Search

Electrical impedance measurements made on white spruce, Picea glauca (Moench) Voss, stems were related to shoot free sugar contents and to osmotic, turgor and water potential. During seasonal dormancy induction, there were commensurate increases in free sugar contents, osmotic potential at full turgor and impedance which resulted in linear relationships among these variables. When measured over the course of laboratory drying, impedance increased curvilinearly with decreasing relative water content. There was a linear increase in impedance with decreasing water potential, with a break point coincident with the turgor loss point, possibly attributed to disruption to current flow through broken plasmodesmatal connections between adjacent cells. This technique offers a non-destructive method to measure tissue free sugar content, and therefore, short- and long-term shifts in parameters historically derived from pressure-volume analysis. [ABSTRACT FROM AUTHOR]

Soil flooding causes rapid reductions in transpiration, stomatal conductance and photosynthesis of many woody plants, which can decrease growth and ultimately result in plant death. This study was conducted to determine the role of the root system in the flooding response. Eastern larch (Larix laricina) seedlings were grown in Plexiglas tubes in which water uptake by flooded and unflooded roots was measured independently. Further flooding studies were conducted with eastern larch and white spruce (Picea glauca) in which stems were girdled. Root hydraulic properties were analyzed using pressure-flow relationships. Transpiration rates of partially flooded plants declined more slowly than fully-flooded plants. Water uptake by unflooded roots of partially flooded seedlings increased momentarily with flooding. After 10d, flooding caused little change in root hydraulic conductance, a decrease in root system reflection coefficient, and an increase in osmotic permeability. Stem girdling had little effect on stomatal conductance and transpiration in comparison to flooding effects. The response of plant tops to flooding appears to be xylem-mediated and in proportion to the amount of root system flooded. Root hydraulic conductance appears to be unaffected by flooding except for a possible temporary increase on the first day following flooding treatments. [ABSTRACT FROM AUTHOR]

Wide variations in total aluminum (Al) concentration reported to have a toxic effect on plants are attributed to imprecise definition of the chemical environment at the root interface. Because Al can complex with natural ligands and form time-dependent metastable species in water, the requirements of a fixed Al speciation in the nutrient medium can only be met by simultancously holding constant the pH, the Al/OH ratio and the renewal time of the solution. It is also important that the root be constantly perfused by a fresh solution so that the root interface is as chemically close to the bulk solution as possible. The rhizostat presented here uses a process controller to constantly replenish four tanks containing different combinations of nutrients and Al. The solution is pumped from each tank to a tray where it is continuously delivered to seedlings growing on artificial medium. This rhizostat provides an accurate control for Al speciation. Preliminary experiments of white spruce seedlings show that levels of 10 micromolal or less total Al are sufficient to cause toxic effects at pH of 4.5 and without the formation of Al complexes. [ABSTRACT FROM AUTHOR]