Size Of Microbial Biomass Research Articles

Microbiological Response to Copper Contamination of a Paddy Soil

Heavy metal contamination of soil is a significant envi-ronmental issue in China in recent years because of rapidindustrialization and wide use of Cu-, Zn-containing fer-tilizers and fungicides. Due to their function and ubiquitouspresence microorganisms can serve as an environmentallyrelevant indicator of pollution. Some features of soilmicroorganisms, such as the microbial biomass size, soilrespiration rate, and soil enzyme activity, are often used asbioindicators for the ecotoxicity of heavy metals (Krasnova1983; Niklin´ska et al. 2005). Brookes (1995) suggested thatthe ratio of basal respiration rate (BR) to microbial biomassC(C

Influence of organic and mineral amendments on microbial soil properties and processes

Microbial diversity in soils is considered important for maintaining sustainability of agricultural production systems. However, the links between microbial diversity and ecosystem processes are not well understood. This study was designed to gain better understanding of the effects of short-term management practices on the microbial community and how changes in the microbial community affect key soil processes. The effects of different forms of nitrogen (N) on soil biology and N dynamics was determined in two soils with organic and conventional management histories that varied in soil microbial properties but had the same fertility. The soils were amended with equal amounts of N (100 kg ha −1) in organic (lupin, Lupinus angustifolius L.) and mineral form (urea), respectively. Over a 91-day period, microbial biomass C and N, dehydrogenase enzyme activity, community structure of pseudomondas ( sensu stricto), actinomycetes and α proteobacteria (by denaturing gradient gel electrophoresis (DGGE) following PCR amplification of 16S rDNA fragments) and N mineralisation were measured. Lupin amendment resulted in a two- to five-fold increase in microbial biomass and enzyme activity, while these parameters did not differ significantly between the urea and control treatments. The PCR–DGGE analysis showed that the addition of mineral and organic compounds had an influence on the microbial community composition in the short term (up to 10 days) but the effects were not sustained over the 91-day incubation period. Microbial community structure was strongly influenced by the presence or lack of substrate, while the type of amendment (organic or mineral) had an effect on microbial biomass size and activity. These findings show that the addition of green manures improved soil biology by increasing microbial biomass and activity irrespective of management history, that no direct relationship existed among microbial structure, enzyme activity and N mineralisation, and that microbial community structure (by PCR–DGGE) was more strongly influenced by inherent soil and environmental factors than by short-term management practices.

Factors controlling decomposition of soil organic matter in fallow systems of the high tropical Andes: A field simulation approach using 14C- and 15N-labelled plant material

Abstract N-rich (C:N=27) and N-poor (C:N=130) wheat straw, labelled with 14C and 15N, was incubated for 2 yr in two major ecosystems of the upper elevation belt of cultivation in the high Andes: the moist Paramo (precipitation=1329 mm, altitude=3400 m asl, Andes of Merida, Venezuela) and the dry Puna (precipitation=370 mm, altitude=3800 m asl, Central Altiplano, Bolivia). The experiment was installed in young (2 yr) and old (7 yr) fallow plots. The following soil analyses were performed at nine sampling occasions: soil moisture, total-14C and -15N, and Microbial Biomass (MB)-14C and -15N. The measured data were fitted by the MOMOS-6 model (a process based model, with five compartments: labile and stable plant material, MB, and labile (HL) and stable humus (HS)) coupled with the SAHEL model (soil moisture prediction) using daily measured and/or predicted meteorological data. The aim was to understand how (1) the climatic conditions, (2) the quality of plant material, (3) the fallow age and (4) the soil properties affect the cycling of C and N within the soil organic matter system. The fallow age (2 and 7 yr) did not affect the measured data or the model predictions, indicating that in these systems the decomposition potential is not affected by fallow length. During the short initial active decomposition phase, the labile plant material was quickly exhausted, enabling a build up of MB and of HL. During the low activity phase, that covered 4/5 of the time of exposure, the MB size decreased slowly and the HL pool was progressively exhausted as it was reused by the MB as substrate. The HL compartment was directly or indirectly the major source for the inorganic 15N production. If the C:N ratio of the added plant material increased, the model predicted (1) a reduction of the decomposition rates of the plant material (essentially the stable plant material) and (2) an increased mortality of the MB which increased the production of HL (microbial cadavers and metabolites). Thus the essential effect of the slower decomposition due to the N-poor plant material was a higher accumulation of C and N in the HL and its slower recycling by the MB during the low activity phase. The labelling experiment allows to understand the higher soil native organic matter content in Paramo soils compared to Puna. The large sequestration of organic matter generally observed in the Paramo soils can be explained by two abiotic factors: the unfavourable soil microstructure and the accumulation of free aluminium linked to the climatic and acid soil conditions, inhibiting the microbial activity physically and chemically.

Microbial Biomass and Tolerance of Microbial Community on an Aged Heavy Metal Polluted Floodplain in Japan

The objective of the present study was to increase understanding of the effects of heavy metal pollution and soil properties on microorganisms in relation to the biomass and microbial functional community. Soil samples were collected from aged polluted and reference sites on a floodplain. The soil Cu, Zn and Pb total concentrations were much higher at the polluted sites (average 231.6–309.9 mg kg−1, 195.7–233.0 mg kg−1, and 72.4–86.0 mg kg−1, respectively) than at the reference site (average 33.3–44.0 mg kg−1, 76.7–98.0 mg kg−1, and 30.8–41.6 mg kg−1, respectively), while the available heavy metal concentrations in CaCl2 extraction were similar in all sites. Small seasonal variations in the size of microbial biomass were observed. Ambient soil properties (e.g. total C, N, pH, moisture content, and CEC) affected the soil microbial biomass more than the heavy metal pollution. However, the aged pollution tended to impact on the composition of the microbial community. PICT (pollution-induced community tolerance) test using BIOLOG Ecoplates showed enhanced tolerance of the microbial community to Cu stress in the polluted site. In non polluted but low nutrient, low pH and low moisture soil, the microbial biomass was lower and the microbial community was more vulnerable to Cu stress. In spite of the low heavy metal availability due to ageing, the BIOLOG technique provided sensitive detection of microbial community level changes in PICT analysis.

Microbial immobilisation and turnover of 15N labelled substrates in two arable soils under field and laboratory conditions

Microbial biomass N dynamics were studied under field and laboratory conditions in soils of high yield (HY) and low yield (LY) areas in an agricultural field. The objective of the study was to determine the size and activity of soil microbial biomass in the soils of the different yield areas and to compare these data obtained under field and laboratory conditions. Soils were amended with 15N labelled mustard ( Sinapis alba) residues (both experiments) and labelled nitrate (laboratory only) at 30 μg N g −1 dry soil. Soil microbial biomass (SMB) N, mineral N (N min) and total N content was monitored both in the field and in the laboratory. N 2O efflux was additionally measured in laboratory treatments. Isotope ratios were determined for SMB in both experiments, for all other parameters only in the laboratory treatments. In the laboratory less amounts of added substrate N were immobilised by the SMB in HY soils compared to LY soils, whereas in the field immobilisation of added N by SMB was higher in HY soils initially and slightly lower after 40 days of incubation. Calculated turnover times in the laboratory nitrate, laboratory mustard and field mustard amendments were 0.18, 0.27 and 0.74 years (HY) and 0.22, 0.61 and 1.01 years (LY), respectively. The turnover times of added substrate N always showed the trend to be faster in HY soils compared to LY soils. A faster turnover of nutrients in the HY soils may involve a better nutrient supply of the plants, which coincides with the higher agricultural yield observed in these areas.

Responses of soil microorganisms to elevated CO2 in experiment sites ofPinus sylvestriformis andPinus koraiensis

Responses of soil microbial activities to elevated CO2 in experiment sites ofPinus sylvestriformis andPinus koraiensis seedlings were studied in summer in 2003. The results indicated the number of bacteria decreased significantly (p<0.05) under elevated CO2 forPinus sylvestriformis andPinus koraiensis. Amylase and invertase activities in soil increased forPinus sylvestriformis and decreased forPinus koraiensis with CO2 enrichment compared with those at ambient (350 μmol·mol−1). The size of microbial biomass C also decreased significantly at 700 μmol·mol−1 CO2. Bacterial community structure had some evident changes under elevated CO2 by DGGE (Denaturing Gradient Gel Electrophoresis) analysis of bacterial 16S rDNA gene fragments amplified by PCR from DNA extracted directly from soil. The results suggested that responses of soil microorganisms to elevated CO2 would be related to plant species exposed to elevated CO2.

Seasonal dynamics of soil microbial biomass in coastal sand dune forest

Sand dunes are a typical landscape in the coast of western Taiwan, where Casuarina forests were established decades ago to stabilize sand dunes and protect the inland vegetation. Study of microbial biomass in such an ecosystem may give insights into the role of microbes in soil fertility and nutrient cycling. We established our study sites in two topographic units based on elevation and drainage types: upland and lowland. The study lasted for 2 years, and soil samples were collected every 3 months. Microbial biomass C (Cmic) and N (Nmic) were high in a shallow humic layer that rested on top of the soil (1222–1319 mg kg−1 for Cmic and 245–276 mg kg−1 for Nmic) and declined sharply to only one-tenth of the above values in the underlying surface soil (0–10 cm depth). Microbial biomass Cmic and Nmic in humic and surface soil were not significantly different between upland and lowland sites. In the upland soils, the mean Cmic was highest in autumn for both the humic and surface soil, and lowest in spring and summer for the humic layer and summer for the surface soil layer. In the lowland soils, the Cmic was highest in winter for both humic and surface soil, and lowest in spring and autumn for the humic layer and spring and summer for surface soil. Strong fluctuations of Cmic and Nmic were associated with the soil moisture prior to sampling, which appeared to control the size of microbial biomass in this environment. Temperature had little effect on the dynamics of soil microbial biomass in the sand dune forest ecosystem.

Effect of freezing and thawing on microbial activity and glyphosate degradation in two Norwegian soils

Little research has been done on pesticide dissipation in cold climates and there is a need to focus on the influence of climate on pesticide degradation in soil. Glyphosate, N-(phosphonomethyl)glycine, is a herbicide frequently used for controlling perennial weeds through application after harvest and was used as a model compound for this study. The effect of freeze-thaw activity on the availability of glyphosate in soil, and consequently its mineralization by soil microorganisms, was studied through laboratory incubations of repacked soil cores treated with 14C-labelled glyphosate and subjected to different freeze-thaw treatments. Winter simulation regimes applied were constant thaw (+5 degrees C), constant freezing (-5 degrees C), unstable conditions with short fluctuations (24 h of -5 degrees C followed by 24 h of +5 degrees C), and long duration fluctuations (3 weeks of -5 degrees C followed by 3 weeks of +5 degrees C). Distribution of 14C-glyphosate was followed during the incubation through measurements of the mineralized fraction (14CO2), soil water fraction, KOH extractable fraction, and non-extractable fraction. Microbial parameters used to characterize the soils were estimates of size of microbial biomass, overall microbial activity and microbial diversity. The constant freezing treatment exhibited the lowest amount of glyphosate mineralization. The constant thawed treatment and the treatments with fluctuating temperature exhibited significantly increased mineralization. These results were in accordance with the observed concentration of glyphosate in soil water; the higher the activity, the lower the concentration. The amount of glyphosate extractable with KOH and the resulting non-extractable fraction, however, were not significantly affected by soil type or temperature regime. The glyphosate mineralization pattern was comparable with the overall microbial activity in the soils. Observed different levels of diversity might explain some of the difference in total glyphosate mineralization between soils.

Microbial immobilisation and turnover of 13C labelled substrates in two arable soils under field and laboratory conditions

Microbial biomass C immobilisation and turnover were studied under field and laboratory conditions in soils of high yield (HY) and low yield (LY) areas within an agricultural field. We compared the size and activity of soil microbial biomass (SMB) in the soils of the different yield areas under field and laboratory conditions. Soils were amended with 13C labelled mustard ( Sinapis alba) residues (both experiments) and labelled glucose (laboratory only) at 500 μg C g −1 dry soil. SMB–C, dissolved organic carbon (DOC) and total C content were monitored in the field and the laboratory. CO 2-efflux was also measured in laboratory treatments. Isotope ratios were determined for SMB in both experiments, but other variables only in the laboratory treatments. A positive priming effect was measured in three of four laboratory treatments. Priming was induced after a significant increase of soil derived C in the microbial biomass. Thereafter, the total C loss through priming was always smaller than or equal to the decline in microbial biomass C. In field and laboratory experiments SMB in the HY soil immobilised less of the added substrate C than LY soil SMB. Calculated turnover times in the laboratory glucose amendment were 0.24 (HY) and 0.31 y (LY), in the laboratory mustard treatment 0.58 (HY) and 0.44 y (LY) and in the field mustard amendments 1.09 (HY) and 1.25 y (LY). In both the field mustard and laboratory glucose treatments turnover in the HY soil tended to exceed that in the LY soil. These turnover times as well as the reaction of SMB–C to drying-rewetting and substrate addition, indicated that the HY soil possessed a more active microbial community with a more rapid C turnover than the LY soil. As C turnover is considered to be closely linked to nutrient cycles, faster turnover in the HY soil may involve a better nutrient supply for crops resulting in higher agricultural yield.

Size, activity and catabolic diversity of the soil microbial biomass as affected by land use

Although the effects of land use on soil organic matter are well known, the effects on the size, activity and diversity of the soil microbial community are less well documented. In this study the effects of agricultural land use (maize ( Zea mays), annual ryegrass ( Lolium multiflorum), permanent kikuyu grass pasture ( Pennisetum clandestinum), gum ( Eucalyptus grandis) and pine ( Pinus patula) forest) on microbial biomass C, microbial and exocellular enzyme activity and heterotrophic functional diversity (by analysis of catabolic response profiles to 36 substrates) was investigated on a site where the long-term history of land management was known. In comparison with native grassland, permanent kikuyu pasture resulted in an increase in organic C, microbial biomass, arginine ammonification rate, flourescein diacetate hydrolysis rate and arylsulphatase activity. By contrast, under maize under both conventional tillage (CT) and zero tillage (ZT) and annual ryegrass there was a reduction in organic matter and microbial biomass content and in measurements of microbial and enzyme activity. However, in these three arable soils, basal respiration, arginine ammonification and fluorescein diacetate (FDA) hydrolysis rates, when expressed per unit of microbial biomass, were higher than under the other land uses, suggesting the presence of a small but highly metabolically active microfloral community. Soils below pine forest tended to have a higher organic C content than those below gum forest, yet microbial biomass C, basal respiration, arginine ammonification rate and arylsulphatase activity were lower under pine forest. This was attributed to the inhibitory effects if phenolic compounds in pine needles. Principal components analysis of catabolic response profiles demonstrated that there were large differences in the catabolic capability of the soil microbial communities inhabiting the various land use types. Values for Shannon’s and Simpson’s diversity indices followed the order: pine<gum<kikuyu pasture=annual ryegrass=maize (ZT)=maize (CT)<native grassland indicating that greatest catabolic diversity existed under native grassland and least diversity existed under exotic forest. It was concluded that land use had substantial effects on the size, activity and diversity of the soil microbial community and that these changes could be broadly related to changes in soil organic matter content.

Effect of arsenic contamination on microbial biomass and its activities in arsenic contaminated soils of Gangetic West Bengal, India

A study was conducted to see the effect of arsenic contamination on soil quality indicators, viz., microbial biomass, soil respiration, fluorescein diacetate and dehydrogenase (DHG) activity in arsenic contaminated soils of West Bengal. All the parameters were significantly and negatively correlated with all the form of arsenic (bioavailable and total) but the microbial metabolic quotient was significantly and positively correlated with all forms of arsenic, indicating arsenic induced stress to the soil microbial community. This may be due to part of the microbial biomass, which is located in the inner parts of the micro-aggregates of soil, which is affected by arsenic accumulates present in soil particles. Linear regression analysis revealed that the bioavailable arsenic exerted greater inhibitory effect on the soil microbial population than the total arsenic content of soils. Water-soluble arsenic showed more inhibitory effect than NaHCO 3 extractable form, in their association with biological properties of the contaminated soils. Water-soluble form of arsenic was much more toxic than insoluble forms. This signified that with increase in bioavailability, the arsenic exerted more inhibitory effect on these parameters. It is thus suggested that the microbial biomass, fluorescein diacetate and dehydrogenase activity alone and expressed on a soil organic matter basis along with the soil respiration parameters can be helpful in assessing the effects of arsenic on the size and activity of microbial biomass in soils.

Land application of biosolids. Soil response to different stabilization degree of the treated organic matter

The effect of land application of biosolids on an agricultural soil was studied in a 2-month incubation experiment. The soil microbial biomass and the availability of heavy metals in the soil was monitored after the application of four different composting mixtures of sewage sludge and cotton waste, at different stages of composting. Land application caused an increase of both size and activity of soil microbial biomass that was related to the stabilization degree of the composting mixture. Sewage sludge stabilization through composting reduced the perturbance of the soil microbial biomass. At the end of the experiment, the size and the activity of the soil microbial biomass following the addition of untreated sewage sludge were twice those developed with mature compost. For the mature compost, the soil microbial biomass recovered its original equilibrium status (defined as the specific respiration activity, qCO 2) after 18 days of incubation, whereas the soil amended with less stabilized materials did not recover equilibrium even after the two-month incubation period. The stabilization degree of the added materials did not affect the availability of Zn, Ni, Pb, Cu, Cr and Cd in the soil in the low heavy metal content of the sewage sludge studied. Stabilization of organic wastes before soil application is advisable for the lower perturbation of soil equilibria status and the more efficient C mineralization.

A priori parameterisation of the CERES soil-crop models and tests against several European data sets

Mechanistic soil-crop models have become indispensable tools to investigate the effect of management practices on the productivity or environmental impacts of arable crops. Ideally these models may claim to be universally applicable because they simulate the major processes governing the fate of inputs such as fertiliser nitrogen or pesticides. However, because they deal with complex systems and uncertain phenomena, site-specific calibration is usually a prerequisite to ensure their predictions are realistic. This statement implies that some experimental knowledge on the system to be simulated should be available prior to any modelling attempt, and raises a tremendous limitation to practical applications of models. Because the demand for more general simulation results is high, modellers have nevertheless taken the bold step of extrapolating a model tested within a limited sample of real conditions to a much larger domain. While methodological questions are often disregarded in this extrapolation process, they are specifically addressed in this paper, and in particular the issue of models a priori parameterisation. We thus implemented and tested a standard procedure to parameterize the soil components of a modified version of the CERES models. The procedure converts routinely-available soil properties into functional characteristics by means of pedo-transfer functions. The resulting predictions of soil water and nitrogen dynamics, as well as crop biomass, nitrogen content and leaf area index were compared to observations from trials conducted in five locations across Europe (southern Italy, northern Spain, northern France and northern Germany). In three cases, the model’s performance was judged acceptable when compared to experimental errors on the measurements, based on a test of the model’s root mean squared error (RMSE). Significant deviations between observations and model outputs were however noted in all sites, and could be ascribed to various model routines. In decreasing importance, these were: water balance, the turnover of soil organic matter, and crop N uptake. A better match to field observations could therefore be achieved by visually adjusting related parameters, such as field-capacity water content or the size of soil microbial biomass. As a result, model predictions fell within the measurement errors in all sites for most variables, and the model’s RMSE was within the range of published values for similar tests. We conclude that the proposed a priori method yields acceptable simulations with only a 50% probability, a figure which may be greatly increased through a posteriori calibration. Modellers should thus exercise caution when extrapolating their models to a large sample of pedo-climatic conditions for which they have only limited information.

Response of microbial biomass to air-drying and rewetting in soils and compost

The activity of microorganisms and the availability of composting substrates for decomposition are seriously affected by drying and rewetting cycles. We have measured microbial biomass C ( B C) and ninhydrin reactive N ( B NIN) of samples of composting material taken at different times from a pile of ligno-cellulosic wastes. Dynamics of these two parameters in control samples that were kept continuously moist were compared with those of samples of the same material that had been subjected to drying and rewetting. The study was also performed on soils to investigate analogies and differences of behaviour of microbial biomass in such different substrates. Moist samples from 10 soils with different organic C content (6.6–41.9 g kg −1 soil) were analyzed for their B C and B NIN content. The soils were then air-dried, rewetted and incubated at 25 °C for 10 days. On days 1, 3, 6 and 10 of incubation, samples were analyzed for B C and B NIN content. Compost samples from different composting stages of a mixture of cotton carding and yard wastes were air-dried, rewetted and incubated at 25 °C for 12 days, together with the corresponding moist samples (control). On days 1, 5 and 12 of incubation period, samples were analyzed for B C and B NIN content. The regression coefficient between B C and B NIN for all the compost data (continuously moist and rewetted) was 21.4 ( r=0.89 P<0.001), very close to values normally found in soils, confirming the reliability of microbial biomass measurements performed on composting substrates. Soil drying caused on average a decrease in the size of microbial biomass with respect to moist samples of 13% for B C and 30% for B NIN. B C and B NIN of moist and rewetted soil samples were always significantly correlated. Microbial biomass content of rewetted compost samples up to 19 days from the beginning of the process were significantly different, but highly correlated with moist controls. No significant differences between moist and rewetted samples (RW) were found in samples collected during the maturing and curing phases. The different response to drying of soils and compost could be related to the greater increase of new available substrate in compost with respect to soil following the drying–rewetting treatment. Dynamics of B C/ B NIN ratio in compost was coherent with the normal trend observed in the composition of microbial community during the process, from prevailing bacteria and actinomycetes to prevailing fungi.

Characterization of carbon and microbial biomass pools in shallow water coastal sediments of the southern Baltic Sea (Nordrügensche Bodden)

Relations between sediment properties and pools of organic carbon and microbial bio- mass were investigated in sediments of shallow water coastal inlets of the southern Baltic Sea (Ras- sower Strom, Nordrugensche Bodden). According to their mud content (percentage of the fraction <63 µm to total sediment dry weight), sediments were grouped into sand, slightly muddy sand, and muddy sand. Phospholipids and ATP were analysed to estimate total and 'active' microbial biomass. From measurements of chlorophyll a (chl a) and total bacterial numbers, photoautotrophic microbial and bacterial biomasses were estimated. Carbon pools were determined by total organic carbon (TOC), dissolved organic and inorganic carbon (DOC, DIC), and available dissolved organic carbon (ADOC). The latter was measured by means of a biosensor consisting of an oxygen microelectrode with bacteria attached to the tip. Nitrogen and phosphorus were also analysed. Size and composition of carbon pools and microbial biomass revealed pronounced differences related to the mud content of the sediments. Sandy sediments were characterized by a high contribution of DOC and ADOC to TOC. Microbial biomass could be equally estimated by phospholipid-, ATP-, and chl-a-based carbon. Bacterial carbon constituted 5% of the total microbial biomass carbon. With increasing mud content from sandy and slightly muddy sand towards muddy sand sediments, TOC and DOC increased, whereas ADOC decreased. In the same way, total microbial (phospholipid based) and bacterial bio- mass increased; whereas the contribution of photoautotrophic (chl a based) and active (ATP based) biomass to total biomass declined to 31 and 18%, respectively. As demonstrated by increasing ratios of carbon to nitrogen, nitrogen to phosphorus, and decreasing ratios of chl a to phaeopigments, the organic matter undergoes increasing aging from sandy to muddy sand sediments. Pronounced rela- tionships between phospholipid and bacterial based biomass on the one hand and between ATP and chl a on the other suggested similar structural and physiological features of corresponding biomass indicators. Total phospholipid based microbial biomass and bacterial biomass were closely related to mud content as well as to organic matter (carbon, nitrogen), whereas photoautotrophic and 'active' microbial biomass measured as chl a and ATP seemed to be inversely related to mud content. From the direct relation between photoautotrophic biomass and ADOC, it is suggested that easily decom- posable carbon for microbial utilization was supported by exudation during photosynthesis.

Combined Effects of Chlorsulfuron and Bensulfuron-Methyl Herbicides on the Size of Microbial Biomass in a loamy sand soil

Combined Effects of Chlorsulfuron and Bensulfuron-Methyl Herbicides on the Size of Microbial Biomass in a loamy sand soil

Comparison of the effects of copper and lead on soil microbial biomass carbon and nitrogen in red soil

A laboratory incubation experiment was conducted to study the effect of copper as cupric sulfate (CuSO4.5H2O), and lead as lead acetate (Pb (OAc)2) on the size of the microbial biomass in red soil. The metals were applied, separately at six different levels: Cu at 50, 100, 200, 300, 400, and 600 μg·g−1 soil and Pb at 100, 200, 400, 600, 800, and 1000 μg·g−1 soil. In comparison to uncontaminated soil, the microbial biomass carbon (Cmic) and biomass nitrogen (Nmic) decreased sharply in soils contaminated with Cu and Pb. The microbial biomass C:N ratio in the metal contaminated soil was observed to be considerably higher than that in untreated control. Between the two tested metals, Cu displayed greater biocidal effect on microbial biomass carbon and nitrogen than Pb, showing their relative toxicity in the order: Cu≫Pb.

The Influence of Synthetic Soil Conditioners on the Size of Soil Microbial Biomass in a Loamy Sand Soil

The Influence of Synthetic Soil Conditioners on the Size of Soil Microbial Biomass in a Loamy Sand Soil

A STUDY OF THE STRUCTURE AND METAL TOLERANCE OF THE SOIL MICROBIAL COMMUNITY SIX YEARS AFTER CESSATION OF SEWAGE SLUDGE APPLICATIONS

Changes in soil microbial community structure and development of metal tolerance as a result of past applications of unamended sewage sludge and metal-amended sewage sludge were found in soils of a long-term field experiment at Braunschweig, Germany. Both the rate of sewage sludge application and metal amendment affected the size and activity of the microbial biomass and had caused changes in microbial community structure as seen by differences in phospholipid fatty acid (PLFA) profiles. Past sewage sludge additions and metal amendment had an effect on the microbial respiratory response to 15 different C substrates, but both the magnitude and the direction of this response were substrate dependent. Differences between the soils in the respiratory response to the substrates were therefore probably largely determined by differences in the composition of the microbial consortia utilizing the substrates. The level of metal tolerance of the soil bacterial community determined by the thymidine incorporation technique and that of the microbial consortium growing on glucose in situ (determined from respiration measurements) increased with the level of metal contamination of the soil. Metal tolerance measurements could identify the metal with the largest toxicity effect in this experiment with multiple metal-polluted sewage sludge.

The role of tree leaf mulch and nitrogen fertilizer on turfgrass soil quality

The influence of tree leaf amendment and N fertilization on soil quality in turfgrass environments was evaluated. Our objective was to assess changes in soil quality after additions of leaf materials and N fertilization by monitoring soil chemical and physical parameters, microbial biomass and soil enzymes. Established perennial ryegrass (Lolium perenne) plots were amended annually with maple (Acer spp.) leaves at three different rates (0, 2240, and 4480 kg ha–1 year–1) and treated with three nitrogen rates (0, 63, and 126 kg N ha–1 year–1). Tree leaf mulching did not significantly affect water infiltration or bulk density. However, trends in the data suggest increased infiltration with increasing leaf application rate. Tree leaf mulching increased total soil C and N at 0–1.3 cm depth but not at 1.3–9.0 cm. Extracted microbial phospholipid, an indicator of microbial biomass size, ranged from 28 to 68 nmol phospholipid g–1 soil at the 1.3–9.0 cm depth. The activity of β-glucosidase estimated on samples from 0–1.3 cm and 1.3–9.0 cm depths, and dehydrogenase activity estimated on samples from 1.3–9.0 cm were significantly increased by leaf mulching and N fertilizer application. Changes in microbial community composition, as indicated by phospholipid fatty acid methyl ester analysis, appear to be due to seasonal variations and did not reflect changes due to N or leaf amendment treatments. There were no negative effects of tree leaf mulching into turfgrass and early data suggest this practice will improve soil chemical, physical, and biological structure.