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Microbial Biomass (microbial + biomass)
Kinds of Microbial Biomass Terms modified by Microbial Biomass Selected AbstractsOrganic matter quality of a forest soil subjected to repeated drying and different re-wetting intensitiesEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2010A. Schmitt Extended drought periods followed by heavy rainfall may increase in many regions of the Earth, but the consequences for the quality of soil organic matter and soil microbial communities are poorly understood. Here, we investigated the effect of repeated drying and re-wetting on microbial communities and the quality of particulate and dissolved organic matter in a Haplic Podzol from a Norway spruce stand. After air-drying, undisturbed soil columns were re-wetted at different intensities (8, 20 and 50 mm per day) and time intervals, so that all treatments received the same amount of water per cycle (100 mm). After the third cycle, SOM pools of the treatments were compared with those of non-dried control columns. Lignin phenols were not systematically affected in the O horizons by the treatments whereas fewer lignin phenols were found in the A horizon of the 20- and 50-mm treatments. Microbial biomass and the ratio of fungi to bacteria were generally not altered, suggesting that most soil microorganisms were well adapted to drying and re-wetting in this soil. However, gram-positive bacteria and actinomycetes were reduced whereas gram-negative bacteria and protozoa were stimulated by the treatments. The increase in the (cy 17: 0 + cy 19: 0)/(16:1,7c + 18:1,7c) ratio indicates physiological or nutritional stress for the bacterial communities in the O, A and B horizons with increasing re-wetting intensity. Drying and re-wetting reduced the amount of hydrolysable plant and microbial sugars in all soil horizons. However, CO2 and dissolved organic carbon fluxes could not explain these losses. We postulate that drying and re-wetting triggered chemical alterations of hydrolysable sugar molecules in organic and mineral soil horizons. [source] Functional microbial community response to nutrient pulses by artificial groundwater recharge practice in surface soils and subsoilsFEMS MICROBIOLOGY ECOLOGY, Issue 3 2010Kirsten Schütz Abstract Subsurface microorganisms are essential constituents of the soil purification processes associated with groundwater quality. In particular, soil enzyme activity determines the biodegradation of organic compounds passing through the soil profile. Transects from surface soil to a depth of 3.5 m were investigated for microbial and chemical soil characteristics at two groundwater recharge sites and one control site. The functional diversity of the microbial community was analyzed via the activity of eight enzymes. Acid phosphomonoesterase was dominant across sites and depths, followed by l -leucine aminopeptidase and ,-glucosidase. Structural [e.g. phospholipid fatty acid (PLFA) pattern] and functional microbial diversities were linked to each other at the nonwatered site, whereas amendment with nutrients (DOC, NO3,) by flooding uncoupled this relationship. Microbial biomass did not differ between sites, whereas microbial respiration was the highest at the watered sites. Hence, excess nutrients available due to artificial groundwater recharge could not compensate for the limitation by others (e.g. phosphorus as assigned by acid phosphomonoesterase activity). Instead, at a similar microbial biomass, waste respiration via overflow metabolism occurred. In summary, ample supply of carbon by flooding led to a separation of decomposition and microbial growth, which may play an important role in regulating purification processes during groundwater recharge. [source] Microbial biomass in arable soils of Germany during the growth period of annual cropsJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 6 2008Rolf Nieder Abstract Results from several field studies involving numerous measurements were used to describe the change of soil microbial biomass C (Cmic) and N (Nmic) during the growth period of annual crops (years 1988,1992, 1994, 1995) under the temperate climatic conditions of central Europe. The data were taken from our own investigations as well as from the literature. Only studies with at least eight measurements on one plot during the growth period were used. The total number of farms (cash crop,production farms) was 7, that of experimental plots was 15. The evaluation of these results through regression analysis demonstrated that Cmic and Nmic from the beginning of a year increased only slightly until summer and subsequently decreased until autumn to their initial levels. This increase on an average corresponded to a C assimilation of approx. 100,kg ha,1 and an N immobilization of approx. 20,kg ha,1 (30,cm),1. The increase in Nmic alone could not explain N immobilization rates frequently observed in different studies using 15N-labeled fertilizers. Most of the labeled N that was immobilized (>50,kg N ha,1) might have accumulated in the matrix of soil organic matter (SOM). Therefore, the changes in microbial biomass may be of less importance for changes in soil N storage as frequently assumed. [source] Microbial biomass and activity under oxic and anoxic conditions as affected by nitrate additionsJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 1 2006Jens Dyckmans Abstract Soil microbial activity, biomass, and community structure were examined during the transition from oxic to anoxic conditions after the addition of glucose and with or without nitrate addition. In two sets of treatments, samples were incubated for up to 35 d in closed ampoules either aerobically until oxygen was depleted or anoxically throughout the experiment. Heat-flow rate was monitored to indicate microbial activity. Microbial biomass and community structure were measured by adenylate and phospholipid fatty acid (PFLA) content, and adenylate energy charge (AEC) was used to monitor the physiological status of the microbial biomass. Microbial activity was highest under oxic conditions and abruptly decreased under anoxic conditions. Activity peaks were observed after about 9 d of anoxic conditions probably triggered by increased nutrient availability from dying microbial biomass, but these peaks were smaller after initial oxic incubation or nitrate addition. Microbial biomass was unchanged under oxic conditions but decreased under anoxic conditions. Most surviving microbes switched into dormancy. Changes in the microbial-population structure were small and occurred only after 9 d of anoxic incubation. The results show that the nutrient status and the availability of electron acceptors such as nitrate were important factors ruling the direction and the extent of shifts in the microbial activity and community structures due to anoxic conditions. Mikrobielle Biomasse und Aktivität unter oxischen und anoxischen Bedingungen in Abhängigkeit von Nitratzugabe Untersucht wurden Aktivität, Menge und Zusammensetzung der mikrobiellen Biomasse im Übergang von oxischen zu anoxischen Bedingungen in Bodenproben nach Zugabe von Glucose sowie mit und ohne Nitratzugabe. Bodenproben wurden bis zu 35 Tage in geschlossenen Gefäßen entweder oxisch bis zum Verbrauch des Sauerstoffs oder von Beginn an anoxisch inkubiert. Dabei wurde der Wärmefluss als Indikator für die mikrobielle Aktivität gemessen. Menge und Zusammensetzung der mikrobiellen Biomasse wurden über die Gehalte an Adenylaten und Phospholipidfettsäuren bestimmt. Der ,Adenylate Energy Charge" (AEC) wurde genutzt, um den physiologischen Status der mikrobiellen Biomasse zu bestimmen. Die mikrobielle Aktivität war unter oxischen Bedingungen am höchsten und ging unter anoxischen Bedingungen drastisch zurück. Aktivitätspeaks wurden nach etwa 10 Tagen anoxischer Inkubation beobachtet und waren vermutlich verursacht durch ein erhöhtes Nährstoffangebot aus der abgestorbenen Biomasse. Diese Peaks waren geringer nach vorhergehender oxischer Inkubation bzw. nach Nitratzugabe. Die mikrobielle Biomasse war unter oxischen Bedingungen unverändert, nahm aber unter anoxischen Bedingungen ab, die meisten überlebenden Mikroben waren dabei dormant. Änderungen in der mikrobiellen Gesellschaft traten nur in geringem Umfang und erst nach 9 Tagen anoxischer Inkubation auf. Unsere Ergebnisse zeigen, dass das Nährstoffangebot und die Verfügbarkeit von Elektronenakzeptoren wie z.,B. Nitrat wichtige Steuergrößen für Richtung und Ausmaß von Veränderungen in der mikrobiellen Aktivität und Zusammensetzung unter anoxischen Bedingungen sind. [source] Microbial biomass and activity in composts of different composition and ageJOURNAL OF PLANT NUTRITION AND SOIL SCIENCE, Issue 5 2004Andreas Gattinger Abstract The aim of this study was to perform a comparison of microbial activity and biomass in biowaste (BWC), yard waste (YWC), and cattle-manure composts (CMC) of different age. Two different methods for either biomass (microbial C following fumigation-extraction and microbial lipid phosphate) or activity measurements (CO2 -production rate and fluorescein diacetate hydrolysis) provided comparable information, as judged from their strong correlation. Microbial biomass and activity declined with time in all composts. Microbial biomass C was strongly correlated with microbial activity but was even stronger correlated with pH. CMC proved to be very distinct from the two other compost types by having the highest biomass and the lowest specific activity (i.e., activity per unit biomass). The microbiological properties analyzed allow us to discriminate among different compost types, helping to assign their potential applications. Mikrobielle Biomasse und Aktivität in Komposten unterschiedlicher Zusammensetzung und unterschiedlichen Alters Ziel dieser Studie war es, Bioabfall-, Grünabfall- und Rindermistkomposte unterschiedlicher Altersgruppen hinsichtlich ihrer mikrobiellen Aktivität und Biomasse zu vergleichen. Die zwei unterschiedlichen Methoden für die Bestimmung der mikrobiellen Biomasse (Cmik mittels Fumigation-Extraktion und Lipidphosphat) und Aktivität (CO2 -Produktion und Hydrolyse von Fluoresceindiacetat) lieferten jeweils vergleichbare Aussagen, die Parameter waren eng miteinander korreliert. Mikrobielle Biomasse und Aktivität nahmen mit zunehmendem Alter in den einzelnen Komposten ab. Mikrobieller C war eng mit der mikrobiellen Aktivität korreliert, jedoch war die Korrelation zwischen dem pH-Wert und Cmik stärker ausgeprägt. Die größte mikrobielle Biomasse und die niedrigste spezifische Aktivität (Aktivität pro Biomasseeinheit) wurden im CMC festgestellt, wodurch sich dieser Kompost deutlich von den beiden anderen Komposten unterschied. Die in dieser Untersuchung beschriebenen mikrobiellen Eigenschaften ermöglichen es, zwischen Komposten unterschiedlicher Zusammensetzung zu unterscheiden und daraus mögliche Anwendungsbereiche für Komposte abzuleiten. [source] Carbon and nutrient limitation of soil microorganisms and microbial grazers in a tropical montane rain forestOIKOS, Issue 6 2010Valentyna Krashevska We investigated the role of carbon, nitrogen and phosphorus as limiting factors of microorganisms and microbial grazers (testate amoebae) in a montane tropical rain forest in southern Ecuador. Carbon (as glucose), nitrogen (as NH4NO3) and phosphorus (as NaH2PO4) were added separately and in combination bimonthly to experimental plots for 20 months. By adding glucose and nutrients we expected to increase the growth of microorganisms as the major food resource of testate amoebae. The response of microorganisms to experimental treatments was determined by analysing microbial biomass (SIR), fungal biomass and microbial community composition as measured by phospholipid fatty acids (PLFAs). We hypothesized that the response of testate amoebae is closely linked to that of microorganisms. Carbon addition strongly increased ergosterol concentration and, less pronounced, the amount of linoleic acid as fungal biomarker, suggesting that saprotrophic fungi are limited by carbon. Microbial biomass and ergosterol concentrations reached a maximum in the combined treatment with C, N and P indicating that both N and P also were in short supply. In contrast to saprotrophic fungi and microorganisms in total, testate amoebae suffered from the addition of C and reached maximum density by the addition of N. The results indicate that saprotrophic fungi in tropical montane rain forests are mainly limited by carbon whereas gram positive and negative bacteria benefit from increased availability of P. Testate amoebae suffered from increased dominance of saprotrophic fungi in glucose treatments but benefited from increased supply of N. The results show that testate amoebae of tropical montane rain forests are controlled by bottom,up forces relying on specific food resources rather than the amount of bacterial biomass with saprotrophic fungi functioning as major antagonists. Compared to temperate systems microbial food webs in tropical forests therefore may be much more complex than previously assumed with trophic links being rather specific and antagonistic interactions overriding trophic interactions. [source] Detection of microbial biomass by intact polar membrane lipid analysis in the water column and surface sediments of the Black SeaENVIRONMENTAL MICROBIOLOGY, Issue 10 2009Florence Schubotz Summary The stratified water column of the Black Sea produces a vertical succession of redox zones, stimulating microbial activity at the interfaces. Our study of intact polar membrane lipids (IPLs) in suspended particulate matter and sediments highlights their potential as biomarkers for assessing the taxonomic composition of live microbial biomass. Intact polar membrane lipids in oxic waters above the chemocline represent contributions of bacterial and eukaryotic photosynthetic algae, while anoxygenic phototrophic bacteria and sulfate-reducing bacteria comprise a substantial amount of microbial biomass in deeper suboxic and anoxic layers. Intact polar membrane lipids such as betaine lipids and glycosidic ceramides suggest unspecified anaerobic bacteria in the anoxic zone. Distributions of polar head groups and core lipids show planktonic archaea below the oxic zone; methanotrophic archaea are only a minor fraction of archaeal biomass in the anoxic zone, contrasting previous observations based on the apolar derivatives of archaeal lipids. Sediments contain algal and bacterial IPLs from the water column, but transport to the sediment is selective; bacterial and archaeal IPLs are also produced within the sediments. Intact polar membrane lipid distributions in the Black Sea are stratified in accordance with geochemical profiles and provide information on vertical successions of major microbial groups contributing to suspended biomass. This study vastly extends our knowledge of the distribution of complex microbial lipids in the ocean. [source] Microbial communities in a porphyry copper tailings impoundment and their impact on the geochemical dynamics of the mine wasteENVIRONMENTAL MICROBIOLOGY, Issue 2 2007Nouhou Diaby Summary The distribution and diversity of acidophilic bacteria of a tailings impoundment at the La Andina copper mine, Chile, was examined. The tailings have low sulfide (1.7% pyrite equivalent) and carbonate (1.4% calcite equivalent) contents and are stratified into three distinct zones: a surface (0-70-80 cm) ,oxidation zone' characterized by low-pH (2.5,4), a ,neutralization zone' (70,80 to 300,400 cm) and an unaltered ,primary zone' below 400 cm. A combined cultivation-dependent and biomolecular approach (terminal restriction enzyme fragment length polymorphism and 16S rRNA clone library analysis) was used to characterize the indigenous prokaryotic communities in the mine tailings. Total cell counts showed that the microbial biomass was greatest in the top 125 cm of the tailings. The largest numbers of bacteria (109 g,1 dry weight of tailings) were found at the oxidation front (the junction between the oxidation and neutralization zones), where sulfide minerals and oxygen were both present. The dominant iron-/sulfur-oxidizing bacteria identified at the oxidation front included bacteria of the genus Leptospirillum (detected by molecular methods), and Gram-positive iron-oxidizing acidophiles related to Sulfobacillus (identified both by molecular and cultivation methods). Acidithiobacillus ferrooxidans was also detected, albeit in relatively small numbers. Heterotrophic acidophiles related to Acidobacterium capsulatum were found by molecular methods, while another Acidobacterium -like bacterium and an Acidiphilium sp. were isolated from oxidation zone samples. A conceptual model was developed, based on microbiological and geochemical data derived from the tailings, to account for the biogeochemical evolution of the Piuquenes tailings impoundment. [source] Flux and turnover of fixed carbon in soil microbial biomass of limed and unlimed plots of an upland grassland ecosystemENVIRONMENTAL MICROBIOLOGY, Issue 4 2005J. Ignacio Rangel-Castro Summary The influence of liming on rhizosphere microbial biomass C and incorporation of root exudates was studied in the field by in situ pulse labelling of temperate grassland vegetation with 13CO2 for a 3-day period. In plots that had been limed (CaCO3 amended) annually for 3 years, incorporation into shoots and roots was, respectively, greater and lower than in unlimed plots. Analysis of chloroform-labile C demonstrated lower levels of 13C incorporation into microbial biomass in limed soils compared to unlimed soils. The turnover of the recently assimilated 13C compounds was faster in microbial biomass from limed than that from unlimed soils, suggesting that liming increases incorporation by microbial communities of root exudates. An exponential decay model of 13C in total microbial biomass in limed soils indicated that the half-life of the tracer within this carbon pool was 4.7 days. Results are presented and discussed in relation to the absolute values of 13C fixed and allocated within the plant,soil system. [source] Degradation of chlorpyrifos, fenamiphos, and chlorothalonil alone and in combination and their effects on soil microbial activityENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2002Brajesh Kumar Singh Abstract The effects of repeated application and of combinations of pesticides on their degradation rates in soil and on some soil microbial properties were studied. Repeated application of chlorpyrifos did not modify its degradation rate, whereas repeated applications of fenamiphos and chlorothalonil suppressed their own rates of degradation. When applied in combination, the presence of chlorothalonil reduced the degradation rate of both chlorpyrifos and fenamiphos, and the half-life of chlorothalonil was extended in the presence of chlorpyrifos. The dynamics of residues of the major metabolites of the different compounds were also affected by the pesticide combinations and, particularly, by the presence of chlorothalonil. The measured soil microbial parameters (enzyme activities and total microbial biomass) were stable in the pesticide-free control soils throughout the 90-d incubation period, but they were all adversely affected by the presence of chlorothalonil in the soil. The effects from fenamiphos or chlorpyrifos on the soil microbial characteristics were either very small or insignificant. [source] Temporal and shrub adaptation effect on soil microbial functional diversity in a desert systemEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 6 2009V. Saul-Tcherkas Summary The Negev Desert is characterized by spatial and temporal patterns of resource distribution, in which soil biota are considered to be among the most sensitive biological characteristics, easily influenced by changes related to soil and abiotic factors. Soil water availability and organic matter are among the most important factors, acting as triggers that determine the length of the period of activity. The main source of organic matter in this xeric environment is input from annual and perennial shrubs. In order to persist and propagate in this xeric environment, the plants have developed different ecophysiological adaptations (e.g. the excretion of salt (Reaumuria negevensis) and chemical compounds (Artemisia sieberi) via the leaves). We found that the values of soil moisture obtained for soil samples collected in the vicinity of R. negevensis were larger than for samples collected in the vicinity of Noaea mucronata and A. sieberi and in the open area. The maximum values of CO2 evolution, microbial biomass and Shannon index (H,) were obtained for the samples collected from the vicinity of N. mucronata. Therefore, we assume that the vicinity of N. mucronata afforded the best conditions for the soil bacterial community. In the Negev Desert, we also found that water availability and pulses of rain compared with frequent rainfall influenced CO2 evolution, microbial biomass, qCO2 and the Shannon index (H,). The differences in water amount and availability between the two rainy seasons caused larger values in most of the properties during the first four seasons (December 2005,November 2006) compared with the last four seasons (December 2006,November 2007) for most of the samples. [source] Organic carbon additions: effects on soil bio-physical and physico-chemical propertiesEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 2 2009A. Bhogal Summary The effects of organic carbon (OC) additions from farm manures and crop residues on selected soil bio-physical and physico-chemical properties were measured at seven experimental sites, on contrasting soil types, with a history of repeated applications of farm manure or differential rates of inorganic fertilizer nitrogen (N). Repeated (> 7 years annual additions) and relatively large OC inputs (up to 65 t OC ha,1) were needed to produce measurable changes in soil properties, particularly physical properties. However, over all the study sites, there was a positive relationship between OC inputs and changes in total soil OC and ,light' fraction OC (LFOC), with LFOC providing a more sensitive indicator of changes in soil organic matter status. Total soil OC increased by an average of 3% for every 10 t ha,1 manure OC applied, whereas LFOC increased by c. 14%. The measured soil OC increases were equivalent to c. 23% of the manure OC applied (up to 65 t OC ha,1 applied over 9 years) and c. 22% of the crop residue OC applied (up to 32 t OC ha,1 over 23 years). The manure OC inputs (but not crop residue OC inputs) increased topsoil porosity and plant available water capacity, and decreased bulk density by 0.6%, 2.5% and 0.5% with every 10 t ha,1 manure OC applied, respectively. Both OC sources increased the size of the microbial biomass (11% increase in biomass C with 10 t OC ha,1 input), but only manure OC increased its activity (16% increase in the soil respiration rate with 10 t OC ha,1 input). Likewise, the potentially mineralizable N pool only increased with manure N inputs (14% increase with 1 t manure total N ha,1). However, these soil quality benefits need to be balanced with any potential environmental impacts, such as excessive nutrient accumulation, increased nitrate leaching and phosphorus losses and gaseous emissions to the atmosphere. [source] Size and phenotypic structure of microbial communities within soil profiles in relation to different playing areas on a UK golf courseEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2008M. D. Bartlett Summary Amenity turf accounts for up to 4% of land-use in urban areas, providing key refuges for both above- and below-ground biodiversity. Golf courses occupy the largest surface area of all sports facilities; however, only a limited amount of microbial ecology has been carried out to investigate differences in the size and structure of microbial communities of the soil. The soil microbial community is a key agent in nutrient cycling and delivery of other ecosystem goods and services; however, there has been little work focused on amenity turf ecosystems in the UK. A study of soil microbial community size and structure, on the range of playing areas maintained for the game of golf at a single golf course in relation to depth through the soil profile, was carried out. Soil from different playing areas showed significant differences in the size (measured using chloroform fumigation extraction) of the microbial community (P < 0.01), with a greater concentration of microbial biomass at 0,75 mm from the surface, compared with deeper zones (P < 0.01). Principal component analysis of phospholipid fatty acid (PLFA) biomarkers indicated that the community structure was significantly different at 0,75 mm from the surface on all areas of the golf course investigated (P < 0.05, in all cases). The PLFA biomarkers consistently associated with such discrimination were 16:0 and 18:1,9 c. These findings suggest that there is a consistently larger and similarly structured microbial community associated with the surface thatch layer, commonly found in amenity turf. [source] Calibration model of microbial biomass carbon and nitrogen concentrations in soils using ultraviolet absorbance and soil organic matterEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2008X. Xu Summary There is a need for a rapid, simple and reliable method of determining soil microbial biomass (SMB) for all soils because traditional methods are laborious. Earlier studies have reported that SMB-C and -N concentrations in grassland and arable soils can be estimated by measurement of UV absorbance in soil extracts. However, these previous studies focused on soils with small soil organic matter (SOM) contents, and there was no consideration of SOM content as a covariate to improve the estimation. In this study, using tropical and temperate forest soils with a wide range of total C (5,204 mg C g,1 soil) and N (1,12 mg N g,1 soil) contents and pH values (4.1,5.9), it was found that increase in UV absorbance of soil extracts at 280 nm (UV280) after fumigation could account for 92,96% of the variance in estimates of the SMB-C and -N concentrations measured by chloroform fumigation and extraction (P < 0.001). The data were combined with those of earlier workers to calibrate UV-based regression models for all the soils, by taking into account their varying SOM content. The validation analysis of the calibration models indicated that the SMB-C and -N concentrations in the 0,5 cm forest soils simulated by using the increase in UV280 and SOM could account for 86,93% of the variance in concentrations determined by chloroform fumigation and extraction (P < 0.001). The slope values of linear regression equations between measured and simulated values were 0.94 ± 0.03 and 0.94 ± 0.04, respectively, for the SMB-C and -N. However, simulation using the regression equations obtained by using only the data for forest profile soils gave less good agreement with measured values. Hence, the calibration models obtained by using the increase in UV280 and SOM can give a rapid, simple and reliable method of determining SMB for all soils. [source] MIOR: an individual-based model for simulating the spatial patterns of soil organic matter microbial decompositionEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2007D. Masse Summary An individual-based model, called MIOR, was designed to assess hypotheses on the effect of the spatial distribution of organic matter and microbial decomposers on soil carbon and nitrogen dynamics. Two main types of object were defined to represent the decomposers and the soil organic substrates. All these objects were positioned in a 3D space. The exchange of carbon and nitrogen between these various entities was simulated. Two scenarios were tested according to the degrees of clustering of organic matter and of microorganisms. The results of simulations highlighted the effect of the ratio of accessible organic carbon to microbial carbon on the dynamics of microbial biomass and CO2 release. This ratio was determined by the number of contacts between one object representing the microbial decomposers and the surrounding objects representing the organic substrates. MIOR: modèle individu-centré de simulation de la distribution spatiale des processus microbiens de la décomposition des matières organiques dans les sols Résumé Un modèle individu-centré, appelé MIOR, a été conçu pour tester les hypothèses concernant les effets de la distribution spatiale des matières organiques et des microdécomposeurs dans les sols sur la dynamique du carbone et de l'azote minéral. Deux principaux types d'objets ont été définis représentant les microorganismes décomposeurs et les substrats organiques. Ces objets sont positionnés dans une espace à trois dimensions. Les échanges de carbone et d'azote entre ces deux entités sont simulés. Deux scénarios sont testés selon des niveaux d'agrégation des microorganismes et celui des matières organiques. Les résultats des simulations mettent en avant l'importance de la quantité de carbone organique accessible par unité de carbone microbien sur la dynamique de la biomasse microbienne et du CO2 dégagé. Cette quantité est déterminée par le nombre de contacts entre un objet représentant des microdécomposeurs et des objets qui l'entourent représentant les substrats organiques. [source] Estimating diesel degradation rates from N2, O2 and CO2 concentration versus depth data in a loamy sandEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2007J. Van De Steene Summary The degradation rate of the pollutant is often an important parameter for designing and maintaining an active treatment system or for determining the rate of natural attenuation. A quasi-steady-state gas transport model based on Fick's law with a correction term for advective flux, for estimating diesel degradation rates from N2, O2 and CO2 concentration versus depth data, was evaluated in a laboratory column study. A loamy sand was spiked with diesel fuel at 0, 1000, 5000 and 10 000 mg kg,1 soil (dry weight basis) and incubated for 15 weeks. Soil gas was sampled weekly at 6 selected depths in the columns and analysed for O2, CO2 and N2 concentrations. The agreement between the measured and the modelled concentrations was good for the untreated soil (R2= 0.60) and very good for the soil spiked with 1000 mg kg,1 (R2= 0.96) and 5000 mg kg,1 (R2= 0.97). Oxygen consumption ranged from ,0.15 to ,2.25 mol O2 m,3 soil day,1 and CO2 production ranged from 0.20 to 2.07 mol CO2 m,3 soil day,1. A significantly greater mean O2 consumption (P < 0.001) and CO2 production (P < 0.005) over time was observed for the soils spiked with diesel compared with the untreated soil, which suggests biodegradation of the diesel substrate. Diesel degradation rates calculated from respiration data were 1.5,2.1 times less than the change in total petroleum hydrocarbon content. The inability of this study to correlate respiration data to actual changes in diesel concentration could be explained by volatilization, long-term sorption of diesel hydrocarbons to organic matter and incorporation of diesel hydrocarbons into microbial biomass, aspects of which require further investigation. [source] Effects of glucose and rhizodeposits (with or without cysteine-S) on immobilized- 35S, microbial biomass- 35S and arylsulphatase activity in a calcareous and an acid brown soilEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2004O. Dedourge Summary Our aim was to study the effects of C (as glucose and artificial rhizodeposits) on S immobilization, in relation to microbial biomass-S and soil arylsulphatase (ARS) activity, in contrasting soils (a calcareous and an acid brown soil). The glucose-C and artificial rhizodeposit-C with or without cysteine were added at six rates (0, 100, 200, 400, 600 and 800 mg kg,1 soil) to the two soils and then incubated with Na235SO4 for 1 week prior to analysis. The percentages of 35S immobilized increased when C as glucose and rhizodeposit (without cysteine) were added to both soils. With cysteine-containing rhizodeposit, the percentages of 35S immobilized remained relatively stable (23.5% to 29.9%) in the calcareous soil, but decreased in the acid brown soil (52.7% to 31.5%). For both soils, cysteine-containing rhizodeposit additions showed no significant correlation between immobilized- 35S and microbial biomass- 35S, suggesting that microorganisms immobilized cysteine-S preferentially instead of 35S from the tracer (Na235SO4). In the calcareous soil, a positive and significant correlation was found between ARS activity and microbial biomass- 35S (r = 0.85, P < 0.05) when glucose was added. We also saw this correlation in the acid brown soil when rhizodeposit-C without cysteine was added (r = 0.90, P < 0.05). Accordingly, the results showed the presence of extracellular arylsulphatase activity of 48.7 mg p -nitrophenol kg,1 soil hour,1 in the calcareous soil and of 27.0 mg p -nitrophenol kg,1 soil hour,1 in the acid brown soil. [source] Importance of rhizodeposition in the coupling of plant and microbial productivityEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2003Eric Paterson Summary Plant roots influence the biological, chemical and physical properties of rhizosphere soil. These effects are a consequence of their growth, their activity and the exudation of organic compounds from them. In natural ecosystems, the linkages between inputs of carbon from plants and microbial activity driven by these inputs are central to our understanding of nutrient cycling in soil and the productivity of these systems. This coupling of plant and microbial productivity is also of increasing importance in agriculture, where the shift towards low-input systems increases the dependence of plant production on nutrient cycling, as opposed to fertilizers. This review considers the processes by which plants can influence the cycling of nutrients in soil, and in particular the importance of organic inputs from roots in driving microbially mediated transformations of N. This coupling of plant inputs to the functioning of the microbial community is beneficial for acquisition of N by plants, particularly in low-input systems. This occurs through stimulation of microbes that produce exoenzymes that degrade organic matter, and by promoting cycling of N immobilized in the microbial biomass via predation by protozoa. Also, plants increase the cycling of N by changes in exudation in response to nitrogen supply around roots, and in response to browsing by herbivores. Plants can release compounds in exudates that directly affect the expression of genes in microbes, and this may be an important way of controlling their function to the benefit of the plant. [source] Fate of microbial residues in sandy soils of the South African Highveld as influenced by prolonged arable croppingEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2002W. Amelung Summary Long-term cultivation of former grassland soils results in a significant decline of both living and dead microbial biomass. We evaluated the effect of duration of cropping on the preservation of fungal and bacterial residues in the coarse-textured soils of the South African Highveld. Composite samples were taken from the top 20 cm of soils (Plinthustalfs) that have been cropped for periods varying from 0 to 98 years in each of three different agro-ecosystems in the Free State Province. Amino sugars were determined as markers for the microbial residues in bulk soil and its particle-size fractions. Long-term cultivation reduced N in the soil by 55% and the contents of amino sugars by 60%. Loss rates of amino sugars followed bi-exponential functions, suggesting that they comprised both labile and stable fractions. With increased duration of cropping the amino sugars attached to silt dissipated faster than those associated with the clay. This dissipation was in part because silt was preferentially lost through erosion, while clay particles (and their associated microbial residues) remained. Erosion was not solely responsible for the reduction in amino sugar concentrations, however. Bacterial amino sugars were lost in preference to fungal ones as a result of cultivation, and this effect was evident in both silt- and clay-sized separates. This shift from fungal to bacterial residues was most pronounced within the first 20 years after converting the native grassland to arable cropland, but continued after 98 years of cultivation. [source] Distribution of microbial biomass and phospholipid fatty acids in Podzol profiles under coniferous forestEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 4 2000H. Fritze Summary Microbial-derived phospholipid fatty acids (PLFAs) can be used to characterize the microbial communities in soil without the need to isolate individual fungi and bacteria. They have been used to assess microbial communities of humus layers under coniferous forest, but nothing is known of their distribution in the deeper soil. To investigate the vertical distribution we sampled nine Podzol profiles on a 100-m-long transect in a coniferous forest and analysed for their microbial biomass and PLFA pattern to a depth of 0.4 m. The transect covered a fertility gradient from Vaccinium vitis-idaea forest site type to Vaccinium myrtillus forest site type. The cores were divided into humus (O) and eluvial (E) layers and below that into 10-cm sections and designated as either illuvial (B) or parent material (C), or as a combination (BC). Two measures of microbial biomass analyses were applied: substrate-induced respiration (SIR) to determine microbial biomass C (Cmic), and the sum of the extracted microbial-derived phospholipid fatty acids (totPLFA). The soil fertility had no effect on the results. The Cmic correlated well with totPLFA (r=,0.86). The microbial biomass decreased with increasing depth. In addition the PLFA pattern changed with increased depth as assessed with principal component analysis, indicating a change in the microbial community structure. The composition of the PLFAs in the O layer differed from that in the E layer and both differed from the upper part of the B layer and from the rest of the BC layers. The deeper parts of the B layer (BC1, BC2 and BC3) were similar to one other. The O layer had more 18:2,6, a PLFA indicator of fungi, whereas the E layer contained relatively more of the PLFAs 16:1,9, 18:1,7 and cy19:0 common in gram-negative bacteria. With increased depth the relative amount of 10Me18:0, the PLFA indicator for actinomycetes, increased. We conclude that the PLFA method is a promising discriminator between the microbial community structures of the horizons in Podzols. [source] Functional microbial community response to nutrient pulses by artificial groundwater recharge practice in surface soils and subsoilsFEMS MICROBIOLOGY ECOLOGY, Issue 3 2010Kirsten Schütz Abstract Subsurface microorganisms are essential constituents of the soil purification processes associated with groundwater quality. In particular, soil enzyme activity determines the biodegradation of organic compounds passing through the soil profile. Transects from surface soil to a depth of 3.5 m were investigated for microbial and chemical soil characteristics at two groundwater recharge sites and one control site. The functional diversity of the microbial community was analyzed via the activity of eight enzymes. Acid phosphomonoesterase was dominant across sites and depths, followed by l -leucine aminopeptidase and ,-glucosidase. Structural [e.g. phospholipid fatty acid (PLFA) pattern] and functional microbial diversities were linked to each other at the nonwatered site, whereas amendment with nutrients (DOC, NO3,) by flooding uncoupled this relationship. Microbial biomass did not differ between sites, whereas microbial respiration was the highest at the watered sites. Hence, excess nutrients available due to artificial groundwater recharge could not compensate for the limitation by others (e.g. phosphorus as assigned by acid phosphomonoesterase activity). Instead, at a similar microbial biomass, waste respiration via overflow metabolism occurred. In summary, ample supply of carbon by flooding led to a separation of decomposition and microbial growth, which may play an important role in regulating purification processes during groundwater recharge. [source] Reversible transition between active and dormant microbial states in soilFEMS MICROBIOLOGY ECOLOGY, Issue 2-3 2001John Stenström Abstract The rate of respiration obtained in the substrate-induced respiration (SIR) method can be divided into the respiration rate of growing (r) and non-growing (K) microorganisms. The fraction of r is generally small (5,20%) in soils with no recent addition of substrates, but can be 100% in soils with high substrate availability. This suggests that substrate availability determines the proportion of biomass between these groups, and implies that transitions between them can take place reversibly. These hypotheses were tested by adding three different amounts of glucose which induced first-order, zero-order, and growth-associated respiration kinetics to three soils at four pre-incubation times (4, 12, 27, and 46 days) before the SIR measurement. An abiotic flush of CO2 in the SIR measurement was detected and corrected for before data analysis. Accumulated CO2 -C over 4 days after glucose addition, corrected for the respiration in unamended controls, corresponded to 41,50% mineralization of the glucose-C, and the relative amount mineralized by each soil was independent of the glucose amount added. The high glucose concentration gave an increased SIR, which reverted to the initial value within 27,46 days. In a specific sample, the maximum respiration rate induced during the pre-incubation, and the amount of organisms transformed from the K to the r state, as quantified in respiration rate units in the SIR measurement, were identical to each other, and these parameters were also highly correlated to the initial glucose concentration. The K,r transition was very fast, probably concurrent with the instantaneous increase in the respiration rate obtained by the glucose amendment. Thereafter, a slow first-order back-transition from the r to the K state ensued, with half-lives of 12, 23, and 70 days for the three soils. The results suggest the existence of community-level controls by which growth within or of the whole biomass is inhibited until it has been completely transformed into the r state. The data also suggest that the microbial specific activity is not related to the availability of exogenous substrate in a continuous fashion, rather it responds as a sharp transition between dormant and fully active. Furthermore, the inherent physiological state of the microbial biomass is strongly related to its history. It is proposed that the normal dynamics of the soil microbial biomass is an oscillation between active and dormant physiological states, while significant growth occurs only at substantial substrate amendment. [source] Organic matter availability structures microbial biomass and activity in a Mediterranean streamFRESHWATER BIOLOGY, Issue 10 2009JOAN ARTIGAS Summary 1. We compared microbial biomass (bacteria, fungi, algae) and the activity of extracellular enzymes used in the decomposition of organic matter (OM) among different benthic substrata (leaves, coarse and fine substrata) over one hydrological year in a Mediterranean stream. 2. Microbial heterotrophic biomass (bacteria plus fungi) was generally higher than autotrophic biomass (algae), except during short periods of high light availability in the spring and winter. During these periods, sources of OM shifted towards autochthonous sources derived mainly from algae, which was demonstrated by high algal biomass and peptidase activity in benthic communities. 3. Heterotrophic activity peaked in the autumn. Bacterial and fungal biomass increased with the decomposition of cellulose and hemicellulose compounds from leaf material. Later, lignin decomposition was stimulated in fine (sand, gravel) and coarse (rocks, boulders and cobbles) substrata by the accumulation of fine detritus. 4. The Mediterranean summer drought provoked an earlier leaf fall. The resumption of the water flow caused the weathering of riparian soils and subsequently a large increase in dissolved organic carbon and nitrate, which led to growth of bacteria and fungi. [source] Effects of drying regime on microbial colonization and shredder preference in seasonal woodland wetlandsFRESHWATER BIOLOGY, Issue 3 2008MARTYN D. INKLEY Summary 1. Energy budgets of wetlands in temperate deciduous forests are dominated by terrestrially derived leaf litter that decays under different drying conditions depending on autumn precipitation. We compared decay rates and microbial colonization of maple leaves under different inundation schedules in a field experiment, and then conducted a laboratory study on shredder preference. In the field, litter bags either remained submerged (permanent), were moved to a dried part of the basin once and then returned (semi-permanent), or were alternated between wet and dry conditions for 8 weeks (temporary). 2. There was no difference in decay rates among treatments, but leaves incubated under permanent and semi-permanent conditions had higher fungal and bacterial biomass, and lower C : N ratios than those incubated under alternating drying and wetting conditions. 3. To determine the effects of these differences in litter nutritional quality on shredder preference, we conducted a laboratory preference test with larvae of leaf-shredding caddisflies that inhabit the wetland. Caddisflies spent twice as much time foraging on permanent and semi-permanent litter than on litter incubated under temporary conditions. 4. There is considerable variation among previous studies in how basin drying affects litter breakdown in wetlands, and no previous information on shredder preference. We found that frequent drying in a shallow wetland reduces the nutritional quality of leaf litter (lower microbial biomass and nitrogen content), and therefore preference by invertebrate shredders. These results suggest that inter-annual shifts in drying regime should alter detritus processing rates, and hence the mobilization of the energy and nutrients in leaf litter to the wetland food web. [source] Litter decomposition in a Cerrado savannah stream is retarded by leaf toughness, low dissolved nutrients and a low density of shreddersFRESHWATER BIOLOGY, Issue 8 2007J. F. GONÇALVES JR Summary 1. To assess whether the reported slow breakdown of litter in tropical Cerrado streams is due to local environmental conditions or to the intrinsic leaf characteristics of local plant species, we compared the breakdown of leaves from Protium brasiliense, a riparian species of Cerrado (Brazilian savannah), in a local and a temperate stream. The experiment was carried out at the time of the highest litter fall in the two locations. An additional summer experiment was conducted in the temperate stream to provide for similar temperature conditions. 2. The breakdown rates (k) of P. brasiliense leaves in the tropical Cerrado stream ranged from 0.0001 to 0.0008 day,1 and are among the slowest reported. They were significantly (F = 20.12, P < 0.05) lower than in the temperate stream (0.0046,0.0055). The maximum ergosterol content in decomposing leaves in the tropical Cerrado stream was 106 ,g g,1, (1.9% of leaf mass) measured by day 75, which was lower than in the temperate stream where maximum ergosterol content of 522 ,g g,1 (9.5% of leaf mass) was achieved by day 30. The ATP content, as an indicator of total microbial biomass, was up to four times higher in the tropical Cerrado than in the temperate stream (194.0 versus 49.4 nmoles g,1). 3. Unlike in the temperate stream, leaves in the tropical Cerrado were not colonised by shredder invertebrates. However, in none of the experiments did leaves exposed (coarse mesh bags) and unexposed (fine mesh bags) to invertebrates differ in breakdown rates (F = 1.15, P > 0.05), indicating that invertebrates were unable to feed on decomposing P. brasiliense leaves. 4. We conclude that the slow breakdown of P. brasiliense leaves in the tropical Cerrado stream was because of the low nutrient content in the water, particularly nitrate (0.05 mgN L,1), which slows down fungal activity and to the low density of invertebrates capable of using these hard leaves as an energy source. [source] The influence of below-ground herbivory and defoliation of a legume on nitrogen transfer to neighbouring plantsFUNCTIONAL ECOLOGY, Issue 2 2007E. AYRES Summary 1Both foliar and root herbivory can alter the exudation of carbon from plant roots, which in turn can affect nitrogen availability in the soil. However, few studies have investigated the effects of herbivory on N fluxes from roots, which can directly increase N availability in the soil and uptake by neighbouring plants. Moreover, the combined effects of foliar and root herbivory on N fluxes remains unexplored. 2We subjected the legume white clover (Trifolium repens L.) to defoliation (through clipping) and root herbivory (by an obligate root-feeding nematode, Heterodera trifolii Goggart) to examine how these stresses individually, and simultaneously, affected the transfer of T. repens -derived N to neighbouring perennial ryegrass (Lolium perenne L.) plants using 15N stable-isotope techniques. We also examined the effects of defoliation and root herbivory on the size of the soil microbial community and the growth response of L. perenne. 3Neither defoliation nor root herbivory negatively affected T. repens biomass. On the contrary, defoliation increased root biomass (34%) and total shoot production by T. repens (100%). Furthermore, defoliation resulted in a fivefold increase in T. repens -derived 15N recovered in L. perenne roots, and increased the size of the soil microbial biomass (77%). In contrast, root herbivory by H. trifolii slightly reduced 15N transfer from T. repens to L. perenne when T. repens root 15N concentration was included as a covariate, and root herbivory did not affect microbial biomass. Growth of L. perenne was not affected by any of the treatments. 4Our findings demonstrate that defoliation of a common grassland legume can substantially increase the transfer of its N to neighbouring plants by directly affecting below-ground N fluxes. These finding require further examination under field conditions but, given the prevalence of N-limitation of plant productivity in terrestrial ecosystems, increased transfer of N from legumes to non-N-fixing species could alter competitive interactions, with implications for plant community structure. [source] Linking the global carbon cycle to individual metabolismFUNCTIONAL ECOLOGY, Issue 2 2005A. P. ALLEN Summary 1We present a model that yields ecosystem-level predictions of the flux, storage and turnover of carbon in three important pools (autotrophs, decomposers, labile soil C) based on the constraints of body size and temperature on individual metabolic rate. 2The model predicts a 10 000-fold increase in C turnover rates moving from tree- to phytoplankton-dominated ecosystems due to the size dependence of photosynthetic rates. 3The model predicts a 16-fold increase in rates controlled by respiration (e.g. decomposition, turnover of labile soil C and microbial biomass) over the temperature range 0,30 °C due to the temperature dependence of ATP synthesis in respiratory complexes. 4The model predicts only a fourfold increase in rates controlled by photosynthesis (e.g. net primary production, litter fall, fine root turnover) over the temperature range 0,30 °C due to the temperature dependence of Rubisco carboxylation in chloroplasts. 5The difference between the temperature dependence of respiration and photosynthesis yields quantitative predictions for distinct phenomena that include acclimation of plant respiration, geographic gradients in labile C storage, and differences between the short- and long-term temperature dependence of whole-ecosystem CO2 flux. 6These four sets of model predictions were tested using global compilations of data on C flux, storage and turnover in ecosystems. 7Results support the hypothesis that the combined effects of body size and temperature on individual metabolic rate impose important constraints on the global C cycle. The model thus provides a synthetic, mechanistic framework for linking global biogeochemical cycles to cellular-, individual- and community-level processes. [source] Soil animals influence microbial abundance, but not plant,microbial competition for soil organic nitrogenFUNCTIONAL ECOLOGY, Issue 5 2004L. COLE Summary 1In a microcosm experiment we examined the effects of individual species of microarthropods, and variations in microarthropod diversity of up to eight species, on soil microbial properties and the short-term partitioning of a dual-labelled organic nitrogen source (glycine-2- 13C- 15N) between a grassland plant, Agrostis capillaris, and the soil microbial biomass, to determine how soil fauna and their diversity influence plant,microbial competition for organic N. 2We hypothesized that variations in the diversity of animals would influence the partitioning of 15N inputs between plants and the microbial biomass, due to the effect of animal grazing on the microbial biomass, and hence its ability to sequester N. 3Certain individual species of Collembola influenced the microbial community of the soil. Folsomia quadrioculata reduced microbial biomass, whereas Mesaphorura macrochaeta enhanced arbuscular mycorrhizal (AM) colonization of A. capillaris roots. Effects of increasing species richness of microarthropods on microbial biomass and AM colonization were detected, but these effects could be interpreted in relation to the presence or absence of individual species. 4Microbial uptake of added 15N was not affected by the presence of any of the individual species of animal in the monoculture treatments. Similarly, increasing diversity of microarthropods had no detectable effect on microbial 15N. 5Root and shoot uptake of 15N was also largely unaffected by both single species and variations in diversity of microarthropods. However, one collembolan species, Ceratophysella denticulata, reduced root 15N capture when present in monoculture. We did not detect 13C in plant tissue under any experimental treatments, indicating that all N was taken up by plants after mineralization. 6Our data suggest that, while single species and variations in diversity of microarthropods influence microbial abundance in soil, there is no effect on microbial or plant uptake of N. Overall, these data provide little support for the notion that microbial-feeding soil animals are regulators of microbial,plant competition for N. [source] Chemical reactivity of microbe and mineral surfaces in hydrous ferric oxide depositing hydrothermal springsGEOBIOLOGY, Issue 3 2007S. V. LALONDE ABSTRACT The hot springs in Yellowstone National Park, USA, provide concentrated microbial biomass and associated mineral crusts from which surface functional group (FG) concentrations and pKa distributions can be determined. To evaluate the importance of substratum surface reactivity for solute adsorption in a natural setting, samples of iron-rich sediment were collected from three different springs; two of the springs were acid-sulfate-chloride (ASC) in composition, while the third was neutral-chloride (NC). At one of the ASC springs, mats of Sº -rich Hydrogenobaculum -like streamers and green Cyanidia algae were also collected for comparison to the sediment. All samples were then titrated over a pH range of 3,11, and comparisons were made between the overall FG availability and the concentration of solutes bound to the samples under natural conditions. Sediments from ASC springs were composed of hydrous ferric oxides (HFO) that displayed surface FGs typical of synthetic HFO, while sediments from the NC spring were characterized by a lower functional group density, reflected by decreased excess charge over the titration range (i.e., lower surface reactivity). The latter also showed a lower apparent point of zero charge (PZC), likely due the presence of silica (up to 78 wt. %) in association with HFO. Variations in the overall HFO surface charge are manifest in the quantities and types of solutes complexed; the NC sediments bound more cations, while the ASC sediments retained significantly more arsenic, presumably in the form of arsenate (H2AsO4,). When the microbial biomass samples were analyzed, FG concentrations summed over the titratable range were found to be an order of magnitude lower for the Sº-rich mats, relative to the algal and HFO samples that displayed similar FG concentrations on a dry weight basis. A diffuse-layer surface complexation model was employed to further illustrate the importance of surface chemical parameters on adsorption reactions in complex natural systems. [source] Long-term ozone effects on vegetation, microbial community and methane dynamics of boreal peatland microcosms in open-field conditionsGLOBAL CHANGE BIOLOGY, Issue 8 2008SAMI K. MÖRSKY Abstract To study the effects of elevated ozone concentration on methane dynamics and a sedge species, Eriophorum vaginatum, we exposed peatland microcosms, isolated by coring from an oligotrophic pine fen, to double ambient ozone concentration in an open-air ozone exposure field for four growing seasons. The field consists of eight circular plots of which four were fumigated with elevated ozone concentration and four were ambient controls. At the latter part of the first growing season (week 33, 2003), the methane emission was 159±14 mg CH4 m,2 day,1 (mean±SE) in the ozone treatment and 214±8 mg CH4 m,2 day,1 under the ambient control. However, towards the end of the experiment the ozone treatment slightly, but consistently, enhanced the methane emission. At the end of the third growing season (2005), microbial biomass (estimated by phospholipid fatty acid biomarkers) was higher in peat exposed to ozone (1975±108 nmol g,1 dw) than in peat of the control microcosms (1589±115 nmol g,1 dw). The concentrations of organic acids in peat pore water showed a similar trend. Elevated ozone did not affect the shoot length or the structure of the sedge E. vaginatum leaves but it slightly increased the total number of sedge leaves towards the end of the experiment. Our results indicate that elevated ozone concentration enhances the general growth conditions of microbes in peat by increasing their substrate availability. However, the methane production did not reflect the increase in the concentration of organic acids, probably because hydrogenotrophic methane production dominated in the peat studied. Although, we used isolated peatland microcosms with limited size as study material, we did not find experimental factors that could have hampered the basic conclusions on the effects of ozone. [source] | |||||||||||||||||||||||||||||||