Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Exploring climate change impacts and adaptation options for maize production in the Central Rift Valley of Ethiopia using different climate change scenarios and crop models
    Kassie, B.T. ; Asseng, S. ; Rotter, R.P. ; Hengsdijk, H. ; Ruane, A.C. ; Ittersum, M.K. van - \ 2015
    Climatic Change 129 (2015)1-2. - ISSN 0165-0009 - p. 145 - 158.
    africa - yield - agriculture - risks - opportunities - vulnerability - temperatures - uncertainty - variability - projections
    Exploring adaptation strategies for different climate change scenarios to support agricultural production and food security is a major concern to vulnerable regions, including Ethiopia. This study assesses the potential impacts of climate change on maize yield and explores specific adaptation options under climate change scenarios for the Central Rift Valley of Ethiopia by mid-century. Impacts and adaptation options were evaluated using three General Circulation Models (GCMs) in combination with two Representative Concentration Pathways (RCPs) and two crop models. Results indicate that maize yield decreases on average by 20 % in 2050s relative to the baseline (1980–2009) due to climate change. A negative impact on yield is very likely, while the extent of impact is more uncertain. The share in uncertainties of impact projections was higher for the three GCMs than it was for the two RCPs and two crop models used in this study. Increasing nitrogen fertilization and use of irrigation were assessed as potentially effective adaptation options, which would offset negative impacts. However, the response of yields to increased fertilizer and irrigation will be less for climate change scenarios than under the baseline. Changes in planting dates also reduced negative impacts, while changing the maturity type of maize cultivars was not effective in most scenarios. The multi-model based analysis allowed estimating climate change impact and adaptation uncertainties, which can provide valuable insights and guidance for adaptation planning.
    Two distinct groups within the Bacillus subtilis group display significantly different spore heat resistance properties
    Berendsen, E.M. ; Zwietering, M.H. ; Kuipers, O.P. ; Wells-Bennik, M.H.J. - \ 2015
    Food Microbiology 45 (2015). - ISSN 0740-0020 - p. 18 - 25.
    thermal inactivation - bacterial-spores - sporulation - food - sporothermodurans - strains - systems - milk - stearothermophilus - temperatures
    The survival of bacterial spores after heat treatment and the subsequent germination and outgrowth in a food product can lead to spoilage of the food product and economical losses. Prediction of time-temperature conditions that lead to sufficient inactivation requires access to detailed spore thermal inactivation kinetics of relevant model strains. In this study, the thermal inactivation kinetics of spores of fourteen strains belonging to the Bacillus subtilis group were determined in detail, using both batch heating in capillary tubes and continuous flow heating in a micro heater. The inactivation data were fitted using a log linear model. Based on the spore heat resistance data, two distinct groups (p <0.001) within the B. subtilis group could be identified. One group of strains had spores with an average D120 °C of 0.33 s, while the spores of the other group displayed significantly higher heat resistances, with an average D120 °C of 45.7 s. When comparing spore inactivation data obtained using batch- and continuous flow heating, the z-values were significantly different, hence extrapolation from one system to the other was not justified. This study clearly shows that heat resistances of spores from different strains in the B. subtilis group can vary greatly. Strains can be separated into two groups, to which different spore heat inactivation kinetics apply.
    Biochar increases plant-available water in a sandy loam soil under an aerobic rice crop system
    Melo Carvalho, M.T. de; Holanda Nunes Maia, A. de; Madari, B.E. ; Bastiaans, L. ; Oort, P.A.J. van; Heinemann, A.B. ; Soler da Silva, M.A. ; Petter, F.A. ; Marimon-Junior, B.H. ; Meinke, H.B. - \ 2014
    Solid Earth 5 (2014). - ISSN 1869-9510 - p. 939 - 952.
    upland rice - hydraulic conductivity - management - productivity - temperatures - fertility - retention - tropics - model
    The main objective of this study was to assess the impact of biochar rate (0, 8, 16 and 32 Mg ha-1) on the water retention capacity (WRC) of a sandy loam Dystric Plinthosol. The applied biochar was a by-product of slow pyrolysis (~450 °C) of eucalyptus wood, milled to pass through a 2000 µm sieve that resulted in a material with an intrinsic porosity =10 µm and a specific surface area of ~3.2 m2 g-1. The biochar was incorporated into the top 15 cm of the soil under an aerobic rice system. Our study focused on both the effects on WRC and rice yields 2 and 3 years after its application. Undisturbed soil samples were collected from 16 plots in two soil layers (5–10 and 15–20 cm). Soil water retention curves were modelled using a nonlinear mixed model which appropriately accounts for uncertainties inherent of spatial variability and repeated measurements taken within a specific soil sample. We found an increase in plant-available water in the upper soil layer proportional to the rate of biochar, with about 0.8% for each Mg ha-1 biochar amendment 2 and 3 years after its application. The impact of biochar on soil WRC was most likely related to an effect in overall porosity of the sandy loam soil, which was evident from an increase in saturated soil moisture and macro porosity with 0.5 and 1.6% for each Mg ha-1 of biochar applied, respectively. The increment in soil WRC did not translate into an increase in rice yield, essentially because in both seasons the amount of rainfall during the critical period for rice production exceeded 650 mm. The use of biochar as a soil amendment can be a worthy strategy to guarantee yield stability under short-term water-limited conditions. Our findings raise the importance of assessing the feasibility of very high application rates of biochar and the inclusion of a detailed analysis of its physical and chemical properties as part of future investigations.
    Spatial precipitation patterns and trends in The Netherlands during 1951–2009
    Daniels, E.E. ; Lenderink, G. ; Hutjes, R.W.A. ; Holtslag, A.A.M. - \ 2014
    International Journal of Climatology 34 (2014)6. - ISSN 0899-8418 - p. 1773 - 1784.
    neerslag - klimaatverandering - statistische analyse - regionale verkenningen - seizoenen - nederland - precipitation - climatic change - statistical analysis - regional surveys - seasons - netherlands - coastal precipitation - urban land - europe - rainfall - temperatures - extremes - feedback - impacts - indexes - soils
    Significant increases in precipitation have been observed in The Netherlands over the last century. At the same time persistent spatial variations are apparent. The objective of this study is to analyse and explain these spatial patterns, focussing on changes in means and extremes for the period 1951–2009. To investigate different possibilities for the causes of spatial variations, a distinction was made between six regions based on mean precipitation, soil type and elevation, and four zones at different distances to the coast. Spatial maxima in mean precipitation inland and over elevated areas are mainly formed in winter and spring, while maxima along the coast are generated in autumn. Daily precipitation maxima are found in the central West coast and over elevated areas. Upward trends in daily precipitation are highest from February to April and lowest from July to September. The strongest and most significant increases are found along the coast. For several seasonal and climatological periods diverging behaviour between coastal and inland zones is observed. We find that distance to the coast gives a more consistent picture for the seasonal precipitation changes than a classification based on surface characteristics. Therefore, from the investigated surface factors, we consider sea surface temperature to have the largest influence on precipitation in The Netherlands.
    Hot fire, cool soil
    Stoof, C.R. ; Moore, D. ; Fernandes, P. ; Stoorvogel, J.J. ; Fernandes, R. ; Ferreira, A.J.D. ; Ritsema, C.J. - \ 2013
    Geophysical Research Letters 40 (2013)8. - ISSN 0094-8276 - p. 1534 - 1539.
    south-eastern australia - intensity - behavior - forest - temperatures - variability - erodibility - germination - california - vegetation
    Wildfires greatly increase a landscape's vulnerability to flooding and erosion events by removing vegetation and changing soils. Fire damage to soil increases with increasing soil temperature, and, for fires where smoldering combustion is absent, the current understanding is that soil temperatures increase as fuel load and fire intensity increase. Here, however, we show that this understanding that is based on experiments under homogeneous conditions does not necessarily apply at the more relevant larger scale where soils, vegetation, and fire characteristics are heterogeneous. In a catchment-scale fire experiment, soils were surprisingly cool where fuel load was high and fire was hot and, conversely, soils were hot where expected to be cooler. This indicates that the greatest fire damage to soil can occur where fuel load and fire intensity are low rather than high, and has important implications for management of fire-prone areas prior to, during, and after fire events.
    Hibernation site requirements of bats in man-made hibernacula in a spatial context
    Boer, W.F. de; Koppel, S. ; Knegt, H.J. de; Dekker, J.J.A. - \ 2013
    Ecological Applications 23 (2013)2. - ISSN 1051-0761 - p. 502 - 514.
    niche factor-analysis - habitat-suitability - selection - scale - landscape - temperatures - chiroptera - myotis
    Bat hibernacula selection depends on various spatial and nonspatial variables that differ widely between sites. However, previous studies have focused mainly on nonspatial variables. This research investigated factors that determined the abundance and species richness of hibernating bats in hibernation objects of the New Dutch Waterline, The Netherlands, and determined the relevant scales over which spatial factors operate using regression techniques and ecological-niche factor analyses. The effects of 32 predictor variables on several response variables, i.e., the total bat abundance, species richness, and abundance and presence of bat species, were investigated. Predictor variables were classified as internal variables (e.g., building size, climatic conditions, and human access) or external variables (e.g., ground and vegetation cover and land cover type) that were measured at different spatial scales to study the influence of the spatial context. The internal building variables (mainly the size of hibernacula and the number of hiding possibilities) affected the hibernating bat abundance and species richness. Climatic variables, such as changes in temperature and humidity, were less important. The hibernation site suitability was also influenced by spatial variables at a variety of scales, thereby indicating the importance of scale- dependent species–environment relationships. The absence of human use and public access enhanced hibernation site suitability, but the internal size-related variables had the greatest positive effect on hibernation site suitability. These results demonstrate the importance of considering the different spatial scales of the surrounding landscape to better understand habitat selection, and they offer directives to managers to optimize objects for hibernating bats and to improve management and bat conservation. The analyses have wider applications to other wildlife–habitat studies.
    Photosynthetic thermotolerance of woody savanna species in China is correlated with leaf life span.
    Zhang, J.L. ; Poorter, L. ; Hao, G.Y. ; Cao, K.F. - \ 2012
    Annals of Botany 110 (2012)5. - ISSN 0305-7364 - p. 1027 - 1033.
    valley-savanna - heat tolerance - fluorescence - evolution - calcium - stress - plants - area - consequences - temperatures
    Background and Aims Photosynthetic thermotolerance (PT) is important for plant survival in tropical and sub-tropical savannas. However, little is known about thermotolerance of tropical and sub-tropical wild plants and its association with leaf phenology and persistence. Longer-lived leaves of savanna plants may experience a higher risk of heat stress. Foliar Ca is related to cell integrity of leaves under stresses. In this study it is hypothesized that (1) species with leaf flushing in the hot-dry season have greater PT than those with leaf flushing in the rainy season; and (2) PT correlates positively with leaf life span, leaf mass per unit area (LMA) and foliar Ca concentration ([Ca]) across woody savanna species. Methods The temperature-dependent increase in minimum fluorescence was measured to assess PT, together with leaf dynamics, LMA and [Ca] for a total of 24 woody species differing in leaf flushing time in a valley-type savanna in south-west China. Key Results The PT of the woody savanna species with leaf flushing in the hot-dry season was greater than that of those with leaf flushing in the rainy season. Thermotolerance was positively associated with leaf life span and [Ca] for all species irrespective of the time of flushing. The associations of PT with leaf life span and [Ca] were evolutionarily correlated. Thermotolerance was, however, independent of LMA. Conclusions Chinese savanna woody species are adapted to hot-dry habitats. However, the current maximum leaf temperature during extreme heat stress (44·3 °C) is close to the critical temperature of photosystem II (45·2 °C); future global warming may increase the risk of heat damage to the photosynthetic apparatus of Chinese savanna species.
    Using life-history traits to explain bird population responses to changing weather variability
    Cormont, A. ; Vos, C.C. ; Turnhout, C.A.M. van; Foppen, R.P.B. ; Braak, C.J.F. ter - \ 2011
    Climate Research 49 (2011)1. - ISSN 0936-577X - p. 59 - 71.
    climate-change - 4th-corner problem - species traits - migratory bird - consequences - netherlands - temperatures - adaptations - resilience - habitats
    Bird population dynamics are expected to change in response to increased weather variability, an expression of climate change. The extent to which species are sensitive to effects of weather on survival and reproduction depends on their life-history traits. We investigated how breeding bird species can be grouped, based on their life-history traits and according to weather-correlated population dynamics. We developed and applied the linear trait–environment method (LTE), which is a modified version of the fourth-corner method. Despite our focus on single traits, 2 strategies—combinations of several traits—stand out. As expected, breeding populations of waterfowl species are negatively impacted by severe winters directly preceding territory monitoring, probably because of increased adult mortality. Waterfowl species combine several traits: they often breed at ground or water level, feed on plant material, are precocial and are generally short-distance or partial migrants. Furthermore, we found a decline in population growth rates of insectivorous long-distance migrants due to mild winters and warm springs in the year before territory monitoring, which may be caused by reduced reproduction due to trophic mismatches. We identify species that are expected to show the most significant responses to changing weather variability, assuming that our conclusions are based on causal relationships and that the way species, weather variables and habitat interact will not alter. Species expected to respond positively can again be roughly categorized as waterfowl species, while insectivorous long-distance migrants are mostly expected to respond negatively. As species traits play an important role in constructing functional groups that are relevant to the provisioning of ecosystem services, our study enables the incorporation of ecosystem vulnerability to climate change into such functional approaches
    Modification of light utilization for skeletal growth by water flow in the scleractinian coral Galaxea fascicularis
    Schutter, M. ; Kranenbarg, S. ; Wijffels, R.H. ; Verreth, J.A.J. ; Osinga, R. - \ 2011
    Marine Biology 158 (2011)4. - ISSN 0025-3162 - p. 769 - 777.
    reef coral - madracis-mirabilis - photosynthesis - calcification - oxygen - respiration - rates - temperatures - mechanisms - organisms
    In this study, we tested the hypothesis that the importance of water flow for skeletal growth (rate) becomes higher with increasing irradiance levels (i.e. a synergistic effect) and that such effect is mediated by a water flow modulated effect on net photosynthesis. Four series of nine nubbins of G. fascicularis were grown at either high (600 µE m-2 s-1) or intermediate (300 µE m-2 s-1) irradiance in combination with either high (15–25 cm s-1) or low (5–10 cm s-1) flow. Growth was measured as buoyant weight and surface area. Photosynthetic rates were measured at each coral’s specific experimental irradiance and flow speed. Additionally, the instantaneous effect of water flow on net photosynthetic rate was determined in short-term incubations in a respirometric flowcell. A significant interaction was found between irradiance and water flow for the increase in buoyant weight, the increase in surface area, and specific skeletal growth rate, indicating that flow velocity becomes more important for coral growth with increasing irradiance levels. Enhancement of coral growth with increasing water flow can be explained by increased net photosynthetic rates. Additionally, the need for costly photo-protective mechanisms at low flow regimes could explain the differences in growth with flow.
    Quantitative Microbial Risk Assessment for Escherichia coli O157:H7, Salmonella enterica, and Listeria monocytogenes in Leafy Green Vegetables Consumed at Salad Bars, Based on Modeling Supply Chain Logistics
    Tromp, S.O. ; Rijgersberg, H. ; Franz, E. - \ 2010
    Journal of Food Protection 73 (2010)10. - ISSN 0362-028X - p. 1830 - 1840.
    iceberg lettuce - dose-response - fresh produce - growth - outbreaks - foodborne - o157h7 - temperatures - restaurant - infection
    Quantitative microbial risk assessments do not usually account for the planning and ordering mechanisms (logistics) of a food supply chain. These mechanisms and consumer demand determine the storage and delay times of products. The aim of this study was to quantitatively assess the difference between simulating supply chain logistics (MOD) and assuming fixed storage times (FIX) in microbial risk estimation for the supply chain of fresh-cut leafy green vegetables destined for working-canteen salad bars. The results of the FIX model were previously published (E. Franz, S. O. Tromp, H. Rijgersberg, and H. J. van der Fels-Klerx, J. Food Prot. 73:274-285, 2010). Pathogen growth was modeled using stochastic discrete-event simulation of the applied logistics concept. The public health effects were assessed by conducting an exposure assessment and risk characterization. The relative growths of Escherichia coli O157 (17%) and Salmonella enterica (15%) were identical in the MOD and FIX models. In contrast, the relative growth of Listeria monocytogenes was considerably higher in the MOD model (1,156%) than in the FIX model (194%). The probability of L. monocytogenes infection in The Netherlands was higher in the MOD model (5.18 × 10-8) than in the FIX model (1.23 × 10-8). The risk of listeriosis-induced fetal mortality in the perinatal population increased from 1.24 × 10-4 (FIX) to 1.66 × 10-4 (MOD). Modeling the probabilistic nature of supply chain logistics is of additional value for microbial risk assessments regarding psychrotrophic pathogens in food products for which time and temperature are the postharvest preventive measures in guaranteeing food safety.
    The role of volatiles in aggregation and host-seeking of the haematophagous poultry red mite Dermanyssus gallinae (Acari: Dermanyssidae)
    Koenraadt, C.J.M. ; Dicke, M. - \ 2010
    Experimental and Applied Acarology 50 (2010)3. - ISSN 0168-8162 - p. 191 - 199.
    gallus-gallus-domesticus - carbon-dioxide - chicken - identification - temperatures - attractants - infections - pheromones - mosquitos - responses
    Infestations with ectoparasitic poultry red mites (Dermanyssus gallinae) pose an increasing threat to poultry health and welfare. Because of resistance to acaricides and higher scrutiny of poultry products, alternative and environmentally safe management strategies are warranted. Therefore, we investigated how volatile cues shape the behavior of D. gallinae and how this knowledge may be exploited in the development of an attractand- kill method to control mite populations. A Y-tube olfactometer bio-assay was used to evaluate choices of mites in response to cues related to conspecific mites as well as related to their chicken host. Both recently fed and starved mites showed a strong preference (84 and 85%, respectively) for volatiles from conspecific, fed mites as compared to a control stream of clean air. Mites were also significantly attracted to ‘aged feathers’ (that had remained in the litter for 3–4 days), but not to ‘fresh feathers’. Interestingly, an air stream containing 2.5% CO2, which mimics the natural concentration in air exhaled by chickens, did attract fed mites, but inhibited the attraction of unfed mites towards volatiles from aged feathers. We conclude that both mite-related cues (aggregation pheromones) and host-related cues (kairomones) mediate the behavior of the poultry mite. We discuss the options to exploit this knowledge as the ‘attract’ component of attract-and-kill strategies for the control of D. gallinae
    Modelling the biological variance of the yellow aspect of Granny smith apple colour
    Tijskens, L.M.M. ; Schouten, R.E. ; Konopacki, P. ; Hribar, J. ; Simcic, M. - \ 2010
    Journal of the Science of Food and Agriculture 90 (2010)5. - ISSN 0022-5142 - p. 798 - 805.
    chlorophyll degradation - chilling injury - storage - quality - texture - fruit - temperatures - constant - tomatoes - bananas
    BACKGROUND: The yellow aspect of colour is usually not considered for produce with a green-to-red or a green-to-yellow transition upon ripening. The magnitude of change is simply too small and, additionally, masked by a large variation. The colour of Granny Smith apples, harvested from three orchards at two stages of maturity, was measured individually using the CIE L*a*b* system during storage in a regular atmosphere at three temperatures: 1, 4 and 10 °C. A model was developed based on a simplified mechanism, consisting of two consecutive reactions, to describe the development of the apple colour expressed as b* and L* values during storage. RESULTS: Monitoring individual apples made it possible to include and describe the biological variance of colour in batches of apples and to extract information on chilling injury, as a process active at 1 °C. All variations could be attributed to a single source related to the amount of yellowing compounds at the moment of harvest, indicating differences in state of maturity between individual apples. The obtained explained part (R2adj), using nonlinear mixed effects regression analysis was well over 90% for all data combined over more than 3000 observations. CONCLUSION: Orchard location had a slight effect on the mean initial colour value, indicating differences in development stage, most probably due to differences in assessing the harvest date. The magnitude of the variation in these colour values was, however, the same for all three orchards. The behaviour of the green colour aspect (a* value) has been reported separately, as this represents the major change in perceived colour. The changes in b* and L* values are rather small, while the biological variation between the individual fruit is at least of the same magnitude. The model presented here is, as far as known, the first model on b* and L* values for green-coloured products. Analysing b* and L* data using this model provides additional information with respect to the stage of maturity at harvest in a batch or for an orchard of Granny Smith apples. All the variation in the yellow colour aspects could be attributed exclusively to the initial level of yellow compounds
    Biological varience in the colour of Granny Smith apples Modelling the effect of senescence and chilling injury
    Tijskens, L.M.M. ; Konopacki, P. ; Schouten, R.E. ; Hribar, J. ; Simcic, M. - \ 2008
    Postharvest Biology and Technology 50 (2008)2-3. - ISSN 0925-5214 - p. 153 - 163.
    keeping quality - chlorophyll degradation - cucumber fruits - storage - temperatures - constant - symptoms - impact - scald
    The colour of `Granny Smith¿ apples, harvested from three orchards at two stages of maturity, was measured individually using the CIE L*a*b* system during storage in regular atmosphere at three temperatures: 1, 4 and 10 °C. A model was developed based on a simplified mechanism to describe the development of the apple colour during storage as affected by senescence (aging) and chilling injury. Monitoring of individual apples made it possible to include and to describe the biological variance of colour in batches of apples and to correct the colour of each apple individually for its own biological shift factor (biological age; random effect). The biological shift factor is related to the initial condition and range of colour change. The rate of the colour development was estimated in common (fixed effects) for all batches using non-linear mixed effects regression analysis. The variance accounted for by the developed model, including effects of temperature, harvest maturity and orchard location, was more than 95% on 3211 observations. The overall reaction rate constant of decolouration, combining the effects of senescence and chilling injury, was found to depend on temperature. The temperature that showed the lowest overall reaction rate of decolouration is 8 °C, which is in contrast with the currently recommended storage temperature for `Granny Smith¿ apples.
    Milk quality assurance for paratuberculosis: simulation of within-herd infection dynamics and economicsof within-herd infection dynamics and economics
    Weber, M.F. ; Nielen, M. ; Velthuis, A.G.J. ; Roermund, H.J.W. van - \ 2008
    Veterinary Research 39 (2008)12. - ISSN 0928-4249 - p. 1 - 20.
    avium subsp paratuberculosis - pasteurized cows milk - bovine johnes-disease - mycobacterium-paratuberculosis - monitoring program - heat inactivation - fecal samples - bulk raw - cattle - temperatures
    bulk milk quality assurance programme for Mycobacterium avium subsp. paratuberculosis (Map) in dairy herds was simulated with a stochastic simulation model (JohneSSim). The aim of this study was to evaluate the epidemiological and economic effects of preventive management measures and various test schemes in a simulated population of closed Dutch dairy herds over a 20-year period. Herds were certified as `low-Map bulk milk' if, with a certain probability, the concentration of Map in bulk milk did not exceed a maximum acceptable concentration of 103 Map organisms per litre (based on pasteurisation studies). The programme started with an initial assessment; test-negative herds entered a surveillance procedure and test-positive herds a control procedure. The simulations showed that herd examinations by ELISA for the initial assessment, surveillance and control procedures effectively ensure the quality of `low-Map bulk milk': > 75% of simulated herds were certified and > 96% of certified herds produced bulk milk with <103 Map/L if the initial herd-level prevalence was 30%. Preventive management measures only had a minor effect on bulk milk quality of certified herds. Culling based on biennial faecal culture was more effective than culling based on annual ELISA. Average total discounted costs for 20-year participation in a programme consisting of initial assessment by ELISA, surveillance by biennial ELISA and control by biennial faecal culture were per herd. In conclusion, this study shows that a bulk milk quality assurance programme for closed Dutch dairy herds is feasible and provides information on the cost-effectiveness of different programmes. The concepts of this study equally apply to other countries because mechanisms of paratuberculosis infection, disease, and testing are comparable in other dairy cattle populations.
    Occurrence and distribution of tetraether membrane lipids in soils: implications for the use of the TEX86 proxy and the BIT index
    Weijers, J.W.H. ; Schouten, S. ; Spaargaren, O.C. ; Sinnige Damsté, J.S. - \ 2006
    Organic Geochemistry 37 (2006)12. - ISSN 0146-6380 - p. 1680 - 1693.
    peat bog - kingdom crenarchaeota - phylogenetic analysis - lake-sediments - forest soil - archaea - abundance - diversity - identification - temperatures
    A diverse collection of globally distributed soil samples was analyzed for its glycerol dialkyl glycerol tetraether (GDGT) membrane lipid content. Branched GDGTs, derived from anaerobic soil bacteria, were the most dominant and were found in all soils. Isoprenoid GDGTs, membrane lipids of Archaea, were also present, although in considerably lower concentration. Crenarchaeol, a specific isoprenoid membrane lipid of the non-thermophilic Crenarchaeota, was also regularly detected and its abundance might be related to soil pH. The detection of crenarchaeol in nearly all of the samples is the first report of this type of GDGT membrane lipid in soils and is in agreement with molecular ecological studies, confirming the widespread occurrence of non-thermophilic Crenarchaeota in the terrestrial realm. The fluvial transport of crenarchaeol and other isoprenoid GDGTs to marine and lacustrine environments could possibly bias the BIT index, a ratio between branched GDGTs and crenarchaeol used to determine relative terrestrial organic matter (TOM) input. However, as crenarchaeol in soils is only present in low concentration compared to branched GDGTs, no large effect is expected for the BIT index. The fluvial input of terrestrially derived isoprenoid GDGTs could also bias the TEX86, a proxy used to determine palaeo surface temperatures in marine and lacustrine settings and based on the ratio of cyclopentane-containing isoprenoid GDGTs in marine and lacustrine Crenarchaeota. Indeed, it is shown that a substantial bias in TEX86-reconstructed sea and lake surface temperatures can occur if TOM input is high, e.g. near large river outflows. (c) 2006 Elsevier Ltd. All rights reserved.
    Survival, elongation, and elevated tolerance of Salmonella enterica serovar Enteritidis at reduced water activity
    Kieboom, J. ; Kusumaningrum, H.D. ; Tempelaars, M.H. ; Hazeleger, W.C. ; Abee, T. ; Beumer, R.R. - \ 2006
    Journal of Food Protection 69 (2006)11. - ISSN 0362-028X - p. 2681 - 2686.
    osmotic-stress - cell-division - single-cell - typhimurium - microorganisms - temperatures - bacteria - glycine - heat - acid
    Growing microorganisms on dry surfaces, which results in exposure to low water activity (aw), may change their normal morphology and physiological activity. In this study, the morphological changes and cell viability of Salmonella enterica serovar Enteritidis challenged to low aw were analyzed. The results indicated that exposure to reduced aw induced filamentation of the cells. The amount of filamentous cells at aw 0.94 was up to 90% of the total number of cells. Surviving filamentous cells maintained their membrane integrity after exposure to low aw for 21 days. Furthermore, cells prechallenged to low aw, obtained with an ionic humectant, demonstrated higher resistance to sodium hypochlorite than control cells. These resistant cells are able to survive disinfection more efficiently and can therefore cause contamination of foods coming in contact with surfaces. This points to the need for increased attention to cleaning of surfaces in household environments and disinfection procedures in processing plants
    Fluorescence microscopy of NaCl-stressed, elongated Salmonella and Listeria cells reveals the presence of septa in filaments
    Hazeleger, W.C. ; Dalvoorde, M. ; Beumer, R.R. - \ 2006
    International Journal of Food Microbiology 112 (2006)3. - ISSN 0168-1605 - p. 288 - 290.
    monocytogenes scott-a - escherichia-coli - enteritidis pt4 - growth - temperatures - environments - replication - morphology
    The cell morphology of Salmonella enteritidis and Listeria monocytogenes after the application of stress was examined. Cells were stressed by plating the bacteria on Tryptone Soya Agar (TSA) plates, with 5¿10% NaCl. The plates were subsequently incubated for 6 days at 25 °C. Finally, the cells were harvested and subjected to different fluorescent probes in order to visualize the possible presence of septa in elongated cells. Use of the stain 4¿,6-Diamidino-2-phenylindole (DAPI), which is a blue fluorescent nucleic acid stain that preferentially stains double-stranded DNA, showed clearly the presence of dark spots, probably cellular partitions where no nucleic acids were present, in both Salmonella and Listeria cells. Another stain, FM 4-64, a lipophilic styryl dye for red staining of the inner membrane, showed the presence of highly fluorescent spots in Listeria cells, probably indicating the presence of membranes. For Salmonella, however, FM 4-64 was not successful in revealing septa in filaments. Double staining applied to elongated Listeria cells showed areas with high fluorescence in DAPI-staining (DNA-rich spots) which contained low fluorescence in FM 4-64-staining (membrane spots) and vice versa, which is a confirmation that the elongated cells are indeed composed of several normal size cells
    Positive feedback between global warming and atmospheric CO2 concentration inferred from past climate change
    Scheffer, M. ; Brovkin, V. ; Cox, P.M. - \ 2006
    Geophysical Research Letters 33 (2006)10. - ISSN 0094-8276 - p. 1 - 4.
    carbon-cycle - ice core - antarctic ice - temperatures - greenhouse - gases - model
    There is good evidence that higher global temperatures will promote a rise of greenhouse gas levels, implying a positive feedback which will increase the effect of anthropogenic emissions on global temperatures. However, the magnitude of this effect predicted by the available models remains highly uncertain, due to the accumulation of uncertainties in the processes thought to be involved. Here we present an alternative way of estimating the magnitude of the feedback effect based on reconstructed past changes. Linking this information with the mid-range Intergovernmental Panel on Climate Change estimation of the greenhouse gas effect on temperature we suggest that the feedback of global temperature on atmospheric CO2 will promote warming by an extra 15¿78% on a century-scale. This estimate may be conservative as we did not account for synergistic effects of likely temperature moderated increase in other greenhouse gases. Our semi-empirical approach independently supports process based simulations suggesting that feedback may cause a considerable boost in warming.
    Bioflocculation of mesophilic and thermophilic activated sludge
    Vogelaar, J.C.T. ; Keizer, A. de; Spijker, S. ; Lettinga, G. - \ 2005
    Water Research 39 (2005)1. - ISSN 0043-1354 - p. 37 - 46.
    geactiveerd slib - afvalwaterbehandeling - biologische behandeling - temperatuur - uitvlokking - adsorptie - hydrofobiciteit - activated sludge - waste water treatment - biological treatment - temperature - flocculation - adsorption - hydrophobicity - paper-mill - water - effluent - temperatures - whitewater - reactors - flocs
    Thermophilic activated sludge treatment is often hampered by a turbid effluent. Reasons for this phenomenon are so far unknown. Here, the hypothesis of the temperature dependency of the hydrophobic interaction as a possible cause for diminished thermophilic activated sludge bioflocculation was tested. Adsorption of wastewater colloidal particles was monitored on different flat surfaces as a function of temperature. Adsorption on a hydrophobic surface varied with temperature between 20 and 60 °C and no upward or downward trend could be observed. This makes the hydrophobic interaction hypothesis unlikely in explaining the differences in mesophilic and thermophilic activated sludge bioflocculation. Both mesophilic and thermophilic biomass did not flocculate with wastewater colloidal particles under anaerobic conditions. Only in the presence of oxygen, with biologically active bacteria, the differences in bioflocculation behavior became evident. Bioflocculation was shown only to occur with the combination of wastewater and viable mesophilic biomass at 30 °C, in the presence of oxygen. Bioflocculation did not occur in case the biomass was inactivated or when oxygen was absent. Thermophilic activated sludge hardly showed any bioflocculation, also under mesophilic conditions. Despite the differences in bioflocculation behavior, sludge hydrophobicity and sludge zetapotentials were almost similar. Theoretical calculations using the DLVO (Derjaguin, Landau, Verweij and Overbeek) theory showed that flocculation is unlikely in all cases due to long-range electrostatic forces. These calculations, combined with the fact that bioflocculation actually did occur at 30 °C and the unlikelyness of the hydrophobic interaction, point in the direction of bacterial exo-polymers governing bridging flocculation. Polymer interactions are not included in the DLVO theory and may vary as a function of temperature.
    Survival and vigour of ultra-dry seeds after ten years of hermetic storage
    Hong, T.D. ; Ellis, R.H. ; Astley, D. ; Pinnegar, A.E. ; Groot, S.P.C. ; Kraak, H.L. - \ 2005
    Seed Science and Technology 33 (2005)2. - ISSN 0251-0952 - p. 449 - 460.
    zaadkieming - groeikracht - uitdrogingstolerantie - daucus carota - aardnoten - koolzaad - allium cepa - opslag van zaden - seed germination - vigour - desiccation tolerance - daucus carota - groundnuts - rape - allium cepa - seed storage - moisture-content limit - logarithmic relation - theoretical basis - longevity - temperatures - groundnut - protocols - lettuce
    Seeds of carrot, groundnut, lettuce, oilseed rape and onion were stored hermetically in laminated aluminium foil packets in four environments (dry or ultra-dry moisture contents combined factorially with temperatures of 20 degrees C or -20 degrees C), replicated at several sites. After ten years' hermetic storage, seed moisture content, equilibrium relative humidity, viability (assessed by ability to germinate normally in standard germination tests) and vigour were determined. After a decade, the change in seed moisture content of samples stored at -20 degrees C was small or nil. Except for groundnut and lettuce (where loss in viability was about 8 and 3%, respectively), no loss in viability was detected after 10 years' hermetic storage at -20 degrees C. In all cases, there was no difference in seed survival between moisture contents at this temperature (P > 0.25). Comparison of seed vigour (root length and rate of germination) also confirmed that drying to moisture contents in equilibrium with 10-12% r.h. had no detrimental effect to longevity when stored at -20 degrees C: the only significant (P <0.05) differences detected were slightly greater root lengths for ultra-dry storage of four of the six seed lots. Seed moisture content had increased after a decade at 20 degrees C (generally to the level in equilibrium with ambient relative humidity). Hence, sub-zero temperature storage helped maintain the long-term integrity of the laminated aluminium foil packets, as well as that of the seeds within.
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