Alain Hambuckers

Soil‐Applied Selenium Effects on Tissue Selenium Concentrations in Cultivated and Adventitious Grassland and Pasture Plant Species

Abstract According to international nutritional standards, plant selenium (Se) concentrations in Belgium are too low. To correct this situation, adding Se in fertilizers for pastures and grasslands is suggested, similar to activities in Finland. However, there is a lack of data on meadow plant species ability to absorb Se. Therefore, a pot experiment was initiated using 24 meadow plant species cultivated on a Belgian cambisol receiving standard fertilizer treatment, with or without the addition of 9 g Se ha−1 yr−1 as sodium selenate. Soil Se analysis confirmed the low Se status of the native soil. Mean foliar Se concentration in the control group was 0.05 mg kg−1. Because plant deficiency may occur at levels less than 0.10 mg Se kg−1, data provided further evidence for Se deficiency in Belgium plant production. When grown with Se, plant species showed wide variations for Se concentration, ranging from 0.08 to 0.49 mg Se kg−1. All values were less than 2 mg Se kg−1, the suggested threshold toxicity level for dairy cattle. There were two different types of plants in terms of response to Se fertilization. Most of the tested plants were known as nonaccumulators. There were also two probable secondary accumulators: Sinapis arvensis and Melilotus albus. Finally, one has to question the reliability of plant Se enhancement using this method when floristic composition is poorly controlled.

Relative importance of factors controlling the leaching and uptake of inorganic ions in the canopy of a spruce forest

Sequential sampling of precipitation under mature spruce trees and time-series analysis of the data were performed in order to assess, in natural conditions, the relative importance of different factors that could influence the leaching and uptake of inorganic ions in the canopy. Eleven rain events were analyzed in order to estimate how external factors, rain intensity, H+, and ionic concentration of the incident rain influence the ionic throughfall concentrations and the net throughfall fluxes.The results led to the conclusion that leaching or uptake mostly occur by diffusion. The influence of the open rain acidity was not conclusive; however, it was shown that the tested external factors only controlled a few percent of the variation of the data. By contrast, the autocorrelation of the data always explained a large portion of the variance. It could result from the gradual changes in the course time of internal factors related to the exchange system including waxes, cuticles, apoplast and xylem sap. These constituents were known to control the exchange at the canopy surface and to be sensitive to the plant physiology and environmental conditions.

Seasonal variations in the crop contents of scavenging Helmeted Guinea Fowls (Numida meleagris, L.) in Parakou (Benin).

1. An experiment was carried out with 120 helmeted guinea fowls during one year in Parakou (Benin). Feed intake, ingredient and chemical composition, along with the nutritional adequacy of scavenging diets were measured during the rainy season (November–February) and dry season (March–October) in order to propose supplementation strategies. Ingredients found in crops were identified and allocated into 6 main categories (supplemental feed, seeds, green forages, animal materials, mineral matter and unidentified materials). 2. Mean dry weights of crop contents were significantly higher in the rainy than in the dry season. Amounts and proportions of supplemental feed and seeds were not significantly different between seasons, whereas those of green forage, animal materials and mineral matter were higher in rainy season. Supplemental feed, especially maize and sorghum, was the largest component of the crop content in both seasons. The most represented grass seeds were Panicum maximum (rainy season) and Rottboellia cochinchinensis (dry season). 3. Dietary concentrations of organic matter, non-nitrogen extract and metabolisable energy were higher in the dry season, while mineral concentrations were higher in the rainy season. There were no significant differences between the two seasons in dry matter, crude protein or crude fibre. 4. Scavenging provided insufficient nutrients and energy to allow guinea fowls to be productive. Therefore, more nutritionally balanced supplementary feed would be required during both seasons.

Nutritional status of declining spruce (Picea abies (L.) Karst.) : effect of soil organic matter turnover rate

Foliar analysis was undertaken in two plots of Picea abies (L.) Karst., located in a watershed of Haute Ardenne, Belgium, in order to estimate the decline of the trees. Apart from a general Mg deficiency, the concentrations of the needles were in the same range as those determined in other European stands. Comparisons between healthy and declining trees within each plot revealed a general pattern of decline similar to that observed elsewhere in Western Europe. This was shown as lower Ca, Mg, Zn concentrations and water content and higher N and P concentrations of the needles collected from declining trees. It is concluded that this decline could be due to N over fertilization by the atmospheric deposition. The difference of decline between the two plots was attributed to the turnover rate of the soil organic layer which was less intensive in the most damaged plot.

Problem of Applying Sodium Selenate to Increase Selenium Concentration in Grassland Plants in Southern Belgium

In a survey of grasslands, mean selenium (Se) concentration in Holcus lanatus was 83 μg kg−1 (less than 100 μg kg−1, the minimal concentration protecting mammals from deficiency disorders). Despite rather high levels of soil extractable Se, plant Se availability was supposed to be low because of high soil humus concentration. A pot experiment with common grassland species showed contrasting responses to selenate addition (9 g Se ha−1 yr−1). Lolium perenne leaves reached 470 μg kg−1, and Trifolium pratense reached 292 μg kg−1. The controls were less than 100 μg kg−1. Leaves of others species showed greater values both in control and treated series and no significant difference. In a second pot experiment, Melilotus albus, a supposed secondary accumulator, and Lolium perenne as a control were submitted to moderate increased selenate additions (up to 45 g Se ha−1 yr−1). The results confirmed that Melilotus albus was a better accumulator with a leaf concentration that could reach the toxicity level of 2 mg kg−1.

Microrefugia, Climate Change, and Conservation of Cedrus atlantica in the Rif Mountains, Morocco

This study reconstructs and interprets the changing range of Atlas cedar in northern Morocco over the last 9,000 years. A synthesis of fossil pollen records indicated that Atlas cedars occupied a wider range at lower elevations during the mid-Holocene than today. The mid-Holocene geographical expansion reflected low winter temperatures and higher water availability over the whole range of the Rif Mountains relative to modern conditions. A trend of increasing aridity observed after 6000 years BP progressively reduced the range of Atlas cedar and prompted its migration towards elevations above 1400 masl. To assess the impact of climate change on cedar populations over the last decades, we performed a transient model simulation for the period between 1960 and 2010. Our simulation showed that the range of Atlas cedar decreased by about 75% over the last 50 years and that the eastern populations of the range in the Rif Mountains were even more threatened by the overall lack of water availability than the western ones. Today, Atlas cedar populations in the Rif Mountains are persisting in restricted and isolated areas (Jbel Kelti, Talassemtane, Jbel Tiziren, Oursane, Tidighine) that we consider to be modern microrefugia. Conservation of these isolated populations is essential for the future survival of the species, preserving polymorphisms and the potential for population recovery under different climatic conditions.

The Role of The Bacterial Community in the Radionuclide Transfers in Freshwater Ecosystems.

Publisher Summary This chapter investigates the radionuclide fluxes between the bacteria and the water in aquatic ecosystem by examining the bulk transfers mediated by a bacterial community isolated from the river sediments. A comparison of the aerobic bacterial communities colonizing the sediments and the water column shows that the bacterial community of the sediments is composed of two sub-communities. The first one is similar to the water column community by its biochemical features; the other one displays quite different characteristics and appears to be more representative of the sediments. An important part of 60 Co and 134 Cs can be immobilized by the bacterial biomass that constitutes a pool of radionuclides, their transfers to the water column being controlled by temperature and pH. The uptake of 60 Co and 134 Cs by bacteria is described by the Michaelis–Menten model. The uptake kinetics depend on the type of radionuclide and the level of radiocontamination in the water column. The highest affinity uptake system is observed for 60 Co at low radiocontamination levels. The decontamination of bacterial biomass develops in two phases. The first phase is characterized by a very short biological half-life, a few seconds or minutes, while the second phase is longer; the biological half-lives reach between 15 h to 461 h for 60 Co and between 39 h and 8,976 h for 134 Cs.

Contrasting climate risks predicted by dynamic vegetation and ecological niche-based models applied to tree species in the Brazilian Atlantic Forest

Climate change is a threat to natural ecosystems. To evaluate this threat and, where possible, respond, it is useful to understand the potential impacts climate change could have on species’ distributions, phenology, and productivity. Here, we compare future-scenario outcomes between a dynamic vegetation model (DVM; CARbon Assimilation In the Biosphere (CARAIB)) and an ecological niche-based model (ENM; maximum entropy model) to outline the risks to tree species in the Brazilian Atlantic Forest, comprising the habitats of several endemic species, including the endangered primate Leontopithecus chrysomelas (golden-headed lion tamarin; GHLT), our species of interest. Compared to MaxENT, the DVM predicts larger present-day species ranges. Conversely, MaxENT ranges are closer to sampled distributions of the realised niches. MaxENT results for two future scenarios in four general circulation models suggest that up to 75% of the species risk losing more than half of their original distribution. CARAIB simulations are more optimistic in scenarios with and without accounting for potential plant-physiological effects of increased CO2, with less than 10% of the species losing more than 50% of their range. Potential gains in distribution outside the original area do not necessarily diminish risks to species, as the potential new zones may not be easy to colonise. It will also depend on the tree species’ dispersal ability. So far, within the current range of L. chrysomelas, CARAIB continues to predict persistence of most resource trees, while MaxENT predicts the loss of up to 19 species out of the 59 simulated. This research highlights the importance of choosing the appropriate modelling approach and interpretation of results to understand key processes.