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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    Chemical communication in tilapia: A comparison of Oreochromis mossambicus with O. niloticus
    Hubbard, P.C. ; Mota, V.C. ; Keller-Costa, T. ; Paulo da Silva, J. ; Canário, A.V.M. - \ 2014
    General and Comparative Endocrinology 207 (2014). - ISSN 0016-6480 - p. 13 - 20.
    maturation-inducing hormone - african cichlid fish - mozambique tilapia - olfactory sensitivity - speciation - pheromone - signals - urine - radiations - evolution
    In allopatric speciation species differentiation generally results from different selective pressures in different environments, and identifying the traits responsible helps to understand the isolation mechanism(s) involved. Male Mozambique tilapia (Oreochromis mossambicus) use urine to signal dominance; furthermore, 5b-pregnane-3a,17,20b-triol-3a-glucuronide (and its a-epimer, 5b-pregnane-3a,17,20atriol-3a-glucuronide), in their urine is a potent pheromone, the concentration of which is correlated with social status. The Nile tilapia (Oreochromis niloticus) is a close relative; species divergence probably resulted from geographical separation around 6 million years ago. This raises the question of whether the two species use similar urinary chemical cues during reproduction. The olfactory potency of urine, and crude extracts, from either species was assessed by the electro-olfactogram and the presence of the steroid glucuronides in urine from the Nile tilapia by liquid-chromatography/mass-spectrometry. Both species showed similar olfactory sensitivity to urine and respective extracts from either species, and similar sensitivity to the steroid glucuronides. 5b-Pregnan-3a,17a,20b-triol-3a-glucuronide was present at high concentrations (approaching 0.5 mM) in urine from Nile tilapia, with 5b-pregnan-3a,17a,20a-triol-3a-glucuronide present at lower concentrations, similar to the Mozambique tilapia. Both species also had similar olfactory sensitivity to estradiol-3-glucuronide, a putative urinary cue from females. Together, these results support the idea that reproductive chemical cues have not been subjected to differing selective pressure. Whether these chemical cues have the same physiological and behavioural roles in O. niloticus as O. mossambicus remains to be investigated.
    Terrestrial selenium distribution in China is potentially linked to monsoonal climate
    Blazina, T. ; Sun, Y. ; Voegelin, A. ; Lenz, M. ; Berg, M. ; Winkel, L.H.E. - \ 2014
    Nature Communications 5 (2014). - ISSN 2041-1723
    red clay formation - loess plateau - atmospheric selenium - trace-metals - adsorption - speciation - pliocene - records - water - soil
    The prevalence of terrestrial environments low in the essential trace element selenium (Se) results in large-scale Se deficiency worldwide. However, the underlying processes leading to Se-depleted environments have remained elusive. Here we show that over the last 6.8 million years (Ma) climatic factors have played a key role in the Se distribution in loess–paleosol sequences in the Chinese Loess Plateau (CLP), which lies in a severely Se-depleted region with a history of Se deficiency-related diseases. We use a combination of geochemical and paleoclimate data to demonstrate that during interglacial periods between 2.30 and 0.16¿Ma, variations in the Se concentration in the CLP are potentially related to variability in Se input via East Asian monsoon-derived precipitation. Our results identify precipitation as an important controlling factor of Se distribution in monsoonal China. We suggest that atmospheric Se inputs via precipitation could also play an important role in other regions worldwide.
    Influence of pH on the redox chemistry of metal (hydr)oxides and organic matter in paddy soils
    Pan, Y. ; Koopmans, G.F. ; Bonten, L.T.C. ; Song, J. ; Luo, Y. ; Temminghoff, E.J.M. ; Comans, R.N.J. - \ 2014
    Journal of Soils and Sediments 14 (2014)10. - ISSN 1439-0108 - p. 1713 - 1726.
    flooded soil - ion-binding - cadmium - iron - speciation - manganese - reduction - sorption - dynamics - mobilization
    The primary purpose of this study was to determine how flooding and draining cycles affect the redox chemistry of metal (hydr)oxides and organic matter in paddy soils and how the pH influences these processes. Our secondary purpose was to determine to what extent a geochemical thermodynamic equilibrium model can be used to predict the solubility of Mn and Fe during flooding and draining cycles in paddy soils. We performed a carefully designed column experiment with two paddy soils with similar soil properties but contrasting pH.We monitored the redox potential (Eh) continuously and took soil solution samples regularly at four depths along the soil profile during two successive flooding and drainage cycles. To determine dominant mineral phases of Mn and Fe under equilibrium conditions, stability diagrams of Mn and Fe were constructed as a function of Eh and pH. Geochemical equilibrium model calculations were performed to identify Mn and Fe solubility-controlling minerals and to compare predicted total dissolved concentrations with their measured values. Flooding led to strong Eh gradients in the columns of both soils. In the acidic soil, pH increased with decreasing Eh and vice versa, whereas pH in the alkaline soil was buffered by CaCO3. In the acidic soil, Mn and Fe solubility increased during flooding due to reductive dissolution of their (hydr)oxides and decreased during drainage because of re-oxidation. In the alkaline soil, Mn and Fe solubility did not increase during flooding due to Mn(II) and Fe(II) precipitation as MnCO3, FeCO3, and FeS. The predicted levels of soluble Mn and Fe in the acidic soil were much higher than their measured values, but predictions and measurements were rather similar in the alkaline soil. This difference is likely due to kinetically limited reductive dissolution of Mn and Fe (hydr)oxides in the acidic soil. During flooding, the solubility of dissolved organic matter increased in both soils, probably because of reductive dissolution of Fe (hydr)oxides and the observed increase in pH. Conclusions Under alternating flooding and draining conditions, the pH greatly affected Mn and Fe solubility via influencing either reductive dissolution or carbonate formation. Comparison between measurements and geochemical equilibrium model predictions revealed that reductive dissolution of Mn and Fe (hydr)oxides was kinetically limited in the acidic soil. Therefore, when applying such models to systems with changing redox conditions, such rate-limiting reactions should be parameterized and implemented to enable more accurate predictions of Mn and Fe solubility.
    Characterization of Phosphorus in Animal Manures Collected from Three (Dairy, Swine, and Broiler) Farms in China
    Li, G. ; Li, H. ; Leffelaar, P.A. ; Shen, J. ; Zhang, F. - \ 2014
    PLoS ONE 9 (2014)7. - ISSN 1932-6203
    magnetic-resonance-spectroscopy - enzymatic-hydrolysis - organic phosphorus - northwest germany - poultry litter - forms - soil - diets - speciation - fractions
    In order to identify the phosphorus species and concentration in animal manure, we comparatively characterized phosphorus in dairy manure, swine manure, and broiler litter, using a sequential procedure, a simplified two-step procedure (NaHCO3/NaOH+EDTA), and a solution Phosphorus-31 Nuclear Magnetic Resonance (31P-NMR) spectroscopy procedure. In the sequential procedure, deionized water extracted 39, 22, and 32%; NaHCO3 extracted 48, 26, and 37%; NaOH extracted 8, 9, and 13.8%; and HCl extracted 3, 42.8, and 17% of the total phosphorus in dairy manure, swine manure and broiler litter, respectively. Total phosphorus extracted by the NaHCO3/NaOH+EDTA procedure was 7.5, 32.4, and 15.8 g P kg-1 for dairy manure, swine manure, and broiler litter, respectively. The solution 31P-NMR procedure detected that 9, 34, and 29% of total phosphorus was phytic acid in dairy manure, swine manure, and broiler litter, respectively. These results show that phosphorus forms, availability, and quantities differ between animal manures, which provides valuable information for P characterization of animal manures in China.
    Multi-face modeling to predict free zinc ion concentrations in low-zinc soils
    Duffner, A. ; Weng, L. ; Hoffland, E. ; Zee, S.E.A.T.M. van der - \ 2014
    Environmental Science and Technology 48 (2014)10. - ISSN 0013-936X - p. 5700 - 5708.
    donnan membrane technique - organic-matter - heavy-metals - contaminated soils - isotopic exchange - humic substances - trace-metals - sandy soil - adsorption - speciation
    Multi-surface models are widely used to assess the potential ecotoxicological risk in metal-contaminated soils. Their accuracy in predicting metal speciation in soils with low metal levels was not yet tested. Now highly sensitive analytical techniques are available to experimentally validate such models at low concentration levels. The objective of this study was to test the accuracy of a multi-surface model to predict the Zn2+ concentration and to improve our understanding of Zn bioavailability in low-Zn soils. High-Zn soils were included as controls. Model parameters were determined independently on the basis of earlier peer-reviewed publications. Model output was validated against free Zn2+ concentrations determined with the soil column Donnan membrane technique in a range of soils varying in potentially available Zn, organic matter, clay silicate, and iron (hydr)oxide contents and pH. Deviations between predicted Zn2+ concentrations and experimentally determined values over the whole Zn concentration range were less or equal to the experimental standard error, except for one low-Zn soil. The Zn2+ concentration was mainly controlled by adsorption, where organic matter was predicted to be the dominant soil sorbent. The predicted Zn2+ concentration depends more sensitively upon changes of the reactive Zn pool (application of 0.6, 1.2, 2.4, and 3.6 mg of Zn kg–1 of soil) and organic matter content (±0.2 and 0.4%) than pH changes (±0.5 and 1 pH unit).
    Natural wetland emissions of methylated trace elements
    Vriens, B. ; Lenz, M. ; Charlet, L. ; Berg, M. ; Winkel, L.H.E. - \ 2014
    Nature Communications 5 (2014). - ISSN 2041-1723
    yellowstone-national-park - selenium volatilization - atmospheric selenium - biomethylation - soil - speciation - bacterium - products - sulfide - sulfur
    Natural wetlands are well known for their significant methane emissions. However, trace element emissions via biomethylation and subsequent volatilization from pristine wetlands are virtually unstudied, even though wetlands constitute large reservoirs for trace elements. Here we show that the average volatile fluxes of selenium (
    Data from: Genetic consequences of breaking migratory traditions in barnacle geese Branta leucopsis
    Jonker, R.M. ; Kraus, Robert ; Zhang, Q. ; Hooft, Pim van; Larsson, K. ; Jeugd, H.P. van der; Kurvers, Ralf ; Wieren, Sip van; Loonen, M.J.J.E. ; Crooijmans, Richard ; Ydenberg, Ron ; Groenen, Martien ; Prins, Herbert - \ 2013
    Wageningen University & Research
    population genetics - SNP - admixture - Branta leucopsis - migration modelling - speciation - cultural evolution
    Cultural transmission of migratory traditions enables species to deal with their environment based on experiences from earlier generations. Also, it allows a more adequate and rapid response to rapidly changing environments. When individuals break with their migratory traditions, new population structures can emerge that may affect gene flow. Recently, the migratory traditions of the Barnacle Goose Branta leucopsis changed, and new populations differing in migratory distance emerged. Here, we investigate the population genetic structure of the Barnacle Goose to evaluate the consequences of altered migratory traditions. We used a set of 358 single nucleotide polymorphism (SNP) markers to genotype 418 individuals from breeding populations in Greenland, Spitsbergen, Russia, Sweden and the Netherlands, the latter two being newly emerged populations. We used discriminant analysis of principal components, FST, linkage disequilibrium and a comparison of geneflow models using migrate-n to show that there is significant population structure, but that relatively many pairs of SNPs are in linkage disequilibrium, suggesting recent admixture between these populations. Despite the assumed traditions of migration within populations, we also show that genetic exchange occurs between all populations. The newly established nonmigratory population in the Netherlands is characterized by high emigration into other populations, which suggests more exploratory behaviour, possibly as a result of shortened parental care. These results suggest that migratory traditions in populations are subject to change in geese and that such changes have population genetic consequences. We argue that the emergence of nonmigration probably resulted from developmental plasticity.
    Mechanisms contributing to the thermal analysis of waste incineration bottom ash and quantification of idfferent carbon species
    Rocca, S. ; Zomeren, A. van; Costa, G. ; Dijkstra, J.J. ; Comans, R.N.J. ; Lombardi, F. - \ 2013
    Waste Management 33 (2013)2. - ISSN 0956-053X - p. 373 - 381.
    loss-on-ignition - fly-ash - unburned carbon - behavior - speciation - residues - coal
    The focus of this study was to identify the main compounds affecting the weight changes of bottom ash (BA) in conventional loss on ignition (LOI) tests and to obtain a better understanding of the individual processes in heterogeneous (waste) materials such as BA. Evaluations were performed on BA samples from a refuse derived fuel incineration (RDF-I) plant and a hospital waste incineration (HW-I) plant using thermogravimetric analysis and subsequent mass spectrometry (TG–MS) analysis of the gaseous thermal decomposition products. Results of TG–MS analysis on RDF-I BA indicated that the LOI measured at 550 °C was due to moisture evaporation and dehydration of Ca(OH)2 and hydrocalumite. Results for the HW-I BA showed that LOI at 550 °C was predominantly related to the elemental carbon (EC) content of the sample. Decomposition of CaCO3 around 700 °C was identified in both materials. In addition, we have identified reaction mechanisms that underestimate the EC and overestimate the CaCO3 contents of the HW-I BA during TG–MS analyses. These types of artefacts are expected to occur also when conventional LOI methods are adopted, in particular for materials that contain CaO/Ca(OH)2 in combination with EC and/or organic carbon, such as e.g. municipal solid waste incineration (MSWI) bottom and fly ashes. We suggest that the same mechanisms that we have found (i.e. in situ carbonation) can also occur during combustion of the waste in the incinerator (between 450 and 650 °C) demonstrating that the presence of carbonate in bottom ash is not necessarily indicative for weathering. These results may also give direction to further optimization of waste incineration technologies with regard to stimulating in situ carbonation during incineration and subsequent potential improvement of the leaching behavior of bottom ash.
    Arsenate and phosphate adsorption in relation to oxides composition in soils: LCD modelling
    Cui, Y. ; Weng, L. - \ 2013
    Environmental Science and Technology 47 (2013)13. - ISSN 0013-936X - p. 7269 - 7276.
    charge-distribution - humic substances - competitive adsorption - ion adsorption - heavy-metals - speciation - parameters - minerals - sorption - binding
    The pH dependent solid-solution distribution of arsenate and phosphate in five Dutch agricultural soil samples was measured in the pH range 4–8, and the results were interpreted using the LCD (ligand and charge distribution) adsorption modeling. The pH dependency is similar for both oxyanions, with a minimum soluble concentration observed around pH 6–8. This pH dependency can be successfully described with the LCD model and it is attributed mainly to the synergistic effects from Ca adsorption. The solubility of phosphate is much lower than that of arsenate. This big difference cannot be sufficiently explained by the reduction of small amount of As(V) into As(III), neither by slow desorption/adsorption. The difference between phosphate and arsenate in their solid-solution distribution becomes larger with the increase of aluminum (hydr)oxides (Al-oxides) contribution to the total amount of metal (Al and Fe) (hydr)oxides. The influence of Al-oxides is much larger than its relative amount extracted from the soils. When Al-oxides account for >40% of the soil oxides, the whole adsorbents behave apparently similarly to that of pure Al-oxides. These results indicated that surface coating and substitution may have modified significantly oxyanion adsorption to Fe-oxides in soils, and how to account for this complexity is a challenge for geochemical modeling.
    The effect of phosphorus binding clay (Phoslock) in mitigating cyanobacterial nuisance: A laboratory study on the effects on water quality variables and plankton
    Oosterhout, J.F.X. ; Lurling, M. - \ 2013
    Hydrobiologia 710 (2013)1. - ISSN 0018-8158 - p. 265 - 277.
    rare-earth-elements - organic-matter - lake restoration - eutrophication - microcystis - netherlands - sediments - blooms - complexation - speciation
    This laboratory study examined the lanthanum modified clay Phoslock® for its effectiveness to bind soluble reactive phosphorus (SRP), release of nutrients from this modified clay, its influence on water quality variables (pH, oxygen saturation %, conductivity and turbidity), effects on phytoplankton growth (green alga Scenedesmus obliquus, cyanobacteria Microcystis aeruginosa and Anabaena sp.), and, lastly, its effect on the population growth of the rotifer Brachionus calyciflorus. A clear dose–response for SRP binding by the modified clay was observed. A small amount of ammonium is released from Phoslock®. We found no effect of Phoslock® on pH or oxygen saturation. Conductivity increased with the increasing concentration of Phoslock®. An application of Phoslock® caused a transient increase of turbidity up to 211 NTU. However, due to rapid settlement, turbidity fell below 13 NTU (~1 m Secchi depth), after 6 h. Phoslock® addition caused a reduction in growth of all phytoplankton species tested that we attribute to the combined effects of light limitation, flocculation with the bentonite and binding of SRP to Phoslock®. We estimated the EC50 of Phoslock® on the population growth of rotifer B. calyciflorus to be 0.15 g Phoslock® l-1. Overall, the results of our study indicate Phoslock® seems to be suitable for field applications.
    Biovailability of copper and zinc in pig and cattle slurries
    Jakubus, M. ; Dach, J. ; Starmans, D.A.J. - \ 2013
    Fressenius Environmental Bulletin 22 (2013)4. - ISSN 1018-4619 - p. 995 - 1002.
    sequential extraction procedures - heavy-metals - soils - fractionation - speciation - sediments - manganese - sludge - nickel - lead
    Slurry is an important source of macronutrients, micro-nutrients and organic matter. Despite the considerable fertilizer value of slurry, it may be abundant in amounts of copper and zinc originating from dietary. The study presents quantitative changes in copper and zinc in individual slurries (pig and cattle slurries). The bioavailability of copper and zinc was estimated on the basis of amounts of the metals in isolated fractions using the sequential extraction method. Sequential techniques identify fractions which describe different connections of metals with the compost solid phase beginning with those that are easiest soluble up to those that dissolve with the greatest difficulties.Pig slurry was characterized by 2-fold higher amounts of copper and zinc in comparison to the levels detected in cattle slurries. Quantitative changes of the elements in the sequentially isolated fractions of analyzed slurries differed. First of all, this was dependent on the chemical character of a given metal, followed by the animal species, or the type of management. Irrespective of the type of slurry, 40-56% of the total amounts of copper were found in hardly available combinations, while available copper forms accounted for only 6.6–10.9%. Zinc was found predominantly in com-binations with iron and manganese oxides which, irrespective of the tested slurry, ranged from 130.64 mg·kg-1 to 293.60 mg·kg-1. Bioavailable metal contents, potentially introduced to soil with slurry doses, calculated as 170 kg total N/ha/year, ranged from 63.6 to 124.5 g for copper, and from 349.5 to 696.4 g for zinc. The estimated amounts of metal inputs to agricultural land demonstrate that soils are potentially at risk of heavy metal accumulation from the application of pig and cattle slurries.
    Crossability patterns in Asia Pacific Oryza series Sativae
    Banaticla-Hilario, M.C.N. ; Sackville Hamilton, R. ; Berg, R.G. van den; McNally, K.L. - \ 2013
    Genetic Resources and Crop Evolution 60 (2013)6. - ISSN 0925-9864 - p. 1899 - 1914.
    reproductive isolation - rice oryza - wild-rice - genome - hybridization - evolution - speciation - diversity - rufipogon - differentiation
    Reproductive barriers are thought to intensify with increasing genetic distance between species. To assess the extent of post-pollination reproductive isolation within and among the Asia Pacific species of Oryza series Sativae, crossing experiments using 15 accessions of O. meridionalis Ng, O. nivara Sharma et Shastry, and O. rufipogon Griff. were conducted. Intra- and interspecific crosses of the selfing species O. meridionalis and O. nivara had very low seed set and produced inviable F1 seeds indicative of strong pre- and post-zygotic barriers. Contrastingly, the outcrossing O. rufipogon exhibited high intraspecific crossability and modest compatibility with O. nivara and O. meridionalis in terms of seed set suggesting substantial pre-zygotic reproductive isolation of the species. O. rufipogon was asymmetrically compatible with O. meridionalis and symmetrically with O. nivara. The two inbreeding species manifested comparable degrees of isolation from O. rufipogon despite differences in strength of several post-zygotic barriers. Mating compatibility within and between the Asia Pacific species of Oryza series Sativae is not strongly spatially influenced, but some resistance to gene flow under sympatric conditions was observed. Intraspecific O. rufipogon F1s were more vegetatively robust and more late-flowering than their parents. Intra- and interspecific hybrids of Australasian O. rufipogon differed phenotypically from crosses with non-Australasian populations. Interspecific hybrids displayed both intermediate and parental character traits. O. nivara and O. rufipogon generated early-flowering F1s that are more similar to the former. O. meridionalis and O. rufipogon produced F1s that varied in phenology and morphology depending on the maternal and paternal species.
    Corresponding Mitochondrial DNA and Niche Divergence for Crested Newt Candidate Species
    Wielstra, B.M. ; Beukema, W. ; Arntzen, J.W. ; Skidmore, A.K. ; Toxopeus, A.G. ; Raes, N. - \ 2012
    PLoS ONE 7 (2012)9. - ISSN 1932-6203
    absence data - models - phylogeography - delimitation - speciation - ecology - areas
    Genetic divergence of mitochondrial DNA does not necessarily correspond to reproductive isolation. However, if mitochondrial DNA lineages occupy separate segments of environmental space, this supports the notion of their evolutionary independence. We explore niche differentiation among three candidate species of crested newt (characterized by distinct mitochondrial DNA lineages) and interpret the results in the light of differences observed for recognized crested newt species. We quantify niche differences among all crested newt (candidate) species and test hypotheses regarding niche evolution, employing two ordination techniques (PCA-env and ENFA). Niche equivalency is rejected: all (candidate) species are found to occupy significantly different segments of environmental space. Furthermore, niche overlap values for the three candidate species are not significantly higher than those for the recognized species. As the three candidate crested newt species are, not only in terms of mitochondrial DNA genetic divergence, but also ecologically speaking, as diverged as the recognized crested newt species, our findings are in line with the hypothesis that they represent cryptic species. We address potential pitfalls of our methodology.
    Determination of free Zn2+ concentration in synthetic and natural samples with AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) and DMT (Donnan Membrane Techniques)
    Chito, D. ; Weng, L.P. ; Galceran, J. ; Companys, E. ; Puy, J. ; Riemsdijk, W.H. van; Leeuwen, H.P. van - \ 2012
    Science of the Total Environment 421-422 (2012). - ISSN 0048-9697 - p. 238 - 244.
    dissolved organic-matter - metal-ion concentrations - humic-acid - electroanalytical technique - lolium-perenne - soil solution - trace-metals - speciation - binding - waters
    The determination of free Zn2+ ion concentration is a key in the study of environmental systems like river water and soils, due to its impact on bioavailability and toxicity. AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) and DMT (Donnan Membrane Technique) are emerging techniques suited for the determination of free heavy metal concentrations, especially in the case of Zn2+, given that there is no commercial Ion Selective Electrode. In this work, both techniques have been applied to synthetic samples (containing Zn and NTA) and natural samples (Rhine river water and soils), showing good agreement. pH fluctuations in DMT and N2/CO2 purging system used in AGNES did not affect considerably the measurements done in Rhine river water and soil samples. Results of DMT in situ of Rhine river water are comparable to those of AGNES in the lab. The comparison of this work provides a cross-validation for both techniques.
    Olivine Weathering in Soil, and Its Effects on Growth and Nutrient Uptake in Ryegrass (lolium perenne L.): A Pot Experiment
    Berge, H.F.M. ten; Meer, H.G. van der; Steenhuizen, J.W. ; Goedhart, P.W. ; Knops, P. ; Verhagen, J. - \ 2012
    PLoS ONE 7 (2012)8. - ISSN 1932-6203
    carbon-dioxide - plant - bioavailability - sequestration - phytotoxicity - serpentine - nickel - co2 - speciation - models
    Mineral carbonation of basic silicate minerals regulates atmospheric CO2 on geological time scales by locking up carbon. Mining and spreading onto the earth's surface of fast-weathering silicates, such as olivine, has been proposed to speed up this natura
    Age structure in neutral theory resolves inconsistencies related to reproductive size threshold
    Rosindell, J. ; Jansen, P.A. ; Etienne, R.S. - \ 2012
    Journal of Plant Ecology 5 (2012)1. - ISSN 1752-9921 - p. 64 - 71.
    species-area relationships - biodiversity - speciation - model - biogeography - limitation - dispersal - diversity - abundance - forests
    Neutral theory consists of a suite of models that assume ecological equivalence among individual organisms. They have been most commonly applied to tropical forest tree communities either as null models or as approximations. Neutral models typically only include reproductive adults; therefore, fitting to empirical tree community data requires defining a reproductive-size threshold, which for trees is usually set arbitrarily to a diameter at breast height (DBH) of 100 mm. The inevitable exclusion of some reproductive adults and inclusion of some saplings cause a non-random sampling bias in neutral model fits. Here, we investigate this problem and resolve it by introducing simple age structure into a neutral model.
    Environmental Selenium Research: From Microscopic Processes to Global Understanding
    Winkel, L.H.E. ; Johnson, C.A. ; Lenz, M. ; Grundl, T. ; Leupin, O.X. ; Amini, M. ; Charlet, L. - \ 2012
    Environmental Science and Technology 46 (2012)2. - ISSN 0013-936X - p. 571 - 579.
    plasma-mass spectrometry - icp-ms - arsenic contamination - agricultural soils - sewage-sludge - speciation - se - chromatography - groundwater - metabolism
    Selenium is a natural trace element that is of fundamental importance to human health. The extreme geographical variation in selenium concentrations in soils and food crops has resulted in significant health problems related to deficient or excess levels of selenium in the environment. To deal with these kinds of problems in the future it is essential to get a better understanding of the processes that control the global distribution of selenium. The recent development of analytical techniques and methods enables accurate selenium measurements of environmental concentrations, which will lead to a better understanding of biogeochemical processes. This improved understanding may enable us to predict the distribution of selenium in areas where this is currently unknown. These predictions are essential to prevent future Se health hazards in a world that is increasingly affected by human activities.
    Hg transfer from contaminated soils to plants and animals
    Rodrigues, S.M. ; Henriques, B. ; Reis, A.T. ; Duarte, A.C. ; Pereira, E. ; Romkens, P.F.A.M. - \ 2012
    Environmental Chemistry Letters 10 (2012)1. - ISSN 1610-3653 - p. 61 - 67.
    potentially toxic elements - chloralkali plant - available pools - total mercury - part ii - speciation - transport - portugal - slovenia - samples
    Understanding the transfer of mercury (Hg) from soil to crops is crucial due to Hg toxicity and Hg occurrence in terrestrial systems. Previous research has shown that available Hg in soils contributes to plant Hg levels. Plant Hg concentrations are related to soil conditions and plant characteristics. Mechanistic models describing such soil–plant interactions are however difficult to quantify. Here we performed a field study in agricultural, mining and industrial areas in Portugal to evaluate potential food chain risks. The uptake of Hg by Italian ryegrass, ryegrass, orchard grass, collard greens and rye was measured to calculate daily intakes (DI) of Hg for cows and sheep grazing. A total of 136 soil samples and 129 plant samples were analysed. Results show that total Hg concentrations ranged from 0.01 to 98 mg kg-1 in soils; 0.01–5.4 mg kg-1 in shoots and 0.01–42 mg kg-1 in roots. Calculated DI ranged from 0.18 to 132 mg d-1 for cows, and from 0.028 to 23 mg d-1 for sheep. In 27 grassland sites, daily intakes exceeded the acceptable daily intake of both cows and sheep in view of food safety considering Hg in animal kidneys evidencing potential risks to human health. The transfer of Hg from soil to crops was described using empirical Freundlich-type functions. For ryegrass, orchard grass and collard greens, the soil-to-root or soil-to-shoot transfer of Hg appeared to be controlled by the total soil Hg concentration and levels of Alox and Feox. Empirical functions allowed us to obtain realistic estimates of Hg levels in crops and can be used as an alternative to mechanistic models when evaluating food chain risks of Hg contamination in agricultural soils.
    Pyrrolizidine alkaloid variation in shoots and roots of segregating hybrids between Jacobaea vulgaris and Jacobaea aquatica
    Cheng, D. ; Kirk, H. ; Mulder, P.P.J. ; Vrieling, K. ; Klinkhamer, P.G.L. - \ 2011
    New Phytologist 192 (2011)4. - ISSN 0028-646X - p. 1010 - 1023.
    senecionine n-oxide - british-isles - natural hybridization - plant hybridization - chemical diversity - tyria-jacobaeae - asteraceae - speciation - evolution - translocation
    Hybridization can lead to novel qualitative or quantitative variation of secondary metabolite (SM) expression that can have ecological and evolutionary consequences.•We measured pyrrolizidine alkaloid (PA) expression in the shoots and roots of a family including one Jacobaea vulgaris genotype and one Jacobaea aquatica genotype (parental genotypes), two F1 hybrid genotypes, and 102 F2 hybrid genotypes using liquid chromatography–tandem mass spectrometry (LC-MS/MS).•We detected 37 PAs in the roots and shoots of J. vulgaris, J. aquatica and the hybrids. PA concentrations and compositions differed between genotypes, and between roots and shoots. Three otosenine-like PAs that only occurred in the shoots of parental genotypes were present in the roots of F2 hybrids; PA compositions were sometimes novel in F2 hybrids compared with parental genotypes, and in some cases transgressive PA expression occurred. We also found that PAs from within structural groups covaried both in the roots and in the shoots, and that PA expression was correlated between shoots and roots.•Considerable and novel variation present among F2 hybrids indicates that hybridization has a potential role in the evolution of PA diversity in the genus Jacobaea, and this hybrid system is useful for studying the genetic control of PA expression
    Unraveling the rapid radiation of crested newts, Triturus cristatus superspecies, using complete mitogenomic sequences
    Wielstra, B.M. ; Arntzen, J.W. - \ 2011
    BMC Evolutionary Biology 11 (2011). - ISSN 1471-2148 - 8 p.
    complete mitochondrial genomes - historical biogeography - phylogenetic analysis - mixed models - dna - salamandridae - phylogeography - nuclear - mtdna - speciation
    Background - The rapid radiation of crested newts (Triturus cristatus superspecies) comprises four morphotypes: 1) the T. karelinii group, 2) T. carnifex - T. macedonicus, 3) T. cristatus and 4) T. dobrogicus. These vary in body build and the number of rib-bearing pre-sacral vertebrae (NRBV). The phylogenetic relationships of the morphotypes have not yet been settled, despite several previous attempts, employing a variety of molecular markers. We here resolve the crested newt phylogeny by using complete mitochondrial genome sequences. Results - Bayesian inference based on the mitogenomic data yields a fully bifurcating, significantly supported tree, though Maximum Likelihood inference yields low support values. The internal branches connecting the morphotypes are short relative to the terminal branches. Seen from the root of Triturus (NRBV = 13), a basal dichotomy separates the T. karelinii group (NRBV = 13) from the remaining crested newts. The next split divides the latter assortment into T. carnifex - T. macedonicus (NRBV = 14) versus T. cristatus (NRBV = 15) and T. dobrogicus (NRBV = 16 or 17). Conclusions - We argue that the Bayesian full mitochondrial DNA phylogeny is superior to previous attempts aiming to recover the crested newt species tree. Furthermore, our new phylogeny involves a maximally parsimonious interpretation of NRBV evolution. Calibrating the phylogeny allows us to evaluate potential drivers for crested newt cladogenesis. The split between the T. karelinii group and the three other morphotypes, at ca. 10.4 Ma, is associated with the separation of the Balkan and Anatolian landmasses (12-9 Ma). No currently known vicariant events can be ascribed to the other two splits, first at ca. 9.3 Ma, separating T. carnifex - T. macedonicus, and second at ca. 8.8 Ma, splitting T. cristatus and T. dobrogicus. The crested newt morphotypes differ in the duration of their annual aquatic period. We speculate on the role that this ecological differentiation could have played during speciation
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