Continuous Water Uptake Research Articles

Effects of Water Deficit Stress on Competitive Interaction of Peanut and Sicklepod

AbstractOne of the potentially deleterious effects of weeds on crop production is competition for water. In this study, competitive interactions between peanut (Arachis hypogaea L.) and sicklepod (Senna obtusifolia L.) were investigated. The two species were grown alone and mixed in a glasshouse in 118‐L barrels (0.65 deep and 0.48 m wide) filled with a Molena sandy soil (sandy, mixed, thermic Psammentic Hapludults). Treatments were either continuously irrigated (WET) or periodically dried (DRY). Measurements included daily soil water content (τ), continuous water uptake, stomatal conductance (g), leaf xylem water potential (Ψ1) and leaf osmotic potential. Water uptake and g were well correlated to τ. With both species, water uptake, g, and Ψ1 all declined when τ in the top half of the barrel was approximately one‐third of the available water (5.8 to 7.4% v/v; equivalent soil water potential, Ψs, −0.20 and −0.08 MPa). The τ‐values at which water uptake and g began to decline (here called inflection points) were always lower for peanut (5.9 to 6.1%; Ψs = The τ‐values at) than for sicklepod (7.4 to 7.5%; Ψs = − 0.08 to − 0.07 MPa). Ψ1 was similar for the two species. The inflection points of water uptake, g, and Ψ1 for both species were always higher when related to τ‐values in the bottom half of the barrel (8.6% to 13.1%, Ψs = − 0.04 and − 0.005 MPa) than when related to τ in the top half of the barrel. This response occurred even though the fraction of fine root length density in the bottom half was more than 45% of the total fine root length density in the DRY treatment of sicklepod and both species mixed. Significant osmotic adjustment was detected in both species following water deficit stress. At full turgor, leaf osmotic potential of all WET treatments reached − 0.99 MPa; at zero turgor, it reached −1.12 MPa. For the DRY treatments, leaf osmotic potential at full turgor dropped to −1.22 and −1.24 MPa in sicklepod and peanut, respectively; at zero turgor, it dropped to − 1.31 and − 1.34 MPa in sicklepod and peanut, respectively, but the difference between species was not significant. As the soil dried, water use by peanut mixed was significantly higher than sicklepod mixed. It appears that peanut can use more water under water deficit stress and can recover faster than sicklepod in a mixed community of the two species.

Moisture Sorption Kinetics for Water-Soluble Substances I: Theoretical Considerations of Heat Transport Control

A model based on heat transport control was developed to describe the uptake of water on a deliquescent solid in an atmosphere of pure water vapor. The model assumes the presence of a saturated liquid film on the surface of the solid. The decrease in the vapor pressure of water over the surface, brought about by the colligative effect of solid dissolved in the liquid film, is effectively offset by the increase in temperature of the film (and the solid) caused by the heat released on condensation of the water vapor. The thermal transients die out quickly and a steady-state analysis is valid. At steady state the temperature of the liquid film (and solid) is that temperature at which the vapor pressure of water above the saturated solution is equal to the chamber pressure. Consequently, water uptake occurs at a rate that depends on the heat flux away from the surface. The water uptake rate, Wʹh, is constant at a given relative humidity and is described by an equation of the form Wʹh=(C+F) ln (RHi/RHo), where C and F are conductive and radiative coefficients, RHi the chamber relative humidity, and RHo the relative humidity at and above which continuous water uptake (deliquescence) occurs. The model contains no adjustable parameters and can thus be directly tested against experimental results.

Studies on the permeability of human oral mucosa. V. The inflow of water through dehydrating oral mucosa.

The inflow of water through human oral mucosa during and after secretion block with scopolamine has been investigated in 9 young adults with healthy mucosae by analysing the changes of weight in water-saturated discs of ash-free filter paper during and after mucosal contact. Buccal and palatal mucosae both showed a continuous uptake of water from the filter paper, proportional in amount to the area of mucosa covered and to the contact period. The inflow ratio for buccal epithelium in relation to palatal epithelium was 2:1. The values in the regression equations for the inflow-time relation corresponded closely to the values for water outflow from analogous slightly dehydrated mucosae, demonstrating a ratio of 1:1 for inflow: outflow of water through oral mucosa.