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Eddy correlation measurements of CO2 exchange were made in intensively managed peat pastures at 2 different groundwater tablesduring most of a growing season. F was separated into a respiratory and an assimilatory CO2 flux. The fit of the Arrhenius temperature response to Fr showed that Fr was generally higher at low groundwater tables. The fit of a hyperbolic irradiance response to Fa showed that Fa was also generally higher at low groundwater tables, more than compensating for higher Fr. The daily CO2 balance suggested thatthe low groundwater pasture was a larger CO2 sink or a smaller CO2 source than the high groundwater pasture during the measurement period. The difference in Fr between the groundwater tables was substantially less than the factor 2 differencein level of soil subsidence. This suggests that oxidization of soil organic matter was a relatively minor factor in soil subsidence. [ABSTRACT FROM AUTHOR]

Aerodynamic measurements of CO2 (F) and latent heat (lambdaE) exchange were made in an intensively managed peat pasture during2 consecutive years; the fetch was approximately 1.5 km. Surface conductance (gs) was calculated from the Penman-Monteith equation. F was split into a respiratory CO2 flux (Fr) and an assimilatory CO2 flux (Fa). Fr was non-linearly related to air temperature (Ta), revealing a distinct seasonal pattern in its value normalized to Ta. Fa was hyperbolically related to short-wave irradiance, the seasonal pattern of its maximum value compared to that of normalized Fr. Ta proved to be a major factor: Fa tended to maintain a positive response to Taover much of the actual Ta range. Aerial vapour pressure deficit (D) was generally too low (<1 kPa) to have an effect on Fa. [ABSTRACT FROM AUTHOR]

Since the pioneering work of C.T. de Wit in the 1960s, the Wageningen group has built a tradition in developing and applying crop models. Rather than focusing on a few models, diversity is its trademark. Here we present an overview of the Wageningen crop and crop-soil modelling approaches along three criteria. The first criterion relates to the production situations the models are dealing with (i.e. potential, water and/or nutrient-limited, and actual production situations including pests, diseases and weeds). Second, models differ as a result of the objectives of model development, and hence required scale and degree of detail and comprehensiveness. Third, models have at least three potential application domains, i.e. research, education and support of learning and decision making processes.We describe both summary and more comprehensive modelling approaches for the major production situations. An overview of most of the Wageningen models is presented together with a more detailed description of LINTUL, SUCROS, ORYZA, WOFOST and INTERCOM. Illustrations for each of the three application domains are presented, i.e. plant type design, guiding experimental research, education, yield gap analysis, evaluation of manure policies, crop growth monitoring system and analysis and design of farming and regional land use systems. We discuss common issues of model verification, model validation, model validity and data requirements, and present information on software implementation, model and software documentation and distribution policy. Finally, we reflect upon the Wageningen modelling approaches and identify a number of key issues for future research.Major achievements of Wageningen modelling efforts include (1) a broad variety of approaches for modelling of systems at different scales and with different purposes; (2) their contribution to quantitative systems thinking in general, also for applications at higher hierarchical levels; (3) a strong linkage between crop modelling and higher education, both at undergraduate, graduate and post-doctoral level. To continually increase our understanding of crops and production systems a diversified approach must be cherished. At the same time we conclude that focus is required on a limited number of modules in a more integrated modelling framework for the benefit of analysing, evaluating and designing cropping systems. This review may be instrumental in the development of such an integrated framework. [Copyright &y& Elsevier]

Effects of increasing carbon dioxide concentration [CO2] on wheat vary depending on water supply and climatic conditions, which are difficult to estimate. Crop simulation models are often used to predict the impact of global atmospheric changes on food production. However, models have rarely been tested for effects on crops of [CO2] and drought for different climatic conditions due to limited data available from field experiments.Simulations of the effects of elevated [CO2] and drought on spring wheat (Triticum aestivum L.) from three crop simulation models (LINTULCC2, AFRCWHEAT2, Sirius), which differ in structure and mechanistic detail, were compared with observations. These were from 2 years of free-air carbon dioxide enrichment (FACE) experiments in Maricopa, Arizona and 2 years of standardised (in crop management and soil conditions) open-top chamber (OTC) experiments in Braunschweig and Giessen, Germany. In a simulation exercise, models were used to assess the possible impact of increased [CO2] on wheat yields measured between 1987 and 1999 at one farm site in the drought prone region of Andalucia, south Spain.The models simulated well final biomass (BM), grain yield (GY), cumulative evapotranspiration (ET) and water use efficiency (WUE) of wheat grown in the FACE experiments but simulations were unsatisfactory for OTC experiments. Radiation use efficiency (RUE) and yield responses to [CO2] and drought were on average higher in OTC than in FACE experiments. However, there was large variation among OTC experiments. Plant growth in OTCs was probably modified by several factors related to plot size, the use (or not use) of border plants, airflow pattern, modification of radiation balance and/or restriction of rooting volume that were not included in the models. Variation in farm yields in south Spain was partly explained by the models, but sources of unexplained yield variation could not be identified and were most likely related to effects of pests and diseases that were not included in the models. Simulated GY in south Spain increased in the range between 30 and 65% due to doubling [CO2]. The simulated increase was larger when a [CO2]×drought interaction was assumed (LINTULCC2, AFRCWHEAT2) than when it was not (Sirius).It was concluded that crop simulation models are able to reproduce wheat growth and yield for different [CO2] and drought treatments in a field environment. However, there is still uncertainty about the combined effects of [CO2] and drought including the timing of drought stress and about relationships that determine yield variation at farm and larger scales that require further investigation including model testing. [Copyright &y& Elsevier]

The Gaussian plume model (GPM) is considered as a valuable tool in predictions of the atmospheric transport of fungal spores and plant pollen in risk assessments. The validity of the model in this important area of application has not been extensively evaluated. A field experiment was set up to test and—if necessary—adapt the GPM, as applied to the dispersal of spores. Spores of the fern Lycopodium clavatum were released artificially over a period of 10 min from a source placed 70 cm above the surface in a potato crop. Spore catches were made with a network of Rotorod and Burkhard samplers, placed up to 100 m downwind from the source and at several heights and crosswind distances from the anticipated plume axis. The width and height of Gaussian plumes depend on atmospheric mixing, as affected by weather. Mixing parameters in risk assessments are commonly predicted on the basis of weather conditions. We found a low correlation (R=0.4) between measured spore concentrations and predicted spore concentrations, using a widely used prediction method (GPM Pasquill Atmospheric Diffusion, 2nd ed., Wiley, New York, 1974), based on cloud cover, wind speed, season and time of day. More precise methods for predicting the width and height of Gaussian plumes require detailed site-specific information (measurements of wind speed and temperature at two heights above the vegetation), and are therefore not readily applicable in risk assessments. An alternative that is often adequate is to use a worst case approach, in which the dispersal parameters are used that give the highest spore concentration at the location of interest. Predictability could be improved by measuring atmospheric stability during and just after weather conditions conducive to release of the pollen or spores of interest. We calibrated the model with a weighted least-squares method. Calibrating the model led to a more than 100-fold decrease in the sum of weighted squares. A comparison of estimated concentrations with the measurements confirmed that spore clouds originating from a point source take the form of a Gaussian plume: the coefficient of correlation between measured spore concentrations and fitted concentrations was 0.8. The fraction of spores that escaped the canopy and was available for long distance dispersal amounted to 64±17%. We found an 83% correlation between this so-called escape fraction and wind speed. [Copyright &y& Elsevier]

Background: Renal tubular acidosis (RTA) is a rare cause of growth failure, therefore it is uncertain whether routine screening with blood gas analysis of short infants and children is cost-effective., Objective: To investigate the clinical, growth and laboratory parameters in children with RTA to estimate the possible value of laboratory screening for this disorder in infants and children referred for short stature according to a recent guideline., Method: Retrospective chart analysis of 30 children diagnosed between 1978 and 2005 in The Netherlands and 3 centers in Belgium., Results: The current guideline for short stature detected 33% of children with RTA. Assuming a pre-test probability of RTA of 0.6 per 100,000 births, the likelihood ratio of poor growth was 58 and 17 below and above 3 years, respectively. Sensitivity was 17/30 and 12/24 for a -2.0 SDS cutoff for weight and body mass index, respectively. In infants and toddlers diagnosed before 3 years of age, the mean weight loss was 1.5 SD, and 0.8 SDS in older children. In short children >3 years RTA was extremely rare, always associated with clinical symptoms, and rarely detected by blood gas analysis., Conclusion: According to our data a decreasing weight SDS for age is a sufficient indication to perform blood gas analysis in children <3 years of age, particularly in the presence of additional clinical features, whereas it can be omitted in short children >3 years of age., (Copyright © 2010 S. Karger AG, Basel.)

The aim of this study was to predict crop growth of year-round cut chrysanthemum (Chrysanthemum morifolium Ramat.) based on an empirical model of potential crop growth rate as a function of daily incident photosynthetically active radiation (PAR, MJ m-2 d-1), using generalized estimated parameters of the expolinear growth equation. For development of the model, chrysanthemum crops were grown in four experiments at different plant densities (32, 48, 64 and 80 plants m-2), during different seasons (planting in January, May-June and September) and under different light regimes [natural light, shading to 66 and 43 % of natural light, and supplementary assimilation light (ASS, 40-48 micro mol m-2 s-1)]. The expolinear growth equation as a function of time (EXPOT) or as a function of incident PAR integral (EXPOPAR) effectively described periodically measured total dry mass of shoot (R2 > 0.98). However, growth parameter estimates for the fitted EXPOPAR were more suitable as they were not correlated to each other. Coefficients of EXPOPAR characterized the relative growth rate per incident PAR integral [rm,i (MJ m-2)-1] and light use efficiency (LUE, g MJ-1) at closed canopy. In all four experiments, no interaction effects between treatments on crop growth parameters were found. rm,i and LUE were not different between ASS and natural light treatments, but were increased significantly when light levels were reduced by shading in the summer experiments. There was no consistent effect of plant density on growth parameters. rm,i and LUE showed hyperbolic relationships to average daily incident PAR averaged over 10-d periods after planting (rm,i) or before final harvest (LUE). Based on those relationships, maximum relative growth rate (rm, g g-1 d-1) and maximum crop growth rate (cm, g m-2 d-1) were described successfully by rectangular hyperbolic relationships to daily incident PAR. In model validation, total dry mass of shoot (Wshoot, g m-2) simulated over time was in good agreement with measured ones in three independent experiments, using daily incident PAR and leaf area index as inputs. Based on these results, it is concluded that the expolinear growth equation is a useful tool for quantifying cut chrysanthemum growth parameters and comparing growth parameter values between different treatments, especially when light is the growth-limiting factor. Under controlled environmental conditions the regression model worked satisfactorily, hence the model may be applied as a simple tool for understanding crop growth behaviour under seasonal variation in daily light integral, and for planning cropping systems of year-round cut chrysanthemum. However, further research on leaf area development in cut chrysanthemum is required to advance chrysanthemum crop growth prediction.

A new empirical equation for the sigmoid pattern of determinate growth, 'the beta growth function', is presented. It calculates weight (w) in dependence of time, using the following three parameters: t(m), the time at which the maximum growth rate is obtained; t(e), the time at the end of growth; and w(max), the maximal value for w, which is achieved at t(e). The beta growth function was compared with four classical (logistic, Richards, Gompertz and Weibull) growth equations, and two expolinear equations. All equations described successfully the sigmoid dynamics of seed filling, plant growth and crop biomass production. However, differences were found in estimating w(max). Features of the beta function are: (1) like the Richards equation it is flexible in describing various asymmetrical sigmoid patterns (its symmetrical form is a cubic polynomial); (2) like the logistic and the Gompertz equations its parameters are numerically stable in statistical estimation; (3) like the Weibull function it predicts zero mass at time zero, but its extension to deal with various initial conditions can be easily obtained; (4) relative to the truncated expolinear equation it provides more reasonable estimates of final quantity and duration of a growth process. In addition, the new function predicts a zero growth rate at both the start and end of a precisely defined growth period. Therefore, it is unique for dealing with determinate growth, and is more suitable than other functions for embedding in process-based crop simulation models to describe the dynamics of organs as sinks to absorb assimilates. Because its parameters correspond to growth traits of interest to crop scientists, the beta growth function is suitable for characterization of environmental and genotypic influences on growth processes. However, it is not suitable for estimating maximum relative growth rate to characterize early growth that is expected to be close to exponential.

It has previously been reported that mice lacking the VLDL receptor (VLDLR-/-) exhibit normal plasma lipid levels and a modest decrease in adipose tissue mass. In the present study, the effect of VLDLR deficiency on profound weight gain was studied in mice. Obesity was induced either by feeding of a high-fat, high-calorie (HFC) diet or by crossbreeding mice onto the genetically obese ob/ob background. After 17 weeks of HFC feeding, VLDLR-/- mice remained lean, whereas their wild-type littermates (VLDLR+/+) became obese. Similarly, the weight gain of ob/ob mice was less profound in the absence of the VLDLR. Moreover, VLDLR deficiency led to increased plasma triglycerides after HFC feeding. The protection from obesity in VLDLR-/- mice involved decreased peripheral uptake of fatty acids, because VLDLR-/- mice exhibited a significant reduction in whole-body free fatty acid uptake, with no clear differences in food intake and fat absorption. These observations were supported by a strong decrease in average adipocyte size in VLDLR-/- mice of both obesity models, implying reduced adipocyte triglyceride storage in the absence of the VLDLR. These results suggest that the VLDLR plays a role in the delivery of VLDL-derived fatty acids into adipose tissue.

Evidence that concentrations of CO2 and trace gases in the atmosphere have increased is irrefutable. Whether or not these increased concentrations will lead to climate changes is still open to debate. Direct effects of increased CO2 concentrations on physiological processes and individual plants have been demonstrated and the consequences for crop growth and production under various circumstances are evaluated with simulation models. The consequences of CO2 enrichment are considerable under optimal growing conditions. However, the majority of crops are grown under sub-optimal conditions where the effects of changes in CO2 are often less. The same holds for the possible indirect effects of environmental changes such as temperature rise. Studies on individual plants under optimal conditions are therefore not sufficient for evaluating the effects at a farm, regional, national or supra-national level. Simulation studies help to bridge the gap between the various aggregation levels and provide a basis for various studies of policy options at various aggregation levels.

For active nodule nitrogen fixation, O(2), N(2), and carbohydrate must be transported throughout the nodule. No quantitative analysis of these transport processes in the nodules has been presented. By invoking several simplifying assumptions, a second-order differential equation for the various gradients and concentrations in the nodule was solved. Even though the nodule can only be approximated in this analysis, it indicates clearly that intercellular gas spaces must exist in nodules for adequate O(2) distribution. To preserve low O(2) concentrations and protect the nitrogenase, these gas spaces cannot be in direct contact with the ambient atmosphere. It is hypothesized that a gas barrier exists in the cortical region of the nodule to limit O(2) diffusion. This barrier would not substantially inhibit N(2) transport. Carbohydrate transport from the vascular tissue via diffusion in the liquid phase can adequately accommodate the requirements within the nodule.