N. D. Ananyeva

Microbial biomass in soils of Russia under long-term management practices

Abstract Non-tilled and tilled plots on a spodosol (Corg 0.65–1.70%; pH 4.1–4.5) and a mollisol (Corg 3.02–3.13%, pH 4.9–5.3), located in the European region of Russia, were investigated to determine variances in soil microbial biomass and microbial community composition. Continuous, long-term management practices, including tillage and treatment with inorganic fertilizers or manure, were used on the spodosol (39 years) and mollisol (22 years). Total microbial biomass (Cmic), estimated by the substrate-induced respiration (SIR) method, and total fungal hyphae length (membrane filter technique) were determined seasonally over a 3-year period. Long-term soil management practices (primarily tillage and fertilizer application) led to decreases in total microbial biomass (80–85% lower in spodosol and 20–55% lower in mollisol), decreases in the contribution of Cmic to Corg (2.3- to 3.5-fold lower in spodosol and 1.2- to 2.3-fold lower in mollisol), and 50–87% decreases in total fungal hyphae length compared to non-tilled control plots. The contribution of fungi to total SIR in virgin mollisol and fallow spodosol plots was approximately 30%. However, the contribution of fungi to SIR was approximately two times greater in tilled spodosol plots compared to a fallow plot. In contrast, the contribution of fungi to SIR in tilled plots of mollisol was less (1.4–4.7 times) than for a virgin plot. In summary, long-term soil management practices such as tillage and treatment with organic or inorganic fertilizers are important determinants of soil microbial biomass and the contribution of fungi to total SIR.

Determination of the soil microbial biomass carbon using the method of substrate-induced respiration

Specific features of determining the carbon content in the soil microbial biomass using the method of substrate-induced respiration (MBSIR) were studied as related to the conditions of the incubation (the glucose concentration and temperature) and pre-incubation (the duration and temperature) of the soil samples collected in the summer (tundra gley and soddy-podzolic soils and chernozems) and in different seasons (for the gray forest soil). The glucose concentration providing the highest substrate-induced respiration (SIR) in the soils studied was shown to be 2–15 mg/g. The MBSIR in the soil samples collected in summer and in the soils pre-incubated for 10 and 22°C (7 days) did not significantly differ. The MBSIR in the gray forest soil pre-incubated at 3, 6, and 10°C (winter, spring/autumn, and summer, respectively) and at 22°C (recommended by the authors of the SIR method) was similar for the cropland in all the seasons. For the meadow, it was the same in the winter, summer, and autumn, and, in summer, it did not differ only for the forest. For the comparative assessment of the MBSIR, soil samples from different ecosystems are recommended to be collected in the autumn or in the summer. Soil samples of 100–500 g should be pre-incubated for 7 days at 22°C and moisture of 60% of the total water capacity; then, 1-2 g soil should be incubated with glucose (10 mg/g) at 22°C for 3–5 hours.

Microbial biomass carbon and the microbial carbon dioxide production by soddy-podzolic soils in postagrogenic biogeocenoses and in native spruce forests of the southern taiga (Kostroma oblast)

In two layers of the humus horizons in soddy-podzolic soils of different biogeocenoses (Kostroma oblast) representing a succession series, the carbon content in the microbial biomass (Cmic) was determined using the method of substrate-induced respiration and the rate of microbial CO2 production (basal respiration, BR). The Cmic content was from 110 to 755 μg/g soil, and the BR was from 0.40 to 2.52 μg CO2-C/g/h. A gradual increase in the Cmic content and BR was found in the following sequence: cropland—fallow (7-year-old)—young (20- and 45-year-old) forests—secondary and native (primary) forests (90- and 450-year-old, respectively). In the litter, the Cmic content was higher in the 45-year-old forest than in the secondary and native forests: 10423, 6459, and 4258 μg C/g of substrate, respectively. The portion of Cmic in the soil organic carbon content in the upper layer of the soils studied varied from 1.3 to 5.4%; its highest value was in the soils under the secondary and native forests. The pool of microbial biomass carbon and the microbial CO2 production in the upper 25-cm layer of the soils were calculated.

Specific Features of the Ecological Functioning of Urban Soils in Moscow and Moscow Oblast

Urban soils (constructozems) were studied in Moscow and several cities (Dubna, Pushchino, and Serebryanye Prudy) of Moscow oblast. The soil sampling from the upper 10-cm-thick layer was performed in the industrial, residential, and recreational functional zones of these cities. The biological (the carbon of the microbial biomass carbon, Cmic and the microbial (basal) respiration, BR) and chemical (pHwater and the contents of Corg, heavy metals, and NPK) indices were determined in the samples. The ratios of BR to Cmic (the microbial respiration quotient, qCO2) and of Cmic to Corg were calculated. The Cmic varied from 120 to 738 μg C/g soil; the BR, from 0.39 to 1.94 μg CO2-C/g soil per hour; the Corg, from 2.52 to 5.67%; the qCO2, from 1.24 to 5.28 μg CO2-C/mg Cmic/g soil per h; and the Cmic/Corg, from 0.40 to 1.55%. Reliable positive correlations were found between the Cmic and BR, the Cmic and Cmic/Corg, and the Cmic and Corg values (r = 0.75, 0.95, and 0.61, respectively), as well as between the BR and Cmic/Corg values (r = 0.68). The correlation between the Cmic/Corg and qCO2 values was negative (r = −0.70). The values of Cmic, BR, Corg, and Cmic/Corg were found to correlate with the ammonium nitrogen content. No correlative relationships were revealed between the determined indices and the climatic characteristics. The principal component analysis described 86% of the variances for all the experimental data and clearly subdivided the locations of the studied soil objects. The ANOVA showed that the variances of Cmic, Corg, and BR are controlled by the site location factor by 66, 63, and 35%, respectively. The specificity of the functioning of the anthropogenic soils as compared with their natural analogues was clearly demonstrated. As shown in this study, measurable biological indices might be applied to characterize the ecological, environmental-regulating, and productive functions of soils, including urban soils.

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.

Microbial biomass carbon in the profiles of forest soils of the southern taiga zone

In the mineral horizons of the soils under different southern taiga forests (oak, archangel spruce, and aspen in the Kaluzhskie Zaseki Reserve of Kaluga region and the green moss spruce and spruce-broadleaved forests of the Zvenigorod Biological Station of Moscow State University in Moscow region), the carbon content in the microbial biomass (Cmic), the rate of the basal respiration (BR), and the specific microbial respiration (qCO2= BR/Cmic) were determined. The Cmic content was measured using the method of substrate-induced respiration (SIR). In the upper humus horizons of the soils, the Cmic content amounted to 762–2545 µg/g and the BR ranged from 1.59 to 7.55 µg CO2-C/g per h. The values of these parameters essentially decreased down the soil profiles. The portion of Cmic in the organic carbon of the humus horizons of the forest soils was 4.4 to 13.2%. The qCO2values increased with the depth in the soils of the Biological Station and did not change in the soils of the Reserve. The pool of Cmic and Corg and the microbial production of CO2 (BR) within the forest soil profiles are presented.

The fungal and bacterial biomass (selective inhibition) and the production of CO2 and N2O by soddy-podzolic soils of postagrogenic biogeocenoses

In the humus horizon of soddy-podzolic soils of postagrogenic cenoses and primary forests, the contributions of the fungi and bacteria were determined by the selective inhibition of the substrate-induced respiration (SIR) by antibiotics; the basal (microbial) respiration and the net-produced nitrous oxide (N2O) were also determined. The procedure of the SIR separation using antibiotics (cycloheximide and streptomycin) into the fungal and bacterial components was optimized. It was shown that the fungi: bacteria ratio was 1.58, 2.04, 1.55, 1.39, 2.09, and 1.86 for the cropland, fallow, and different-aged forests (20, 45, 90, and 450 years), respectively. The fungal and bacterial production of CO2 in the primary forest soil was higher than in the cropland by 6.3 and 11.4 times, respectively. The production of N2O in the soils of the primary and secondary (90-year-old) forests (3 and 7 ng N-N2O/g soil per hour, respectively) was 2–13 times lower than in the postagrogenic cenoses, where low values were also found for the microbial biomass carbon (Cmic), its components (the Cmic-bacteria and Cmic-fungi), and the portion of Cmic in the organic carbon of the soil. A conclusion was drawn about the misbalance of the microbial processes in the overgrown cropland accompanied by the increased production of N2O by the soil during its enrichment with an organic substrate (glucose).

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).

The microbial biomass and its activity and structure in the soils of old forests in the European Russia

The humus-accumulative layer of soils (podzolic, gray, rzhavozem, burozem, and karbolitozem) of old-age forests (>60–450 years old) localized in various vegetation subzones (middle-taiga, southern taiga, subtaiga, dark coniferous forests outside the boreal region, and mountain forests) of the European part of Russia (22 sites of soil sampling of them, 13 in nature reserves and specially protected territories) was studied. The carbon content of the microbial biomass (Cmic) in the soil was determined by the substrate-induced respiration method. The fungal to bacterial ratio was determined by the selective inhibition technique with antibiotics. The basal respiration (BR) was also measured. The BR/Cmic = qCO2 ratio and the portion of Cmic in the total organic soil carbon was determined. It was shown that the Cmic and BR in the soils of a separate vegetation subzone varied significantly; however, their values increased from the middle-taiga to dark coniferous subzone and decreased in the mountain-forest zone (348 ± 44, 670 ± 66, 1000 ± 86, 1142 ± 49, 789 ± 79 μkg C/g soil and from 0.68 ± 0.23, 1.85 ± 0.10, 2.13 ± 0.15, 1.56 ± 0.14, 0.92 ± 0.07 μkg CO2-C/soil h, respectively). The fungal component in the humus-accumulative layer of soils is 53–99% of the total Cmic; however, its absolute values increase from the middle subzone to the southern one. The Cmic pool and the total BR in the profile of some soils (mineral horizons and forest litter) were calculated.

Structure of the microbial community in soil catena of the right bank of the Oka River

The structure of the microbial community (the fungi-to-bacteria ratio) has been assessed by selective inhibition of the substrate-induced respiration (SIR) using streptomycin sulfate and cycloheximide antibiotics in the gray forest soil of eluvial, transite, transite-accumulative, and accumulative (meadow alluvial) parts of slope landscape on the right bank of the Oka River (near Pushchino, Moscow oblast) which represents an fallow, small-leaved wood, spruce forest, and meadow. The concentrations of bactericide and fungicide were selected experimentally for each landscape parts which provide the greatest SIR inhibition of the soil upon their individual application and in combination. Fungi were established to be predominant in the contribution to the total SIR which was found to be 82–97%. A dependence between the structure of the microbial community and the C/N ratio and pH of the soil was shown.