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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The relevance of spatial scales in nutrient balances on dairy farms
Leeuwen, M.W.J. van; Middelaar, C.E. van; Oenema, J. ; Dam, J.C. van; Stoorvogel, J.J. ; Stoof, C.R. ; Boer, I.J.M. de - \ 2019
Agriculture, Ecosystems and Environment 269 (2019). - ISSN 0167-8809 - p. 125 - 139.
Policy makers and farmers use tools, such as a nutrient balance, to gain insight into the environmental impact of agricultural practices. A discrepancy, however, exists between the needs of policy makers and farmers, about the use and the spatial scale of such tools. Farm balances calculate nutrient balances across all agricultural fields within a farm without distinguishing separate fields, whereas field balances calculate a nutrient balance on a delineated field. For farmers, a nutrient balance at field level is more useful than at crop or farm level, because decision making and fine-tuning management occurs at the field level. A field balance, however, requires more detailed data than a farm balance and therefore is less easy to implement. As soil types influence nutrient balances, we hypothesize that if within-farm variation in soil types is low, there is no need to replace a farm balance by a field balance. To test this hypothesis, we computed nutrient balances at farm and field level on five Dutch dairy farms (three on sand, two on clay), varying in degree of within-farm variation in soil series. A full year of soil nitrogen (N) and phosphorus (P) input and output data on farm and field level were provided by farmers, while soil variation was determined using the Dutch 1:50.000 soil map. The Annual farm Nutrient Cycle Assessment (ANCA) was used to calculate soil N and P surpluses, and soil nutrient fluxes such as nitrate leaching and nitrous oxide emission at farm and field level. Even on farms with few soil series, a considerable variation in N and P inputs, outputs and balances across fields was found, due to management differences and soil properties not represented by the soil map. Furthermore, field-level balances better represented nitrogen leaching than farm-level balances on farms with diverse soils (reflected by different leaching factors) and negative nitrogen field balances (deficits). Also, using field balances, for one case study farm the highest soil N surplus (kg ha−1) was found on grass fields with the highest risk of N leaching. A field balance, therefore, provides more meaningful information than a farm balance when variation in soil types and/or management factors is found within the farm, because soil types and management factors affect N and P balances, N leaching and N emissions. For farms with the highest variation in soil types and/or management, we recommend using field-level nutrient balances in order to detect extreme surpluses, deficits, leaching and/or emissions, to improve management decisions.

Monitoring integraal duurzame stallen : Peildatum 1 januari 2018
Peet, G.F.V. van der; Meer, R.W. van der; Docters van Leeuwen, H. ; Wageningen-Lucardie, S.R.M. van - \ 2018
Wageningen : Wageningen Livestock Research (Wageningen Livestock Research rapport 1114) - 20
Sinds 2008 voert WUR in opdracht van het ministerie van Landbouw, Natuur en Voedselkwaliteit (LNV) de monitor integraal duurzame stallen uit. De monitor laat zien dat op 1 januari 2018 in Nederland 15,0 % van alle rundvee-, varkens- en pluimveestallen integraal duurzaam is---Since 2008 commissioned by the Ministry of agriculture, nature and food quality (LNV) WUR conducts the monitor integral sustainable stables. The monitor shows that on 1 January 2018 in the Netherlands 15.0% of all cattle, pig and poultry houses are integral sustainable
Functional principles of steerable multi-element probes in insects
Cerkvenik, Uroš ; Dodou, Dimitra ; Leeuwen, Johan L. van; Gussekloo, Sander W.S. - \ 2018
Biological reviews (2018). - ISSN 1464-7931 - 20 p.
buckling avoidance - hemipterans - mosquitoes - multi-element probes - parasitic wasps - spatial probing - steering

Hemipterans, mosquitoes, and parasitic wasps probe in a variety of substrates to find hosts for their larvae or food sources. Probes capable of sensing and precise steering enable insects to navigate through solid substrates without visual information and to reach targets that are hidden deep inside the substrate. The probes belong to non-related taxa and originate from abdominal structures (wasps) or mouthparts (hemipterans and mosquitoes), but nevertheless share several morphological characteristics. Although the transport function clearly differs (egg laying and acquisition of liquid food), the functional demands on the mechanical behaviour of the probe within the substrate tend to be similar. The probe needs to be thin to limit substrate deformation, and long, in order to attain substantial path lengths or depths. We linked the morphology across taxa to the different functional requirements, to provide insights into the biology of probing insects and the evolution of their probes. Current knowledge of insect probes is spread over many taxa, which offers the possibility to derive general characteristics of insect probing. Buckling during initial puncturing is limited by external support mechanisms. The probe itself consist of multiple (3–6) parts capable of sliding along one another. This multi-part construction presumably enables advancement and precise three-dimensional steering of the probe through the substrate with very low net external pushing forces, preventing buckling during substrate penetration. From a mechanical viewpoint, a minimum of three elements is required for 3D steering and volumetric exploration, as realised in the ovipositors of wasps. More elements, such as in six-element probes of mosquitoes, may enhance friction in soft substrates. Alternatively, additional elements can have functions other than ‘drilling’, such as saliva injection in mosquitoes. Despite the gross similarities, probes show differences in their cross sections, tip morphologies, relative lengths of their elements, and the shape of their interconnections. The hypothesis is that the probe morphology is influenced by the substrate properties, which are mostly unknown. Correlating the observed diversity to substrate-specific functional demands is therefore currently impossible. We conclude that a multipart probe with sliding elements is highly effective for volumetric substrate probing. Shared functional demands have led to an evolutionary convergence of slender multi-element probes in disparate insect taxa. To fully understand 3D probing, it is necessary to study the sensory and material properties, as well as the detailed kinematics and dynamics of the various probes in relation to the nature of the selective pressure originating from the species-specific substrates. Such knowledge will deepen our understanding of probing mechanisms and may support the development of slender, bio-inspired probes.

Plant functional diversity and nutrient availability can improve restoration of floating fens via facilitation, complementarity and selection effects
Zuidam, Jeroen P. van; Leeuwen, Casper H.A. van; Bakker, Elisabeth S. ; Verhoeven, Jos T.A. ; Ijff, Stéphanie ; Peeters, Edwin T.H.M. ; Zuidam, Bastiaan G. van; Soons, Merel B. - \ 2018
Journal of Applied Ecology (2018). - ISSN 0021-8901
assisted colonization - floating fen - functional diversity - peat formation - restoration - rhizome formation - terrestrialization - wetlands

Peat-forming wetlands, particularly floating fens that form the initial stages of these ecosystems, are declining globally due to excavation, dehydration and eutrophication. Restoration typically involves reestablishment of early-successional open-water stages, with oligotrophic conditions that are characteristic for these systems. However, restoration success is notoriously limited. A potential improvement may be to initiate succession by reintroducing of target plant species. Knowledge is therefore needed on (a) which plant functional groups should be re-introduced to stimulate fen formation; and (b) how to manage nutrient levels during restoration, considering that plant growth may be slow in oligotrophic conditions. We hypothesized that increasing functional diversity of introduced species would stimulate the formation of peat-forming target communities, their biomass accumulation and expansion onto open water. We also hypothesized that nutrient availability would mediate the relative contribution of specific functional groups to these effects. We investigated this in 36 artificial outdoor ponds by manipulating plant functional diversity (clonal dominants, clonal stress-tolerators and interstitials) on constructed rafts with fen-forming communities, and subjected these to a range of nutrient loadings over 2 years. Increasing functional diversity as well as increasing nutrient loadings had stimulating effects on plant biomass accumulation, cover formation and rhizome growth onto open water. Both complementarity (due to niche partitioning or facilitation) and selection effects were mechanisms underlying the diversity effect, with a constant relative importance over the entire range of nutrient availabilities. Different functional groups were important for biomass production at different nutrient availabilities. Rhizome formation by clonal stress-tolerators contributed disproportionately to open water colonization, identifying this functional group as key across all nutrient levels. Synthesis and applications. Restoration of floating fen communities can be stimulated during the first 2 years by introducing a high functional diversity of plant species. There include fast-growing clonal species, clonal stress-tolerators and interstitials, which facilitate each other. Restoration is dependent on the presence of clonal stress-tolerators such as Calla palustris, Comarum palustre and Menyanthes trifoliata for expansion onto the open water. Furthermore, restoration can start under a wide range of water nutrient levels, including eutrophic conditions.

Data from: Three-dimensional analysis of the fast-start escape response of the least killifish, Heterandria formosa
Fleuren, M. ; Leeuwen, J.L. van; Quicazan Rubio, E.M. ; Pieters, R.P.M. ; Pollux, B.J.A. ; Voesenek, C.J. - \ 2018
3D tracking - C start - biomechanics - fish behaviour - swimming - Heterandria formosa
Fish make C-starts to evade predator strikes. Double-bend (DB) C-starts consist of three stages: Stage 1, in which the fish rapidly bends into a C-shape; Stage 2, in which the fish bends in the opposite direction; and a variable Stage 3. In single-bend (SB) C-starts, the fish immediately straightens after Stage 1. Despite fish moving in 3D space, fast-start responses of adult fish have mainly been studied in a horizontal plane. Using automated 3D tracking of multi-camera high-speed video sequences, we show that both SB and DB fast-starts by adult female least killifish (Heterandria formosa) often contain a significant vertical velocity component, and large changes in pitch (DB: up to 43 deg) and roll (DB: up to 77 deg) angles. Upwards and downwards elevation changes are correlated with changes in pitch angle of the head; movement in the horizontal plane is correlated with changes in yaw angle of the head. With respect to the stimulus, escape heading correlates with the elevation of the fish at the onset of motion. Irrespective of the initial orientation, fish can escape in any horizontal direction. In many cases, the centre of mass barely accelerates during Stage 1. However, it does accelerate in the final direction of the escape in other instances, indicating that Stage 1 can serve a propulsive role in addition to its preparatory role for Stage 2. Our findings highlight the importance of large-scale 3D analyses of fast-start manoeuvres of adult fish in uncovering the versatility of fish escape repertoire.
Nanoparticles reveal Extreme Size-Sorting and Morphologies in Complex Coacervate Superstructures
Hove, Jan Bart ten; Oosterom, Matthias N. van; Leeuwen, Fijs W.B. van; Velders, Aldrik H. - \ 2018
Scientific Reports 8 (2018)1. - ISSN 2045-2322

We here provide detailed insight in self-assembled complex coacervate systems exploiting gold nanoparticles for cryoTEM contrast. Nanoparticle-containing dendrimicelles are formed from fifth-generation dendrimer-encapsulated nanoparticles (DENs) and dendrimer-stabilized nanoparticles (DSNs). The complex coacervate structures self-organize in biconcave thin water layers into size-sorted monolayer superstructures. The embedded nanoparticles are a straightforward tool to visualize dendrimicelles and determine the aggregation number and polydispersity. The superstructure shows extreme size-sorting patterns which, contrary to related systems with higher generation dendrimers, consists not only of dendrimicelles but also much bigger complex coacervate nanoassemblies, such as vesicles.

Flight behaviour of malaria mosquitoes around odour-baited traps : Capture and escape dynamics
Cribellier, Antoine ; Erp, Jens A. van; Hiscox, Alexandra ; Lankheet, Martin J. ; Leeuwen, Johan L. van; Spitzen, Jeroen ; Muijres, Florian T. - \ 2018
Royal Society Open Science 5 (2018)8. - ISSN 2054-5703
Anopheles coluzzii - Avoidance manoeuvres - Host-seeking - Insect flight behaviour - Trap efficiency - Vector control

Host-seeking mosquitoes rely on a range of sensory cues to find and approach blood hosts, as well as to avoid host detection. By using odour blends and visual cues that attract anthropophilic mosquitoes, odour-baited traps have been developed to monitor and control human pathogen-transmitting vectors. Although long-range attraction of such traps has already been studied thoroughly, close-range response of mosquitoes to these traps has been largely ignored. Here, we studied the flight behaviour of female malaria mosquitoes (Anopheles coluzzii) in the immediate vicinity of a commercially available odour-baited trap, positioned in a hanging and standing orientation. By analysing more than 2500 three-dimensional flight tracks, we elucidated how mosquitoes reacted to the trap, and how this led to capture. The measured flight dynamics revealed two distinct stereotypical behaviours: (i) mosquitoes that approached a trap tended to simultaneously fly downward towards the ground; (ii) mosquitoes that came close to a trap changed their flight direction by rapidly accelerating upward. The combination of these behaviours led to strikingly different flight patterns and capture dynamics, resulting in contrasting short-range attractiveness and capture mechanism of the oppositely oriented traps. These new insights may help in improving odour-baited traps, and consequently their contribution in global vector control strategies.

Force-transmitting structures in the digital pads of the tree frog Hyla cinerea : a functional interpretation
Langowski, Julian K.A. ; Schipper, Henk ; Blij, Anne ; Berg, Frank T. van den; Gussekloo, Sander W.S. ; Leeuwen, Johan L. van - \ 2018
Journal of anatomy 233 (2018)4. - ISSN 0021-8782 - p. 478 - 495.
attachment organ - bioadhesion - collagen - connective tissue - fibre-matrix-composite - material stiffness - shear load - smooth muscle

The morphology of the digital pads of tree frogs is adapted towards attachment, allowing these animals to attach to various substrates and to explore their arboreal habitat. Previous descriptions and functional interpretations of the pad morphology mostly focussed on the surface of the ventral epidermis, and little is known about the internal pad morphology and its functional relevance in attachment. In this study, we combine histology and synchrotron micro-computer-tomography to obtain a comprehensive 3-D morphological characterisation of the digital pads (in particular of the internal structures involved in the transmission of attachment forces from the ventral pad surface towards the phalanges) of the tree frog Hyla cinerea. A collagenous septum runs from the distal tip of the distal phalanx to the ventral cutis and compartmentalises the subcutaneous pad volume into a distal lymph space and a proximal space, which contains mucus glands opening via long ducts to the ventral pad surface. A collagen layer connects the ventral basement membrane via interphalangeal ligaments with the middle phalanx. The collagen fibres forming this layer curve around the transverse pad-axis and form laterally separated ridges below the gland space. The topological optimisation of a shear-loaded pad model using finite element analysis (FEA) shows that the curved collagen fibres are oriented along the trajectories of the maximum principal stresses, and the optimisation also results in ridge-formation, suggesting that the collagen layer is adapted towards a high stiffness during shear loading. We also show that the collagen layer is strong, with an estimated tensile strength of 2.0–6.5 N. Together with longitudinally skewed tonofibrils in the superficial epidermis, these features support our hypothesis that the digital pads of tree frogs are primarily adapted towards the generation and transmission of friction rather than adhesion forces. Moreover, we generate (based on a simplified FEA model and predictions from analytical models) the hypothesis that dorsodistal pulling on the collagen septum facilitates proximal peeling of the pad and that the septum is an adaptation towards detachment rather than attachment. Lastly, by using immunohistochemistry, we (re-)discovered bundles of smooth muscle fibres in the digital pads of tree frogs. We hypothesise that these fibres allow the control of (i) contact stresses at the pad–substrate interface and peeling, (ii) mucus secretion, (iii) shock-absorbing properties of the pad, and (iv) the macroscopic contact geometry of the ventral pad surface. Further work is needed to conclude on the role of the muscular structures in tree frog attachment. Overall, our study contributes to the functional understanding of tree frog attachment, hence offering novel perspectives on the ecology, phylogeny and evolution of anurans, as well as the design of tree-frog-inspired adhesives for technological applications.

Die Auswirkungen eines Brexits auf den Agrarhandel in den Niederlanden
Berkum, Siemen van; Jongeneel, Roel ; Leeuwen, Myrna van - \ 2018
EuroChoices 17 (2018)2. - ISSN 1478-0917 - p. 38 - 46.

The UK is an important market for the Dutch agri-food sector, 10 per cent of all Dutch agricultural exports find their way to the UK. In this article the effects of two possible post-Brexit trade scenarios on Dutch agricultural trade are quantified. Model simulations indicate that Dutch exports to the UK and the rest of the world will be affected only marginally under a Free Trade Agreement between the EU and the UK. A WTO scenario will have more, yet still relatively modest, impact on Dutch exports as a result of Dutch price competitiveness in the UK market. The agricultural production value in the Netherlands will decline by around 2 per cent, mainly because of declining prices that are the result of price pressure in the EU market as a consequence of Brexit-related trade distortions. Possible impacts of non-tariff measures on trade costs are not included in the quantification. However, the UK government could request quality and/or food safety conditions on imports that are different from the current EU trade conditions. Whether the UK will do so is yet unknown, and hence provides an enormous uncertainty to businesses engaged in trade with the UK.

Tree frog attachment : Mechanisms, challenges, and perspectives
Langowski, Julian K.A. ; Dodou, Dimitra ; Kamperman, Marleen ; Leeuwen, Johan L. van - \ 2018
Frontiers in Zoology 15 (2018)1. - ISSN 1742-9994
Attachment organ - Bioadhesion - Biomimetics - Biotribology - Capillary adhesion - Drainage - Litoria caerulea - Lubrication - Toe pad - Van der Waals

Tree frogs have the remarkable ability to attach to smooth, rough, dry, and wet surfaces using their versatile toe pads. Tree frog attachment involves the secretion of mucus into the pad-substrate gap, requiring adaptations towards mucus drainage and pad lubrication. Here, we present an overview of tree frog attachment, with focus on (i) the morphology and material of the toe pad; (ii) the functional demands on the toe pad arising from ecology, lifestyle, and phylogenetics; (iii) experimental data of attachment performance such as adhesion and friction forces; and (iv) potential perspectives on future developments in the field. By revisiting reported data and observations, we discuss the involved mechanisms of attachment and propose new hypotheses for further research. Among others, we address the following questions: Do capillary and hydrodynamic forces explain the strong friction of the toe pads directly, or indirectly by promoting dry attachment mechanisms? If friction primarily relies on van der Waals (vdW) forces instead, how much do these forces contribute to adhesion in the wet environment tree frogs live in and what role does the mucus play? We show that both pad morphology and measured attachment performance suggest the coaction of several attachment mechanisms (e.g. capillary and hydrodynamic adhesion, mechanical interlocking, and vdW forces) with situation-dependent relative importance. Current analytical models of capillary and hydrodynamic adhesion, caused by the secreted mucus and by environmental liquids, do not capture the contributions of these mechanisms in a comprehensive and accurate way. We argue that the soft pad material and a hierarchical surface pattern on the ventral pad surface enhance the effective contact area and facilitate gap-closure by macro- to nanoscopic drainage of interstitial liquids, which may give rise to a significant contribution of vdW interactions to tree frog attachment. Increasing the comprehension of the complex mechanism of tree frog attachment contributes to a better understanding of other biological attachment systems (e.g. in geckos and insects) and is expected to stimulate the development of a wide array of bioinspired adhesive applications.

Soil food web assembly and vegetation development in a glacial chronosequence in Iceland
Leeuwen, J.P. van; Lair, G.J. ; Gísladóttir, G. ; Sandén, T. ; Bloem, J. ; Hemerik, L. ; Ruiter, P.C. de - \ 2018
Pedobiologia 70 (2018). - ISSN 0031-4056 - p. 12 - 21.
Ecosystem functioning - Glacial succession - Iceland - Soil food web structure - Vegetation development

Worldwide human activities threaten soil quality in terms of the soil's ability to deliver ecosystem services. This ongoing process of land degradation asks for effective strategies of soil protection. In this context, it is important to understand processes that build up and regenerate soil. The present study investigated how the soil ecosystem, including soil organisms, vegetation and soil ecological processes, develops during the process of soil formation in a chronosequence in a glacier forefield in Iceland. We hypothesised that along successional age we see increases in nutrient content, vegetation cover, and plant species richness linked to increases in soil food webs biomass and complexity. In line with our expectations all measured pools of carbon and nitrogen, and vegetation cover increased with age in the glacial forefield, but plant species richness levelled off after 30 years. Soil organisms generally increased in biomass with successional age, although some of the groups of soil organisms peaked at an intermediate successional stage. In contrast to our expectations, some of the calculated food web complexity metrics such as the number of trophic groups and trophic chain length did not increase linearly, but showed an intermediate peak or even decreased with successional age. However, plant cover and pools of carbon and nitrogen still increased after 120 years. From these results we conclude that soil ecosystem development takes more than a century under Icelandic climatic conditions to fully develop in terms of vegetation succession, food web structure and biogeochemical cycling.

Poisson-Boltzmann Electrostatics and Ionic Partition Equilibration of Charged Nanoparticles in Aqueous Media
Duval, Jérôme F.L. ; Town, Raewyn M. ; Leeuwen, Herman P. van - \ 2018
The Journal of Physical Chemistry Part C: Nanomaterials and Interfaces 122 (2018)30. - ISSN 1932-7447 - p. 17328 - 17337.

Most nanoparticles (NPs) dispersed in aqueous media carry a net charge. The ensuing electric field plays a fundamental role in determining the thermodynamic and chemodynamic features of the interactions between NPs and dissolved metal species and their lability and bioavailability in environmental and biological matrices. Although increasing attention is being paid to the analysis of metal ion speciation in dispersions of charged complexing NPs, so far the electrostatic features of NPs have only been described on the sole basis of their structural charge properties, that is, the number of (potentially) charged groups they carry. This approach intrinsically ignores the impact of counterion accumulation at/within the particle body/surface during equilibration of the system, which effectively lowers the magnitude of the net NP charge density. Herein, we present the first analysis of the potential profile of NPs after their physicochemical equilibration with the aqueous medium, and we discuss the implications thereof in terms of counterion accumulation within and/or in the vicinity of hard, soft, and core-shell NPs. The focus is on soft or core-soft shell NPs in the thick double layer limit for which bulky Donnan features are not applicable. The new conceptual framework identifies the spatial zone over which divalent counterion accumulation is significant as a function of size, charge density, and type of NP, as well as the ionic strength and electrolyte composition (1-1 and 2-1) of the aqueous medium for the most common case of negatively charged NPs.

Selective and energy efficient extraction of functional proteins from microalgae for food applications
Suarez Garcia, E. ; Leeuwen, J. van; Safi, C. ; Sijtsma, L. ; Eppink, M.H.M. ; Wijffels, R.H. ; Berg, C. van den - \ 2018
Bioresource Technology 268 (2018). - ISSN 0960-8524 - p. 197 - 203.
Bead milling - Energy efficient - Functional protein - Gelation - Surface activity

The use of a single controlled bead milling step of the microalga Tetraselmis suecica resulted in a soluble fraction, rich in functional proteins. This was achieved by fine-tuning the processing time, thereby exploiting the difference in rates of protein and carbohydrate release during milling. Soluble proteins were extracted under mild conditions -room temperature, no addition of chemicals, pH 6.5-, with a yield of 22.5% and a specific energy consumption of 0.6 kWh kgDW −1, which is within the recommended minimum energy for an extraction step in a biorefinery process. The resulting protein extract contained 50.4% (DW) of proteins and 26.4% carbohydrates, showed light green color and displayed superior surface activity and gelation behavior compared to whey protein isolate. The proposed process is simple (only one bead milling step), scalable, and allows the mild extraction of functional proteins, making it interesting for industrial applications in the food industry.

Techno-Functional Properties of Crude Extracts from the Green Microalga Tetraselmis suecica
SuarezGarcia, E. ; Leeuwen, J.J.A. Van; Safi, C. ; Sijtsma, L. ; Broek, L.A.M. van den; Eppink, M.H.M. ; Wijffels, R.H. ; Berg, C. van den - \ 2018
Journal of Agricultural and Food Chemistry 66 (2018)29. - ISSN 0021-8561 - p. 7831 - 7838.
bead milling - crude extract - filtration - gelation - surface activity

A mild fractionation process to extract functional biomolecules from green microalgae was implemented. The process includes bead milling, centrifugation, and filtration with several membrane cut-offs. For each fraction, the corresponding composition was measured, and the surface activity and gelation behavior were determined. A maximum protein yield of 12% was obtained in the supernatant after bead milling and between 3.2 and 11.7% after filtration. Compared to whey protein isolate, most of the algae fractions exhibited comparable or enhanced functionality. Surface activity for air-water and oil-water interfaces and gelation activities were notably superior for the retentate fractions compared to the permeates. It is proposed that such functionality in the retentates is due to the presence of hydrophobic compounds and molecular complexes exhibiting a similar behavior as Pickering particles. We demonstrated that excellent functionality can be obtained with crude fractions, requiring minimum processing and, thus, constituting an interesting option for commercial applications.

Effects of mechanical loads on the deformation and health status of claws in dairy cows
Ouweltjes, Wijbrand - \ 2018
University. Promotor(en): Johan van Leeuwen, co-promotor(en): Sander Gussekloo; Kees Spoor. - Wageningen : Wageningen University - ISBN 9789463438711 - 158
Contaminanten in Chinese wolhandkrab : Resultaten van 2016 en 2017
Brust, G.M.H. ; Hoogenboom, L.A.P. ; Kotterman, M.J.J. ; Leeuwen, S.P.J. van - \ 2018
Wageningen : RIKILT Wageningen University & Research (RIKILT-rapport 2018.004) - 23
Linking diagnostic features to soil microbial biomass and respiration in agricultural grassland soil : A large-scale study in Ireland
Richter, A. ; Huallacháin, D.O. ; Doyle, E. ; Clipson, N. ; Leeuwen, J.P. van; Heuvelink, G.B. ; Creamer, R.E. - \ 2018
European Journal of Soil Science 69 (2018)3. - ISSN 1351-0754 - p. 414 - 428.
The functional potential of soil ecosystems can be predicted from the activity and abundance of the microbial community in relation to key soil properties. When describing microbial community dynamics, soil physicochemical properties have traditionally been used. The extent of correlations between properties, however, differs between studies, especially across larger spatial scales. In this research we analysed soil microbial biomass and substrate-induced respiration of 156 samples from Irish grasslands. In addition to the standard physicochemical, soil type and land management variables, soil diagnostic properties were included to identify if these important soil-landscape genesis classes affected microbial biomass and respiration dynamics in Irish soil. Apart from physicochemical properties, soil drainage class was identified as having an important effect on microbial properties. In particular, biomass-specific basal (qCO2) and substrate-induced respiration (SIR:CFE) were explained best by the soil drainage. Poorly drained soil had smaller values of these respiration measures than well-drained soil. We concluded that this resulted from different groups within the microbial community that could use readily available carbon sources, which suggests a change in microbial community dynamics associated with soil texture and periods of water stress. Overall, our results indicate that soil quality assessments should include both physicochemical properties and diagnostic classes, to provide a better understanding of the behaviour of soil microbial communities. Highlights: Assessing the effect of soil diagnostic features and properties on microbial biomass and respiration A soil biological survey from 156 grassland sites in Ireland Soil drainage class has an important effect on microbial properties Soil quality assessments should include both physicochemical properties and diagnostic classes
Land in post-conflict situations : War, decentralization, land governance and state formation In Northern Uganda
Kobusingye, Doreen Nancy - \ 2018
University. Promotor(en): Han van Dijk, co-promotor(en): M. van Leeuwen. - Wageningen : Wageningen University - ISBN 9789463437721 - 142
Why do placentas evolve? Evidence for a morphological advantage during pregnancy in live-bearing fish
Fleuren, Mike ; Quicazan-Rubio, Elsa M. ; Leeuwen, Johan L. van; Pollux, Bart J.A. - \ 2018
PLoS One 13 (2018)4. - ISSN 1932-6203
A live-bearing reproductive strategy can induce large morphological changes in the mother during pregnancy. The evolution of the placenta in swimming animals involves a shift in the timing of maternal provisioning from pre-fertilization (females supply their eggs with sufficient yolk reserves prior to fertilization) to post-fertilization (females provide all nutrients via a placenta during the pregnancy). It has been hypothesised that this shift, associated with the evolution of the placenta, should confer a morphological advantage to the females leading to a more slender body shape during the early stages of pregnancy. We tested this hypothesis by quantifying three-dimensional shape and volume changes during pregnancy and in full-grown virgin controls of two species within the live-bearing fish family Poeciliidae: Poeciliopsis gracilis (non-placental) and Poeciliopsis turneri (placental). We show that P. turneri is more slender than P. gracilis at the beginning of the interbrood interval and in virgins, and that these differences diminish towards the end of pregnancy. This study provides the first evidence for an adaptive morphological advantage of the placenta in live-bearing fish. A similar morphological benefit could drive the evolution of placentas in other live-bearing (swimming) animal lineages.
Pathogenicity of Diaporthe spp. on two blueberry cultivars (Vaccinium corymbosum)
Cardinaals, J. ; Wenneker, M. ; Voogd, J.G.B. ; Leeuwen, G.C.M. van - \ 2018
EPPO Bulletin 48 (2018)1. - ISSN 0250-8052 - p. 128 - 134.
Diaporthe vaccinii causes twig blight and fruit rot and is currently listed as a quarantine organism for the European Union. In the Netherlands, two species from the same genus, Diaporthe eres and Diaporthe rudis, are regularly isolated from blighted twigs of Vaccinium corymbosum. This study compared the pathogenicity of these two species to D. vaccinii. To develop a pathogenicity test a field experiment was performed at an experimental station, testing isolates of D. rudis and D. eres. Most of the isolates tested did not cause statistically significantly larger lesions compared to the control treatment (P > 0.05). In a greenhouse experiment a similar test was conducted, comparing D. vaccinii with the closely related species D. eres. Two cultivars of blueberry, Duke and Liberty, were inoculated using two D. vaccinii and two D. eres isolates. Stem canker lesions caused by D. vaccinii were larger than these caused by D. eres isolates. The majority of the lesions caused by D. vaccinii did not pass the first node of the inoculated shoot, which might be an explanation for the ‘mild’ symptoms of D. vaccinii in V. corymbosum, which appear not to cause crop losses. The results of this study suggest that D. vaccinii may not be a major threat to blueberry production in Europe. Further data is required to be able to conclude whether the quarantine status of D. vaccinii is still appropriate.
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