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A few principles relative to the presentation and use of nitrogen stable isotopic data are briefly reviewed. Some classical relationships between the isotope composition of a substrate undergoing a single-step unidirectional reaction, are introduced. They are illustrated through controlled experiments on denitrification in a soil, and through nitrification(More)
The use of variations in natural abundance of15N between nitrogen fixing and non nitrogen fixing soybeans was investigated for quantitative estimate of symbiotic nitrogen fixation. Isotopic analysis of 4 varieties of inoculated and non-inoculated soybeans growing under field conditions, with and without N-fertilizer was determined. It was found that(More)
Nitrogen isotope fractionation by Pearl Millet (Pennisetum americanum L. and P. mollissimum L.) grown on nitrate was associated with nitrate reductase activity. Fractionation was evidenced at the step of nitrate reduction when the substrate-to-enzyme ratio was high (possibly saturating for the active sites of the nitrate reductase enzyme), for instance in(More)
The ability of earthworms to assimilate soil organic pools of different ages was investigated in field conditions through natural 13C labelling. Provided that 13C natural abundance of earthworm tissues is determined by their diet, the assimilation of soil organic matter by earthworms was estimated by measuring 13C/12C ratio of tissues of earthworms sampled(More)
Most savanna water balance models assume water partitioning between grasses and shrubs in a two-layer hypothesis, but this hypothesis has not been tested for humid savanna environments. Spatial partitioning of soil water between grasses and shrubs was investigated in a West African humid savanna by comparing the isotopic composition (oxygen-18 and(More)
In southwest France, thick humic acid loamy soils have developed from Quaternary silty alluvial deposits. On these soils, most forest lands have been converted to continuous intensive maize cropping and the loss of C upon conversion to intensive agriculture has been shown to be significant. The objective of this study was to determine if a study of natural(More)
In India, the stability of the forest savanna boundary (ecotone) has been questioned. To investigate the possibility of vegetation change at this boundary, we used the natural difference in the stable carbon isotope ratio (13C/12C, expressed as δ13C) of C3 (forest) and C4 (savanna) plants, which is preserved in the isotopic composition of soil organic(More)