Xylem Potential Research Articles

Phosphorus effects on zinc translocation in maize

Abstract Interactions of P and Zn in roots and shoots of maize were studied in greenhouse using three different type of Egyptian soils (one alluvial and two calcareous). No Zn deficiency symptoms were seen in maize. The concentration of Zn in shoots was reduced due to P application. Its concentration in roots was hardly influenced by added P. Added P increased its concentration in the shoots much more than in the roots. Added Zn increased its concentration in roots more than in shoots. These findings suggest that applied P had no effect on Zn absorption by the roots. The main effect was a physiological inhibition in the translocation of Zn from roots to shoots, probably due to the indirect effect on increasing salt concentration in the root medium added as CaH2PO4. This may have depolarized the xylem potential resulting in increasing the anion influx and decreasing that of the cation into the relatively less negatively charged xylem vessels. As the xylem potential appears to be in the stele at the interface between the xylem vessels and the pericycle cells. Results of the calcareous soils suggest that excess of CaCO3 influences P‐Zn relationship within the plant by decreasing the translocation of Zn and increasing that of P from roots to shoots.

Plant Water Stress of Soybean (Glycine max) and Common Cocklebur (Xanthium pensylvanicum): A Comparison Under field Conditions

The study was conducted to determine the seasonal and diurnal water stress of soybeans [Glycine max (L.) Merr. ‘Lee 74′] grown under intraspecific competition (competition between plants of the same species) and interspecific competition (competition between plants of different species) with common cocklebur (Xanthium pensylvanicum Wallr.). Midday xylem potentials decreased as the season progressed and were lower in common cocklebur during vegetative growth of soybean and in soybean during reproductive growth. For a given species differences in xylem potential due to mode of competition were small. In the diurnal studies xylem potential for each species decreased to a minimum in the early afternoon but recovered to the original pre-dawn values at night. As the season progressed leaf xylem potential (a) decreased at a greater rate, (b) decreased sooner in the day, and (c) recovered at a slower rate. It was shown that differences in xylem potential between soybean and common cocklebur on a given day were small. Greater diffusive resistance values generally were found with soybean than with common cocklebur and with each species grown under interspecific competition.

Seasonal Water Stress in Some Chilean Matorral Shrubs

Environmental and plant characteristics relating to plant water stress were measured in seven shrub species, Satureja gilliesii, Cryptocarya alba, Quillaja saponaria, Lithraea caustica, Colliguaya odorifera, Retanilla ephedra, and Proustia cinerea, growing on equator- (EFS) and pole-facing (PFS) slopes in the mediterranean region of central Chile. Midday air temperatures and vapor pressure deficits were greater on the EFS than on the PFS. Soil moisture was greater during the winter but less during the summer on the EFS. Midday xylem potentials in all species decreased during the summer, increased after the first rain, and were lower on the EFS. Mean leaf size was smaller on the EFS. Stomatal frequency differed only for Q. saponaria and C. odorifera. Species with shallow root systems had lower xylem potentials.

Diffusion Resistance and Xylem Potential in Stressed and Unstressed Northern Hardwood Trees

In a northern hardwood forest in central New Hampshire, daytime diffusion resistances of abaxial leaf surfaces were independent on light level above 250 @mE/(m2°s), increased as vapor pressure deficit increased, and decreased as temperature increased. High vapor pressure deficit at midday caused slight stomatal closure, which appeared to be independent of leaf H_2O potential. Low plant H2O potential may have produced additional closure at high atmospheric demand even though soil—water potential was > —0.2 bar. At an atmospheric demand of 250 W/m2 xylem potential averaged —16 bar for Betula alleghaniensis, —21 bar for Acer saccharum, and —23 bar for Fagus gradifolia, and decreased only slightly as demand increased further. Daytime diffusion resistance averaged 2.5 s/cm for B. alleghaniensis, 3.1 s/cm for A. Saccharum, and 3.3 s/cm for F. grandifolia when light was adequate. The resistance difference implies the possibility of higher transpiration rates in B. alleghaniensis. Several trees were artificially stressed by trenching around them and covering the soil block with polyethylene. After 2—3 wk with rain excluded, soil—water potential ranged from —0.4 to —0.8 bar, and daytime diffusion resistance averaged 5 s/cm, indicating significant stomatal closure caused by H_2O stress. However daytime xylem potentials on stressed trees were the same as or higher than those on unstressed trees. Stomatal control effectively prevented excessive H_2O loss and prevented xylem potential from declining below normal operating levels.

Leaf Water Stress in Engelmann Spruce

The response of xylem pressure potential of Engelmann spruce (Picea engelmannii Engelm.) to environmental factors was studied in the natural subalpine environment. Data were analyzed in the context of a leaf water potential model based upon the van den Honert model for water transport through the soil-plant-atmosphere continuum. At soil temperatures of 10 to 15 C, xylem pressure potential decreased to about -10 bars as the ratio of leaf to air absolute humidity difference to leaf diffusion resistance (an estimate of transpiration) increased. The potentials were slightly lower at all flux rates above zero when the soil temperature was 5 to 10 C, and at temperatures of 0 to 5 C the potentials decreased sharply to as low as -20.4 bars, even though the soil water supply was adequate. The relative viscosity of water and soil to leaf resistances for flow were compared for Engelmann spruce and citrus at low soil temperatures. These comparisons indicated that decreased root permeability was probably not an important factor causing higher stresses in spruce at 5 to 10 C, but for citrus, root permeability became limiting at soil temperatures as high as 13.5 C. Xylem pressure potential was correlated with net radiation during the daytime when soil temperature was above 7 C. Under other conditions, however, xylem potential and net radiation apparently had a different relationship. The relationship between flux density and potential was the same on unshaded and shaded portions of the crown, with differences in potential related to differences in flux density.

Water Potentials in Nonwilted Dianthus Grown in Different Nutrient Solution Concentrations1

AbstractExperiments were undertaken to determine if Dianthus caryophyllus L. adjusted its internal osmotic potential downward with decreasing solution potential and the concomitant effects on water and turgor potentials. Plants were grown in a gravel substrate, irrigated two to four times daily with solutions of varying potentials, and measurements were made from before sunrise to noon or shortly thereafter on clear days. Plant osmotic potentials adjusted to increase the potential gradient between solution and plant with decreasing solution potential. There were no observable differences between treatments with respect to stomatal aperture or leaf diffusion resistance. The xylem hydrostatic pressure decreased to a greater extent in plants grown in —1.0 bar solutions than in those grow in −0.3 bar solutions as atmospheric evaporative demand increased. Polynomial regressions of potential on evaporative demand had calculated correlations exceeding 0.90. Differentiation to determine the rate of hydrostatic potential change with change in evaporative demand showed the rate to be highest at low evaporative demands in plants grown in −1.0 bar solutions, gradually decreasing to 0 at high vapor pressure differences near 16 mm Hg. Carnations in −0.3 bar solutions had rates approaching O at low and high atmospheric demands, with a definite maximum near 9 to 10 mm Hg. The differences between hydrostatic potential and plant osmotic potential, ignoring matric and xylem potentials, showed carnations in −1.0 bar solutions to have consistently lower turgor potentials than plants grown in less concentrated solutions.

Evidence for Error in Pressure‐Bomb Estimates of Stem Xylem Potentials

The hydrostatic component of water potential was measured concurrently in stems and needles of five species of conifers (Pinus contorta, P. jeffreyi, Pseudotsuga menziesii, Abies amabilis, and A. procera). In Douglas—fir and the true firs pressure—chamber measurements of potentials were up to 4 bars more negative in stems than in needles. The difference appears to be due to filling of non—vascular xylem tissue with fluid during measurement. This tissue seems to function as a water reservoir, enabling needles to maintain relatively high turgor levels during periods of rapid transpiration.