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.     

Long-term effects of mineral fertilizers on soil microorganisms – A review

Increasing nutrient inputs into terrestrial ecosystems affect not only plant communities but also associated soil microbial communities. Studies carried out in predominantly unmanaged ecosystems have found that increasing nitrogen (N) inputs generally decrease soil microbial biomass; less is known about long-term impacts in managed systems such as agroecosystems. The objective of this paper was to analyze the responses of soil microorganisms to mineral fertilizer using data from long-term fertilization trials in cropping systems. A meta-analysis based on 107 datasets from 64 long-term trials from around the world revealed that mineral fertilizer application led to a 15.1% increase in the microbial biomass (C_mic) above levels in unfertilized control treatments. Mineral fertilization also increased soil organic carbon (C_org) content and our results suggest that C_org is a major factor contributing to the overall increase in C_mic with mineral fertilization. The magnitude of the effect of fertilization on C_mic was pH dependent. While fertilization tended to reduce C_mic in soils with a pH below 5 in the fertilized treatment, it had a significantly positive effect at higher soil pH values. Duration of the trial also affected the response of C_mic to fertilization, with increases in C_mic most pronounced in studies with a duration of at least 20 years. The input of N per se does not seem to negatively affect C_mic in cropping systems. The application of urea and ammonia fertilizers, however, can temporarily increase pH, osmotic potential and ammonia concentrations to levels inhibitory to microbial communities. Even though impacts of fertilizers are spatially limited, they may strongly affect soil microbial biomass and community composition in the short term. Long-term repeated mineral N applications may alter microbial community composition even when pH changes are small. How specific microbial groups respond to repeated applications of mineral fertilizers, however, varies considerably and seems to depend on environmental and crop management related factors.     

Effects of tree harvesting, forest floor removal, and compaction on soil microbial biomass, microbial respiration, and N availability in a boreal aspen forest in British Columbia

The effects of timber harvesting and the resultant soil disturbances (compaction and forest floor removal) on relative soil water content, microbial biomass C and N contents (C_mic and N_mic), microbial biomass C:N ratio (C_mic-to-N_mic), microbial respiration, metabolic quotient (qCO₂), and available N content in the forest floor and the uppermost mineral soil (0-3 cm) were assessed in a long-term soil productivity (LTSP) site and adjacent mature forest stands in northeastern British Columbia (Canada). A combination of principal component analysis and redundancy analysis was used to test the effects of stem-only harvest, whole tree harvest plus forest floor removal, and soil compaction on the studied variables. Those properties in the forest floor were not affected by timber harvesting or soil compaction. In the mineral soil, compaction increased soil total C and N contents, relative water content, and N_mic by 45%, 40%, 34% and 72%, respectively, and decreased C_mic-to-N_mic ratio by 29%. However, these parameters were not affected by stem only harvesting or whole tree harvesting plus forest floor removal, contrasting the reduction of white spruce and aspen growth following forest floor removal and soil compaction reported in an earlier study. Those results suggest that at the study site the short-term effects of timber harvesting, forest floor removal, and soil compaction are rather complex and that microbial populations might not be affected by the perturbations in the same way as trees, at least not in the short term.     

Carbon stocks, soil respiration and microbial biomass in fire-prone tropical grassland, woodland and forest ecosystems

A thorough understanding of the role of microbes in C cycling in relation to fire is important for estimation of C emissions and for development of guidelines for sustainable management of dry ecosystems. We investigated the seasonal changes and spatial distribution of soil total, dissolved organic C (DOC) and microbial biomass C during 18 months, quantified the soil CO₂ emission in the beginning of the rainy season, and related these variables to the fire frequency in important dry vegetation types grassland, woodland and dry forest in Ethiopia. The soil C isotope ratios (δ¹³C) reflected the 15-fold decrease in the grass biomass along the vegetation gradient and the 12-fold increase in woody biomass in the opposite direction. Changes in δ¹³C down the soil profiles also suggested that in two of the grass-dominated sites woody plants were more frequent in the past. The soil C stock ranged from being 2.5 (dry forest) to 48 times (grassland) higher than the C stock in the aboveground plant biomass. The influence of fire in frequently burnt wooded grassland was evident as an unchanged or increasing total C content down the soil profile. DOC and microbial biomass measured with the fumigation-extraction method (C_mic) reflected the vertical distribution of soil organic matter (SOM). However, although SOM was stable throughout the year, seasonal fluctuations in C_mic and substrate-induced respiration (SIR) were large. In woodland and woodland-wooded grassland C_mic and SIR increased in the dry season, and gradually decreased during the following rainy season, confirming previous suggestions that microbes may play an important role in nutrient retention in the dry season. However, in dry forest and two wooded grasslands C_mic and SIR was stable throughout the rainy season, or even increased in this period, which could lead to enhanced competition with plants for nutrients. Both the range and the seasonal changes in soil microbial biomass C in dry tropical ecosystems may be wider than previously assumed. Neither SIR nor C_mic were good predictors of in situ soil respiration. The soil respiration was relatively high in infrequently burnt forest and woodland, while frequently burnt grasslands had lower rates, presumably because most C is released through dry season burning and not through decomposition in fire-prone systems. Shifts in the relative importance of the two pathways for C release from organic matter may have strong implications for C and nutrient cycling in seasonally dry tropical ecosystems.     

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).     

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.     

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.     

Effect of lithological substrate on microbial biomass and enzyme activity in brown soil profiles in the northern Apennines (Italy)

The aim of the present study was to investigate the microbial activity along forest brown soil profiles sequence developed on different lithological substrates (carbonate or non-carbonated cement in sandstone formations) at different altitudes. The main question posed was: does carbonate affect the biochemical activity of brown soil profiles at different altitudes? For the purpose of this study, four soil profiles with different amounts and compositions of SOM developed on different lithological substrates were selected: two with carbonate (MB and MZ) and the other two with non-carbonated cement in the sandstone formations (MF1 and MF2). Chemical and biochemical properties of soil were analysed along soil profiles in order to assess the SOM quantity and quality, namely total organic C (C_org), water extractable organic C (WEOC) and humification indices (HI, DH, HR). Microbial biomass (C_mic and N_mic) content, as well as the specific activities of acid phosphatase, β-glucosidase and chitinase enzymes were chosen as indicators of biochemical activity. The soil biochemical properties provided evidence of better conditions for microorganisms in MB than in MF1, MF2 and MZ soil profiles, since patterns of microbial biomass content and activity might be expected in response to the amount and quality of organic substances. The different lithological substrates did not show any clear effect on soil microbial biomass content, since similar values were obtained in MF1, MF2 (with non-carbonated cement) and MZ (with carbonate). However, the specific activities of acid phosphatase (per unit of C_org and per unit of C_mic) were higher in soils with no carbonate (MF1 and MF2) than in soils with carbonate (MB and MZ). In conclusion, the biochemical activity along brown soil profiles was mainly regulated by different soil organic matter content and quality, while the two different lithological substrates (with carbonate or non-carbonated cement in the sandstone formations) did not show any direct effect on microbial biomass and its activity. However, the activity of acid phosphatase per unit of C was particularly enhanced in soil with non-carbonate cement in the sandstone formations.     

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.     

Experimental assessment of the contribution of plant root respiration to the emission of carbon dioxide from the soil

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

The adverse effects of soil salinization on the growth of Trifolium alexandrinum L. and associated microbial and biochemical properties in a soil from Iran

The aim of this study was to determine the effects of increasing concentrations of salt solutions (including 0.12, 2, 6, and 10 dS m⁻¹) on the growth of berseem clover (Trifolium alexandrinum L.) and related soil microbial activity, biomass and enzyme activities. Results showed that the dry weights of root and shoot decreased with an increase in the concentrations of salt solutions. Soil salinization depressed the microbiological activities including soil respiration and enzyme activities. Substrate-induced respiration was consistently lower in salinized soils, whereas microbial biomass C did not vary among salinity levels. Higher metabolic quotients (qCO₂) and unaffected microbial biomass C at high EC values may indicate that salinity is a stressful factor, inducing either a shift in the microbial community with less catabolic activity or reduced efficiency of substrate utilization. Acid phosphatase and alkaline phosphatase activities decreased with increasing soil salinity. We found significant, positive correlations between the activities of phosphatase enzymes and plant's root mass, suggesting that any decrease in the activities of the two enzymes could be attributed to the reduced root biomass under saline conditions.     

Long-term application of compost influences microbial biomass and enzyme activities in a tropical Aeric Endoaquept planted to rice under flooded condition

In a field study, long-term application of compost to a tropical Aeric Endoaquept under continuous rice growing in a rice-rice-fallow sequence resulted in the stimulation of microbial biomass and select soil enzyme activities. Mean seasonal soil microbial biomass-C (C_mic) increased by 42%, 39% and 89% in inorganic fertilizer, compost and compost+inorganic fertilizer treatments, respectively, over the unamended control. C_mic content was also influenced by the rice crop growth stage and was highest at maximum tillering stage irrespective of treatments and declined thereafter. Soil organic C (C_org) content showed highly significant positive correlation with dehydrogenase, urease, cellulase, β-glucosidase and fluorescein di-acetate (FDA) hydrolysis activity, and a positive but not significant correlation with invertase and amidase activity. C/N ratio which was lowest in unamended control plots showed a significant positive relationship with only the enzymes involved in C cycle. Stepwise regression analysis revealed that for prediction of both total organic C and total N, FDA hydrolysis activity contributed significantly for the variance and explained up to 85-96% variability. Results demonstrated that microbial biomass and soil enzyme activity is sensitive in discriminating between long-term organic residue amendment practices.     

Assessment of soil quality in different ecosystems (with soils of Podolsk and Serpukhov districts of Moscow oblast as examples)

The values of the soil-ecological index and microbiological parameters (the carbon of microbial biomass C_mic, its ratio to the total organic carbon C_mic/C_org, and basal respiration) were determined for the soddy-podzolic, soddy-gley, bog-podzolic, meadow alluvial, and gray forest soils under different land uses (forest, fallow, cropland, and urban areas) in the Podolsk and Serpukhov districts of Moscow oblast (237 and 45 sampling points, respectively). The soil sampling from the upper 10 cm (without the litter horizon) was performed in September and October. To calculate the soil-ecological index, both soil (physicochemical and agrochemical) and climatic characteristics were taken into account. Its values for fallow, cropland, and urban ecosystems averaged 70.2, 72.8, and 64.2 points (n = 90, 17, and 24, respectively). For the soils of forest ecosystems, the average value of the soil-ecological index was lower (54.4; n = 151). At the same time, the micro-biological characteristics of the studied forest soils were generally higher than those in the soils of fallow, cropland, and urban ecosystems. In this context, to estimate the soil quality in different ecosystems on the basis of the soil-ecological index, the use of a correction coefficient for the biological properties of the soils (the C_mic content) was suggested. The ecological substantiation of this approach for assessing the quality of soils in different ecosystems is presented in the paper.     

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     

Responses of soil microbial biomass and activity for practices of organic and conventional farming systems in Piauí state,Brazil

The aim of this work was to investigate the response of soil microbial biomass and activity to practices in organic and conventional farming systems. The study was carried out at the Irrigation District of Piauí, Brazil. Five different plots planted with “acerola” orchard (Malpighia glaba) and established at the following management were evaluated: (1) under 12 months of soil conventional management (CNV); (2) under six months of soil organic management (ORG6); (3) under 12 months of soil organic management (ORG12); (4) under 18 months of soil organic management (ORG18); and (5) under 24 months of soil organic management (ORG24). Soil microbial biomass C (C_mic), basal respiration, organic carbon (C_org), C_mic-to-C_org ratio and metabolic quotient (qCO₂) were evaluated in soil samples collected at 0–10 cm depth. The highest C_org and C_mic levels occurred in organic system plots ORG18 and ORG24 compared to the conventional system. Soil respiration and C_mic-to-C_org ratio were significantly enhanced by the organic system plots. The qCO₂ was greater in conventional than in organic system. These results indicate that the organic practices rapidly improved soil microbial characteristics and slowly increase soil organic C.     

Effects of multiple heavy metal contamination and repeated phytoextraction by Sedum plumbizincicola on soil microbial properties

The threat of heavy metal contamination to food and human health in south and east China has become a public concern as industrial development continues. The aims of this study were to investigate the influence of repeated phytoextraction over a two-year period by successive crops of the Zn and Cd hyperaccumulator Sedum plumbizincicola on multiple metal contaminated soils and to assess recovery of soil quality. Total and NH₄OAc-extractable Zn and Cd concentrations were significantly reduced in planted soils compared to unplanted soils. Microbial biomass C (C_mic), basal respiration and microbial quotient (qM) were significantly and positively correlated and soil metabolic quotient (qCO₂) was negatively correlated with heavy metal concentrations in unplanted soils (P < 0.05). However, C_mic, basal respiration and qM values increased significantly after phytoremediation by five crops over two years compared to unplanted soil. Urease, β-glucosidase, neutral phosphatase and arylsulfatase activities also increased significantly with decreasing heavy metal contents and hydrolase activity was enhanced in planted soil (P < 0.05) compared to the unplanted control. The data indicate the capacity of S. plumbizincicola to extract Zn and Cd from contaminated soil and also that phytoremediation had beneficial effects on soil microbial and hydrolase activities, with the metal phytoextraction procedure restoring soil quality.     

Successional changes in microbial biomass,respiration and nutrient status during litter decomposition in an aspen and pine forest

Microbial biomass, microbial respiration, metabolic quotient (qCO₂), C_mic/C_org ratio and nutrient status of the microflora was investigated in different layers of an aspen (Populus tremuloides Michx.) and pine forest (Pinus contorta Loud.) in southwest Alberta, Canada. Changes in these parameters with soil depth were assumed to reflect successional changes in aging litter materials. The microbial nutrient status was investigated by analysing the respiratory response of glucose and nutrient (N and P) supplemented microorganisms. A strong decline in qCO₂ with soil depth indicated a more efficient C use by microorganisms in later stages of decay in both forests. C_mic/C_org ratio also declined in the aspen forest with soil depth but in the pine forest it was at a maximum in the mineral soil layer. Microbial nutrient status in aspen leaf litter and pine needle litter indicated N limitation or high N demand, but changes in microbial nutrient status with soil depth differed strongly between both forests. In the aspen forest N deficiency appeared to decline in later stages of decay whereas P deficiency increased. In contrast, in the pine forest microbial growth was restricted mainly by N availability in each of the layers. Analysis of the respiratory response of CNP-supplemented microorganisms indicated that growth ability of microorganisms is related to the fungal-bacterial ratio.     

Influence of Tea Cultivation on Soil Microbial Biomass and Substrate Utilization Pattern

Abstract

The study was conducted to evaluate the effect of tea cultivation on soil microbial biomass and community structure. Soil pH, extractable aluminum (Al), organic carbon (C_org) and total nitrogen were considerably modified by tea cultivation. Long‐term tea cultivation resulted in the increase of microbial biomass C (C_mic), microbial biomass N (N_mic), and basal respiration. The metabolic quotient declined as the tea cultivation age increased. The adjacent citrus orchard soil showed a higher C_mic/C_org ratio than the tea orchard soils. Microtitration plates with 21 carbon sources and two different pH levels (4.7 and 7.0) were used to determine the substrate utilization pattern of these soils. The average well color development (AWCD) of the carbon sources in the plates did not vary in a consistent manner with the microbial biomass. Multivariate analysis of sole carbon source utilization pattern demonstrated that land‐use history had a significant effect on substrate utilization pattern. The pH 4.7 characterization medium can increase the discrimination of this technique and is more adequate than the conventional neutral medium for the tea orchard soils.     

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.     

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