Hydrolase activities, microbial biomass and bacterial community in a soil after long-term amendment with different composts

The use of composts in agricultural soils is a widespread practice and the positive effects on soil and plants are known from numerous studies. However, there have been few attempts to compare the effects of different kinds of composts in one single study. The aim of this paper is to investigate to what extent and to which soil depth four major types of composts would affect the soil and its microbiota.In a crop-rotation field experiment, composts produced from (i) urban organic wastes, (ii) green wastes, (iii) manure and (iv) sewage sludge were applied at a rate equivalent to 175 kg N ha⁻¹ yr⁻¹ for 12 years. General (total organic C (C_org), total N (N_t), microbial biomass C (C_mic), and basal respiration), specific (enzyme activities related to C, N and P cycles), biochemical properties and bacterial genetic diversity (based on DGGE analysis of 16S rDNA) were analyzed at different depths (0-10, 10-20 and 20-30 cm).Compost treatment increased C_org at all depths from 11 g kg⁻¹ for control soil to 16.7 g kg⁻¹ for the case of sewage sludge compost. Total N increased with compost treatment at 0-10 cm and 10-20 cm depths, but not at 20-30 cm. Basal respiration and C_mic declined with depth, and the composts resulted in an increase of C_mic and basal respiration. Enzyme activities were different depend on the enzyme and among compost treatments, but in general, the enzyme activities were higher in the upper layers (0-10 and 10-20 cm) than in the 20-30 cm layer. Diversity of ammonia oxidizers and bacteria was lower in the control than in the compost soils. The type of compost had less influence on the composition of the microbial communities than did soil depth.Some of the properties were sensitive enough to distinguish between different compost, while others were not. This stresses the need of multi-parameter approaches when investigating treatment effects on the soil microbial community. In general, with respect to measures of activity, biomass and community diversity, differences down the soil profile were more pronounced than those due to the compost treatments.     

Is the soil microbial community related to the basal area of trees in a Scots pine stand?

The main energy sources of soil microorganisms are litter fall, root litter and exudation. The amount on these carbon inputs vary according to basal area of the forest stand. We hypothesized that soil microbes utilizing these soil carbon sources relate to the basal area of trees. We measured the amount of soil microbial biomass, soil respiration and microbial community structure as determined by phospholipid fatty acid (PLFA) profiles in the humus layer (FH) of an even-aged stand of Scots pine (Pinus sylvestris L.) with four different basal area levels ranging from 19.9 m² ha⁻¹ in the study plot Kasper 1 to 35.7 m² ha⁻¹ in Kasper 4. Increasing trend in basal respiration, total PLFAs and fungal-to-bacterial ratio was observed from Kasper 1 to Kasper 3 (basal area 29.2 m² ha⁻¹). The soil microbial community structure in Kasper 3 differed from that of the other study plots.     

Maßstabsabhängige räumliche Variabilität mikrobieller Bodenkenngrößen in einem Buchenwald

Scale-dependent spatial variability of microbiological characteristics in soil of a beech forest The spatial variability of the microbial biomass content (C_mic), the microbial respiration rate (basal respiration) and the metabolic quotient (qCO₂) was analyzed in sandy Cambisols and Luvisols in a beech forest in Northern Germany. Highest variability of microbiological features and, thus, the distance of independent samples was around 10 m that is discussed with reference to spatial hierarchy. Structural changes between the 10 m and 50 m grid were suggested for the Ah horizon due to the break of correlations of C_mic content and the contents of C_org and plant-available Ca, Mg, K and N_t. The C_mic content correlated with the C_org content close to tree trunks and ecotones like borders of the forest and clearings. The qCO₂ did not generally increase with declining pH value. High H⁺ concentrations and C_org content in the litter layer near to the tree trunk indicated retarded microbial mineralization rates. High proportion of microorganisms that are resistant to low pH value and adjusted ro readily-degradable substrates seems to dominate in the soil close to the tree.     

Tropical savannah woodland: effects of experimental fire on soil microorganisms and soil emissions of carbon dioxide

Burning of the vegetation in the African savannahs in the dry season is widespread and may have significant effects on soil chemical and biological properties. A field experiment in a full factorial randomised block design with fire, ash and extra grass biomass as main factors was carried out in savannah woodland of the Gambella region in Ethiopia. The microbial biomass C (C_mic) was 52% (fumigation-extraction) and 20% (substrate-induced respiration) higher in burned than unburned plots 12 d after burning. Both basal respiration and potential denitrification enzyme activity (PDA) immediately responded to burning and increased after treatment. However, in burned plots addition of extra biomass (fuel load) led to a reduction of C_mic and PDA due to enhanced fire temperature. Five days after burning, there was a short-lived burst in the in situ soil respiration following rainfall, with twice as high soil respiration in burned than unburned plots. In contrast, 12 d after burning soil respiration was 21% lower in the burned plots, coinciding with lower soil water content in the same plots. The fire treatment resulted in higher concentrations of dissolved organic C (24-85%) and nitrate (47-76%) in the soil until 90 d after burning, while soil NH₄⁺-N was not affected to the same extent. The increase in soil NO₃⁻-N but not NH₄⁺-N in the burned plots together with the well-aerated soil conditions indicated that nitrifying bacteria were stimulated by fire and immediately oxidised NH₄⁺-N to NO₃⁻-N. In the subsequent rainy season, NO₃⁻-N and, consequently, PDA were reduced by ash deposition. Further, C_mic was lower in burned plots at that time. However, the fire-induced changes in microbial biomass and activity were relatively small compared to the substantial seasonal variation, suggesting transient effects of the low severity experimental fire on soil microbial functioning.     

Characterization of the forest humus microbial community in a heavy metal polluted area

Various parameters of the soil microbial community may be used in soil quality evaluation and environmental risk assessment. The objectives of this study were to assess the effects of different environmental factors on the characteristics of forest humus microbial communities, and to test which environmental factors most affect the gross microbial indices and physiological profiles of these communities. Samples were taken at 71 plots located in a heavily polluted area of the Krakowsko-Cze¸stochowska upland in southern Poland. The samples were analyzed for pH in KCl (pH_KCl), organic C (C_org), total N (N_t) and S (S_t), and for total and soluble Zn, Pb and Cd concentrations. The considered microbial parameters included basal respiration (BAS), microbial biomass (C_mic), C_mic-to-C_org ratio, and community-level physiological profiles (CLPPs) studied using BIOLOG^® Ecoplates. Multiple regression analysis was used to estimate the effects of humus properties on the microbial parameters. It indicated that S_t and C_org-to-N_t ratio were the most important factors positively affecting C_mic (β=0.15 and 0.11, respectively) and BAS (β=0.13 and 0.08, respectively). The C_mic-to-C_org ratio was related positively to S_t (β=0.12) but negatively to N_t (β=−0.08). The effects of pH_KCl and heavy metals on the gross microbial indices were significant but less important. The most important effect on microbial activity on BIOLOG^® plates and CLPPs was from pH_KCl. The other significant variables included S_t, C_org-to-N_t and interactions of heavy metals with pH_KCl. It was concluded that C_mic, C_mic-to-C_org and BAS might be good indicators of the general status of soil microbial communities, but their use in studying heavy metal effects may entail difficulties in separating the effects of other factors. The sensitivity of the BIOLOG^® test to pH_KCl suggests that it may be useful for studying the effects of acidification or liming on soil microbial communities. The significant effect of the interactions between heavy metals and other variables on physiological profiles indicated that high heavy metal content affects the metabolic functions of soil microbial populations.     

Microbial activities in forest floor layers under silver birch, Norway spruce and Scots pine

The aim of this study was to compare microbial activities in the litter (L), fermentation (F) and humified (H) layers of the forest floor under silver birch (Betula pendula Roth), Norway spruce (Picea abies (L.) Karst) and Scots pine (Pinus sylvestris L.). Soil pH, C-to-N ratio, respiration rates, concentration of NH₄-N, net N mineralization and nitrification rates, gross NH₄⁺ production and consumption rates and amounts of C (C_mic) and N (N_mic) in the microbial biomass were determined from samples taken from the L, F and H layers under silver birch, Norway spruce and Scots pine. The forest floors under birch and spruce were more active than that under pine, having higher respiration and net N mineralization rates, and higher C_mic and N_mic values than pine forest floor. Differences between tree species were smaller in the H layer than in the L and F layers. The L layer had the highest rates of respiration for all tree species, while rates of net N mineralization were highest in the F layer for birch and spruce. Pine showed negligible net N mineralization in all layers. Concentration of NH₄-N was the best predictor of rate of net N mineralization (r=0.748). In general, C_mic and N_mic were higher in the L and F layers than in the H layer, as were their relative proportions of total C (C_tot) and N (N_tot), respectively. C_mic correlated positively with soil respiration (r=0.980) and N_mic with concentration of NH₄-N (r=0.915).     

Soil biochemical activity and phosphorus transformations and losses from acidified forest soils

Three Bohemian Forest catchments, Plešné, ?erné and ?ertovo, were studied. These catchments have similar climatic conditions, relief and vegetation, but differ in their bedrock composition. The granitic bedrock in the Plešné catchment was more susceptible to phosphorus (P) leaching under acid conditions than was the mica schist bedrock in the other catchments. The goal of this study was to determine if higher P leaching from the Plešné catchment was associated with differences in microbial P transformations and enzymatic P hydrolysis. Phosphorus and nitrogen contents in soil microbial biomass (P_MB, N_MB; chloroform fumigation), C mineralisation rate (C_min; CO₂ production by GC) and phosphatase activity (MUF-phosphate), were measured in three successive years. Phosphatase activity, P_MB, and C_min were used to characterise the enzymatic hydrolysis of organic P, microbial P accumulation, and microbial mineralisation rates of organic compounds, respectively. Soil chemical properties were characterised by C, N and P content, pH, and by oxalate-extractable P, Fe and Al. Spatial variability in N_MB, P_MB, C_min and phosphatase activity within the catchment was higher (coefficient of variation, CV<50%) than their temporal variability (CV<30%). Multivariate analysis revealed a significant soil layer effect but not that of catchment. When soil layers were evaluated separately, a difference between the Plešné and ?erné or ?ertovo catchments was found in litter and mineral layers, even though the variability within one catchment was high. Within soil profile, phosphatase activity was positively correlated with C_tot, N_MB and C_min (r²=0.89-0.92) being very correlated with P_MB (r²=0.99). Phosphatase activity was higher in the litter (14.0 nmol g⁻¹ h⁻¹) and humus (8.65 nmol g⁻¹ h⁻¹) layers of Plešné than in the same layers of the ?erné (9.65 and 6.40 nmol g⁻¹ h⁻¹) and ?ertovo (12.8 and 6.0 nmol g⁻¹ h⁻¹) soils. Similarly, P_MB in the litter and humus layers of Plešné soil (161 and 93 μg g⁻¹) was higher than P_MB of the same layers of the ?erné (120 and 66 μg g⁻¹) and ?ertovo (148 and 89 μg g⁻¹) soils. High MUFP hydrolysis rate: C_min molar ratio (0.16-1.17 M of P per 1 M of respired C) indicated that potential enzymatic P hydrolysis exceeded estimated microbial P demand (0.034 M of P per 1 M of respired C) in all catchments. The results suggest that higher microbial P transformations and enzymatic P hydrolysis could contribute to enhanced P leaching from the Plešné catchment, which could be enhanced by the lower Fe content in the soil of this catchment as compared to the ?erné and ?ertovo catchments.     

Spatial variability in the carbon of microbial biomass and microbial respiration in soils of the south of Moscow oblast

Soil samples from the upper 10-cm-thick layer of the humus horizon (without forest litter) were taken in Podol’sk and Serpukhov districts (1130 and 1080 km², respectively) of Moscow oblast. At each sampling site, ecosystem (forest, plowland, or fallow), soil (soddy-podzolic, soddy-gley, bog-podzolic, meadow alluvial, gray forest, and anthropogenically transformed soils of lawns and industrial zones), predominant vegetation, and topography (floodplain and low, medium, and upper parts of watersheds) were determined. The carbon content of the microbial biomass (C_mic) was determined by the method of substrate-induced respiration; we also determined the rate of basal (microbial) respiration (BR) and the organic carbon content, pH, and particle-size distribution. Overall, 237 samples from Serpukhov district and 45 samples from Podol’sk district were analyzed. The BR/C_mic ratios (respiration quotient qCO₂) and C_mic/C_org ratios were calculated. The C_mic content in the soils ranged from 43 to 1394 μg C/kg; the BR varied from 0.06 to 25 μg CO₂-C/g per h, qCO₂, from 0.34 to 6.52 μg CO₂-C/mg C_mic per h; and the C_mic/C_org ratio, from 0.19 to 10.65%. It was found that the most significant factors affecting the variability of the C_mic and BR are the parameters of ecosystem (50% and 80%, respectively) and soil (30% and 9%, respectively). The most significant variability of these indices was found in forest soils; it was mainly controlled by the soil texture (33 and 23%) and the C_org content (19 and 24%). The C_mic parameter made it possible to differentiate the soils of the territory for the purposes of their evaluation, monitoring, and biological assessment more clearly than the BR value and the soil chemical characteristics.     

Rainfall manipulation effects on litter decomposition and the microbial biomass of the forest floor

Simple structures aimed at regulating the amount of rain water dropping into the forest floor were installed to determine the impact of rainfall on leaf litter mass loss, respiration rates, microbial biomass C (C_mic) and metabolic quotient (qCO₂). The rainfall manipulation treatments were (I) fully covered (100% reduction); (II) partially covered (50% reduction) and (III) control (fully exposed). Using the litterbag technique, the mass losses of covered Quercus serrata, Quercus acutissima, Acer rufinerve and Pinus densiflora leaf litter were reduced (P<0.01) by 19–26% compared to fully exposed litter. A positive linear relationship (r=0.90; P<0.0001) between litter C_mic and mass loss was noted across all litter types and covering regimes. The mass losses in fully exposed litter were attributed to the leaching effect of rainfall coupled with the synergistic actions of microbes and soil fauna, as suggested by their respiration and microbial biomass. In the covered litter, C_mic was generally reduced (P<0.01) while fully and partially exposed litter were comparable (P>0.05). On the other hand, respiration rates and qCO₂ were variable and showed no consistent treatment effect except for respiration rates at 3 months. Similarly, soil respiration rates and C_mic were not consistently affected by cover treatments. Evidently, the zero-rainfall condition negatively affected some biological processes in the litter layer but sporadically affected soil processes. The absence of rainfall, even if the soil moisture content was maintained, could affect organic matter turnover in the forest floor.     

Belowground carbon allocation patterns in a dry Mediterranean ecosystem: A comparison of two models

Total belowground C allocation (TBCA) accounts for a large fraction of gross primary production, it may overtake aboveground net primary production, and contributes to the primary source of detrital C in the mineral soil. Here, we measure soil respiration, water erosion, litterfall and estimate annual changes in C stored in mineral soil, litter and roots, in three representative land uses in a Mediterranean ecosystem (late-successional forest, abandoned agricultural field, rain-fed olive grove), and use two C balance approaches (steady-state and non-steady-state) to estimate TBCA. Both TBCA approaches are compared to assess how different C fluxes (outputs and inputs) affect our estimates of TBCA within each land use. In addition, annual net primary productivity is determined and C allocation patterns are examined for each land use. We hypothesized that changes in C stored in mineral soil, litter and roots will be slight compared to soil respiration, but will still have a significant effect on the estimates of TBCA. Annual net primary productivity was 648 ± 31.5, 541 ± 42.3 and 324 ± 22.3 g C m⁻² yr⁻¹ for forest, abandoned agricultural field and olive grove, respectively. Across land uses, more than 60% of the C was allocated belowground. Soil respiration (F_S) was the largest component in the TBCA approaches across all land uses. Annual C losses through water erosion were negligible compared to F_S (less than 1%) and had little effect on the estimates of TBCA. Annual changes in C stored in the soil, litter layer and roots were low compared to F_S (16, 24 and 10% for forest, abandoned agricultural field and olive grove, respectively), but had a significant effect on the estimates of TBCA. In our sites, an assumption that Δ[C_S + C_R + C_L]/Δt = 0 will underestimate TBCA, particularly in the abandoned agricultural field, where soil C storage may be increasing more rapidly. Therefore, the steady-state model is unsuited to these Mediterranean ecosystems and the full model is recommended.     

Humus accumulation and microbial activities in calcari-epigleyic fluvisols under grassland and forest diked in for 30 years

The accumulation and transformation of organic matter during soil development is rarely investigated although such processes are relevant when discussing about carbon sequestration in soil. Here, we investigated soils under grassland and forest close to the North Sea that began its genesis under terrestrial conditions 30 years ago after dikes were closed. Organic C contents of up to 99 mg g⁻¹ soil were found until 6 cm soil depth. The humus consisted mainly of the fraction lighter than 1.6 g cm⁻³ which refers to poorly degraded organic carbon. High microbial respiratory activity was determined with values between 1.57 and 1.17 μg CO₂-C g⁻¹ soil h⁻¹ at 22 °C and 40 to 70% water-holding capacity for the grassland and forest topsoils, respectively. The microbial C to organic C ratio showed values up to 20 mg C_mic g⁻¹ C_org. Although up to 2.69 kg C m⁻² were estimated to be sequestered during 30 years, the microbial indicators showed intensive colonisation and high transformation rates under both forest and grassland which were higher than those determined in agricultural and forest topsoils in Northern Germany.     

Carbon dynamics determined by natural C abundance in microcosm experiments with soils from long-term maize and rye monocultures

Understanding carbon dynamics in soil is the key to managing soil organic matter. Our objective was to quantify the carbon dynamics in microcosm experiments with soils from long-term rye and maize monocultures using natural ¹³C abundance. Microcosms with undisturbed soil columns from the surface soil (0-25 cm) and subsoil (25-50 cm) of plots cultivated with rye (C₃-plant) since 1878 and maize (C₄-plant) since 1961 with and without NPK fertilization from the long-term experiment ‘Ewiger Roggen’ in Halle, Germany, were incubated for 230 days at 8 °C and irrigated with 2 mm 10⁻² M CaCl₂ per day. Younger, C₄-derived and older, C₃-derived percentages of soil organic carbon (SOC), dissolved organic carbon (DOC), microbial biomass (C_mic) and CO₂ from heterothropic respiration were determined by natural ¹³C abundance. The percentage of maize-derived carbon was highest in CO₂ (42-79%), followed by C_mic (23-46%), DOC (5-30%) and SOC (5-14%) in the surface soils and subsoils of the maize plots. The percentage of maize-derived C was higher for the NPK plot than for the unfertilized plot and higher for the surface soils than for the subsoils. Specific production rates of DOC, CO₂-C and C_mic from the maize-derived SOC were 0.06-0.08% for DOC, 1.6-2.6% for CO₂-C and 1.9-2.7% for C_mic, respectively, and specific production rates from rye-derived SOC of the continuous maize plot were 0.03-0.05% for DOC, 0.1-0.2% for CO₂-C and 0.3-0.5% for C_mic. NPK fertilization did not affect the specific production rates. Strong correlations were found between C₄-derived C_mic and C₄-derived SOC, DOC and CO₂-C (r≥0.90), whereas the relationship between C₃-derived C_mic and C₃-derived SOC, DOC and CO₂-C was not as pronounced (r≤0.67). The results stress the different importance of former (older than 40 years) and recent (younger than 40 years) litter C inputs for the formation of different C pools in the soil.     

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 (C_mic) was determined using the method of substrate-induced respiration and the rate of microbial CO₂ production (basal respiration, BR). The C_mic 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 C_mic 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 C_mic 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 C_mic 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.     

Consumption and release of nitrogen by the harvester termite Anacanthotermes ubachi navas in the northern Negev desert, Israel

The harvester termite, Anacanthotermes ubachi Navas (Hodotermitidea) occurs throughout the desert regions of Israel. This species nests in subsurface galleries where dead plant material, the termite's main food source, and feces are stored. We measured potential net nitrogen (N) mineralization and nitrification and soil respiration in 7-day laboratory incubations of plant litter at different stages of termite processing, termite feces and termite gallery soil (carton) following wetting. Our objectives were (1) to characterize the amount of potential N release from termite-affected plant and soil materials, (2) to evaluate the potential for leaching of N from the galleries and (3) to make a preliminary evaluation of the importance of termites to the carbon (C) and N cycles of the Negev desert. Two distinct phases were seen in the dynamics of inorganic N during the 7 day incubations: (1) release of N following wetting and (2) immobilization of N from day 1 to day 7 of the incubation. The percent of inorganic N produced in 1 day that disappeared by day 7 was significantly higher in the surface and gallery litter in comparison to the feces and the carton. High levels of nitrate (NO₃⁻: 87.5 g N kg⁻¹) compared to ammonium (NH₄⁺: 4.5 g N kg⁻¹) release from the surface and gallery litter samples suggest that there is a potential for leaching of NO₃⁻ from the galleries to surrounding environments. Gallery litter, i.e. litter that had been processed by termites, released significantly less inorganic N and had a higher C:N ratio than surface litter that had not been affected by termite activity. These results suggest that termites actively remove N for their own nutrition, leaving behind litter of lower quality than was produced by plants. Comparison of the C:N ratios of litter and feces suggest that approximately 80% of the C and 65% of the N in the surface and the gallery litter was decomposed and released in the transformation to feces. Given mean annual biomass production in the study site (740 kg ha⁻¹ with 296 kg C ha⁻¹ and 6.6 kg N ha⁻¹), this decomposition represents a release of 237 kg C ha⁻¹ and 4.3 kg N ha⁻¹, supporting the idea that termites function as keystone species in desert ecosystems.     

Microbial and enzyme properties of apple orchard soil as affected by long-term application of copper fungicide

Copper-based fungicides have been applied in apple orchards for a long time, which has resulted in increasing soil Cu concentration. However, the microbial and enzyme properties of the orchard soils remain poorly understood. This study aimed to evaluate the effect of long-term application of Cu-based fungicides on soil microbial (microbial biomass carbon (C_mic), C mineralization, and specific respiration rate) and enzyme (urease, acid phosphatase, and invertase activities) properties in apple orchards. Soil samples studied were collected from apple orchards 5, 15, 20, 30, and 45 years old, and one adjacent forest soil as for reference. The mean Cu concentrations of orchard soils significantly increased with increasing orchard ages ranging from 21.8 to 141 mg kg⁻¹, and the CaCl₂-extractable soil Cu concentrations varied from 0.00 to 4.26 mg kg⁻¹. The soil mean C_mic values varied from 43.6 to 116 mg kg⁻¹ in the orchard soils, and were lower than the value of the reference soil (144 mg kg⁻¹). The ratio of soil C_mic to total organic C (C_org) increased from 8.10 to 18.3 mg C_mic g⁻¹ C_org with decreasing orchard ages, and was 26.1 mg C_mic g⁻¹ C_org for the reference soil. A significant correlation was observed between total- or CaCl₂-extractable soil Cu and soil C_mic or C_mic/C_org, suggesting that the soil Cu was responsible for the significant reductions in C_mic and C_mic/C_org. The three enzyme activity assays also showed the similar phenomena, and declined with the increasing orchard ages. The mean soil C mineralization rates were elevated from 110 to 150 mg CO₂-C kg⁻¹ soil d⁻¹ compared with the reference soil (80 mg CO₂-C kg⁻¹ soil d⁻¹), and the mean specific respiration rate of the reference soil (0.63 mg CO₂-C mg⁻¹ biomass C d⁻¹) was significantly smaller than the orchard soils from 1.19 to 3.55 mg CO₂-C mg⁻¹ biomass C d⁻¹. The soil C mineralization rate and the specific respiration rate can be well explained by the CaCl₂-extractable soil Cu. Thus, the long-term application of copper-based fungicides has shown adverse effects on soil microbial and enzyme properties.     

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 (C_mic), the rate of the basal respiration (BR), and the specific microbial respiration (qCO₂= BR/C_mic) were determined. The C_mic content was measured using the method of substrate-induced respiration (SIR). In the upper humus horizons of the soils, the C_mic 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 C_mic 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 C_mic and C_org and the microbial production of CO₂ (BR) within the forest soil profiles are presented.     

Medium-term effects of a single application of mustard residues on soil microbiota and C content of vertisols

 A study of the effects of different qualities (fresh and composted) and rates (equivalent to 120, 240, and 360 kg N ha^–1) of mustard meal application on wheat yields on humid tropical vertisol was started in 1990 at Ginchi Research Station in Ethiopia. After continuous wheat cropping for 7 years and without any further fertilisation, soil microbial parameters (basal respiration, microbial biomass-C and N, organic-C, and ecophysiological quotients) were studied during one growth period. After 7 years of application, mustard meal still exerted a significant positive effect on microbial biomass, basal respiration, organic-C, C_mic : N_mic ratio, and metabolic quotient (qCO₂). Organic-C, qCO₂ and C_mic : N_mic ratios were higher for the compost-amended plots than plots amended with fresh mustard meal. Basal respiration, C_mic, and C_mic : N_mic ratio showed a clear seasonality, but only in manured plots. The data indicate shifts in microbial community structure (from bacteria to fungi and from r to K strategists) and suggest positive medium-term effects of mustard meal on humid tropical vertisol biological qualities. Received: 25 May 1999     

Effect of forest and soil type on microbial biomass carbon and respiration

The aim of study was to evaluate the variation of soil microbial biomass carbon (C_mic) and microbial respiration (M_R) in three types soil (Chromic Cambisols, Chromic Luvisols and Eutric Leptosols) of mixed beech forest (Beech- Hornbeam and Beech- Maple). Soil was randomly sampled from 0–10 cm layer (plant litter removed), 90 soil samples were taken. C_mic determined by the fumigation-extraction method and M_R by closed bottle method. Soil C_org, N_tot and pH were measured. There are significant differences between the soil types concerning the C_mic content and M_R. These parameters were highest in Chromic Cambisols following Chromic Luvisols, while the lowest were in Eutric Leptosols. A similar trend of C_org and N_tot was observed in studied soils. Two-way ANOVA indicated that soil type and forest type have significantly effect on the most soil characteristics. Chromic Cambisols shows a productive soil due to have the maximum C_mic, M_R, C_org and N_tot. In Cambisols under Beech- Maple forest the C_mic value and soil C/N ratio were higher compared to Beech-Hornbeam (19.5 and 4.1 mg C g^–1, and 16.3 and 3.3, respectively). This fact might be indicated that Maple litter had more easy decomposable organic compounds than Hornbeam. According to regression analysis, 89 and 68 percentage of C_mic variability could explain by soil C_org and N_tot respectively.     

Nitrogen fixation by biological soil crusts and heterotrophic bacteria in an intact Mojave Desert ecosystem with elevated CO2 and added soil carbon

Fixation of N by biological soil crusts and free-living heterotrophic soil microbes provides a significant proportion of ecosystem N in arid lands. To gain a better understanding of how elevated CO₂ may affect N₂-fixation in aridland ecosystems, we measured C₂H₂ reduction as a proxy for nitrogenase activity in biological soil crusts for 2 yr, and in soils either with or without dextrose-C additions for 1 yr, in an intact Mojave Desert ecosystem exposed to elevated CO₂. We also measured crust and soil δ¹⁵N and total N to assess changes in N sources, and δ¹³C of crusts to determine a functional shift in crust species, with elevated CO₂. The mean rate of C₂H₂ reduction by biological soil crusts was 76.9±5.6 μmol C₂H₄ m⁻² h⁻¹. There was no significant CO₂ effect, but crusts from plant interspaces showed high variability in nitrogenase activity with elevated CO₂. Additions of dextrose-C had a positive effect on rates of C₂H₂ reduction in soil. There was no elevated CO₂ effect on soil nitrogenase activity. Plant cover affected soil response to C addition, with the largest response in plant interspaces. The mean rate of C₂H₂ reduction in soils either with or without C additions were 8.5±3.6 μmol C₂H₄ m⁻² h⁻¹ and 4.8±2.1 μmol m⁻² h⁻¹, respectively. Crust and soil δ¹⁵N and δ¹³C values were not affected by CO₂ treatment, but did show an effect of cover type. Crust and soil samples in plant interspaces had the lowest values for both measurements. Analysis of soil and crust [N] and δ¹⁵N data with the Rayleigh distillation model suggests that any plant community changes with elevated CO₂ and concomitant changes in litter composition likely will overwhelm any physiological changes in N₂-fixation.     

Soil microbial biomass C and N changes in relation to forest conversion in the Northwestern Turkey

Tree species differ in their effect on soil development and nutrient cycling. Conversion of beech coppice to pine plantations can alter soil physical and chemical properties, which in turn may have significant impacts on soil microbial biomass C and N (C_mic, N_mic). The major objective of this study was to evaluate soil quality changes associated with the forest conversion in humid NW Turkey. Results from this study showed that levels of soil organic carbon (C_org), total nitrogen (N_t), moisture, C_mic and N_mic under beech coppice were consistently higher but levels of pH, CaCO₃ and EC were lower compared to pine plantation. Differences between the forest stands in C_mic and N_mic were mainly related to the size of the C_org stores in soil and to tree species. In addition, high level of CaCO₃ is likely to reduce pools of soil organic C and possibly even microbial biomass C and N in pine forests. The average C_mic:N_mic ratios were higher in soils under beech coppice than pine plantation, while C_mic:C_org and N_mic:N_t percentages were similar in both forest types. These results revealed the differences in microbial community structure associated with different tree species and the complex interrelationships between microbial biomass, soil characteristics, litter quantity and quality. Copyright © 2008 John Wiley & Sons, Ltd.