Water tension

Ou L, Rao PS, Davidson JM. 1983. Methyl parathion degradation in soil Influence of soil-water tension. Soil Biol Biochem 15 211-215. 

The hydrophobic waxy cuticle of plants can inhibit the movement and accessibility of nutrients to bacterial cells. However, biosurfactants produced by the majority of epiphytic Pseudomonas spp. decreases the water tension, enabling relatively free movement across the leaf surface to nutrient sources and natural openings such as stomata. Pseudomonas are also known to release a toxin called syringomycin that can produce holes in the plant cell membrane allowing access to intracellular nutrients without necessarily resulting in disease symptoms (Cao et al.r 2005). 

In all cases the anisotropic polymerization mixtures (10% by weight) could be used directly in the formation of dry-jet wet-spun fibers. Monofilament fibers were obtained by coagulation in water, tension dried at 150 °C and heat treated at 500-600 °C with a 30s residence time. The best fibers were obtained from the high molecular weight PBZT polymer (VII) which exhibited modulus values that ranged between 172 GPa and 207 GPa and tenacity values up to 2.4 GPa. Unfortunately, the compressive property as measured by the tensile recoil test was only 380 MPa, showing only a slight improvement over PBZT. 

It is usual to consider the course of emulsion polymerization to proceed through three intervals [16,17]. The particle number increases with time in Interval I, where latex particles are being formed, and then remains constant during Intervals II and II. The monomer concentration in particles is in equilibrium with a monomer saturated aqueous solution. Swelling is limited only by the opposite force of the particle surface/water tension. Hence, the concentration of monomer in the particles is usually taken as constant up to the point where free monomer droplets disappear. In Intervals I and II, the monomer concentration... 

Table I. Monomer Water Tensions Solubility and Polymer Critical Surface...

Hamdi, Y.A., 1971. Soil water tension and the movement of rhyzobia. Soil Biol. Biochem., 3 121. 

For a soil that is barely saline (EC 4 mS/cm), an osmotic pressure of about 1.5 atmospheres would result. In other words, the water in this moist soil would not be freely available to plant roots, but would be retained in a lowered free energy state equivalent to 1.5 atmospheres of water tension. This, however, is insufficient tension to seriously impede water uptake by plants. More important effects of soil salinity are likely to include particular ion toxicity effects (e.g., Na, Cl ) and nutritional imbalances (e.g., excessive Na" or uptake relative to Ca " and Mg ). 

Most plants reach their permanent wilting point at about 15 atmospheres of water tension. 

In the case of paraffin, no film pressures are available, since two-liquid adhesion tension data are lacking. Thus, it was necessary to assume a film pressure for one of the liquids in contact with paraffin. For this, a value of 1 dyne per cm. was taken as the film pressure of tert-butylnaphthalene. If a higher value had been chosen, the solid-vacuum and solid-liquid water tensions would have been correspondingly higher. Since the interfacial tension with water in this case seems already high, in comparison with liquid-liquid interfacial tensions for paraffin hydrocarbons [23], the quoted film pressure was adopted. 

Moisture content can better be expressed in units of tension, either as centimeters of water or in bar units, the bar being just slightly less than one atmosphere (76 cm Hg). In the studies of Bhaumik and Clark (1948) the peak rate of carbon dioxide production was observed at or near the 50 cm (0.05 bar) water tension for all soils, but the total production during a 15-day period was not markedly different over the range of 1-3,160 cm (3 bars) of water tension. Miller and Johnson (1964) observed peak production at... 

If the endpoints are close to one another, then neither of the terms on the right-hand side of the above inequality can become very large. Hence the oil/water interfacial tension must also be small. The argument is correct in that a small oil/water tension will surely follow if the two critical endpoints are close together, but there seems no reason a priori why this should be so. Further it is easy to imagine a situation in which the endpoints are not close, so that the right-hand side of the above inequality is not small, yet the oil/water tension would be small. 

In the capping system the desiccation processes are driven by water evaporation into the atmosphere and by the transpiration of the plants. Small deviations of water vapour saturation in the air will cause enormous water tensions thereby effectively reducing the water content of a soil... 

Table 4.1. The percentage germination of the seeds of various species sown on sintered glass plates at controlled water tensions...

So far as static terrestrial organisms are concerned, the dimensions of the exosphere frequently vary with changes in the water tension of the soil, in the physical characteristics of the soil, in air movement over aerial plant organs, in relative humidity, and in relative proportions of the constituent gases of the air. 

NYHAN J.W. 1976. Influence of Soil Temperature and Water Tension on the decomposition rate of carbon-14 labeled Herbage. Soil Science, 121, 288-293.. 

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