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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Rain events decrease boreal peatland net CO2 uptake through reduced light availability
Nijp, J.J. ; Limpens, J. ; Metselaar, K. ; Peichl, M. ; Nilsson, M. ; Zee, S.E.A.T.M. van der; Berendse, F. - \ 2015
Global Change Biology 21 (2015)6. - ISSN 1354-1013 - p. 2309 - 2320.
carbon-dioxide - soil respiration - sphagnum mosses - water-content - solar-radiation - climate-change - precipitation - accumulation - drought - balance
Boreal peatlands store large amounts of carbon, reflecting their important role in the global carbon cycle. The short-term exchange and the long-term storage of atmospheric carbon dioxide (CO2) in these ecosystems are closely associated with the permanently wet surface conditions and are susceptible to drought. Especially, the single most important peat forming plant genus, Sphagnum, depends heavily on surface wetness for its primary production. Changes in rainfall patterns are expected to affect surface wetness, but how this transient rewetting affects net ecosystem exchange of CO2 (NEE) remains unknown. This study explores how the timing and characteristics of rain events during photosynthetic active periods, that is daytime, affect peatland NEE and whether rain event associated changes in environmental conditions modify this response (e.g. water table, radiation, vapour pressure deficit, temperature).
Plant functional types define magnitude of drought response in peatland CO2 exchange
Kuiper, J.J. ; Mooij, W.M. ; Bragazza, L. ; Robroek, B.J.M. - \ 2014
Ecology 95 (2014)1. - ISSN 0012-9658 - p. 123 - 131.
sphagnum mosses - nitrogen availability - removal experiment - species-diversity - moisture controls - water-content - carbon - ecosystems - grassland - bog
Peatlands are important sinks for atmospheric carbon (C), yet the role of plant functional types (PFTs) for C sequestration under climatic perturbations is still unclear. A plant-removal experiment was used to study the importance of vascular PFTs for the net ecosystem CO2 exchange (NEE) during (i.e., resistance) and after (i.e., recovery) an experimental drought. The removal of PFTs caused a decrease of NEE, but the rate differed between microhabitats (i.e., hummocks and lawns) and the type of PFTs. Ericoid removal had a large effect on NEE in hummocks, while the graminoids played a major role in the lawns. The removal of PFTs did not affect the resistance or the recovery after the experimental drought. We argue that the response of Sphagnum mosses (the only PFT present in all treatments) to drought is dominant over that of coexisting PFTs. However, we observed that the moment in time when the system switched from C sink to C source during the drought was controlled by the vascular PFTs. In the light of climate change, the shifts in species composition or even the loss of certain PFTs are expected to strongly affect the future C dynamics in response to environmental stress.
Comparison of remote sensing and plant trait-based modelling to predict ecosystem services in subalpine grasslands
Homolova, L. ; Schaepman, M.E. ; Lamarque, P. ; Clevers, J.G.P.W. ; Bello, F. de; Thuiller, W. ; Lavorel, S. - \ 2014
Ecosphere 5 (2014)8. - ISSN 2150-8925
land-use change - leaf chlorophyll content - imaging spectroscopy - water-content - aviris data - spectral reflectance - hyperspectral data - species richness - area index - vegetation
There is a growing demand for spatially explicit assessment of multiple ecosystem services (ES) and remote sensing (RS) can provide valuable data to meet this challenge. In this study, located in the Central French Alps, we used high spatial and spectral resolution RS images to assess multiple ES based on underpinning ecosystem properties (EP) of subalpine grasslands. We estimated five EP (green biomass, litter mass, crude protein content, species diversity and soil carbon content) from RS data using empirical RS methods and maps of ES were calculated as simple linear combinations of EP. Additionally, the RS-based results were compared with results of a plant trait-based statistical modelling approach that predicted EP and ES from land use, abiotic and plant trait data (modelling approach). The comparison between the RS and the modelling approaches showed that RS-based results provided better insight into the fine-grained spatial distribution of EP and thereby ES, whereas the modelling approach reflected the land use signal that underpinned trait-based models of EP. The spatial agreement between the two approaches at a 20-m resolution varied between 16 and 22% for individual EP, but for the total ecosystem service supply it was only 7%. Furthermore, the modelling approach identified the alpine grazed meadows land use class as areas with high values of multiple ES (hot spots) and mown-grazed permanent meadows as areas with low values and only few ES (cold spots). Whereas the RS-based hot spots were a small subset of those predicted by the modelling approach, cold spots were rather scattered, small patches with limited overlap with the modelling results. Despite limitations associated with timing of assessment campaigns and field data requirements, RS offers valuable data for spatially continuous mapping of EP and can thus supply RS-based proxies of ES. Although the RS approach was applied to a limited area and for one type of ecosystem, we believe that the broader availability of high fidelity airborne and satellite RS data will promote RS-based assessment of ES to larger areas and other ecosystems.
Stimulation of colonic motility by oral PEG electrolyte bowel preparation assessed by MRI: comparison of split vs single dose
Marciani, L. ; Garsed, K.C. ; Hoad, C.L. ; Fields, A. ; Fordham, I. ; Pritchard, S.E. ; Placidi, E. ; Murray, K. ; Chaddock, G. ; Costigan, C. ; Lam, C. ; Jalanka-Tuovinen, J. ; Vos, W.M. de; Gowland, P.A. ; Spiller, R.C. - \ 2014
Neurogastroenterology & Motility 26 (2014)10. - ISSN 1365-2982 - p. 1426 - 1436.
randomized controlled-trial - whole-gut transit - water-content - polyethylene-glycol - gastric-motility - healthy-subjects - ascorbic-acid - colonoscopy - time - constipation
Background Most methods of assessing colonic motility are poorly acceptable to patients. Magnetic resonance imaging (MRI) can monitor gastrointestinal motility and fluid distributions. We predicted that a dose of oral polyethylene glycol (PEG) and electrolyte solution would increase ileo-colonic inflow and stimulate colonic motility. We aimed to investigate the colonic response to distension by oral PEG electrolyte in healthy volunteers (HVs) and to evaluate the effect of single 2 L vs split (2 × 1 L) dosing. Methods Twelve HVs received a split dose (1 L the evening before and 1 L on the study day) and another 12 HVs a single dose (2 L on the main study day) of PEG electrolyte. They underwent MRI scans, completed symptom questionnaires, and provided stool samples. Outcomes included small bowel water content, ascending colon motility index, and regional colonic volumes. Key Results Small bowel water content increased fourfold from baseline after ingesting both split (p = 0.0010) and single dose (p = 0.0005). The total colonic volume increase from baseline was smaller for the split dose at 35 ± 8% than for the single dose at 102 ± 27%, p = 0.0332. The ascending colon motility index after treatment was twofold higher for the single dose group (p = 0.0103). Conclusions & Inferences Ingestion of 1 and 2 L PEG electrolyte solution caused a rapid increase in the small bowel and colonic volumes and a robust rise in colonic motility. The increase in both volumes and motility was dose dependent. Such a challenge, being well-tolerated, could be a useful way of assessing colonic motility in future studies.
Can frequent precipitation moderate the impact of drought on peatmoss carbon uptake in northern peatlands?
Nijp, J.J. ; Limpens, J. ; Metselaar, K. ; Zee, S.E.A.T.M. van der; Berendse, F. ; Robroek, B.J.M. - \ 2014
New Phytologist 203 (2014)1. - ISSN 0028-646X - p. 70 - 80.
sphagnum mosses - climate-change - water-content - co2 exchange - soil respiration - vegetation - accumulation - desiccation - boreal - bog
Northern peatlands represent a large global carbon store that can potentially be destabilized by summer water table drawdown. Precipitation can moderate the negative impacts of water table drawdown by rewetting peatmoss (Sphagnum spp.), the ecosystem's key species. Yet, the frequency of such rewetting required for it to be effective remains unknown. We experimentally assessed the importance of precipitation frequency for Sphagnum water supply and carbon uptake during a stepwise decrease in water tables in a growth chamber. CO2 exchange and the water balance were measured for intact cores of three peatmoss species (Sphagnum majus, Sphagnum balticum and Sphagnum fuscum) representative of three hydrologically distinct peatland microhabitats (hollow, lawn and hummock) and expected to differ in their water table–precipitation relationships. Precipitation contributed significantly to peatmoss water supply when the water table was deep, demonstrating the importance of precipitation during drought. The ability to exploit transient resources was species-specific; S. fuscum carbon uptake increased linearly with precipitation frequency for deep water tables, whereas carbon uptake by S. balticum and S. majus was depressed at intermediate precipitation frequencies. Our results highlight an important role for precipitation in carbon uptake by peatmosses. Yet, the potential to moderate the impact of drought is species-specific and dependent on the temporal distribution of precipitation.
Toluene biodegradation rates in unsaturated soil systems versus liquid batches and their relevance to field conditions
Picone, S. ; Grotenhuis, J.T.C. ; Gaans, P. van; Valstar, J. ; Langenhoff, A.A.M. ; Rijnaarts, H. - \ 2013
Applied Microbiology and Biotechnology 97 (2013)17. - ISSN 0175-7598 - p. 7887 - 7898.
vapor intrusion - vadose-zone - aerobic biodegradation - petroleum-hydrocarbons - numerical-model - carbon-dioxide - water-content - new-jersey - kinetics - benzene
Contaminant biodegradation in unsaturated soils may reduce the risks of vapor intrusion. However, the reported rates show large variability and are often derived from slurry experiments that are not representative of unsaturated conditions. Here, different laboratory setups are used to derive the biodegradation capacity of an unsaturated soil layer through which gaseous toluene migrates from the water table upwards. Experiments in static unsaturated soil microcosms at 6-30 % water-filled porosity (WFP) and unsaturated soil columns at 9, 14, and 27 % WFP were compared with liquid batches containing the same culture of Alicycliphilus denitrificans. The biodegradation rates for the liquid batches were orders of magnitude lower than for the other setups. Hence, liquid batches do not necessarily reflect optimal conditions for bacteria; either oxygen or toluene mass transfer at the cell scale or the absence of soil-water-air interfaces seemed to be limiting bacterial activity. For the column setup, the rates were limited by mass supply. The microcosm results could be described by apparent first-order biodegradation constants that increased with WFP or through a numerical model that included biodegradation as a first-order process taking place in the liquid phase only. The model liquid phase first-order rates varied between 6.25 and 20 h(-1) and were not related to the water content. Substrate availability was the primary factor limiting bioactivity, with evidence for physiological stress at the lowest water-filled porosity. The presented approach is useful to derive liquid phase biodegradation rates from experimental data and to include biodegradation in vapor intrusion models.
Comparison of Soil Respiration in Typical Conventional and New Alternative Cereal Cropping Systems on the North China Plain
Gao, B. ; Ju, X.T. ; Su, F. ; Gao, F.B. ; Cao, Q.S. ; Oenema, O. ; Christie, P. ; Chen, X.P. ; Zhang, F.S. - \ 2013
PLoS One 8 (2013)11. - ISSN 1932-6203
carbon-dioxide - water-content - temperature - nitrogen - dependence - ecosystem - tillage - forest - management - moisture
We monitored soil respiration (Rs), soil temperature (T) and volumetric water content (VWC%) over four years in one typical conventional and four alternative cropping systems to understand Rs in different cropping systems with their respective management practices and environmental conditions. The control was conventional double-cropping system (winter wheat and summer maize in one year - Con. W/M). Four alternative cropping systems were designed with optimum water and N management, i.e. optimized winter wheat and summer maize (Opt. W/M), three harvests every two years (first year, winter wheat and summer maize or soybean; second year, fallow then spring maize - W/M-M and W/S-M), and single spring maize per year (M). Our results show that Rs responded mainly to the seasonal variation in T but was also greatly affected by straw return, root growth and soil moisture changes under different cropping systems. The mean seasonal CO2 emissions in Con. W/M were 16.8 and 15.1 Mg CO2 ha(-1) for summer maize and winter wheat, respectively, without straw return. They increased significantly by 26 and 35% in Opt. W/M, respectively, with straw return. Under the new alternative cropping systems with straw return, W/M-M showed similar Rs to Opt. W/M, but total CO2 emissions of W/S-M decreased sharply relative to Opt. W/M when soybean was planted to replace summer maize. Total CO2 emissions expressed as the complete rotation cycles of W/S-M, Con. W/M and M treatments were not significantly different. Seasonal CO2 emissions were significantly correlated with the sum of carbon inputs of straw return from the previous season and the aboveground biomass in the current season, which explained 60% of seasonal CO2 emissions. T and VWC% explained up to 65% of Rs using the exponential-power and double exponential models, and the impacts of tillage and straw return must therefore be considered for accurate modeling of Rs in this geographical region.
Influence of lysophosphatidylcholine on the gelation of diluted wheat starch suspensions
Ahmadi-Abhari, S. ; Woortman, A.J.J. ; Hamer, R.J. ; Oudhuis, A.A.C.M. ; Loos, K. - \ 2013
Carbohydrate Polymers 93 (2013)1. - ISSN 0144-8617 - p. 224 - 231.
amylose-lipid complexes - water-content - gelatinization - digestibility - glycerophosphatidylcholine - cultivars - systems - index
Starch is an omnipresent constituent which is used for its nutritional and structuring properties. Recently concerns have been raised since starch is a source of readily available glucose which is tightly correlated with diabetes type II and obesity. For this reason, the possibilities for modulating the digestibility of starch while preserving its functional properties were investigated; therefore the focus of this paper is on starch gelatinization and the effect of lysophosphatidylcholine (LPC) on the structuring properties of wheat starch. The effect of LPC on thermal properties and viscosity behavior of starch suspensions was studied using DSC and RVA, respectively. The influence on granular structure was observed by light microscopy. The RVA profile demonstrated no viscosity increase at high LPC concentrations which proves intact granular structure after gelatinization. LPC in intermediate concentrations resulted in a notable delay of pasting; however the peak and end viscosities were influenced as well. Lower LPC concentrations demonstrated a higher peak viscosity as compared with pure starch suspensions. DSC results imply that inclusion complexes of amylose–LPC might be formed during pasting time. Since the viscosity profiles are changed by LPC addition, swelling power and solubility of starch granules are influenced as well. LPC hinders swelling power and solubility of starch granules which are stimulated by heating.
Concentration profiles of CH4, CO2 and N2O in soils of a wheat-maize rotation ecosystem in North China Plain, measured weekly over a whole year
Wang, Y.Y. ; Hu, C.S. ; Ming, H. ; Zhang, Y.M. ; Li, X.X. ; Dong, W. ; Oenema, O. - \ 2013
Agriculture, Ecosystems and Environment 164 (2013). - ISSN 0167-8809 - p. 260 - 272.
nitrous-oxide - atmospheric methane - carbon-dioxide - n-fertilization - hardwood forest - water-content - land-use - emissions - fluxes - denitrification
Agricultural soils are main sources and sinks of the greenhouse gases carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). The source–sink function depends on soil characteristics, climate and management. Emission measurements usually quantify the net result of production, consumption and transport of these gases in the soil; they do not provide information about the depth distributions of the concentrations of these gases in the soil. Here we report on concentrations of CO2, CH4 and N2O in air of 300 cm deep soil profiles, at resolutions of 30–50 cm, over a full year. Gas samples were taken weekly in a long-term field experiment with an irrigated winter wheat–summer maize double cropping system, and four fertilizer N application rates (0, 200, 400 and 600 kg N ha-1 year-1). The results showed distinct differences in CH4, CO2 and N2O concentrations profiles with soil depth. The concentrations of CO2 in soil air increased with soil depth and showed a seasonal pattern with relatively high concentrations in the warm and moist maize growing season and relatively low concentrations in the winter-wheat growing season. In contrast, CH4 concentrations decreased with depth, and did not show a distinct seasonal cycle. Urea application did not have a large effect on CH4 or CO2 concentrations, neither in the topsoil nor the subsoil. Concentrations of N2O responded to N fertilizer application and irrigation. Application of fertilizer strongly increased grain and straw yields of both winter wheat and summer maize, relatively to the control, but differences in yield between the treatments N200, N400 and N600 were not statistically significant. However, it significantly increased mean N2O concentrations peaks at basically all soil depths. Interestingly, concentrations of N2O increased almost instantaneously in the whole soil profile, which indicates that the soil had a relatively high diffusivity, despite compacted subsoil layers. In conclusion, the frequent measurements, at high depth resolutions, of concentrations of CH4, CO2 and N2O in soil air under a winter wheat–summer maize double crop rotation provide detailed insight into the production, consumption and transport of these gases in the soil. Concentrations of CH4, CO2 and N2O responded differently to management activities and weather conditions.
Seed storage at elevated partial pressure of oxygen, a fast method for analysing seed ageing under dry conditions
Groot, S.P.C. ; Surki, A.A. ; Vos, R.C.H. de; Kodde, J. - \ 2012
Annals of Botany 110 (2012)6. - ISSN 0305-7364 - p. 1149 - 1159.
controlled deterioration - moisture-content - vitamin-e - gaseous environment - digitalis-purpurea - lipid-peroxidation - water-content - barley seeds - longevity - germination
Background and Aims Despite differences in physiology between dry and relative moist seeds, seed ageing tests most often use a temperature and seed moisture level that are higher than during dry storage used in commercial practice and gene banks. This study aimed to test whether seed ageing under dry conditions can be accelerated by storing under high-pressure oxygen. Methods Dry barley (Hordeum vulgare), cabbage (Brassica oleracea), lettuce (Lactuca sativa) and soybean (Glycine max) seeds were stored between 2 and 7 weeks in steel tanks under 18 MPa partial pressure of oxygen. Storage under high-pressure nitrogen gas or under ambient air pressure served as controls. The method was compared with storage at 45 °C after equilibration at 85 % relative humidity and long-term storage at the laboratory bench. Germination behaviour, seedling morphology and tocopherol levels were assessed. Key Results The ageing of the dry seeds was indeed accelerated by storing under high-pressure oxygen. The morphological ageing symptoms of the stored seeds resembled those observed after ageing under long-term dry storage conditions. Barley appeared more tolerant of this storage treatment compared with lettuce and soybean. Less-mature harvested cabbage seeds were more sensitive, as was the case for primed compared with non-primed lettuce seeds. Under high-pressure oxygen storage the tocopherol levels of dry seeds decreased, in a linear way with the decline in seed germination, but remained unchanged in seeds deteriorated during storage at 45 °C after equilibration at 85 % RH. Conclusions Seed storage under high-pressure oxygen offers a novel and relatively fast method to study the physiology and biochemistry of seed ageing at different seed moisture levels and temperatures, including those that are representative of the dry storage conditions as used in gene banks and commercial practice
Soil moisture monitoring for climate research: evaluation of a low cost sensor in the framework of the Swiss soil Expperiment (SwissSMEX) campaign
Mittelbach, H. ; Casini, F. ; Lehner, I. ; Teuling, A.J. ; Seneviratne, S.I. - \ 2011
Journal of Geophysical Research: Atmospheres 116 (2011)D5. - ISSN 2169-897X - 11 p.
time-domain reflectometry - water-content - global-models - calibration - land - variability - atmosphere - dynamics - europe - system
Soil moisture measurements are essential to understand land surface–atmosphere interactions. In this paper we evaluate the performance of the low-cost 10HS capacitance sensor (Decagon Devices, United States) using laboratory and field measurements. Measurements with 10HS sensors of volumetric water content (VWC, Vol.%), integrated absolute soil moisture (millimeters) over the measured soil column, and the loss of soil moisture (millimeters) for rainless days are compared with corresponding measurements from gravimetric samples and time domain reflectometry (TDR) sensors. The field measurements were performed at two sites with different soil texture in Switzerland, and they cover more than a year of parallel measurements in several depths down to 120 cm. For low VWC, both sensor types present good agreement for laboratory and field measurements. Nevertheless, the measurement accuracy of the 10HS sensor reading (millivolts) considerably decreases with increasing VWC: the 10HS sensors tend to become insensitive to variations of VWC above 40 Vol.%. The field measurements reveal a soil type dependency of the 10HS sensor performance, and thus limited applicability of laboratory calibrations. However, with site-specific exponential calibration functions derived from parallel 10HS and TDR measurements, the error of the 10HS compared to the TDR measurements can be decreased for soil moisture contents up to 30 Vol.%, and the day-to-day variability of soil moisture is captured. We conclude that the 10HS sensor is appropriate for setting up dense soil moisture networks when focusing on medium to low VWC and using an established site-specific calibration function. This measurement range is appropriate for several applications in climate research, but the identified performance limitations should be considered in investigations focusing on humid conditions and absolute soil moisture
Differentiation of nitrous oxide emission factors for agricultural soils
Lesschen, J.P. ; Velthof, G.L. ; Vries, W. de; Kros, J. - \ 2011
Environmental Pollution 159 (2011)11. - ISSN 0269-7491 - p. 3215 - 3222.
volatile fatty-acids - n2o emissions - cattle slurry - crop residues - fertilizer application - grassland soil - animal manures - gas emissions - water-content - barley field
Nitrous oxide (N2O) direct soil emissions from agriculture are often estimated using the default IPCC emission factor (EF) of 1%. However, a large variation in EFs exists due to differences in environment, crops and management. We developed an approach to determine N2O EFs that depend on N-input sources and environmental factors. The starting point of the method was a monitoring study in which an EF of 1% was found. The conditions of this experiment were set as the reference from which the effects of 16 sources of N input, three soil types, two land-use types and annual precipitation on the N2O EF were estimated. The derived EF inference scheme performed on average better than the default IPCC EF. The use of differentiated EFs, including different regional conditions, allows accounting for the effects of more mitigation measures and offers European countries a possibility to use a Tier 2 approach
Mapping soil clay contents in Dutch marine districts using gamma-ray spectrometry
Klooster, E. van der; Egmond, F.M. van; Sonneveld, M.P.W. - \ 2011
European Journal of Soil Science 62 (2011)5. - ISSN 1351-0754 - p. 743 - 753.
plant-available potassium - radiometric data - water-content - topsoil - netherlands - sediments - spectra - models - part
Conventional soil sampling methods to obtain high-resolution soil data are labour intensive and costly. Recently, gamma ray spectrometry has emerged as a promising technique to overcome these obstacles. The objective of our study was to investigate the prediction of soil clay contents using gamma-ray spectrometry in three marine clay districts in the Netherlands: the southwestern marine district (SMD), the IJsselmeerpolder district (IJPD) and the northern marine district (NMD). The performance of linear regression models was investigated at field (1000 km2) scales and for all the Dutch marine districts together. For this study, a database was available with 1371 gamma-ray spectra measured on arable fields in marine clay districts during the period 2005–2008 and these were all linked to laboratory analyses of clay contents. At the field scale, linear regression models based on 40K, 232Th, or a combination of these revealed much smaller root mean squared error (RMSE) values (2–3%) compared with a model based on the field mean (8–10%). At the district scale, the regression models for the SMD and IJPD, which have comparable sediments, performed better than for the NMD. This indicates that the prediction of clay contents in late Holocene marine sediments may be made with gamma-ray spectrometry provided that the origin of the parent material results in a unique fingerprint. Because of the heterogeneous parent material of all marine districts taken together, our study shows that no unique and precise fingerprint exists, and the RMSE of 6% between clay contents and gamma-ray spectra is not much different from the RMSE of 7% when using the overall mean as a predictor.
Polymer tensiometers with ceramic cones: direct observations of matric pressures in drying soils
Ploeg, M.J. van der; Gooren, H.P.A. ; Bakker, Gerben ; Hoogendam, C.W. ; Huiskes, C. ; Koopal, L.K. ; Kruidhof, H. ; Rooij, G.H. de - \ 2010
Hydrology and Earth System Sciences 14 (2010)10. - ISSN 1027-5606 - p. 1787 - 1799.
time-domain reflectometry - hydraulic-properties - osmotic tensiometer - tensile-strength - water-content - suction - performance - sensor
Measuring soil water potentials is crucial to characterize vadose zone processes. Conventional tensiometers only measure until approximately -0.09 MPa, and indirect methods may suffer from the non-uniqueness in the relationship between matric potential and measured properties. Recently developed polymer tensiometers (POTs) are able to directly measure soil matric potentials until the theoretical wilting point (-1.6 MPa). By minimizing the volume of polymer solution inside the POT while maximizing the ceramic area in contact with that polymer solution, response times drop to acceptable ranges for laboratory and field conditions. Contact with the soil is drastically improved with the use of cone-shaped solid ceramics instead of flat ceramics. The comparison between measured potentials by polymer tensiometers and indirectly obtained potentials with time domain reflectometry highlights the risk of using the latter method at low water contents. By combining POT and time domain reflectometry readings in situ moisture retention curves can be measured over the range permitted by the measurement range of both POT and time domain reflectometry
Relations between sensorial crispness and molecular mobility of model bread crust and its main components as measured by PTA, DSC and NMR
Nieuwenhuijzen, N.H. van; Tromp, R.H. ; Mitchell, J.R. ; Primo-Martin, C. ; Hamer, R.J. ; Vliet, T. van - \ 2010
Food Research International 43 (2010)1. - ISSN 0963-9969 - p. 342 - 349.
glass-transition temperature - wheat-starch - fracture-behavior - pulsed h-1-nmr - water-content - gluten - foods - state
Consumer appreciation of brittle cellular foods, like bread crusts, depends on textural properties such as crispness. This crispy character is lost above a certain water activity. It is not known what exactly is happening in these crusts when water enters. So is it unclear whether it is the change in the starch or the gluten that initiates the loss of crispness with ageing time. In this paper the effect of water on the glass transition of model bread crusts was studied using two complementary techniques: phase transition analysis (PTA) and temperature modulated differential scanning calorimetry (TMDSC). The mobility of water was studied with nuclear magnetic resonance (NMR). The results were compared with sensory data. Bread crusts prepared with different types of flour were tested to evaluate the effect of flour composition on the crispness of model crusts equilibrated at different relative humidities. In addition the single flour components starch and gluten were studied. Sensory crispness scores decreased with increasing aw from 0.55 upwards. At aw 0.70 sensory crispness was completely lost. Both DSC and PTA showed a transition point at an aw of 0.70-0.75. NMR gave a transition point in the mobility of the protons of water at aw 0.58. This supports the hypothesis that loss of crispness starts as a result of processes at a molecular level, before the macroscopic glass transition. This also suggests that the presence of water that is not directly attached to the solid matrix causes the loss of crispness at low aw. At higher aw increased mobility of the macromolecules will start to play a role. NMR experiments with the separate flour components indicate that the T2 transition point in starch samples occurs at a lower RH than for gluten. This could imply that starch loses crispness at lower aw than gluten. Increased mobility of small components and side chains might induce increased energy dissipation upon deformation of the material resulting in less available energy for fracture propagation and with that in a less crispy product.
PROSPECT and SAIL models: a review of use for vegetation characterization
Jacquemond, S. ; Verhoef, W. ; Baret, F. ; Bacour, C. ; Zarco-Tejada, P. ; Asner, G.P. ; Francois, C. ; Ustin, S.L. - \ 2009
Remote Sensing of Environment 113 (2009)Suppl 1. - ISSN 0034-4257 - p. S56 - S66.
radiative-transfer models - remote-sensing data - leaf optical-properties - canopy reflectance models - cyclopes global products - sugar-beet canopies - chlorophyll content - water-content - area index - bidirectional reflectance
The combined PROSPECT leaf optical properties model and SAIL canopy bidirectional reflectance model, also referred to as PROSAIL, has been used for about sixteen years to study plant canopy spectral and directional reflectance in the solar domain. PROSAIL has also been used to develop new methods for retrieval of vegetation biophysical properties. It links the spectral variation of canopy reflectance, which is mainly related to leaf biochemical contents, with its directional variation, which is primarily related to canopy architecture and soil/vegetation contrast. This link is key to simultaneous estimation of canopy biophysical/structural variables for applications in agriculture, plant physiology, or ecology, at different scales. PROSAIL has become one of the most popular radiative transfer tools due to its ease of use, general robustness, and consistent validation by lab/field/space experiments over the years. However, PROSPECT and SAIL are still evolving: they have undergone recent improvements both at the leaf and the plant levels. This paper provides an extensive review of the PROSAIL developments in the context of canopy biophysics and radiative transfer modeling
Photosynthetic performance in Sphagnum transplanted along a latitudinal nitrogen deposition gradient
Granath, G. ; Strengbom, J. ; Breeuwer, A.J.G. ; Heijmans, M.M.P.D. ; Berendse, F. ; Rydin, H. - \ 2009
Oecologia 159 (2009)4. - ISSN 0029-8549 - p. 705 - 715.
atmospheric nitrogen - n deposition - boreal mire - chlorophyll fluorescence - physiological-responses - parasitic fungus - water-content - growth - mosses - vegetation
Increased N deposition in Europe has affected mire ecosystems. However, knowledge on the physiological responses is poor. We measured photosynthetic responses to increasing N deposition in two peatmoss species (Sphagnum balticum and Sphagnum fuscum) from a 3-year, north-south transplant experiment in northern Europe, covering a latitudinal N deposition gradient ranging from 0.28 g N m(-2) year(-1) in the north, to 1.49 g N m(-2) year(-1) in the south. The maximum photosynthetic rate (NPmax) increased southwards, and was mainly explained by tissue N concentration, secondly by allocation of N to the photosynthesis, and to a lesser degree by modified photosystem II activity (variable fluorescence/maximum fluorescence yield). Although climatic factors may have contributed, these results were most likely attributable to an increase in N deposition southwards. For S. fuscum, photosynthetic rate continued to increase up to a deposition level of 1.49 g N m(-2) year(-1), but for S. balticum it seemed to level out at 1.14 g N m(-2) year(-1). The results for S. balticum suggested that transplants from different origin (with low or intermediate N deposition) respond differently to high N deposition. This indicates that Sphagnum species may be able to adapt or physiologically adjust to high N deposition. Our results also suggest that S. balticum might be more sensitive to N deposition than S. fuscum. Surprisingly, NPmax was not (S. balticum), or only weakly (S. fuscum) correlated with biomass production, indicating that production is to a great extent is governed by factors other than the photosynthetic capacity.
Mixing ratio and species affect the use of substrate-derived CO2 by Sphagnum
Limpens, J. ; Robroek, B.J.M. ; Heijmans, M.M.P.D. ; Tomassen, H.B.M. - \ 2008
Journal of Vegetation Science 19 (2008)6. - ISSN 1100-9233 - p. 841 - 848.
carbon-dioxide - water-content - photosynthesis - growth - permeability - desiccation - vegetation - mosses
Question: Can mixing ratio and species affect the use of substrate-derived CO2 by Sphagnum? Location: Poor fen in south Sweden and greenhouse in Wageningen, The Netherlands. Methods: Two mixing ratios of Sphagnum cuspidatum and S. magellanicum were exposed to two levels of CO2 by pumping CO2 enriched and non-enriched water through aquaria containing the species mixtures in the greenhouse. Results: Enhanced CO2 stimulated the production of S. cuspidatum, but only in aquaria co-dominated by S. magellanicum, coinciding with higher CO2 concentrations in the water layer. The denser growing S. magellanicum seemed to reduce gas escape from the water, resulting in accumulation of dissolved CO2. Adding CO2 did not affect species replacement. Conclusions: The use of substrate-derived CO2 for Sphagnum production depended on species identity and mixing ratio. The effect of mixing ratio on CO2 concentrations in the water layer suggests that species composition may affect both the efficiency with which substrate-derived CO2 is trapped and subsequently used. This could result in hitherto unexplored feedbacks between vegetation composition and gas exchange.
Seed dormancy release in Arabidopsis Cvi by dry after-ripening, low temperature, nitrate and light shows common quantitative patterns of gene expression directed by environment specific sensing
Finch-Savage, W.E. ; Cadman, C.S.C. ; Toorop, P.E. ; Lynn, J.R. ; Hilhorst, H.W.M. - \ 2007
The Plant Journal 51 (2007)1. - ISSN 0960-7412 - p. 60 - 78.
dose-response analysis - gibberellin biosynthesis - sisymbrium-officinale - thaliana seeds - abscisic-acid - nitric-oxide - negative regulators - secondary dormancy - water-content - germination
The depth of seed dormancy can be influenced by a number of different environmental signals, but whether a common mechanism underlies this apparently similar response has yet to be investigated. Full-genome microarrays were used for a global transcript analysis of Arabidopsis thaliana Cape Verde Island accession seeds exposed to dry after-ripening (AR), or low temperature, nitrate and light when imbibed. Germination studies showed that the sensitivity of imbibed seeds to low temperature, nitrate and light was dependant upon the length of time spent AR following harvest. Seeds had an absolute requirement for light to complete dormancy release in all conditions, but this effect required an exposure to a prior dormancy relieving environment. Principal component analyses of the expression patterns observed grouped physiological states in a way that related to the depth of seed dormancy, rather than the type of environmental exposure. Furthermore, opposite changes in transcript abundance of genes in sets associated with dormancy, or dormancy relief through AR, were also related to the depth of dormancy and common to different environments. Besides these common quantitative changes, environment-specific gene expression patterns during dormancy relief are also described. For example, higher transcript abundance for genes linked to the process of nitrate accumulation, and nitrate reduction was associated with dormancy relief. The quantity of GA3ox1 transcripts increased during dormancy relief in all conditions, in particular when dormancy relief was completed by exposure to light. This contrasts with transcripts linked to abscisic acid (ABA) synthesis, which declined. The results are consistent with a role for the ABA/gibberellic acid balance in integrating dormancy-relieving environmental signals.
Comparison of methods to determine the degree of gelatinisation for both high and low starch concentrations
Baks, T. ; Ngene, I.S. ; Soest, J.J.G. van; Janssen, A.E.M. ; Boom, R.M. - \ 2007
Carbohydrate Polymers 67 (2007)4. - ISSN 0144-8617 - p. 481 - 490.
differential scanning calorimetry - high hydrostatic-pressure - partial molar volumes - potato starches - water-content - wheat-starch - birefringence measurements - crystalline polymorph - phase-transformations - enzymatic-hydrolysis
A general procedure was developed to measure the degree of gelatinisation in samples over a broad concentration range. Measurements based on birefringence, DSC (Differential scanning calorimetry), X-ray and amylose-iodine complex formation were used. If a 10 w/w % wheat starch-water mixture was used, each method resulted in approximately the same degree of gelatinisation vs. temperature curve. In case the gelatinisation of a 60 w/w % wheat starch-water mixture was followed as a function of the temperature, each method resulted in a different degree of gelatinisation vs. temperature curve. DSC and X-ray measurements are preferred, because they can be used to determine when the final stage of the gelatinisation process has been completed. Birefringence and amylose-iodine complex formation measurements are suitable alternatives if DSC and X-ray equipment is not available, but will lead to different results. The differences between the methods can be explained by considering the phenomena that take place during the gelatinisation at limiting water conditions. Based on the experimental data obtained with DSC and X-ray measurements, the gelatinisation of 10 w/w % and 60 w/w % wheat starch-water mixtures started at the same temperature (approximately 50 °C). However, complete gelatinisation was reached at different temperatures (approximately 75 °C and 115 °C for, respectively, 10 w/w % and 60 w/w % wheat starch-water mixtures) according to the experimental DSC and X-ray data. These results are in accordance with independent DSC measurements that were carried out. The Flory equation was adapted to provide a quantitative explanation for the curves describing the degree of starch gelatinisation as a function of the starch-water ratio and the temperature. The gelatinisation curves that were obtained with the model are in good agreement with the experimentally determined curves. The parameters Tm0, ¿Hu and ¿12 that resulted in the lowest sum of the squared residuals are 291 ± 63 °C, 29.2 ± 3.9 kJ/mol and 0.53 ± 0.05 (95% confidence interval). These values agree with other values reported in literature
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