Potentiel hydrique

Résumé

Le potentiel hydrique est une variable physique homogène à une pression qui quantifie le niveau d'énergie des molécules d'eau d'une solution, autrement dit la "force" avec laquelle cette solution retient ses molécules d'eau. Elle a été conçue par des physiologistes pour modéliser les transferts d'eau entre différentes solutions séparées par des membranes. L'eau ne quitte une solution pour une autre que si le potentiel hydrique de la seconde solution est inférieur à la première. Plus la solution est concentrée en substances dissoutes, et plus son potentiel hydrique est bas. Utilité En physiologie végétale le potentiel hydrique permet de déterminer le sens des échanges hydriques entre :

différentes parties de la plante (organes, cellules...).
le sol et la plante.
la plante et l'atmosphère.

En effet, l'eau circule toujours des potentiels hydriques les plus élevés vers les potentiels hydriques les plus bas (convention de signes). Composantes Le potentiel h

Source officielle

https://fr.wikipedia.org/wiki/Potentiel_hydrique

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The porous surface model, a novel experimental system for online quantitative observation of microbial processes under unsaturated conditions

Gamze Gülez, Dani Or

Water is arguably the most important constituent of microbial microhabitats due to its control of physical and physiological processes critical to microbial activity. In natural environments, bacteria often live on unsaturated surfaces, in thin (micrometric) liquid films. Nevertheless, no experimental systems are available that allow real-time observation of bacterial processes in liquid films of controlled thickness. We propose a novel, inexpensive, easily operated experimental platform, termed the porous surface model (PSM) that enables quantitative real-time microscopic observations of bacterial growth and activity under controlled unsaturated conditions. Bacteria are inoculated on a porous ceramic plate, wetted by a liquid medium. The thickness of the liquid film at the surface of the plate is set by imposing suction, corresponding to soil matric potential, to the liquid medium. The utility of the PSM was demonstrated using Pseudomonas putida KT2440 tagged with gfp as a model bacterium. Single cells were inoculated at the surface of the PSM, and the rate at which colonies expanded laterally was measured for three matric potentials (-0.5, -1.2, and -3.6 kPa). The matric potential exerted significant influence on colony expansion rates, with a faster rate of spreading at -0.5 than at -1.2 or -3.6 kPa (diameter increase rate, ca. 1,000, 200, and 17 mu m h(-1), respectively). These differences can be attributed to cell motility, strongly limited under the most negative matric potential. The PSM constitutes a tool uniquely adapted to study the influence of liquid film geometry on microbial processes. It should therefore contribute to uncovering mechanisms of microbial adaptation to unsaturated environments.

2008

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Review of heat and water movement in field soils

Marc Parlange

1998

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During recent years, aggressive air pollution mitigation measures in northern China have resulted in considerable changes in gas and aerosol chemical composition. But it is unclear whether aerosol water content and acidity respond to these changes. The two parameters have been shown to affect heterogeneous production of winter haze aerosols. Here, we performed thermodynamic equilibrium modeling using chemical and meteorological data observed in urban Beijing for four recent winter seasons and quantified the changes in the mass growth factor and pH of inorganic aerosols. We focused on high relative humidity (>60%) conditions when submicron particles have been shown to be in the liquid state. From 2014/2015 to 2018/2019, the modeled mass growth factor decreased by about 9%-17% due to changes in aerosol compositions (more nitrate and less sulfate and chloride), and the modeled pH increased by about 0.3-0.4 unit mainly due to rising ammonia. A buffer equation is derived from semivolatile ammonia partitioning, which helps understand the sensitivity of pH to meteorological and chemical variables. The findings provide implications for evaluating the potential chemical feedback in secondary aerosol production and the effectiveness of ammonia control as a measure to alleviate winter haze.

AMER CHEMICAL SOC2019

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