were left in the field for 7–10 days for the compaction of soil and the stabilization of microbial activity under natural conditions. Then, the values of kmic were determined in the root-free soil under field conditions or in the laboratory at the same temperature and water content. The contribution of root respiration as determined by the laboratory version of the substrate-induced respiration method (7–36%) was lower compared to two field versions of the method (27–60%). Root respiration varied in the range of 24–60% of the total CO2 emission from the soil surface in meadow ecosystems and in the range of 7–56% in forest ecosystems depending on the method and soil type.

Changa in the structure and activity of a soil microbial community caused by inorganic nitrogen fertilization

The changes in the structure and activity of a soil microbial community caused by addition of moderate and high rates of the mineral nitrogen fertilizer (KNO3) were studied in a laboratory incubation experiment. The structure of the microbial community was evaluated from the phospholipid fatty acid (PLFA) profile; specific growth rate of the microorganisms was determined by the method of the kinetics of substrate-induced respiration; the total pool of microbial carbon was estimated by the fumigation-extraction method. The amounts of nitrogen fertilizer applied in three treatments of the experiment were 0 (control), 100, and 2000 μg N/g soil. Even in the absence of additional sources of organic carbon, a considerable portion of the added 15N (up to 74%) was immobilized. No significant increase in the amount of microbial carbon was observed during incubation. The specific growth rate of the microbial community in soil supplemented with glucose decreased twofold after addition of 2000 μg N/g soil. In this treatment, the ratio of cyclic fatty acids to their monoenoic precursors also increased, indicating the adaptation of microbial cells to extremely high amounts of nitrogen fertilizer. Moreover, considerable changes in the structure of the soil microbial community, such as an increase in the ratio of fungalto bacterial markers and a decrease in the ratio between PLFA of gram-positive and gram-negative bacteria, were observed in the treatment with addition of 2000 μg N/g soil. Our data clearly indicate that mineral nitrogen fertilization of soil under carbon limitation has a pronounced impact on the structure and activity of soil microbial communities.

Identification of Labile and Stable Pools of Organic Matter in an Agrogray Soil

The intensity of decomposition of the organic matter in the particle-size fractions from a agrogray soil sampled in a 5-year-long field experiment on the decomposition of corn residues was determined in the course of incubation for a year. The corn residues were placed into the soil in amounts equivalent to the amounts of plant litter in the agrocenosis and in the meadow ecosystem. A combination of three methods—the particle-size fractionation, the method of 13C natural abundance by C3–C4 transition, and the method of incubation—made it possible to subdivide the soil organic matter into the labile and stable pools. The labile pool reached 32% in the soil of the agrocenosis and 42% in the meadow soil. Owing to the negative priming effect, the addition of C4 (young) carbon favored the stabilization of the C3 (old) carbon in the soil. When the young carbon was absent, destabilization or intense decomposition of the old organic matter was observed. This process was found even in the most stable fine silt and clay fractions.

Determination of root and microbial contributions to the CO2 emission from soil by the substrate-induced respiration method.

The contributions of root and microbial respiration to the CO2 emission from the surface of gray forest and soddy-podzolic soils under meadow and forest vegetation were determined in field and laboratory experiments. In the field, a new modification of the substrate-induced respiration (SIR) method was applied. According to this method, the contribution of root respiration was estimated at 41–50% for meadow cenoses and 33% for forest cenoses; similar values were obtained in the course of separate incubation of roots and soil in laboratory (42–57% and 29–32%, respectively) and with the use of the laboratory version of the SIR method (35–40% and 21–31%, respectively). The analysis of difference between the values of root respiration and microbial respiration obtained by the field and laboratory methods for the same experimental plots and the comparison of advantages and disadvantages of these methods made it possible to outline the ways for the further improvement of the field version of the SIR method.

Interaction between rhizosphere microorganisms and plant roots: 13C fluxes in the rhizosphere after pulse labeling

The input dynamics of labeled C into pools of soil organic matter and CO2 fluxes from soil were studied in a pot experiment with the pulse labeling of oats and corn under a 13CO2 atmosphere, and the contribution of the root and microbial respiration to the emission of CO2 from the soil was determined from the fluxes of labeled C in the microbial biomass and the evolved carbon dioxide. A considerable amount of 13C (up to 96% of the total amount of the label found in the rhizosphere soil) was incorporated into the biomass of the rhizosphere microorganisms. The diurnal fluctuations of the labeled C pools in the microbial biomass, dissolved organic carbon, and CO2 released in the rhizosphere of oats and corn were related to the day/night changes, i.e., to the on and off periods of the photosynthetic activity of the plants. The average contribution of the corn root respiration (70% of the total CO2 emission from the soil surface) was higher than that of the oats roots (44%), which was related to the lower incorporation of rhizodeposit carbon into the microbial biomass in the soil under the corn plants than in the soil under the oats plants.

Distribution of Stable Carbon Isotopes in an Agrochernozem during the Transition from C 3 Vegetation to a Corn Monoculture

The distribution of carbon in an agrochernozem’s profile was studied by the natural 13C abundance method during the C3-C4 vegetation transition and the analysis of the soil phytolith complex under a continuous corn monoculture. A young pool of soil organic matter (SOM) formed during 43 years of monoculture growing was detected by the isotope analysis in the 0-to 60-cm layer, while the analysis of the phytolith complex identified this pool deeper: corn phytoliths were detected in the 0- to 80-cm layer. The maximum size of the young pool was found in the upper soil horizon; it reached 6.4% of the SOM in the 0- to 20-cm layer. The apparent time of the SOM turnover was 635 and 2225 years in the 0- to 20- and 40- to 60-cm layers, respectively. The high values of the mean residence time were related to the low input of plant residues to the soil at the growing of corn for silage and the high initial content of organic carbon in the chernozem. The changes in the isotope composition after the decalcification of the soil to remove carbonates and the variation of the δ13C in the corn biomass during the vegetation period significantly affected the calculated value of the mean residence time.

The Rates of Organic Matter Renewal in Gray Forest Soils and Chernozems

The rates of soil carbon renewal were determined by the method of natural 13C abundance in a chernozem under a 40-year-long monoculture of corn and in a gray forest soil after application of corn residues. The mean rate of soil carbon renewal in the chernozem reached 1271–1498 years, whereas in the gray forest soil it depended on the amount of carbon introduced with corn residues and varied from 19 to 63 years. The rate of organic carbon renewal in the chernozem decreased from 697 years in the upper horizon to 2742 years in the layer of 40–60 cm. The mean residence time of organic carbon generally increased with a decrease in the size of particle-size fractions.