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.     

Soil microbial biomass C and N along a climatic transect in the Mongolian steppe

The relationships of soil microbial biomass C (C_mic) or N (N_mic) with mean annual precipitation and temperature were studied along a climatic transect in the Mongolian steppe. Soil organic C (C_org) and total N (N_t), respiration rate, C_mic and N_mic at depths of 0–5 and 5–10 cm decreased with increasing aridity. The contents of C_org and N_t in the 0- to 5-cm soil layers decreased linearly with precipitation reduction along the transect. C_mic and N_mic changes with precipitation were not linear, with higher changes between 330 and 128 mm mean annual precipitation. C_mic/C_org and N_mic/N_t increased with increasing aridity. The metabolic quotient qCO₂ of 0- to 5-cm soil layers was low between 330 and 273 mm precipitation. The relationship between the qCO₂ of the 0- to 5-cm soil layers and the mean annual precipitation was well fitted with a quadratic function y =0.0006x² –0.40x +86.0, where y is the qCO₂ (µmol CO₂-C mmol^–1 C_mic) and x is the mean annual precipitation (mm). C_org, N_t, C_mic, N_mic and respiration rate decreased exponentially with increasing mean annual temperature in both the 0- to 5- and 5- to 10-cm soil layers, and change rate was lower when the mean annual temperature was higher than 2.6°C. The close relationships of the mean annual precipitation or temperature with soil C_org, N_t, C_mic, N_mic, C_mic/C_org and qCO₂ indicate that each parameter can be calculated by determining the other parameters in this specific climatic range.     

Energetic eco‐physiology of the soil microbiota in two landscapes of southern and northern Germany

Interactions between microbial communities and organic matter were analyzed for soils from the project regions ’︁Ecosystem Research in the Agricultural Landscape/FAM, Munich’ in southern Germany and ’︁Ecosystem Research in the Bornhöved Lake district’ from northern Germany using ratios between microbial biomass content (C_mic), microbial metabolic quotient (qCO₂) and organic carbon content (C_org). In the agricultural soils in southern Germany, the qCO₂/C_org ratio differed significantly with respect to agricultural management in contrast to ecophysiological C_mic/C_org ratio. In addition, C_mic/C_org ratio decreased from 39 to 21 mg C_mic g^—1 C_org and qCO₂/C_org ratio increased from 72 to 180 mg CO₂‐C g^—1 C_mic h^—1 (g C_org g^—1 soil)^—1 with increasing soil depth. For the upper soil horizons from the landscape in northern Germany the two quotients differed significantly with reference to land use showing highest microbial colonization under grassland and lowest under beech forest. In contrast, C use efficiency was lowest in arable field under maize monoculture and highest in a wet grassland having a high organic C content.     

Microbial diversity in three floodplain soils at the Elbe River (Germany)

Microbial communities in floodplain soils are exposed to periodical flooding. A long-term submerged Eutric Gleysol (GLe), an intermediate flooded Eutric Fluvisol (FLe), and a short-time flooded Mollic Fluvisol (FLm) at the Elbe River (Germany) with similar organic carbon contents (C_org) between 8.1% and 8.9% were selected to test the quality of phospholipid fatty acids (PLFA), soil microbial carbon (C_mic), basal respiration (BR), metabolic quotient (qCO₂), and C_mic/C_org ratio to characterize and discriminate these soils with microbial parameters.The three floodplain soils can be differentiated by C_mic and by total PLFA-biomass. Due to the different flooding durations and the time since the soils were last flooded C_mic and PLFA-biomass increase in the order GLe<FLe<FLm. Both parameters correlate significantly (r=0.999;p<0.05). The C_mic/C_org ratios are low in comparison to terrestrial soils and revealed the same ranking over the three soils like C_mic. Contrary, qCO₂ and BR are highest in GLe and lowest in FLm according to inundation regime. The diminished C_mic, high BR, and high qCO₂ values in GLe seem to be an unspecific response of aerobic soil microorganisms on the long flooding period and the resulting short time for developing after last flooding as well as the low pH value. Different plant communities and their residues may influence the microbial diversity additionally.The PLFA profiles were dominated by the group of saturated fatty acids that together constituted almost 62-72% of the total fatty acids identified in the soils. In GLe all groups of PLFA, inclusive monounsaturated fatty acids, are lowest and in FLm highest, while in FLe the PLFA fractions show an intermediary amount of the three soils. The FLm had most of the time aerobic conditions and revealed therefore the highest C_mic, PLFA-biomass, especially monounsaturated fatty acids, C_mic/C_org ratio as well as relatively low BR and qCO₂ value. These indicate that microorganisms in FLm are more efficiently in using carbon sources than those in GLe and FLe.All 26 identified PLFA were found in FLe and FLm, while the polyunsaturated fungi biomarker 18:2ω6,9c could not be detected in GLe. In this long-time submerged soil the environmental conditions which microorganisms are exposed might be disadvantageous for fungi.     

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.     

Adaptive responses of soil microbial communities under experimental acid stress in controlled laboratory studies

Soil samples from nine different beech forest sites (A_h horizon) with a mean initial soil pH close to neutral (6.4, SD 0.6) were treated with different amounts of H⁺-ions using acid water of pH 0.5 (H₂SO₄). The H⁺-input needed to lower the pH by one or more than three units was in the range between 0.006 and 0.6 mg H⁺ kg⁻¹, designated as mild, strong or extreme acid stress. The soil samples were incubated for a maximum of 200 days at 20°C and their microbial biomass-C (C_mic), qCO₂ and pH was measured at intervals. In addition, the ratio of fungal:bacterial contributions to total respiration was determined at the beginning and end of the experimental period. The extent of microbial biomass-C loss (32–87%) and the increase in the qCO₂ (1.8–>7 times) in comparison to acid-untreated samples followed the amount of initial H⁺-ion input. Differences between treatments based on one-way ANOVA were significant for C_mic depression at day 8 (p<0.01) and day 80 (p<0.05), and for qCO₂ at the beginning (p<0.001) and at day 80 only between mild and extreme acid stress (p<0.027). Over time some recovery of the microbial biomass was observed with a concomitant decrease in the qCO₂, an indication of adaptation to acidic conditions by the surviving and newly formed biomass. After 80 days of incubation microbial biomass values expressed as percent microbial-C in total soil carbon (C_mic:C_org) resembled those recorded for natural sites at comparable soil pH. There was a strong reduction in bacterial respiration following mild, strong or extreme acid treatment. A recovery here over time was only noted for mild or strong acid treatments. The results confirm that soil pH is a significant controlling parameter for microbial biomass build-up and the fungal:bacterial ratio as found previously with natural site studies.     

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.     

Discriminating factors of the spatial variability of soil quality parameters at landscape‐scale

The aim of the study was to evaluate the spatial variability pattern of some soil quality parameters at landscape‐scale, particularly soil microbial biomass‐C (C_mic) and ‐N (N_mic), and soil microbial activity (respiration) as well as soil organic carbon (C_org), and hot water extractable carbon (C_hwe) by multivariate analyses of variance and canonical discriminant analyses (CDA). The study area was the Trier region, Rhineland‐Palatinate, which is characterized by a wide range of soil types developed from various parent materials. Additionally, the investigated fields differed in soil management intensity (conventional, integrated, organic farming) and crops grown. Within the whole study area CDA revealed a separation into three sub‐areas. Within the sub‐areas the soil quality parameters were significantly influenced by the soil management systems and the crops grown. Despite the spatial variability and the relationship to soil management, the contents of C_mic could be predicted by stepwise multiple linear regression models, both for arable and grassland soils. The explained variance for the regression models were 72 % for arable soils and 63 % for grassland soils, respectively. Regression models for predicting N_mic and microbial activity revealed an explained variance between 30 and 58 %.     

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 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.     

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 (C_mic), the rate of the basal (microbial) respiration (BR), and the physical parameters (the particle size distribution (PSD), organic carbon (C_org), pH, heavy metals, and nutrients (NPK)) have been determined. High spatial variability has been revealed for C_mic 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 (C_mic by the PSD and PSD × C_org; 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 C_mic 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.     

Spatial structure of microbial biomass and activity in prairie soil ecosystems

Management of soil ecosystems requires assessment of key soil physicochemical and microbial properties and the spatial scale over which they operate. The objectives were to determine the spatial structure of microbial biomass and activity and related soil properties, and to identify spatial relationships of these properties in prairie soils under different management histories. Soil were sampled along a transect at 0.2 m intervals in each of five long-term treatments, namely, undisturbed, cattle grazed at two intensities, and cultivated with either wheat (Triticum aestivum L.) or cotton (Gossypium hirsutum L.). Contents of organic carbon (C_org), dissolved organic C (DOC), soluble nitrogen (N_sol), and microbial biomass C (C_mic) and N (N_mic) as well as dehydrogenase activity (DH) in 70 samples were evaluated. Results showed that long-term soil management altered the spatial structure and dependence of C_org and microbial biomass and activity. Cultivation has contributed to high nugget variance for C_org, C_mic, N_mic and DH which interfered with detection of spatial structure at the sampling scale used. Contents of C_org were spatially connected to microbial biomass and activity and to DOC in the uncultivated but not in the cultivated soils, indicating that various factors affected by management may operate at different spatial scales.     

SOIL MICROBIAL BIOMASS AND NITROGEN MINERALIZATION RATES ALONG AN ALTITUDINAL GRADIENT ON THE COFRE DE PEROTE VOLCANO (MEXICO): THE IMPORTANCE OF LANDSCAPE POSITION AND LAND USE

A study was conducted to examine the responses of microbial activity and nitrogen (N) transformations along an altitudinal gradient. The gradient was divided into three parts. Three areas were sampled: upper part (UP): coniferous forest, corn field, and abandoned corn field; middle part (MP): tropical cloud forest, grassland, and corn field (COL); and lower part (LP): tropical deciduous forest and sugarcane. The results showed that soil microbial biomass carbon (C) and basal respiration were significantly higher in MP and UP than in LP, whereas the microbial quotient (C_mic/C_org) was higher in LP and MP than in UP. The metabolic quotient (qCO₂) was similar among gradient parts evaluated. Net N mineralization, ammonification, and nitrification rates were higher in UP than MP and LP. We found that in UP, the forest conversion to cropland resulted in no significant differences in microbial activity and N transformation rates between land uses. In MP, microbial biomass C, ammonification, and net N mineralization rates decreased significantly with conversion to cropland, but C_mic/C_org and nitrification were higher in COL. Basal respiration and qCO₂ were significantly lower in COL when compared with other land uses. In LP, lower microbial biomass C, C_mic/C_org, and nitrification rates but higher ammonification and net N mineralization rates were observed in tropical deciduous forest than in sugarcane. No significant differences in basal respiration and qCO₂ were found between uses of LP. Clearly, then, soil organic C is not equally accessible to the microbial community along the gradient studied. Copyright © 2012 John Wiley & Sons, Ltd.     

Microbial C,N, and P relationships in moisture‐stressed soils of Potohar,Pakistan

In 11 rain‐fed arable soils of the Potohar plateau, Pakistan, the amounts of microbial‐biomass C (C_mic), biomass N (N_mic), and biomass P (P_mic) were analyzed in relation to the element‐specific total storage compartment, i.e., soil C_org, N_t, and P_t. The effects of climatic conditions and soil physico‐chemical properties on these relationships were highlighted with special respect to crop yield levels. Average contents of soil C_org, N_t, and P_t were 3.9, 0.32, and 0.61 mg (g soil)^–1, respectively. Less than 1% of P_t was extractable with 0.5 M NaHCO₃. Mean contents of C_mic, N_mic, and P_mic were 118.4, 12.0, and 3.9 µg (g soil)^–1. Values of C_mic, N_mic, P_mic, soil C_org, and N_t were all highly significantly interrelated. The mean crop yield level was closely connected with all soil organic matter– and microbial biomass–related properties, but showed also some influence by the amount of precipitation from September to June. Also the fraction of NaHCO₃‐extractable P was closely related to soil organic matter, soil microbial biomass, and crop yield level. This reveals the overwhelming importance of biological processes for P turnover in alkaline soils.     

Size and activity of the soil microbial biomass under grass and arable management

 The effects of 5 years of continuous grass/clover (Cont grass/clover) or grass (Cont grass) pasture or 5 years of annual grass under conventional (Ann grass CT) or zero tillage (Ann grass ZT) were compared with that of 5 years of continuous barley (LT arable) on a site which had previously been under arable crops for 11 years. For added comparison, a long-term grass/clover pasture site (LT past) nearby was also sampled. Soil organic C (C_org) content followed the order LT arable=Ann grass CT<Ann grass ZT<Cont grass=Cont grass/clover<LTpast. Trends with treatment for microbial biomass C (C_mic), basal respiration, flourescein diacetate (FDA) hydrolytic activity, arginine ammonification rate and the activities of dehydrogenase, protease, histidase, acid phosphatase and arylsulphatase enzymes were broadly similar to those for C_org. For C_mic, FDA hydrolysis, arginine ammonification and the activities of histidase, acid phosphatase and arylsulphatase, the percentage increase caused by 5 years of continuous pasture (in comparison with LT arable) was 100–180%, which was considerably greater than that for organic C (i.e. 60%). The microbial metabolic quotient (qCO₂) was higher for the two treatments which were mouldboard ploughed annually (LT arable and Ann grass CT) than for the undisturbed sites. At the undisturbed sites, C_org declined markedly with depth (0–15 cm) and there was a similar stratification in the size and activity of C_mic and enzyme activity. The microbial quotient (C_mic/C_org) declined with depth whilst qCO₂ tended to increase, reflecting a decrease in the proportion of readily available substrate with depth. Received: 7 July 1998     

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, C_mic and the microbial (basal) respiration, BR) and chemical (pH_water and the contents of C_org, heavy metals, and NPK) indices were determined in the samples. The ratios of BR to C_mic (the microbial respiration quotient, qCO₂) and of C_mic to C_org were calculated. The C_mic 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 C_org, from 2.52 to 5.67%; the qCO₂, from 1.24 to 5.28 μg CO₂-C/mg C_mic/g soil per h; and the C_mic/C_org, from 0.40 to 1.55%. Reliable positive correlations were found between the C_mic and BR, the C_mic and C_mic/C_org, and the C_mic and C_org values (r = 0.75, 0.95, and 0.61, respectively), as well as between the BR and C_mic/C_org values (r = 0.68). The correlation between the C_mic/C_org and qCO₂ values was negative (r = −0.70). The values of C_mic, BR, C_org, and C_mic/C_org 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 C_mic, C_org, 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.     

Arylsulfatase activity of soil microbial biomass along a Mediterranean-arid transect

The relationships between arylsulfatase and microbial activity were investigated in regional and microenvironmental scales, at three study sites in Israel, that represent different climatic regions—Mediterranean (sub-humid), mildly arid and arid.Total arylsulfatase activity was divided into extracellular and intracellular (microbial biomass enzyme) activities according to the chloroform-fumigation method. The results show that with increasing aridity, C_org (soil organic carbon), C_mic (soil microbial biomass carbon), N_mic (soil microbial biomass nitrogen) and respiration rate decreased, while C_mic/C_org and metabolic quotient (qCO₂) increased. Total, extracellular and microbial biomass arylsulfatase activities decreased with aridity. Expressed as percentage of total activity, the arylsulfatase activity of microbial biomass in the soil, at 0-2 cm and 5-10 cm depths, accounted for more than 50% of the total, in most measurements. This activity was significantly higher in the arid sites than that found in the Mediterranean one for the 0-2 cm soil. The results indicate the importance of the microflora as an enzyme source in soils, especially in arid climate conditions.Enzyme activity in the different study sites was found to be influenced by microenvironmental conditions. The Mediterranean site showed a much higher enzyme activity under shrubs than that under rock fragments and in bare soil. In the arid site rock fragments created a favorable microenvironment for microbial activity on soil surface, which resulted in a much higher microbial biomass and arylsulfatase activity than that in bare soil.The total, extracellular and intracellular arylsulfatase activities, were significantly correlated with C_org, C_mic, N_mic and respiration rate (p<0.05) at all study sites. The correlation coefficients between microbial biomass and arylsulfatase activity were usually higher than those between organic carbon and enzyme activity, especially in the arid sites. Close relationships between microbial biomass and arylsulfatase activities in all the studied sites supported the hypothesis that C_org content and enzyme activities should be related to each other via microbial biomass. Arylsulfatase activity was found to be a good indicator of microbial one. The regression equations between these factors can be incorporated into models of biogeochemical cycling for their easy method of analysis.     

Microbial enzyme activities in leaf litter, humus and mineral soil layers of European forests

The rationale of the study was to investigate microbial activity in different soil horizons in European forests. Hence, activities of chitinase and cellulase, microbial biomass carbon (C_mic) and basal respiration were measured in litter, fragmentation, humus and mineral soil layers collected several times from various beech and spruce forests. Sites were selected to form a gradient in N availability. Analyses were also performed on beech litter from a litterbag transplant experiment. Furthermore, microbiological parameters were measured in horizons of beech and spruce chronosequence sites with different stand age in order to investigate the influence of forest rotation, and hence changes in soil organic matter (SOM) dynamics, on microbial activity. Finally in horizons of one beech forest, the seasonal variation of selected microbiological parameters was measured more intensively. β-Glucosaminidase and cellobiohydrolase activities were measured using fluorogenic 4-methylumbelliferyl substrates to estimate chitinase and cellulase activities, respectively. On a spatial scale, chitinase and cellulase activities, C_mic determined by substrate induced respiration, and basal respiration ranged from 144 to 1924 and 6-177 nmol 4-MU g⁻¹ org-C h⁻¹, 8-48 mg C g⁻¹ org-C and 11-149 μg CO₂-C g⁻¹ org-C h⁻¹, respectively; in general values were significantly lower in layers of humus and mineral soil than of litter. Chitinase activity, C_mic and basal respiration from humus and mineral soil layers, together, correlated positively, while none correlated with cellulase activity. Similarly in the litter layer, no correlations were found between the microbiological parameters. On a seasonal scale, a time lag between a burst in basal respiration rate and activities of both enzymes were observed. In general, activities of cellulase and chitinase, C_mic and basal respiration, did not change with stand age, except in the humus layer in the spruce chronosequence, where C_mic decreased with stand age. In the litter layer, cellulase activity was significantly and positively related to the C:N ratio, while only a tendency for chitinase activity was shown, indicating that enzyme activities decreased with increasing N availability. In accordance, the enzyme activities and C_mic decreased significantly with increasing chronic N deposition in the humus layer, while basal respiration only tended to decrease with increasing N deposition. In contrast, enzyme activities in beech litter from litterbags after 2 years of incubation were generally higher at sites with higher N deposition. The results show different layer-specific responses of enzyme activities to changes in N availability, indicating different impacts of N availability on decomposition of SOM and stage of litter decomposition.     

The role of soil chemical properties,land use and plant diversity for microbial phosphorus in forest and grassland soils

Management intensity modifies soil properties, e.g., organic carbon (C_org) concentrations and soil pH with potential feedbacks on plant diversity. These changes might influence microbial P concentrations (P_mic) in soil representing an important component of the P cycle. Our objectives were to elucidate whether abiotic and biotic variables controlling P_mic concentrations in soil are the same for forests and grasslands, and to assess the effect of region and management on P_mic concentrations in forest and grassland soils as mediated by the controlling variables. In three regions of Germany, Schwäbische Alb, Hanich‐Dün, and Schorfheide‐Chorin, we studied forest and grassland plots (each n = 150) differing in plant diversity and land‐use intensity. In contrast to controls of microbial biomass carbon (C_mic), P_mic was strongly influenced by soil pH, which in turn affected phosphorus (P) availability and thus microbial P uptake in forest and grassland soils. Furthermore, P_mic concentrations in forest and grassland soils increased with increasing plant diversity. Using structural equation models, we could show that soil C_org is the profound driver of plant diversity effects on P_mic in grasslands. For both forest and grassland, we found regional differences in P_mic attributable to differing environmental conditions (pH, soil moisture). Forest management and tree species showed no effect on P_mic due to a lack of effects on controlling variables (e.g., C_org). We also did not find management effects in grassland soils which might be caused by either compensation of differently directed effects across sites or by legacy effects of former fertilization constraining the relevance of actual practices. We conclude that variables controlling P_mic or C_mic in soil differ in part and that regional differences in controlling variables are more important for P_mic in soil than those induced by management.     

Near-infrared spectroscopy for analysis of chemical and microbiological properties of forest soil organic horizons in a heavy-metal-polluted area

In industrial areas, heavy metals may accumulate in forest soil organic horizons, affecting soil microorganisms and causing changes in the chemical composition of the accumulated organic matter. The objectives of this study were to test the ability of near-infrared spectroscopy (NIRS) to detect heavy metal effects on the chemical composition of forest soil O horizons and to test whether NIRS may be used to quantitatively determine total and exchangeable concentrations of Zn and Pb (Zn_t, Pb_t, Zn_ex, Pb_ex) and other chemical and microbial properties in forest soil O horizons polluted with heavy metals. The samples of O horizons (n = 79) were analyzed for organic C (C_org), total N and S (N_t, S_t), Zn_t, Pb_t, Zn_ex, Pb_ex, basal respiration (BR), microbial biomass (C_mic) and C_mic-to-C_org ratio. Spectra of the samples were recorded in the Vis-NIR range (400–2,500 nm). To detect heavy-metal-induced changes in the chemical composition of O horizons principal components (PC1–PC7) based on the spectral data were regressed against Zn_t + Pb_t values. A modified partial least squares method was used to develop calibration models for prediction of various chemical and microbial properties of the samples from their spectra. Regression analysis revealed a significant relationship between PC3 and PC5 (r = −0.27 and −0.34, respectively) and Zn_t + Pb_t values, indicating an effect of heavy metal pollution on the spectral properties of the O horizons and thus on their chemical composition. For quantitative estimations, the best calibration model was obtained for C_org-to-N_t ratio (r = 0.98). The models for C_org, N_t, and microbial properties were satisfactory but less accurate. NIRS failed to accurately predict S_t, C_org-to-S_t, Zn_t, Pb_t, Zn_ex, and Pb_ex.