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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Economics of Sustainable Development and the Bioeconomy
Zilberman, David ; Gordon, Ben ; Hochman, Gal ; Wesseler, J.H.H. - \ 2018
Applied Economics Perspectives and Policy 40 (2018)1. - ISSN 2040-5790 - p. 22 - 37.
Sustainable development - bioeconomy - dynamics - heterogeneity - adoption - renewable resources
Sustainable development can be attained by policies that are derived by analyses that integrate biophysical considerations into economic models. We show that policies and incentives that correct market failure can attain sustainable resources, and development of the bioeconomy, which relies on biological processes and feed-stock to produce renewable products. The design of sustainable development policies and analysis of the bioeconomy pose new challenges to applied economists, who are uniquely qualified to integrate economic analysis with biophysical considerations.
In vivo 1H NMR methods to study dynamics of chloroplast water and thylakoid membrane lipids in leaves and in photosynthetic microorganisms
Pagadala, Shanthi - \ 2017
University. Promotor(en): Herbert van Amerongen, co-promotor(en): Henk van As. - Wageningen : Wageningen University - ISBN 9789463431569 - 130
cell membranes - membranes - chloroplasts - thylakoids - photosynthesis - in vivo experimentation - stress conditions - stress - proteins - lipids - mobility - dynamics - celmembranen - membranen - chloroplasten - thylakoïden - fotosynthese - in vivo experimenten - stress omstandigheden - eiwitten - lipiden - mobiliteit - dynamica

Dynamics of thylakoid membranes and mobility of pigment-protein complexes therein are essential for survival of photosynthetic organisms under changing environmental conditions. The published approaches to probe mobility of the thylakoid membrane lipids and protein complexes are either dependent on the use of external labels or are used only for in vitro studies. Here, we present non-invasive 1H NMR methods (DOSY and DRCOSY) to study dynamics of water in chloroplasts, lipids in oil bodies and in thylakoid membranes and pigment-protein complexes under complete in vivo conditions in leaf disks of F. benjamina and A. platanoides and in suspensions of the green alga Chlamydomonas reinhardtii and blue-green alga Synechocystissp.PCC 6803.

In leaf disks of Ficus benjamina and Acer platanoides, water in chloroplasts could be clearly discriminated from other pools. Both water in chloroplasts, and water in vacuoles of palisade and spongy cells showed resonances in the high field part of the spectra (with respect to pure water), in contrast to what has been reported in literature. Subepidermal cells (present only in F. benjamina but not in A. platanoides) may act as a water storage, buffer pool during drought. This pool prevented the fast loss of water from the chloroplasts. Nutrient stress and excess salt stress resulted in accumulated lipid bodies and in striking differences in the dynamics and spectra/composition of the different components. T2 values of the different components are compared with those observed in suspensions of Synechocystissp.PCC 6803. The differences in membrane composition (ratio of the different membrane lipids) were clearly observed in the DANS of the oil bodies and the (thylakoid) membranes, but the diffusion coefficients were quite comparable. Also the DANS of the component that is assigned to the pigment-protein complexes are quite different, reflecting the differed composition. The diffusion coefficients of this component in isolated spinach thylakoids and in C. reinhardtii are very comparable, but about a factor of 10 lower with respect to that of Synechocystis at short diffusion times. The dynamics of these complexes in these systems are thus quite different.

Microbial interactions in the fish gut
Giatsis, Christos - \ 2016
University. Promotor(en): Johan Verreth, co-promotor(en): Marc Verdegem; Detmer Sipkema. - Wageningen : Wageningen University - ISBN 9789462578777 - 196
fishes - tilapia - larvae - microbial interactions - intestinal microorganisms - intestines - dynamics - fish feeding - probiotics - fish culture - aquaculture - vissen - larven - microbiële interacties - darmmicro-organismen - darmen - dynamica - visvoeding - probiotica - visteelt - aquacultuur

Aquaculture has realized considerable growth over the past years while the world demand on seafood has been increasing. As aquaculture intensifies, the production sector needs to tackle major bottlenecks such as suboptimal growth and high and unpredictable mortality, especially in larval cultures. Fish-microbe interactions are closely related to overall fish health. To obtain a healthy and resilient microbial community (MC), it is important to understand the underlying mechanisms of microbial colonization in the fish gut.

The goal of this thesis was to investigate the role of water and feed microbial communities on shaping gut communities during early development of Nile tilapia.

To determine the contribution of stochasticity to overall variation, we first characterized the spatio-temporal variation in MC composition between individuals reared within the same or in replicate recirculating or active suspension systems (RAS vs. AS). Highly similar MCs developed in the gut when larvae shared the same water and diet. Rearing larvae in replicate production systems resulted in significantly different gut communities indicating that compositional replication of the MCs of an ecosystem is not fully predictable. We found that mainly water MCs, and to a lesser degree feed MCs, were associated with changes in MCs. Thus, we could conclude that steering gut MCs can be possible through water MC management tailored on the specifications of the rearing system in use.

Next, the possibility of early life steering of gut communities via microbial manipulations of feed MCs was explored. We hypothesized that gut microbial composition is strongly shaped by selective pressures in the gut and by the MCs present in the water. Thus similar MCs should develop between treatments regardless of the dietary treatments. Fish larvae were fed either a control feed or the control feed containing MCs derived from aerobic, methanogenic or denitrifying sludge reactors. We found that gut microbiota shared a much higher number of operational taxonomic units (OTUs) with microbiota in sludge-based feeds than with water, resulting in distinct gut MCs between treatments. Our findings suggest that Nile tilapia gut MC has a certain plasticity, which makes it amenable to interventions through proper feed microbial management.

Subsequently, we tested the imprinting effect of early exposure to the probiotic Bacillus subtilis on shaping gut MC composition even after the administration of the probiotic discontinues. For this, we constrained the initial contact with microbes from the environment by producing axenic tilapia larvae, which were then exposed to normal husbandry conditions. Early life probiotic exposure affected gut MC composition during B. subtilis administration but also within the first two weeks after its administration stopped, thus indicating that early exposure to the probiotic strain via the water had a sustained impact on gut MC composition.

Finally, overall conclusions and practical implications of our results for aquaculture production were presented. A meta-analysis was also performed to examine (1) the phylogenetic similarity among gut MCs of the same and different fish species reared in different habitats, fed different diets and at different developmental stages and (2) the factors primarily shaping gut MCs. We showed that the selective pressure responsible in shaping gut MC composition highly depends on the host as gut communities clustered primarily together by host and to a lesser extent reflected differences in habitat and diet. The phylogenetic analysis of gut communities revealed a clear clustering by study thus indicating that manipulation of gut communities is conceivable. Study-to-study variation could be attributed to the methodology used for MC analysis highlighting also the importance of methodological uniformity when comparisons between studies are made.

Overall, this thesis provided fundamental knowledge on MC composition and development in aquaculture rearing systems. Although the insights generated by this thesis are still premature to fully explain, predict or steer MC composition, and though additional studies are needed, we believe that, in the long run, this approach will facilitate the development of safe and effective methods for manipulating gut microbial composition to promote fish health in aquaculture rearing systems.

Dynamics of adaptation in experimental yeast populations exposed to gradual and abrupt change in heavy metal concentration
Gorter, Florien ; Aarts, Mark ; Zwaan, B.J. ; Visser, J.A.G.M. de - \ 2015
adaptation - ecology - evolutionary - microbial - Environmental variability - evolution - fitness - genetics - population - dynamics - fungi - heavy metals - pleiotropy
Directional environmental change is a ubiquitous phenomenon that may have profound effects on all living organisms. However, it is unclear how different rates of such change affect the dynamics and outcome of evolution. We studied this question using experimental evolution of heavy metal tolerance in the baker´s yeast Saccharomyces cerevisiae. To this end, we grew replicate lines of yeast for 500 generations in the presence of (i) a constant high concentration of cadmium, nickel or zinc, or (ii) a gradually increasing concentration of these metals. We found that gradual environmental change leads to a delay in fitness increase compared to abrupt change, but not necessarily to a different fitness of evolutionary endpoints. For the non-essential metal cadmium this delay is due to reduced fitness differences between genotypes at low metal concentrations, consistent with directional selection to minimize intracellular concentrations of this metal. In contrast, for the essential metals nickel and zinc different genotypes are selected at different concentrations, consistent with stabilizing selection to maintain constant intracellular concentrations of these metals. These findings indicate diverse fitness consequences of evolved tolerance mechanisms for essential and non-essential metals, and imply that the rate of environmental change and the nature of the stressor are crucial determinants of evolutionary dynamics.
Dynamiek van schelpdierbanken in de nederlandse kustzone
Kamermans, P. ; Goudswaard, P.C. ; Asch, M. van; Bos, O.G. - \ 2015
Yerseke : IMARES (Rapport / IMARES C186/15) - 31 p.
schaaldieren - dynamica - aquatische ecosystemen - kustgebieden - kustwateren - karteringen - nederland - shellfish - dynamics - aquatic ecosystems - coastal areas - coastal water - surveys - netherlands
Oral coatings: a study on the formation, clearance and perception
Camacho, S. - \ 2015
University. Promotor(en): Kees de Graaf, co-promotor(en): Markus Stieger; F. van de Velde. - Wageningen : Wageningen University - ISBN 9789462575653 - 223
afdeklagen - eiwitten - orale toediening - tong - mond - smering - emulsies - in vivo experimenten - sensorische evaluatie - perceptie - dynamica - zoetheid - fluorescentie - coatings - proteins - oral administration - tongue - mouth - lubrication - emulsions - in vivo experimentation - sensory evaluation - perception - dynamics - sweetness - fluorescence

Oral coatings are residues of food and beverages that coat the oral mucosa after consumption. Several studies have reported on the lubrication properties in mouth, and the after-feel and after-taste impact of oral coatings. Further, oral coatings have been suggested to influence subsequent taste perception. Although it is well known that oral coatings can influence sensory perception, there was little information available on the chemical composition and physical properties of oral coatings. As such, the aim of this thesis was to understand which factors influence the composition of oral coatings and their sensory perception.

This study started with the development of an appropriate calibration method for an already described methodology to quantify oil oral coatings: in vivo fluorescence. Further, the samples studied were shifted from pure oil (used on previous studies) to a more realistic food beverage: o/w emulsions. Pig´s tongues are known to be a good model of human tongue. As such, Chapter 2 used pig´s tongues on the calibration of the method, to mimic the fluorescence in mouth of oil coatings. On chapter 2, Confocal Scanning Laser Microscopy images showed that stable o/w emulsions (1-20% (w/w)) stabilised by Na-caseinate created individual oil droplets on the surface of the pigs tongue, as such a new descriptor for oil coatings was developed. Oil fraction, i.e. mass of oil per surface area of the tongue, was shown to be higher on the back compared to the front anterior part of the tongue. This is thought to be due to the morphology of the tongue and abrasion of the oil coating owed to the rubbing with the palate. Further, in vivo measurements showed that oil fraction deposited on the tongue increased linearly with oil content of o/w emulsions. Coating clearance from the tongue was a fast process with around 60% of the oil being removed on the first 45s. After-feel perception (Fatty Film and Flavour Intensity) was shown to be semi-logarithmic related to oil fraction on the tongue.

Chapter 3, further investigated different properties of 10% (w/w) o/w emulsions that influence the oil fraction deposited on the tongue, its clearance and after-feel perception. Three different properties were studied: protein type, protein content and viscosity of the o/w emulsions. To study the influence of protein type, two different proteins which behave differently in-mouth were studied: Na-caseinate - creates emulsions which do not flocculate under in mouth conditions, and lysozyme – creates emulsions which flocculate under in mouth conditions. To study the influence of protein content, three concentrations of Na-caseinate and lysozyme were used (0.2, 3, 5.8% (w/w) all in excess to stabilize the water/oil interface). To study the influence of viscosity of o/w emulsions, three o/w emulsions stabilized with 3% (w/w) Na-caseinate were thickened with varying concentrations of xanthan gum (0-0.5%) (w/w).

Generally, the irreversible flocculation of lysozyme stabilized emulsions with saliva did not create a significant difference on oil deposition compared to emulsions stabilized with Na-caseinate, immediately after expectoration of the emulsions. Nevertheless, lysozyme stabilised emulsions caused slower oil clearance from the tongue surface compared to emulsions stabilized with Na-caseinate. Protein content had a negative relation with oil fraction on the tongue for lysozyme stabilized emulsions and no relation for Na-caseinate stabilized emulsions. The presence of thickener decreased deposition of oil on tongue, although viscosity differences (i.e., thickener content) did not affect oil fraction. After-feel perception of creaminess and fatty-film was strongly influenced by the presence of thickener likely due to lubrication in-mouth, i.e., the higher the concentration of thickener in the emulsions the stronger was the perception. Oral coatings perception was further influenced by the protein used in the emulsions, with Na-caseinate stabilised emulsions creating coatings with higher perception on creaminess and fatty-film.

Chapter 2 and chapter 3 provided knowledge on the deposition and clearance of oil coatings, but little was known on the formation of oil coatings. Chapter 4 focused on the formation of oil coatings formed by Na-caseinate stabilised o/w emulsions (1-20% (w/w)). The formation of oil coatings was a rapid process, where the maximum oil deposition was achieved at normal drinking behaviour (~3s). Further, in Chapter 4 we investigated the hypothesis often referred on literature, in which oil coatings form a physical barrier which prevents tastants to reach the taste buds, and thus create a reduction on taste perception. It was concluded that oil coatings formed by emulsions within one sip did not affect subsequent sweetness perception of sucrose solutions. We suggested that the oil droplets deposited on the tongue (as seen on chapter 2) did not form a hydrophobic barrier that is sufficient to reduce the accessibility of sucrose to the taste buds and consequently does not suppress taste perception.

Previous chapters focused on oral coatings formed by liquid o/w emulsions, however studies describing oral coatings formed by semi-solids and solids are scarce. As such, chapter 5 focused on the formation, clearance and sensory perception of fat coatings from emulsion-filled gels. Four emulsion-filled gelatin gels varying in fat content and type of emulsifier (whey protein isolate - created fat droplets bound to matrix; tween 20 - created fat droplets unbound to matrix) were studied. As in for oil coatings formed by liquid o/w emulsions, fat coatings formed by emulsion-filled gels reach their maximum deposition in the first seconds of mastication. This suggests that the first bites are the most relevant for the formation of fat coatings on the tongue. Further, fat fraction deposited on tongue increased when oral processing time of the gels increased. This trend was clearer for gels with higher fat content (15%) compared to gels with lower fat content (5%). Fatty perception increased with increasing mastication time, and decreased after expectoration with increasing clearance time. Fat fraction deposited on tongue and fatty perception are higher in gels with unbound droplets compared to bound droplets, as well as in gels with 15% fat compared to 5% fat.

To elucidate the role of protein on oral coatings, Chapter 6 focused on the development of a method to quantify protein in the oral coatings. Further, Chapter 6 studied the influence of protein content, in-mouth protein behaviour (lysozyme - protein which creates flocs with saliva vs. Na-Caseinate - protein which does not create flocs with saliva) and presence of thickener on the formation of protein oral coatings and sensory perception of protein coatings. Protein coatings were collected from the front and middle part of the anterior tongue using cotton swabs after subjects orally processed protein solutions for different time periods. Protein concentration of the coating (mass protein/mass coating) was quantified with the Lowry method. Similarly to oil/fat coatings, results show protein coatings are formed rapidly, reaching maximum deposition on the first seconds of the samples´ oral processing. Further, different protein in mouth-behaviour (Na-caseinate vs. lysozyme) did not create differences on protein deposition on the tongue. Presence of xanthan-gum in the processed samples decreased protein deposition on the tongue, compared to when samples without xanthan-gum were processed. The perception of protein coatings was strongly influenced by the viscosity and protein used in the samples. Higher viscosity of the samples lead to higher intensity on creaminess and thickness. Lysozyme samples created coatings with high sweetness and astringent intensity, which is related to the molecular structure of the protein.

Changes in the viscosity of beverages can cause changes in thickness perception. The changes in thickness perception can be accompanied by differences in other sensory properties, such as sweetness and creaminess which might be undesirable when reformulating beverages or developing new products. Knowledge on the differences by which viscosity of beverages can be modified to create a difference in sensory perception is currently lacking. Chapter 7 focus on the determination of the Just Noticeable Difference (the minimal difference that can be detected between two stimuli) for thickness perception of beverages. Oral thickness sensitivity (K=0.26) was found to be comparable to literature values for kinesthetic food firmness and spreadability, creaminess, sourness and bitterness perception.

The aim of this thesis was to determine and characterize factors influencing oral coatings and their sensory perception. For this purpose, reliable methods to quantify oil and protein deposited on the tongue had to be developed to later study the macronutrients deposition. Further, the influence of stimulus properties on the formation and clearance dynamics of oral coatings and their impact on sensory perception were investigated.

Eutrophication, Nile perch and food-web interactions in south-east Lake Victoria
Cornelissen, I.J.M. - \ 2015
University. Promotor(en): Johan Verreth, co-promotor(en): Leo Nagelkerke; R. Vijverberg. - Wageningen : Wageningen University - ISBN 9789462575660 - 163
lates niloticus - eutrofiëring - voedselwebben - interacties - visserijbiologie - visstand - dynamica - fytoplankton - distributie - voedingsgedrag - victoriameer - tanzania - eutrophication - food webs - interactions - fishery biology - fish stocks - dynamics - phytoplankton - distribution - feeding behaviour - lake victoria

The increasing eutrophication, the introduction of Nile perch (Lates niloticus) and the increasing fishing pressure has changed Lake Victoria tremendously the last century. Since the 1960s, eutrophication increased primary production, enabling an increase in fish production. However, eutrophication also created hypoxia pockets, which reduced the available habitats for fish. In addition, the endemic haplochromines declined, whereas the introduced Nile perch boomed in the 1980s. The Nile perch boom and increased fish production resulted in the largest freshwater fisheries of the world. However, it is unclear whether fish production can still increase with further eutrophication as maximum primary production rates may have been reached. Fish stocks fluctuate since the 1980s and in order to manage these, it is important to understand how eutrophication and fisheries affect the Nile perch population. The present study investigates the bottom-up effects of eutrophication on the Nile perch and food-web dynamics in south-east Lake Victoria. We analysed the level of eutrophication along an eutrophication gradient in the Mwanza Gulf. Phytoplankton biomass varied spatially and seasonally and was limited by nutrients in deep water and by light in shallow water. Fish distributions were dynamic, with environmental factors depth and temperature influencing Nile perch size structure and distribution patterns similarly on small and large spatial scales. Although prey densities of haplochromines and Caridina nilotica shrimp did not explain Nile perch distributions, ontogenetic diet shifts and composition were related to prey densities, suggesting an opportunistic feeding behaviour of Nile perch. Small Nile perch however, showed some preference to shrimp and Nile perch preferred haplochromines above Dagaa (Rastrineobola argentea) and juvenile Nile perch as fish prey. On a food-web level, the base of the food web was spatially and seasonally highly dynamic. The onset of rains caused a spatial differentiation in littoral/benthic and pelagic carbon sources, affecting the whole food web. Trophic levels of fish were related to the spatial variation in diet compositions. Although a large heterogeneity was found in water quality, fish distributions and food-web structure, bottom-up processes affected the food web similarly. Despite the ongoing nutrient load in Lake Victoria, water quality has improved since the 1990s. Climate forcing through increasing wind speeds increased visibility and oxygen levels. Global climate change will therefore be an important driver of the water quality and fish distributions of Lake Victoria.

The sensitivity of wet and dry tropical forests to climate change in Bolivia
Seiler, C. ; Hutjes, R.W.A. ; Kruijt, B. ; Hickler, T. - \ 2015
Journal of Geophysical Research: Biogeosciences 120 (2015)3. - ISSN 2169-8953 - p. 399 - 413.
global vegetation models - soil respiration - terrestrial biosphere - plant geography - carbon-dioxide - amazon dieback - rain-forest - dynamics - water - temperature
Bolivia's forests contribute to the global carbon and water cycle, as well as to global biodiversity. The survival of these forests may be at risk due to climate change. To explore the associated mechanisms and uncertainties, a regionally adapted dynamic vegetation model was implemented for the Bolivian case, and forced with two contrasting climate change projections. Changes in carbon stocks and fluxes were evaluated, factoring out the individual contributions of atmospheric carbon dioxide ([CO2]), temperature, and precipitation. Impacts ranged from a strong increase to a severe loss of vegetation carbon (cv), depending on differences in climate projections, as well as the physiological response to rising [CO2]. The loss of cv simulated for an extremely dry projection was primarily driven by a reduction in gross primary productivity, and secondarily by enhanced emissions from fires and autotrophic respiration. In the wet forest, less precipitation and higher temperatures equally reduced cv, while in the dry forest, the impact of precipitation was dominating. The temperature-related reduction of cv was mainly due to a decrease in photosynthesis and only to lesser extent because of more autotrophic respiration and less stomatal conductance as a response to an increasing atmospheric evaporative demand. Under an extremely dry projection, tropical dry forests were simulated to virtually disappear, regardless of the potential fertilizing effect of rising [CO2]. This suggests a higher risk for forest loss along the drier southern fringe of the Amazon if annual precipitation will decrease substantially.
Monitoring protein capsid assembly with a conjugated polymer strain sensor
Cingil, E.H. ; Storm, I.M. ; Yorulmaz, Y. ; Brake, D.W. te; Vries, R.J. de; Cohen Stuart, M.A. ; Sprakel, J.H.B. - \ 2015
Journal of the American Chemical Society 137 (2015)31. - ISSN 0002-7863 - p. 9800 - 9803.
beta-phase formation - polyfluorene - poly(9,9-dioctylfluorene) - morphology - photophysics - copolymers - molecules - dynamics - length
Semiconducting polymers owe their optoelectronic properties to the delocalized electronic structure along their conjugated backbone. Their spectral features are therefore uniquely sensitive to the conformation of the polymer, where mechanical stretching of the chain leads to distinct vibronic shifts. Here we demonstrate how the optomechanical response of conjugated polyelectrolytes can be used to detect their encapsulation in a protein capsid. Coating of the sensor polymers by recombinant coat proteins induces their stretching due to steric hindrance between the proteins. The resulting mechanical planarizations lead to pronounced shifts in the vibronic spectra, from which the process of capsid formation can be directly quantified. These results show how the coupling between vibronic states and mechanical stresses inherent to conjugated polymers can be used to noninvasively measure strains at the nanoscale.
Hydrodynamic model for drying emulsions
Feng Huanhuan, Huanhuan ; Sprakel, J.H.B. ; Gucht, J. van der - \ 2015
Physical Review. E, Statistical nonlinear, and soft matter physics 92 (2015). - ISSN 2470-0045 - 8 p.
latex film formation - atomic-force microscopy - foam drainage - phase inversion - coalescence - dynamics - surfactant - stability - fracture
We present a hydrodynamic model for film formation in a dense oil-in-water emulsion under a unidirectional drying stress. Water flow through the plateau borders towards the drying end leads to the buildup of a pressure gradient. When the local pressure exceeds the critical disjoining pressure, the water films between droplets break and the droplets coalesce. We show that, depending on the critical pressure and the evaporation rate, the coalescence can occur in two distinct modes. At low critical pressures and low evaporation rates, coalescence occurs throughout the sample, whereas at high critical pressures and high evaporation rate, coalescence occurs only at the front. In the latter case, an oil layer develops on top of the film, which acts as a diffusive barrier and slows down film formation. Our findings, which are summarized in a state diagram for film formation, are in agreement with recent experimental findings.
Seeing Central African forests through their largest trees
Bastin, J.F. ; Barbier, N. ; Réjou-Méchain, M. ; Fayolle, A. ; Gourlet-Fleury, S. ; Maniatis, D. ; Haulleville, T. De; Baya, F. ; Beeckman, H. ; Beina, D. ; Couteron, P. ; Chuyong, G. ; Dauby, G. ; Doucet, J.L. ; Droissart, V. ; Dufrêne, M. ; Ewango, C.E.N. ; Gillet, F. ; Gonmadje, C.H. ; Hart, T. ; Kavali, T. ; Kenfack, D. ; Libalah, M. ; Malhi, Y. ; Makana, J.R. ; Pélissier, R. ; Ploton, P. ; Serckx, S. ; Sonké, B. ; Stevart, T. ; Thomas, D.W. ; Cannière, C. De; Bogaert, J. - \ 2015
Scientific Reports 5 (2015). - ISSN 2045-2322 - 8 p.
tropical forest - biomass - size - distributions - diversity - dynamics
Large tropical trees and a few dominant species were recently identified as the main structuring elements of tropical forests. However, such result did not translate yet into quantitative approaches which are essential to understand, predict and monitor forest functions and composition over large, often poorly accessible territories. Here we show that the above-ground biomass (AGB) of the whole forest can be predicted from a few large trees and that the relationship is proved strikingly stable in 175 1-ha plots investigated across 8 sites spanning Central Africa. We designed a generic model predicting AGB with an error of 14% when based on only 5% of the stems, which points to universality in forest structural properties. For the first time in Africa, we identified some dominant species that disproportionally contribute to forest AGB with 1.5% of recorded species accounting for over 50% of the stock of AGB. Consequently, focusing on large trees and dominant species provides precise information on the whole forest stand. This offers new perspectives for understanding the functioning of tropical forests and opens new doors for the development of innovative monitoring strategies.
Interactions among drainage flows, gravity waves and turbulence: a BLLAST case study
Román Cascón, C. ; Yagüe, C. ; Mahrt, L. ; Sastre, M. ; Steeneveld, G.J. ; Pardyjak, E. ; Boer, A. van de; Hartogensis, O.K. - \ 2015
Atmospheric Chemistry and Physics 15 (2015). - ISSN 1680-7316 - p. 9031 - 9047.
stable boundary-layer - intermittent turbulence - density-current - flux - field - wind - disturbances - simulations - stability - dynamics
The interactions among several stable-boundary-layer (SBL) processes occurring just after the evening transition of 2 July 2011 have been analysed using data from instruments deployed over the area of Lannemezan (France) during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field campaign. The near-calm situation of the afternoon was followed by the formation of local shallow drainage flows (SDFs) of less than 10 m depth at different locations. The SDF stage ended with the arrival of a stronger wind over a deeper layer more associated with the mountain-plain circulation, which caused mixing and destruction of the SDFs. Several gravity-wave-related oscillations were also observed on different time series. Wavelet analyses and wave parameters were calculated from high resolution and accurate surface pressure data of an array of microbarometers. These waves propagated relatively long distances within the SBL. The effects of these phenomena on turbulent parameters (friction velocity and kinematic heat flux) have been studied through multi-resolution flux decomposition methods performed on high frequency data from sonic anemometers deployed at different heights and locations. With this method, we were able to detect the different time-scales involved in each turbulent parameter and separate them from wave contributions, which becomes very important when choosing averaging-windows for surface flux computations using eddy covariance methods. The extensive instrumentation allowed us to highlight in detail the peculiarities of the surface turbulent parameters in the SBL, where several of the noted processes were interacting and producing important variations in turbulence with height and between sites along the sloping terrain.
Partitioned EDGE devices for high throughput production of monodisperse emulsion droplets with two distinct sizes
Sahin, S. ; Schroën, C.G.P.H. - \ 2015
Lab on a Chip 15 (2015). - ISSN 1473-0197 - p. 2486 - 2495.
flow membrane emulsification - microchannel emulsification - generation - dynamics - model - geometries - parallel
We present a novel microfluidic EDGE (Edge based Droplet GEneration) device with regularly spaced micron-sized partitions, which is aimed at upscaling of o/w emulsion preparation. By this means, remarkably higher pressure stability was obtained, and two orders of magnitude higher droplet formation frequency was achieved compared to regular EDGE devices. Interestingly, we observed two different monodisperse droplet formation regimes for plateaus that were 2 micrometres in height, and to the best of our knowledge, no other microfluidic device has this ability. The average diameters of the droplets were 9 and 28 µm, both with a coefficient of variation (CV) below 5%. Based on the experimental throughput and a plausible mass parallelization scenario, the amount of hexadecane that can be emulsified is estimated to be between 6 and 25 m3 m-2 h-1 depending on the required droplet size. With its high throughput potential and ability to produce uniform droplets of two different sizes, the partitioned EDGE device is promising for industrial emulsion production.
The supramolecular organization of a peptide-based nanocarrier at high molecular detail
Rad-Malekshahi, M. ; Visscher, K.M. ; Rodrigues, J.P.G.L.M. ; Vries, R.J. de; Hennink, W.E. ; Baldus, M. ; Bonvin, A.M.J.J. ; Mastrobattista, E. - \ 2015
Journal of the American Chemical Society 137 (2015)24. - ISSN 0002-7863 - p. 7775 - 7784.
solid-state nmr - protein secondary structure - chemical-shift index - force-field - polypeptide vesicles - drug-delivery - beta-sheet - dynamics - nanovesicles - spectroscopy
Nanovesicles self-assembled from amphiphilic peptides are promising candidates for applications in drug delivery. However, complete high-resolution data on the local and supramolecular organization of such materials has been elusive thus far, which is a substantial obstacle to their rational design. In the absence of precise information, nanovesicles built of amphiphilic “lipid-like” peptides are generally assumed to resemble liposomes that are organized from bilayers of peptides with a tail-to-tail ordering. Using the nanocarrier formed by the amphiphilic self-assembling peptide 2 (SA2 peptide) as an example, we derive the local and global organization of a multimega-Dalton peptide-based nanocarrier at high molecular detail and at close-to physiological conditions. By integrating a multitude of experimental techniques (solid-state NMR, AFM, SLS, DLS, FT-IR, CD) with large- and multiscale MD simulations, we show that SA2 nanocarriers are built of interdigitated antiparallel ß-sheets, which bear little resemblance to phospholipid liposomes. Our atomic level study allows analyzing the vesicle surface structure and dynamics as well as the intermolecular forces between peptides, providing a number of potential leads to improve and tune the biophysical properties of the nanocarrier. The herein presented approach may be of general utility to investigate peptide-based nanomaterials at high-resolution and at physiological conditions.
An integrated ecosystem approach for assessing the potential role of cultivated bivalve shells as part of the carbon trading system
Filgueira, R. ; Byron, C.J. ; Comeau, L.A. ; Jansen, H.M. ; Smaal, A.C. - \ 2015
Marine Ecology Progress Series 518 (2015). - ISSN 0171-8630 - p. 281 - 287.
mussel mytilus-edulis - coastal embayment - carrying-capacity - light limitation - oyster reefs - aquaculture - culture - dynamics - growth - farms
The role of bivalve mariculture in the CO2 cycle has been commonly evaluated as the balance between respiration, shell calcium carbonate sequestration and CO2 release during biogenic calcification. However, this approach neglects the ecosystem implications of cultivating bivalves at high densities, e.g. the impact on phytoplankton dynamics and benthic-pelagic coupling, which can significantly contribute to the CO2 cycle. Therefore, an ecosystem approach that accounts for the trophic interactions of bivalve aquaculture, including dissolved and particulate organic and inorganic carbon cycling, is needed to provide a rigorous assessment of the role of bivalve mariculture in the CO2 cycle. On the other hand, the discussion about the inclusion of shells of cultured bivalves into the carbon trading system should be framed within the context of ecosystem goods and services. Humans culture bivalves with the aim of producing food, not sequestering CO2 in their shells, therefore the main ecosystem good provided by bivalve aquaculture is meat production, and shells should be considered as by-products of this human activity. This reasoning provides justification for dividing up respired CO2 between meat and shell when constructing a specific bivalve CO2 budget for potential use of bivalve shells in the carbon trading system. Thus, an integrated ecosystem approach, as well as an understanding of the ecosystems goods and services of bivalve aquaculture, are 2 essential requisites for providing a reliable assessment of the role of bivalve shells in the CO2 cycle.
Adaptability of two weevils (Neochetina bruchi and Neochetina eichhorniae) with potential to control water hyacinth in the Rift Valley of Ethiopia
Firehun, Y. ; Struik, P.C. ; Lantinga, E.A. ; Taye, T. - \ 2015
Crop Protection 76 (2015). - ISSN 0261-2194 - p. 75 - 82.
successful biological-control - control agent - life-cycle - curculionidae - coleoptera - crassipes - pontederiaceae - waterhyacinth - dynamics - hustache
Neochetina weevils have potential as biocontrol agents for water hyacinth, an aquatic weed which seriously affects irrigation water supply in sugarcane, vegetables and other horticultural crop production in the Rift Valley of Ethiopia. A study was conducted on (i) the adaptability and duration of developmental stages of Neochetina weevils and (ii) the damage they cause to water hyacinth in the Rift Valley of Ethiopia. The Rift Valley weather conditions appeared to be suitable for the two weevil species studied, enabling them to produce four generations per year. The egg hatching period of Neochetina bruchi ranged from 4 to 10 days, while Neochetinaeichhorniae took 8–12 days. Larvae of N. bruchi took a comparatively shorter period (32–38 days) than N. eichhorniae (52–60 days) to complete their development. N. bruchi laid a maximum of 10.4 eggs female-1 day-1, whereas N. eichhorniae laid 8.2 eggs female-1 day-1. The intrinsic rate of increase of N. bruchi was found to be 0.06 with a generation time of 74.8 days and a population doubling period of 14.3 days. The intrinsic rate of increase of N. eichhorniae was 0.046 accompanied by a generation time of 94.8 days and a doubling period of 18.7 days. Feeding by adult weevils and tunnelling by larvae significantly impacted the vigour and reproduction of water hyacinth plants. N. bruchi and N. eichhorniae affected plants had about 72% (76%) and 66% (58%) reduction in fresh (and dry) weight, respectively. Thus, based on their damage potential and difference in rate of population growth, it is concluded that N. bruchi could be considered as a promising candidate for biological control of water hyacinth under Ethiopian conditions.
Encapsulation of GFP in complex coacervate core micelles
Nolles, A. ; Westphal, A.H. ; Hoop, J.A. de; Fokkink, R.G. ; Kleijn, J.M. ; Berkel, W.J.H. van; Borst, J.W. - \ 2015
Biomacromolecules 16 (2015)5. - ISSN 1525-7797 - p. 1542 - 1549.
fluorescence correlation spectroscopy - protein - dynamics - behavior - nanocontainers - purification - copolymers - lipase - tag
Protein encapsulation with polymers has a high potential for drug delivery, enzyme protection and stabilization. Formation of such structures can be achieved by the use of polyelectrolytes to generate so-called complex coacervate core micelles (C3Ms). Here, encapsulation of enhanced green fluorescent protein (EGFP) was investigated using a cationic-neutral diblock copolymer of two different sizes: poly(2-methyl-vinyl-pyridinium)41-b-poly(ethylene-oxide)205 and poly(2-methyl-vinyl-pyridinium)128-b-poly(ethylene-oxide)477. Dynamic light scattering and fluorescence correlation spectroscopy (FCS) revealed a preferred micellar composition (PMC) with a positive charge composition of 0.65 for both diblock copolymers and micellar hydrodynamic radii of approximately 34 nm. FCS data show that at the PMC, C3Ms are formed above 100 nM EGFP, independent of polymer length. Mixtures of EGFP and nonfluorescent GFP were used to quantify the amount of GFP molecules per C3M, resulting in approximately 450 GFPs encapsulated per micelle. This study shows that FCS can be successfully applied for the characterization of protein-containing C3Ms.
Comparison of structured adsorbents for the adsorptive isolation of food ingredients from large streams
Rodriguez Illera, M. ; Boon, M.A. ; Boom, R.M. ; Janssen, A.E.M. - \ 2015
Chemical Engineering Research & Design 98 (2015). - ISSN 0263-8762 - p. 240 - 251.
stationary phases - moment equations - monolithic adsorbents - liquid-chromatography - aspect ratio - performance - separation - media - diffusion - dynamics
We present guidelines for the configuration of industrial scale chromatographic separation of small molecules. We compared the performance of different axial packed beds, channeled monoliths and a continuous monolith assuming silica as base material. The calculated mass transfer rates were used to calculate the height of a theoretical plate (HETP). The HETP and pressure drop relations as a function of velocity were used to calculate the resultant velocity and packing length for different conditions (efficiency, pressure drop, affinity constant and throughput). The specific productivity of channeled monoliths can be up to 2.5 orders of magnitude higher than that of a packed bed. This implies that at large scales (in which the pressure drops need to be limited, and the flow rate is high), channeled monoliths are preferred since they may reduce the equipment size up to 100 times and the required resin volume up to 1000 times. Accordingly, we demonstrate the potential of channeled monoliths in chromatographic processes but also draw a window pointing out the feasible configurations to use with the highest productivity for a given set of process requirements.
Can we infer plant facilitation from remote sensing? A test across global drylands
Xu, C. ; Holmgren, M. ; Nes, E.H. van; Maestre, F.T. ; Soliveres, S. ; Berdugo, M. ; Kefi, S. ; Marquet, P.A. ; Abades, S. ; Scheffer, M. - \ 2015
Ecological Applications 25 (2015)6. - ISSN 1051-0761 - p. 1456 - 1462.
positive interactions - vegetation patterns - spatial-patterns - ecosystems - desertification - distributions - environments - competition - dynamics - ecology
Facilitation is a major force shaping the structure and diversity of plant communities in terrestrial ecosystems. Detecting positive plant-plant interactions relies on the combination of field experimentation and the demonstration of spatial association between neighboring plants. This has often restricted the study of facilitation to particular sites, limiting the development of systematic assessments of facilitation over regional and global scales. Here we explore whether the frequency of plant spatial associations detected from high-resolution remotely-sensed images can be used to infer plant facilitation at the community level in drylands around the globe. We correlated the information from remotely-sensed images freely available through Google EarthTM with detailed field assessments, and used a simple individual-based model to generate patch-size distributions using different assumptions about the type and strength of plant-plant interactions. Most of the patterns found from the remotely-sensed images were more right-skewed than the patterns from the null model simulating a random distribution. This suggests that the plants in the studied drylands show stronger spatial clustering than expected by chance. We found that positive plant co-occurrence, as measured in the field, was significantly related to the skewness of vegetation patch-size distribution measured using Google EarthTM images. Our findings suggest that the relative frequency of facilitation may be inferred from spatial pattern signals measured from remotely-sensed images, since facilitation often determines positive co-occurrence among neighboring plants. They pave the road for a systematic global assessment of the role of facilitation in terrestrial ecosystems.
Modelling the rheology of anisotropic particles adsorbed on a two-dimensional fluid interface
Luo, A.M. ; Sagis, L.M.C. ; Oettinger, H.C. ; Michele, C. de; Ilg, P. - \ 2015
Soft Matter 11 (2015). - ISSN 1744-683X - p. 4383 - 4395.
complex fluids - capillary interactions - constitutive equation - general formalism - liquid-crystals - dynamics - thermodynamics - emulsions
We present a general approach based on nonequilibrium thermodynamics for bridging the gap between a well-defined microscopic model and the macroscopic rheology of particle-stabilised interfaces. Our approach is illustrated by starting with a microscopic model of hard ellipsoids confined to a planar surface, which is intended to simply represent a particle-stabilised fluid-fluid interface. More complex microscopic models can be readily handled using the methods outlined in this paper. From the aforementioned microscopic starting point, we obtain the macroscopic, constitutive equations using a combination of systematic coarse-graining, computer experiments and Hamiltonian dynamics. Exemplary numerical solutions of the constitutive equations are given for a variety of experimentally relevant flow situations to explore the rheological behaviour of our model. In particular, we calculate the shear and dilatational moduli of the interface over a wide range of surface coverages, ranging from the dilute isotropic regime, to the concentrated nematic regime.
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