François Beaujard

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Les formes libres d'azote (NO 3 − , NO 2 − et NH 4 + ) et les capacités Nitrate Réductase (NRase) et Glutamate Déhydrogénase (GDH) sont analysées chez des vitroplants d'Erica × darleyensis transférés sur 4 solutions nutritives. Chez les vitroplants, les activités NRase et GDH se répartissent pour moitié dans les racines et les parties aériennes; au cours du(More)
Energy dispersive X-ray fluorescence (EDXRF) provides highly sensitive and precise spatial resolution of cation content in individual annual growth rings in trees. The sensitivity and precision have prompted successful applications to forensic dendrochemistry and the timing of environmental releases of contaminants. These applications have highlighted the(More)
When tree stems are mechanically stimulated, a rapid long-distance signal is induced that slows down primary growth. An investigation was carried out to determine whether the signal might be borne by a mechanically induced pressure pulse in the xylem. Coupling xylem flow meters and pressure sensors with a mechanical testing device, the hydraulic effects of(More)
Measurements of air and soil temperatures and xylem pressure were made on 17-year-old orchard trees and on 5-year-old potted trees of walnut (Juglans regia L.). Cooling chambers were used to determine the relationships between temperature and sugar concentration ([glucose] + [fructose] + [sucrose], GFS) and seasonal changes in xylem pressure development.(More)
Tree nutrient research concentrated on endogenous C and N remobilisation in spring has neglected to acknowledge the possibilities of significant effects of N uptake before bud break, especially on the quality of regrowth and N reserve remobilisation. To investigate this subject, experimental studies were performed on young poplars (Populus tremula Populus(More)
We studied the short-term (i.e., a few days) effect of a sudden increase in CO2 uptake by shoots on nutrient (NO3-, P ion, K+, Ca2+ and Mg2+) uptake by roots during vegetative growth of young walnut (Juglans nigra x J. major L.) trees. The increase in CO2 uptake was induced by a sudden increase in atmospheric CO2 concentration ([CO2]). Twelve 2-year-old(More)
Trees can take up and assimilate contaminants from the soil, subsurface, and groundwater. Contaminants in the transpiration stream can become bound or incorporated into the annual rings formed in trees of the temperate zones. The chemical analysis of precisely dated tree rings, called dendrochemistry, can be used to interpret past plant interactions with(More)
Nitrate and potassium uptake are strongly correlated in deciduous trees from bud break to leaf fall. A conceptual model for potassium cycling is proposed to explain this result. We have studied the correlation between nitrate and potassium uptake in spring and autumn in two deciduous tree species: walnut and sycamore maple. Two-year-old trees were(More)
Rhododendron catawbiense cv. Album propagated in vitro were transferred ex vitro and grown in a greenhouse, under long or short days. Under long days, the rhythmic growth led to an acrotonous development. In contrast, under short days, the upper buds were unable to burst, allowing basitony. In both photoperiodic conditions, the apical buds were sampled at(More)
In order to control young plant form by modifying culture conditions, plants of Rhododendron catawbiense from in vitro culture were grown in a greenhouse under different photoperiodic treatments (long or short days) combined or not with a several-week nitrogen starvation. After 12 weeks of culture under long days (16 h) with nitrogen supply, plants showed a(More)
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