Papers by Veerle De Schepper
Communications in agricultural and applied biological sciences, 2006
The toxic effects of a widely used herbicide (Dikamin D containing 72% 2,4-D-amine Na as active i... more The toxic effects of a widely used herbicide (Dikamin D containing 72% 2,4-D-amine Na as active ingredient) applied alone or in combination with three heavy elements (copper sulphate, cadmium sulphate and lead acetate) modelling the heavy metal load of the environment were studied on chicken embryos with injection treatment. The treatment was done on day 0 of incubation. Solutions and emulsions of different concentrations were made from the test materials and injected in 0.1 ml volume into the air space of eggs. The macroscopical evaluations were done on day 19 of the incubation. Summarizing the findings, it can be established that the individual administration of the 72% 2,4-D containing herbicide formulation was less toxic compared to the control group than the simultaneous administration of the pesticide and heavy elements. As compared with each other the results from the combined administrations of the 72% 2,4-D containing herbicide formulation and heavy elements the simultaneous administration of cadmium and the herbicide caused the highest embryomortality while the incidence of developmental anomalies were the highest in the interaction study of the copper and the pesticide.
Water Science & Technology, 2007
To gain insight into the dynamics of pesticides in the different compartments of a river system, ... more To gain insight into the dynamics of pesticides in the different compartments of a river system, an intensive monitoring campaign was set up. An extensive dataset is useful when planning to model the fate of pesticides in river systems. In this study we focus on the Nil, a small, hilly basin situated in the central part of Belgium. Two automatic samplers were placed in the river basin, i.e., one at the mouth and one upstream, taking composite samples of water and suspended solids. Undisturbed sediment samples were taken by means of a macro-core and immediately frozen with CO 2 -ice. The samples were sliced and analysed for pesticides in pore water and on sediment. The results of the study revealed the dynamics of the different compartments of a river system. The water compartment showed hourly variations in pesticide peak concentrations, regularly exceeding the standards. The amount of pesticides transported by suspended solids increased after a rainfall event. The concentration of pesticides in pore water, measured on a monthly basis, followed the trends of the water compartment remarkably well, but in a significantly lower concentration. These observations may be explained by combined diffusion, biodegradation and chemical reactions occurring in the water column and the sediment. Further insight into the importance of each of these processes can be gained by dynamic modelling, an approach that is currently being followed.
Biotechnology and Bioengineering, 2006
In order to fill the knowledge gaps between lab/pilot-scale and full-scale operations and contrib... more In order to fill the knowledge gaps between lab/pilot-scale and full-scale operations and contribute basic information to long-term and stable operation of large-scale membrane bioreactors (MBRs), a systematic investigation was first conducted focused on soluble microbial products (SMPs) in 10 large-scale MBRs (capacity over 10,000 m 3 /d) for municipal wastewater treatment distributed in 4 different areas of China from fall to winter. The majority of these MBR plants had been operated stably for at least 1 year. Fundamental properties of SMPs were investigated, including composition, molecular weight distribution, hydrophobicity, fluorescent characteristics and fouling potential. The results showed that the concentration of SMPs ranged roughly from 5 to 25 mg TOC/L, with the major component being polysaccharides (ca. 3-18 mg/L) followed by humic substances (ca. 2-10 mg/L); while the protein concentration was relatively low (o5 mg/L). The SMPs presented a broad molecular weight distribution from smaller than 1 kDa to over 100 kDa. About half of the SMPs were hydrophilic substances mainly contributed by polysaccharides; humic substances were concentrated in hydrophobic fractions while proteins showed a relatively wide distribution. The fluorescent properties were found to be affected appreciably by the influent quality. The batch fouling tests indicated that the initial fouling rate correlated significantly with SMPs concentrations, which was particularly the case for hydrophilic and large-molecular-weight fractions. These findings may contribute to better understanding of membrane fouling in engineering conditions and assist in long-term and stable operation of full-scale MBRs.
Tree physiology, Jan 30, 2014
Plant drought responses are still not fully understood. Improved knowledge on drought responses i... more Plant drought responses are still not fully understood. Improved knowledge on drought responses is, however, crucial to better predict their impact on individual plant and ecosystem functioning. Mechanistic models in combination with plant measurements are promising for obtaining information on plant water status and can assist us in understanding the effect of limiting soil water availability and drought stress. While existing models are reliable under sufficient soil water availability, they generally fail under dry conditions as not all appropriate mechanisms seem yet to have been implemented. We therefore aimed at identifying mechanisms underlying plant drought responses, and in particular investigated the behaviour of hydraulic resistances encountered in the soil and xylem for grapevine (Vitis vinifera L.) and oak (Quercus robur L.). A variable hydraulic soil-to-stem resistance was necessary to describe plant drought responses. In addition, implementation of a variable soil-to-...
Annals of botany, 2011
Girdling, or the removal of a strip of bark around a tree's outer circumference, is often use... more Girdling, or the removal of a strip of bark around a tree's outer circumference, is often used to study carbon relationships, as it triggers several carbon responses which seem to be interrelated. An existing plant model describing water and carbon transport in a tree was used to evaluate the mechanisms behind the girdling responses. Therefore, the (un)loading functions of the original model were adapted and became a function of the phloem turgor pressure. The adapted model successfully simulated the measured changes in stem growth induced by girdling. The model indicated that the key driving variables for the girdling responses were changes in turgor pressure due to local changes in sugar concentrations. Information about the local damage to the phloem system was transferred to the other plant parts (crown and roots) by a change in phloem pressure. After girdling, the loading rate was affected and corresponded to the experimentally observed feedback inhibition. In addition, the...
Frontiers in Plant Science, 2013
Carbon transport processes in plants can be followed non-invasively by repeated application of th... more Carbon transport processes in plants can be followed non-invasively by repeated application of the short-lived positron-emitting radioisotope 11 C, a technique which has rarely been used with trees. Recently, positron emission tomography (PET) allowing 3D visualization has been adapted for use with plants. To investigate the effects of stem girdling on the flow of assimilates, leaves on first order branches of two-year-old oak (Quercus robur L.) trees were labeled with 11 C by supplying 11 CO 2 -gas to a leaf cuvette. Magnetic resonance imaging gave an indication of the plant structure, while PET registered the tracer flow in a stem region downstream from the labeled branches. After repeated pulse labeling, phloem translocation was shown to be sectorial in the stem: leaf orthostichy determined the position of the phloem sieve tubes containing labeled 11 C. The observed pathway remained unchanged for days. Tracer time-series derived from each pulse and analysed with a mechanistic model showed for two adjacent heights in the stem a similar velocity but different loss of recent assimilates. With either complete or partial girdling of bark within the monitored region, transport immediately stopped and then resumed in a new location in the stem cross-section, demonstrating the plasticity of sectoriality. One day after partial girdling, the loss of tracer along the interrupted transport pathway increased, while the velocity was enhanced in a non-girdled sector for several days. These findings suggest that lateral sugar transport was enhanced after wounding by a change in the lateral sugar transport path and the axial transport resumed with the development of new conductive tissue.
Journal of Experimental Botany, 2012
In trees, stem diameter variations are related to changes in stem water content, because internal... more In trees, stem diameter variations are related to changes in stem water content, because internally stored water is depleted and replenished over a day. To confirm this relationship, non-invasive magnetic resonance imaging (MRI) was combined with point dendrometer measurements in three actively transpiring oak (Quercus robur L.) trees. Two of these oak trees were girdled to study the stem increment above the girdling zone. MRI images and micrographs of stem cross-sections revealed a close link between the water distribution and the anatomical features of the stem. Stem tissues with the highest amount of water were physiologically the most active ones, being the youngest differentiating xylem cells, the cambium and the youngest differentiating and conductive phloem cells. Daily changes in stem diameter corresponded well with the simultaneously MRI-measured amount of water, confirming their strong interdependence. MRI images also revealed that the amount of water in the elastic bark tissues, excluding cambium and the youngest phloem, contributed most to the daily stem diameter changes. After bark removal, an additional increase in stem diameter was measured above the girdle. This increase was attributed not only to the cambial production of new cells, but also to swelling of existing bark cells. In conclusion, the comparison of MRI and dendrometer measurements confirmed previous interpretations and applications of dendrometers and illustrates the additional and complementary information MRI can reveal regarding water relations in plants.
Environmental and Experimental Botany, 2010
Stem diameter variations are not solely driven by the water status of a tree, but also by the car... more Stem diameter variations are not solely driven by the water status of a tree, but also by the carbon status in the phloem. We mechanically changed the carbon status in young oak trees (Quercus robur L.) by girdling the stem in order to investigate its effect on stem diameter variations. The stem was girdled at two heights by removing the bark which contains the carbon conducting phloem. The upper stem zone (U) still received new assimilates from the leaves, while the lowest stem zone (L) received only stored carbon from the roots. The middle stem zone (M) was completely isolated from crown and roots.
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Papers by Veerle De Schepper