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Microbial Decomposition (microbial + decomposition)
Selected AbstractsFemales of the European beewolf preserve their honeybee prey against competing fungiECOLOGICAL ENTOMOLOGY, Issue 2 2001Erhard Strohm Summary 1. Females of the European beewolf Philanthus triangulum (Hymenoptera, Sphecidae) provision brood cells with paralysed honeybees as larval food. Because brood cells are located in warm, humid locations there is a high risk of microbial decomposition of the provisions. Low incidence of fungus infestation (Aspergillus sp.) in nests in the field suggested the presence of an anti-fungal adaptation. 2. To test whether the paralysis caused the protection from fungus infestation, the timing of fungus growth on bees that were freeze-killed, paralysed but not provisioned, and provisioned regularly by beewolf females was determined. Fungus growth was first detected on freeze-killed bees, followed by paralysed but not provisioned bees. By contrast, fungus growth on provisioned bees was delayed greatly or even absent. Thus, paralysis alone is much less efficient in delaying fungus growth than is regular provisioning. 3. Observations of beewolves in their nests revealed that females lick the body surface of their prey very thoroughly during the period of excavation of the brood cell. 4. To separate the effect of a possible anti-fungal property of the brood cell and the licking of the bees, a second experiment was conducted. Timing of fungus growth on paralysed bees did not differ between artificial and original brood cells. By contrast, fungus growth on bees that had been provisioned by a female but were transferred to artificial brood cells was delayed significantly. Thus, the treatment of the bees by the female wasp but not the brood cell caused the delay in fungus growth. 5. Beewolf females most probably apply anti-fungal chemicals to the cuticle of their prey. This is the first demonstration of the mechanism involved in the preservation of provisions in a hunting wasp. Some kind of preservation of prey as a component of parental care is probably widespread among hunting wasps and might have been a prerequisite for the evolution of mass provisioning. [source] Temperature and soil moisture effects on dissolved organic matter release from a moorland Podzol O horizon under field and controlled laboratory conditionsEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 5 2007M. I. Stutter Summary Organic upland soils store large amounts of humified organic matter. The mechanisms controlling the leaching of this C pool are not completely understood. To examine the effects of temperature and microbial cycling on C leaching, we incubated five unvegetated soil cores from a Podzol O horizon (from NE Scotland), over a simulated natural temperature cycle for 1 year, whilst maintaining a constant soil moisture content. Soil cores were leached with artificial rain (177 mm each, monthly) and the leachates analysed for dissolved organic carbon (DOC) and their specific C-normalized UV absorbance determined (SUVA, 285 nm). Monthly values of respiration of the incubated soils were determined as CO2 efflux. To examine the effects of vegetation C inputs and soil moisture, in addition to temperature, we sampled O horizon pore waters in situ and collected five additional field soil cores every month. The field cores were leached under controlled laboratory conditions. Hysteresis in the monthly amount of DOC leached from field cores resulted in greater DOC on the rising, than falling temperature phases. This hysteresis suggested that photosynthetic C stimulated greater DOC losses in early summer, whereas limitations in the availability of soil moisture in late summer suppressed microbial decomposition and DOC loss. Greater DOC concentrations of in-situ pore waters than for any core leachates were attributed to the effects of soil drying and physico-chemical processes in the field. Variation in the respiration rates for the incubated soils was related to temperature, and respiration provided a greater pathway of C loss (44 g C m,2 year,1) than DOC (7.2 g C m,2 year,1). Changes in SUVA over spring and summer observed in all experimental systems were related to the period of increased temperature. During this time, DOC became less aromatic, which suggests that lower molecular weight labile compounds were not completely mineralized. The ultimate DOC source appears to be the incomplete microbial decomposition of recalcitrant humified C. In warmer periods, any labile C that is not respired is leached, but in autumn either labile C production ceases, or it is sequestered in soil biomass. [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] Photodegradation leads to increased carbon dioxide losses from terrestrial organic matterGLOBAL CHANGE BIOLOGY, Issue 11 2010SUSANNA RUTLEDGE Abstract CO2 production in terrestrial ecosystems is generally assumed to be solely biologically driven while the role of abiotic processes has been largely overlooked. In addition to microbial decomposition, photodegradation , the direct breakdown of organic matter (OM) by solar irradiance , has been found to contribute to litter mass loss in dry ecosystems. Previous small-scale studies have shown that litter degradation by irradiance is accompanied by emissions of CO2. However, the contribution of photodegradation to total CO2 losses at ecosystems scales is unknown. This study determined the proportion of the total CO2 losses caused by photodegradation in two ecosystems: a bare peatland in New Zealand and a seasonally dry grassland in California. The direct effect of solar irradiance on CO2 production was examined by comparing daytime CO2 fluxes measured using eddy covariance (EC) systems with simultaneous measurements made using an opaque chamber and the soil CO2 gradient technique, and with night-time EC measurements under the same soil temperature and moisture conditions. In addition, a transparent chamber was used to directly measure CO2 fluxes from OM caused by solar irradiance. Photodegradation contributed 19% of the annual CO2 flux from the peatland and almost 60% of the dry season CO2 flux from the grassland, and up to 62% and 92% of the summer mid-day CO2 fluxes, respectively. Our results suggest that photodegradation may be important in a wide range of ecosystems with exposed OM. Furthermore, the practice of partitioning daytime ecosystem CO2 exchange into its gross components by assuming that total daytime CO2 losses can be approximated using estimates of biological respiration alone may be in error. To obtain robust estimates of global ecosystem,atmosphere carbon transfers, the contribution of photodegradation to OM decomposition must be quantified for other ecosystems and the results incorporated into coupled carbon,climate models. [source] Belowground carbon allocation by trees drives seasonal patterns of extracellular enzyme activities by altering microbial community composition in a beech forest soilNEW PHYTOLOGIST, Issue 3 2010Christina Kaiser Summary ,Plant seasonal cycles alter carbon (C) and nitrogen (N) availability for soil microbes, which may affect microbial community composition and thus feed back on microbial decomposition of soil organic material and plant N availability. The temporal dynamics of these plant,soil interactions are, however, unclear. ,Here, we experimentally manipulated the C and N availability in a beech forest through N fertilization or tree girdling and conducted a detailed analysis of the seasonal pattern of microbial community composition and decomposition processes over 2 yr. ,We found a strong relationship between microbial community composition and enzyme activities over the seasonal course. Phenoloxidase and peroxidase activities were highest during late summer, whereas cellulase and protease peaked in late autumn. Girdling, and thus loss of mycorrhiza, resulted in an increase in soil organic matter-degrading enzymes and a decrease in cellulase and protease activity. ,Temporal changes in enzyme activities suggest a switch of the main substrate for decomposition between summer (soil organic matter) and autumn (plant litter). Our results indicate that ectomycorrhizal fungi are possibly involved in autumn cellulase and protease activity. Our study shows that, through belowground C allocation, trees significantly alter soil microbial communities, which may affect seasonal patterns of decomposition processes. [source] Effects on litter-dwelling earthworms and microbial decomposition of soil-applied imidacloprid for control of wood-boring insectsPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 2 2008David P Kreutzweiser Abstract BACKGROUND: Imidacloprid is an effective, systemic insecticide for the control of wood-boring insect pests in trees. Systemic applications to trees are often made by soil injections or drenches, and the resulting imidacloprid concentrations in soil or litter may pose a risk of harm to natural decomposer organisms. The authors tested effects of imidacloprid on survival and weight gain or loss of the earthworms Eisenia fetida (Savigny) and Dendrobaena octaedra (Savigny), on leaf consumption rates and cocoon production by D. octaedra and on microbial decomposition activity in laboratory microcosms containing natural forest litter. RESULTS:Dendrobaena octaedra was the most sensitive of the two earthworm species, with an LC50 of 5.7 mg kg,1, an LC10 of about 2 mg kg,1 and significant weight losses among survivors at 3 mg kg,1. Weight losses resulted from a physiological effect rather than from feeding inhibition. There were no effects on cocoon production among survivors at 3 mg kg,1. The LC50 for E. fetida was 25 mg kg,1, with significant weight losses at 14 mg kg,1. There were no significant effects on microbial decomposition of leaf material at the maximum test concentration of 1400 mg kg,1. CONCLUSION: The results indicate that, when imidacloprid is applied as a systemic insecticide to the soil around trees, it is likely to cause adverse effects on litter-dwelling earthworms if concentrations in the litter reach or exceed about 3 mg kg,1. Copyright © 2007 Her Majesty the Queen in the Right of Canada, Canadian Forest Service. Published by John Wiley & Sons, Ltd. [source] Incubation temperatures and sex ratios in Australian brush-turkey (Alectura lathami) moundsAUSTRAL ECOLOGY, Issue 4 2007ANN GÖTH Abstract Megapodes are exceptional among birds because they use external heat sources for incubating their eggs. In Australian brush-turkeys (Alectura lathami), this source is the heat produced by microbial decomposition in mounds of leaf litter. A recent laboratory study showed that artificial incubation of eggs at different temperatures affects the sex ratio of brush-turkey hatchlings. Here, this phenomenon is confirmed for eggs incubated in natural incubation mounds. Eggs from which females hatched were found at significantly higher incubation temperatures in the mounds (mean 33.7°C) than those from which males hatched (mean 32.9°C). Also, sex ratios of chicks from individual mounds were significantly correlated with mean incubation temperatures in those mounds. Furthermore, incubation temperatures differed significantly between incubation mounds during the same month of the year. Within some mounds, incubation temperatures differed up to 9°C between eggs, in others this difference was only up to 1°C. These latter results show that males differ in their ability to maintain stable incubation temperatures. While the effect of incubation temperatures on sex ratio is a novel discovery for any bird, it was previously suggested that incubation temperatures in megapodes also affect embryo mortality and chick survival. These combined effects of incubation temperature, and the limited ability of males to provide optimal temperatures, seem to provide answers to the question why so few birds have adopted this unusual mode of reproduction , a question asked by many behavioural ecologists and evolutionary biologists. [source] | ||||||||||