Vol 51, No 6 (2018)

Studies on the assessment of soil respiration and ecosystem CO₂ sink in the territory of Russia are reviewed over the period since the adoption of the United Nations Framework Convention on Climate Change (Rio de Janeiro, 1992). The first estimates of total soil respiration in the entire territory of Russia, made in 1995 to 1998, amount to 3.1 and 4.3 Gt C per growing season and per year, respectively. On average, soil CO₂ efflux over the cold season (November–March) accounts for 20–30% of annual efflux. The contribution of heterotrophic respiration (R_H) to the total soil respiration (R_S) may reach 30–70%, depending on ecosystem type. Despite differences in methods used to measure R_H, the results obtained by different authors vary within a relatively narrow range, from 2.9 to 3.5 Gt C/year at an uncertainty level of about 20%. The soil cover of Russia (11.7% of the global land area) accounts for 6.3% of global soil CO₂ efflux. The data on ecosystem CO₂ sink are widely scattered among publications. Estimates of carbon balance differ depending on approaches and methods used to determine its individual components and the level of uncertainty in the results. However, most of them confirm the main conclusion: the territory of Russia with its forests is an absolute CO₂ sink with a potential of 200 Mt C/year. This conclusion has been corroborated in the absolute majority of studies performed by Russian and international research teams.

Statistical analysis of a vast body of data collected during five field seasons (2011–2015) was performed to characterize the biological activity of soils in the northern taiga ecosystems of Western Siberia. Automorphic forest soils, hydromorphic (oligotrophic bog) soils, and semihydromorphic (flat-topped and large peat mounds) soils were characterized. Statistically significant differences of average levels of CO₂ emission from the soils were identified at the ecosystem level. The CO₂ emission from podzols of automorphic forest ecosystems at the peak of the growing season (205 ± 30 to 410 ± 40 mg CO₂/(m² h)) was significantly higher than the emission from semihydromorphic soils of peat mounds (70 ± 20 to 116 ± 10 mg CO₂/(m² h)). The presence and depth of permafrost was a significant factor that affected ecosystem diversity and biological activity of northern taiga soils. Statistically significant differences in the total, labile, and microbial carbon pools were observed for the studied soils. Labile and microbial carbon pools in the organic layer (10 cm) of forest podzols amounted to 0.19 and 0.66 t/ha, respectively; those in the organic layer (40 cm) of peat cryozems of flat-topped peat mounds reached 1.24 and 3.20 t/ha, and those in the oligotrophic peat soils (50 cm) of large peat mounds were 2.76 and 1.35 t/ha, respectively. The portion of microbial carbon in the total carbon pool (C_micr/C_tot, %) varied significantly; according to the values of this index, the soils were arranged into the following sequence: oligotrophic peat soil < peat cryozem < podzol.

Specific features of the transformation of humic substances in particle-size fractions of drained soddy-podzolic soils were studied on a field (12 ha) of the Experimental and Educational Center of Lomonosov Moscow State University in Moscow oblast. The field had a clearly pronounced microtopography. Surface-gleyed soddy-podzolic soils (Albic Stagnic Glossic Retisols (Loamic, Aric, Ochric)) of microdepressions with excessive surface moistening and nongleyed soddy-podzolic soils (Albic Glossic Retisols (Loamic, Aric, Ochric)) of elevated positions were examined. These soils were studied before the field drainage and during 25 years after drainage works in the periods differing in conditions of humification and with due account for not only drainage works but also other factors, such as topography and agrotechnology and their joint action. The specificity of transformation of humic substances in the soils and their particle-size fractions was analyzed in the basis of data on the organic carbon content, group and fractional composition of humus, the intensity of individual stages of humification (the neoformation of humic acids and the formation of humates), and the optical density of the fractions of humic acids. The results of the study of these properties in the fine soil fractions (<50 μm) made it possible to assess the response of the clay (<1 μm) and silt (1–5, 5–10, 10–50 μm) fractions to changes in the ecological situation and the role of separate particle-size fractions in the degradation of humus under adverse impacts. Overall, a clear tendency toward worsening of the humus quality was observed in both soils during the 25-year-long period, which is related to the long-term (20 years) agricultural use of the reclaimed field without application of agrochemicals. The features of humus degradation were mainly manifested in the finest (<10 μm) fractions with a general decrease in the humus content, slowing down of the formation of humic acids and humates, and considerable loss of humic acids, including their agronomically valuable fractions HA1 and HA2. The degradation of humus quality in the clay fraction was largely due to the impact of the reclamation (drainage) factor; the degradation of humus quality in the fine and medium silt fractions was mainly due to the negative changes in the agricultural background. Among negative consequences of the worsening humus quality, the lowering of soil fertility, ecological sustainability, and productivity of agrocenoses should be noted.

The structural state of modern and buried chestnut soils on the Privolzhskaya Upland (Volgograd oblast) was studied in order to determine changes in the soil structure in dependence on the time of soil burying. The soils buried 3500, 1700, and 700 years ago and modern background chestnut soils were examined. The structural state of soils was determined via their fractionation on a set of sieves (10–0.25 mm) in the air-dry state. We determined the contents of coarse aggregates, total aggregates, disperse soil matter, aggregation coefficient, and the degree of differentiation of the soil profiles. It was found that the structure of buried soils is preserved for 3500 years after the soil burying. The structural state of the studied soils changed with time depending on the climatic conditions that existed at the moment of soil burying. In humid periods, the amount of coarse aggregates (lumps) decreased, and the content of aggregated fractions increased; the reverse processes took place in arid epochs. Thus, it was shown that the aggregate composition of soils is specific for each period of soil formation and depends on the degree of climatic humidity. It is preserved in the buried soils independently on the duration of their existence in the buried state. We determined the impact of aggregate size on the C_org tolerance toward mineralization processes. It was shown that the content of organic carbon and its physical protection from mineralization are determined by different mechanisms of its fixing in aggregates of different sizes and depend on the conditions for the development of soil structure before burying and on the duration of the soil existence in the buried state. The results obtained in this study can be used as a retrospective basis for predicting changes in the physical properties of soils under conditions of changing climate.

Soil fungal pathogens are the most common cause of diseases in commercial strawberry crops worldwide. Since simultaneous infections by different pathogens can severely damage the crop, understanding the associated fungal communities can be helpful to mitigate crop loss. Herein, we used Illumina metabarcoding to assess the structure of fungal communities in five strawberry production areas in Estonia. Our analysis revealed 990 to 1430 operational taxonomic units (OTUs) per soil sample (pools of eight soil samples per production area). Based on our analyses, Ascomycota (55.5%) and Basidiomycota (25.0%) were the most OTUs-rich. Amongst the 24 most abundant OTUs, Geomyces, Rhodotorula, Verticillium and Microdochium were the most abundant genera, which were found across nearly all the soil samples. The OTUs were also clustered into three distinct groups, corresponding to different functional guilds of fungi. In addition, Fusarium solani, V. dahliae, Rhizoctonia solani and Colletotrichum truncatum were enormously abundant in the fields with disease symptoms, whereas arbuscular mycorrhizal fungi especially Rhizophagus irregularis were considerably more abundant in the fields with healthy plants. These findings provide support that mycorrhizal fungi may play an important role in suppressing pathogens. Our study for the first time shows the usefulness of Illumina technology in surveying the communities of soil fungi in strawberry fields effectively, which may improve available disease management strategies against strawberry diseases.

The influence of moisture and salinity of quartz sand on activation of the CO₂ emission and water consumption by seeds of spring wheat (Triticum), winter rye (Secále cereále), triticale (Triticosecale), and spring barley (Hórdeum) treated by a stimulant was studied under conditions of a model experiment. It was found that the seeds treated with a stimulant get advantages in the development upon a decrease in the water content of quartz sand. However, in the case of sand salinization, stimulant application did not lead to acceleration of seed development. The deficiency of moisture in saline sand also resulted in the increase of stimulant application efficiency. It was supposed that optimum moisture contents of quartz sand for seed germination and for the development of endophytic microorganisms do not coincide: active development of endophytic microorganisms stimulating seed development began under a lower moisture in comparison with that of the active seed development. Thus, active development of endophytic microorganisms upon the low moisture content mitigates the deceleration of seed development in the case of water deficiency. Hence, application of the microbial stimulant for seeds should be efficient in the cases, when germination of seeds proceeds under conditions of possible moisture deficiency, i.e., in the regions, where early spring droughts are frequent.

An algorithm of regional assessment of the size and structure of the actual (corresponding to the modern state of ecosystems and land use patterns) and potential (for hypothetic natural ecosystems analogous to modern native ecosystems) pools of carbon has been developed and tested. A comparison between actual and potential values of carbon pools makes it possible to assess the integral result of land use in the studied region with multiple changes in the types of land use during the historical period. The calculations are made using a unified cartographic base and take into account the taxonomic position and texture of soil units, the types of modern land use, and the type and age structure of the reconstructed and actual vegetation. The results obtained for the southern taiga and forest-steppe zones of European Russian indicate that the modern actual carbon pool is 24% less than the potential carbon pool in Kostroma oblast (southern taiga zone) and 32% less than the potential carbon pool in Kursk oblast (forest-steppe zone). The actual phytomass reserves in these two regions have decreased by 40 and 75%, respectively, relative the potential phytomass reserves, so the portion of the soil carbon pool in the total carbon pool has increased. It is argues that the use of the territory for forestry and agriculture increases the role of the soil cover in sustaining the carbon budget of the region.