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Eingeladener Vortrag
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A mathematical model to predict the heating-up in open air wood chip piles has been developed. This model includes the heat production from chemical, physical and microbial exothermal processes. In the manuscript the laboratory experiments needed to develop and validate the model are described. In addition, temperature and gas concentrations were measured in two large-scale wood piles (volumes bigger than 1000 m³), in order to provide the applicability of the model to large-scale scenarios. The predictions of the model and the large-scale experimental data showed good agreement concerning the maximum temperature reached inside an open air wood pile. Special attention has been devoted to the microbial processes, since they proved to be the most important cause of heat production in the early stages of storage. This work is intended to help in predicting and thus avoiding possible self-ignition scenarios for this type of wood storage.
Methanotrophs in the rhizosphere of rice field ecosystems attenuate the emissions of CH4 into the atmosphere and thus play an important role for the global cycle of this greenhouse gas. Therefore, we measured the activity and composition of the methanotrophic community in the rhizosphere of rice microcosms. Methane oxidation was determined by measuring the CH4 flux in the presence and absence of difluoromethane as a specific inhibitor for methane oxidation. Methane oxidation started on day 24 and reached the maximum on day 32 after transplantation. The total methanotrophic community was analysed by terminal restriction fragment length polymorphism (T-RFLP) and cloning/sequencing of the pmoA gene, which encodes a subunit of particulate methane monooxygenase. The metabolically active methanotrophic community was analysed by stable isotope probing of microbial phospholipid fatty acids (PLFA-SIP) using 13C-labelled CH4 directly added to the rhizospheric region. Rhizospheric soil and root samples were collected after exposure to 13CH4 for 8 and 18 days. Both T-RFLP/cloning and PLFA-SIP approaches showed that type I and type II methanotrophic populations changed over time with respect to activity and population size in the rhizospheric soil and on the rice roots. However, type I methanotrophs were more active than type II methanotrophs at both time points indicating they were of particular importance in the rhizosphere. PLFA-SIP showed that the active methanotrophic populations exhibit a pronounced spatial and temporal variation in rice microcosms.
Methanotrophs in the rhizosphere play an important role in global climate change since they attenuate methane emission from rice field ecosystems into the atmosphere. Most of the CH4 is emitted via transport through the plant gas vascular system. We used this transport for stable isotope probing (SIP) of the methanotrophs in the rhizosphere under field conditions and pulse-labelled rice plants in a Chinese rice field with CH4 (99% 13C) for 7 days. The rate of 13CH4 loss rate during 13C application was comparable to the CH4 oxidation rate measured by the difluoromethane inhibition technique. The methanotrophic communities on the roots and in the rhizospheric soil were analyzed by terminal-restriction fragment length polymorphism (T-RFLP), cloning and sequencing of the particulate methane monooxygenase (pmoA) gene. Populations of type I methanotrophs were larger than those of type II. Both methane oxidation rates and composition of methanotrophic communities suggested that there was little difference between urea-fertilized and unfertilized fields. SIP of phospholipid fatty acids (PLFA-SIP) and rRNA (RNA-SIP) were used to analyze the metabolically active methanotrophic community in rhizospheric soil. PLFA of type I compared with type II methanotrophs was labelled more strongly with 13C, reaching a maximum of 6.8 atom-% . T-RFLP analysis and cloning/sequencing of 16S rRNA genes showed that methanotrophs, especially of type I, were slightly enriched in the 'heavy' fractions. Our results indicate that CH4 oxidation in the rice rhizosphere under in situ conditions is mainly due to type I methanotrophs.
Emissions of the greenhouse gas CH4, which is often produced in contaminated aquifers, are reduced or eliminated by microbial CH4 oxidation in the overlying vadose zone. The aim of this field study was to estimate kinetic parameters and isotope fractionation factors for CH4 oxidation in situ in the vadose zone above a methanogenic aquifer in Studen, Switzerland, and to characterize the involved methanotrophic communities. To quantify kinetic parameters, several field tests, so-called gas push-pull tests (GPPTs), with CH4 injection concentrations ranging from 17 to 80 mL L-1 were performed. An apparent Vmax of 0.70 ± 0.15 mmol CH4 (L soil air)-1 h-1 and an apparent Km of 0.28 ± 0.09 mmol CH4 (L soil air)-1 was estimated for CH4 oxidation at 2.7 m depth, close to the groundwater table. At 1.1 m depth, Km (0.13 ± 0.02 mmol CH4 (L soil air)-1) was in a similar range, but Vmax (0.076 ± 0.006 mmol CH4 (L soil air)-1 h-1) was an order of magnitude lower. At 2.7 m, apparent first-order rate constants determined from a CH4 gas profile (1.9 h-1) and from a single GPPT (2.0 ± 0.03 h-1) were in good agreement. Above the groundwater table, a Vmax much higher than the in situ CH4 oxidation rate prior to GPPTs indicated a high buffer capacity for CH4. At both depths, known methanotrophic species affiliated with Methylosarcina and Methylocystis were detected by cloning and sequencing. Apparent stable carbon isotope fractionation factors a for CH4 oxidation determined during GPPTs ranged from 1.006 to 1.032. Variability was likely due to differences in methanotrophic activity and CH4 availability leading to different degrees of mass transfer limitation. This complicates the use of stable isotopes as an independent quantification method.
The wood protection industry has refined their products from chrome-, copper-, and arsenate-based wood preservatives toward solely copper-based preservatives in combination with organic biocides. One of these is Cu-HDO, containing the chelation product of copper and N-cyclohexyldiazenium dioxide (HDO). In this study, the fate of isotope-labeled (13C) and nonlabeled (12C) Cu-HDO incorporated in wood sawdust mixed with soil was investigated. HDO concentration was monitored by high-pressure liquid chromatography. The total carbon and the δ13C content of respired CO2, as well as of the soil-wood-sawdust mixture, were determined with an elemental analyzer-isotopic ratio mass spectrometer. The concentration of HDO decreased significantly after 105 days of incubation, and after 24 days the 13CO2 concentration respired from soil increased steadily to a maximum after 64 days of incubation. Phospholipid fatty acid-stable isotope probing (PFA-SIP) analysis revealed that the dominant PFAs C19:0d8,9, C18:0, C18:1ω7, C18:2ω6,9, C17:1d7,8, C16:0, and C16:1ω7 were highly enriched in their δ13C content. Moreover, RNA-SIP identified members of the phylum Acidobacteria and the genera Phenylobacterium and Comamonas that were assimilating carbon from HDO exclusively. Cu-HDO as part of a wood preservative effectively decreased fungal wood decay and overall microbial respiration from soil. In turn, a defined bacterial community was stimulated that was able to metabolize HDO completely.
As a glacier retreats, it leaves behind it a forefield that has a natural gradient of soil formation age. We systematically sampled the Damma glacier forefield (Switzerland) along a temporal gradient of soils deglaciated between 1956 and 2002. A significant change in organic carbon content, sulfate concentration, pH, water and nucleic acid content was observed along the forefield chronosequence. Based on 16S rRNA gene based fingerprinting, the structure of the bacterial community also shifted along the forefield. Shifts in the structure of the bacterial community were significantly correlated to changes of pH, soil water content and soil age. To test the impacts of an array of environmental variables including soil age, soil water content, and different anions on the structure of the bacterial community we incubated different glacier forefield soils under specific treatment conditions for 30 days at 25 °C. The incubation of recently deglaciated soils resulted into an increase of bacteria from the family Methylocystaceae and from the class Betaproteobacteria while the community composition from matured soil changed to a lesser extent. The total nitrogen concentration in matured soil doubled during incubation, whereas the nitrogen concentrations in recently deglaciated soil stayed constant. This suggested that the microbial ecosystem functioned differently in the mature versus the recently deglaciated soils. Only soil age and soil water content could be singled out as having significant effects on the structure and composition of the bacterial community, despite the fact that bacterial communities in glacier forefields are exposed to other steep environmental gradients.
The main wood degraders in aerobic terrestrial ecosystems belong to the white- and brown-rot fungi, where their biomass can be created on wood decay only. However, total sulfur (S) concentration in wood is very low and only little is known about the different sulfur compounds in wood today. Sulfur-starved brown-rot fungi Gloeophyllum trabeum and Oligoporus placenta were incubated on sterilized pine wood blocks whereas Lentinus cyathiformis and the white-rot fungi Trametes versicolor were incubated on sterilized beech wood blocks. After 19 weeks of incubation, the S oxidation status was analyzed in wood, in degraded wood, and in biomass of wood-degrading fungi by synchrotron based S K-edge XANES, and total S and sulfate were quantified. Total sulfur and sulfate content in pine wood blocks were approximately 50 and 1 µg g-1, respectively, while in beech wood approximately 100 and 20 µg g-1 were found, respectively. Sulfur in beech was dominated by sulfate-esters. In contrast, pine wood also contained larger amounts of reduced S. Three out of four selected fungi caused a reduction of the S oxidation state in wood from oxidized S (sulfate-ester, sulfate) to intermediate S (sulfonate, sulfoxide) or reduced S (thiols, e.g., proteins, peptides, enzyme cofactors). Only O. placenta shifted thiol to sulfonate. Growth experiments of these fungi on selective minimal media showed that in particular cysteine (thiol), sulfonates, and sulfate enhanced total mycelium growth. Consequently, wood-degrading fungi were able to utilize a large variety of different wood S sources for growth but preferentially transformed in vivo sulfate-esters and thiol into biomass structures.
The microbial community structure was investigated together with the path of methane production in Italian rice field soil incubated at moderate (35 °C) and high (45 °C) temperature using terminal restriction fragment length polymorphism and stable isotope fractionation. The structure of both the archaeal and bacterial communities differed at 35 °C compared with 45 °C, and acetoclastic and hydrogenotrophic methanogenesis dominated, respectively. Changing the incubation of the 45 °C soil to different temperatures (25, 30, 35, 40, 45, 50 °C) resulted in a dynamic change of both microbial community structure and stable isotope fractionation. In all treatments, acetate first accumulated and then decreased. Propionate was also transiently produced and consumed. It is noteworthy that acetate was also consumed at thermophilic conditions, although archaeal community composition and stable isotope fractionation indicated that acetoclastic methanogenesis did not operate. Instead, acetate must have been consumed by syntrophic acetate oxidizers. The transient accumulation and subsequent consumption of acetate at thermophilic conditions was specifically paralleled by terminal restriction fragments characteristic for clostridial cluster I, whereas those of clostridial clusters I and III, Acidaminococcaceae and Heliobacteraceae, paralleled the thermophilic turnover of both acetate and propionate.
Das Interesse für erneuerbare Energieträger ist in den letzten Jahren stark angestiegen.
Im Bereich Biomasse als erneuerbarer Energieträger wird besonders Holz ein großes
Wachstum auf dem Energiesektor prognostiziert (NITSCH 2007). Die Speicherung dieser
Energie erfolgt meist durch Holzhackschnitzelhalden in der Umwelt. Um ein tieferes Verständnis
der in der Halde ablaufenden mikrobiologischen Prozesse erhalten zu können,
wurden in einer neu aufgebauten Kiefernholzhackschnitzelhalde mit den Ausmaßen
15 m x 20 m x 6 m folgende Messungen durchgeführt: a.) Messung der Gaskonzentration
von Sauerstoff, Kohlendioxid als auch der Temperaturentwicklung innerhalb der Halde; b.)
Messung der Veränderung der Holzzusammensetzung innerhalb der Halde über die Zeit;
c.) Charakterisierung der Veränderung der Zusammensetzung der bakteriellen als auch
der pilzlichen Lebensgemeinschaften über die Zeit; d.) Charakterisierung von dominanten
Vertretern der bakteriellen als auch der pilzlichen Lebensgemeinschaften. Die Ergebnisse
zeigen, dass sich die Funktion und die Zusammensetzung der Lebensgemeinschaften
über die Dauer der Holzhackschnitzellagerung ändern, und dass diese Änderungen nur
zum Teil mit den Prozessen bei Kompostierungsanlagen vergleichbar sind.
Fast growing softwood species such as pine are preferred for biomass-based heat as well as electricity production and stored in large quantities. A newly established outdoor pile of freshly cut pine-wood chips was monitored to analyze exothermic processes. Inside the pile, a mean temperature increase of up to 44 °C was measured after six days of piling which was paralleled by a decrease of O2-concentration and an increase of CO2-concentration. Thereafter four additional CO2 maxima were observed, while O2-concentration remained at ambient concentration. The fungal community structure remained almost unchanged after four weeks, while the bacterial community structure was characterized by continuous shifts over time. The rapid heating in the early stage of storage corresponded to high relative abundance of microbial strains belonging to the genera Pseudomonas, Luteibacter and Caulobacter, ascomycetous genera Sphaeropsis and Cadophora and basidiomycetous order Polyporales and genus Sistotremastrum. The late stage was composed by a broader diversity of microorganisms, and heating processes inside the wood pile were attributed mainly to physicochemical processes. Taken together, these observations suggest that the early bacterial and fungal communities are key players in exothermic processes and were replaced by a broader diversity of highly adapted microorganisms.
Exothermic processes in outdoor pine wood chip piles are linked to microbial community shifts
(2009)
The microbial community in anoxic rice field soil produces CH4 over a wide temperature range up to 55°C. However, at temperatures higher than about 40°C, the methanogenic path changes from CH4 production by hydrogenotrophic plus acetoclastic methanogenesis to exclusively hydrogenotrophic methanogenesis and simultaneously, the methanogenic community consisting of Methanosarcinaceae, Methanoseataceae, Methanomicrobiales, Methanobacteriales and Rice Cluster I (RC-1) changes to almost complete dominance of RC-1. We studied changes in structure and function of the methanogenic community with temperature to see whether microbial members of the community were lost or their function impaired by exposure to high temperature. We characterized the function of the community by the path of CH4 production measuring δ13C in CH4 and CO2 and calculating the apparent fractionation factor (αapp) and the structure of the community by analysis of the terminal restriction fragment length polymorphism (T-RFLP) of the microbial 16S rRNA genes. Shift of the temperature from 45°C to 35°C resulted in a corresponding shift of function and structure, especially when some 35°C soil was added to the 45°C soil. The bacterial community (T-RFLP patterns), which was much more diverse than the archaeal community, changed in a similar manner upon temperature shift. Incubation of a mixture of 35°C and 50°C pre-incubated methanogenic rice field soil at different temperatures resulted in functionally and structurally well-defined communities. Although function changed from a mixture of acetoclastic and hydrogenotrophic methanogenesis to exclusively hydrogenotrophic methanogenesis over a rather narrow temperature range of 42-46°C, each of these temperatures also resulted in only one characteristic function and structure. Our study showed that temperature conditions defined structure and function of the methanogenic microbial community.