Jean Remacle

Changes in chemical composition of Pinus sylvestris needle litter during decomposition along a European coniferous forest climatic transect.

The objective of this investigation was to assess the changes in chemical composition (lignin, cellulose, hemicelluloses, non-structural compounds, N, and ash) of decomposing litter. Standard Pinus sylvestris needle litter, originating from southern Sweden, was incubated in litterbags at 15 sites selected from the Netherlands to south Spain. The changes in chemical composition of this litter were determined using near infrared reflectance spectroscopy. The hypothesis was that standard (chemically uniform) litter decomposing under a range of climates would show different dynamics of accumulation and loss of C-fractions, N, and ash, relative to mass loss. It was shown that, for a given mass-loss value (10, 20, 30, 40, or 50%), the proportion of lignin, cellulose, hemicelluloses, non-structural compounds, N, and ash in the decomposing pine needles differed between sites. Lignin concentration in the litter residue at 50% mass loss ranged from approximately 26 to 43%, cellulose from 19 to 27%, hemicelluloses from 7 to 11%, non-structural compounds from 19 to 25%, N from 0.7 to 1.3%, and ash content from 1.4 to 10.1%. Lignin concentrations showed the highest range of variation. Lignin concentrations during decomposition were positively related to moisture factors as significant correlations were found with actual evapotranspiration and were improved in multiple regressions by the mean annual precipitation or the water surplus. Cellulose was degraded further at sites with high precipitation whereas hemicellulose degradation was related to temperature. This leads to the conclusion that the remaining organic matter produced by standard litter decomposition within the studied climatic range of variations tended to be more recalcitrant under wet and warm climatic conditions than under cold or dry climate.

Factors affecting the concentrations of cadmium, zinc, copper and lead in the sediments of the Vesdre River

Abstract The main factors influencing Cd, Zn, Cu and Pb concentrations in the sediments of the highly polluted Vesdre River (eastern Belgium) have been investigated. Only negative correlations were demonstrated between the clay content and heavy metals. The composition of the clay minerals could partially explain this paradox. However, the pretreatment of the minerals might influence the geochemical data obtained from analysis. Iron-hydroxides and phosphates seem to be the main sinks for Pb, Cd and Zn whereas organic components might play a less important role.

Cadmium removal by a strain of Alcaligenes denitrificans isolated from a metal-polluted pond

Abstract A strain of Alcaligenes denitrificans was isolated which had resistance to cadmium. The aerobic growth of the microbe in the presence of 10 or 90 mg cadmium/l resulted in removal of more than 95% of the dissolved metal. The settled material contained up to 51% cadmium. Much, if not all, of the cadmium occurred as cadmium carbonate as shown by the amounts of carbonate and cadmium, the stoichiometric ratio Cd/CO 3 and the X-ray diffraction analysis. It is shown that A. denitrificans provoked the precipitation of cadmium carbonate in aerobiosis by making the solution alkaline in a protein-free culture.

Cadmium fate in bacterial microcosms

Mixed bacterial cultures were incubated in chemostats to mimic natural conditions as close as possible. When they had reached a steady state, they received a flux containing 0.5 mg Cd l−1. The responses of bacterial systems were examined at 20 and 10°C. Moreover, the Cd accumulation by bacteria was analyzed with regard to the bacterial productivity. The cellular Cd repartition was compared in Cd-resistant and Cd-sensitive strains. Finally, the role played by the attached bacteria was exemplified in the Cd transfers in the freshwater bacterial community.

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.

Influence of environmental factors upon the leaching of cations from undisturbed microcosms of beech and spruce litters

Abstract The leaching of nutrient cations (Na + , K + , Mg 2+ and Ca 2+ ) from undisturbed beech and spruce litters was followed in relation to the following environmental factors: nature of the organic layers, temperature, rainfall, quality of rain and stage of humus development. Among them, temperature, quality of rain and type of humus were predominant in modifying leaching rates of the nutrients. But, when the time of sampling was considered, the effects of physical, chemical and biological transformations of the humus on the leaching of cations had to be accounted for. The complexity of the interactions occurring during leaching is also exemplified.

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.

Principal component analysis applied to nutrient balances in organic layers of beech and spruce forests

Abstract Yearly nutrient balances were established between August 1979 and October 1981 for the organic layers of beech and spruce forests. Principal component analysis has been applied to the monthly nutrient balances in order to understand the important differences which appear between both types of organic layers. Three main processes affect the redistribution of elements from the organic layers: exchange and solubilization, organic matter mineralization and nitrate immobilization and release. The relative importance of these three processes within the beech and the spruce layers is different. Moreover, it is shown that variations in the rainfall regime is an important factor which govern nitrogen redistribution and that rainfall acidity promotes phosphate leachings from the organic layers of both forests.

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.

Population micromycetique de quelques types forestiers du Plateau du Sart Tilman (Liege, Belgique)

ResuméSept espèces constituent la base de la population fongique des chênaies du Sart Tilman.Les deux stations qui présentent la flore microfongique la plus variée sont la chênaie fraîche àAcer pseudoplatanus et la chênaie sessiliflore àHolcus mollis. Aspergillus fumigatus, espèce courante des sols méridionnaux est hébergée dans des stations peu ombragées: chênaie àHolcus mollis, chênaie àDeschampsia flexuosa et chênaie àPteridium aquilinum. Penicillium frequentans colonise les sols en voie de podzolisation.Trichoderma viride etMortierella ramanniana se cantonnent dans les horizons supérieurs tandis quePenicillium nigricans etPenicillium sériecyclopium colonisent souvent les horizons les plus bas. Pseudeurotium zonatum semble se localiser dans les milieux peu aérés: horizons profonds de la chênaie à Erable et de la chênaie à myrtillier.