scholarly journals An Apparatus For Measuring Water Potentials in the Xylem of Intact Plants

1965 ◽  
Vol 18 (3) ◽  
pp. 487 ◽  
Author(s):  
ARG Lang ◽  
HD Barrs
Keyword(s):  
Water Potential ◽  
New Method ◽  
Intact Plants ◽  
Water Potentials ◽  
Pepper Plants

A new method and apparatus for estimating water potentials in the xylem of intact plants are described. The apparatus is based on the thermocouple psychro-meter method of measuring water potentials, but measurements are made on leaves which remain attached to plants. Illustrative experiments are described, in which continuous records of the estimated water potential in the xylem of cotton and pepper plants are given for periods of up to 10 hr.

Xylem water potentials and hydraulic conductances in eight species of ferns

1985 ◽  
Vol 63 (3) ◽  
pp. 632-637 ◽  
Author(s):  
Howard W. Calkin ◽  
Arthur C. Gibson ◽  
Park S. Nobel
Keyword(s):  
Water Potential ◽  
Water Flow ◽  
Leaf Morphology ◽  
Close Agreement ◽  
Flow Rates ◽  
Xylem Structure ◽  
Physical Constraints ◽  
Intact Plants ◽  
Water Potentials ◽  
Potential Gradients

Water potentials, flow rates, and anatomy of xylary elements were studied in eight species of ferns to assess the physical constraints that xylem structure presents to water flow. Comparisons were made among ferns of different leaf morphology as well as between a fern with vessels and ferns with tracheids only. Hydraulic conductance was measured by forcing a solution through excised plant segments. These hydraulic conductances were in close agreement with conductances calculated from water potential gradients and flows measured in intact plants. In three species, backflushing excised segments by forcing a basipetal flow increased subsequently measured conductances two- to six-fold, indicating that the xylem of these three species was partially blocked in intact plants. Hagen–Poiseuille estimates of conductance based on xylary element diameters were 1.8–2.7 times the conductances measured for excised segments. Hydraulic conductances of tracheids and vessels of ferns thus deviate from those of ideal capillaries of similar diameter to about the same extent as has been reported for tracheids in conifers and for vessels in dicotyledons.

NITROGEN TRANSFORMATIONS NEAR UREA IN SOIL WITH DIFFERENT WATER POTENTIALS

1988 ◽  
Vol 68 (3) ◽  
pp. 569-576 ◽  
Author(s):  
YADVINDER SINGH ◽  
E. G. BEAUCHAMP
Keyword(s):  
Water Potential ◽  
Soil Water ◽  
Incubation Period ◽  
Relative Rate ◽  
Soil Water Potential ◽  
Nitrification Inhibitor ◽  
Silt Loam ◽  
Nitrogen Transformations ◽  
Water Potentials ◽  
Initial Soil

Two laboratory incubation experiments were conducted to determine the effect of initial soil water potential on the transformation of urea in large granules to nitrite and nitrate. In the first experiment two soils varying in initial soil water potentials (− 70 and − 140 kPa) were incubated with 2 g urea granules with and without a nitrification inhibitor (dicyandiamide) at 15 °C for 35 d. Only a trace of [Formula: see text] accumulated in a Brookston clay (pH 6.0) during the transformation of urea in 2 g granules. Accumulation of [Formula: see text] was also small (4–6 μg N g−1) in Conestogo silt loam (pH 7.6). Incorporation of dicyandiamide (DCD) into the urea granule at 50 g kg−1 urea significantly reduced the accumulation of [Formula: see text] in this soil. The relative rate of nitrification in the absence of DCD at −140 kPa water potential was 63.5% of that at −70 kPa (average of two soils). DCD reduced the nitrification of urea in 2 g granules by 85% during the 35-d period. In the second experiment a uniform layer of 2 g urea was placed in the center of 20-cm-long cores of Conestogo silt loam with three initial water potentials (−35, −60 and −120 kPa) and the soil was incubated at 15 °C for 45 d. The rate of urea hydrolysis was lowest at −120 kPa and greatest at −35 kPa. Soil pH in the vicinity of the urea layer increased from 7.6 to 9.1 and [Formula: see text] concentration was greater than 3000 μg g−1 soil. There were no significant differences in pH or [Formula: see text] concentration with the three soil water potential treatments at the 10th day of the incubation period. But, in the latter part of the incubation period, pH and [Formula: see text] concentration decreased with increasing soil water potential due to a higher rate of nitrification. Diffusion of various N species including [Formula: see text] was probably greater with the highest water potential treatment. Only small quantities of [Formula: see text] accumulated during nitrification of urea – N. Nitrification of urea increased with increasing water potential. After 35 d of incubation, 19.3, 15.4 and 8.9% of the applied urea had apparently nitrified at −35, −60 and −120 kPa, respectively. Nitrifier activity was completely inhibited in the 0- to 2-cm zone near the urea layer for 35 days. Nitrifier activity increased from an initial level of 8.5 to 73 μg [Formula: see text] in the 3- to 7-cm zone over the 35-d period. Nitrifier activity also increased with increasing soil water potential. Key words: Urea transformation, nitrification, water potential, large granules, nitrifier activity, [Formula: see text] production

Photosynthesis Response of Sunlit and Shade Pepper (Capsicum annuum) Leaves at Different Positions in the Canopy Under Two Water Regimes

1994 ◽  
Vol 21 (3) ◽  
pp. 377 ◽  
Author(s):  
A Alvino ◽  
M Centritto ◽  
FD Lorenzi
Keyword(s):  
Water Potential ◽  
Capsicum Annuum ◽  
Leaf Water Potential ◽  
Co2 Exchange ◽  
Leaf Water ◽  
Predawn Leaf Water Potential ◽  
Water Regimes ◽  
Water Potentials ◽  
Sun And Shade ◽  
Shade Leaves

Pepper (Capsicum annuum L.) plants were grown in 1 m2 lysimeters under two different water regimes in order to investigate differences in the spatial arrangements of the leaves and to relate this to daily assimilation rates of leaves of the canopy. The control regime (well-watered (W) treatment) was irrigated whenever the accumulated 'A' pan evaporation reached 4 cm, whereas the water-stressed (S) treatment was watered whenever the predawn leaf water potential fell below -1 MPa. During the growing cycle, equal numbers of sun and shade leaves were chosen from the apical, middle and basal parts of the canopy, corresponding to groups of leaves of increasing age. The CO2 exchange rate (CER) was measured at 0830, 1230 and 1530 hours on 8 days along the crop cycle, on leaves in their natural inclination and orientation. Leaf water potentials were measured on apical leaves before dawn and concurrently with gas exchange measurements. Control plants maintained predawn leaf water potential at -0.3 MPa, but S plants reached values lower than -1.2 MPa. Midday leaf water potentials were about twice as low in the S plants as in the controls. Water stress reduced LA1 during the period of crop growth, and dry matter production at harvest. Stressed apical leaves appeared to reduce stress by changing their inclination. They were paraheliotropic around midday and diaheliotropic at 0830 and 1530 hours. The CER values of the S treatment were significantly lower than those of the W treatment in apical and middle leaves, whereas the CER of basal leaves did not differ in either treatments. In the S treatment, reduction in the CER values of sunlit apical leaves was more evident in the afternoon than at midday or early in the morning, whereas basal leaves were less affected by water than basal stress leaves if sunlit, and negligibly in shaded conditions.

scholarly journals Dehydration of Macromolecules I. Effect of Dehydration-Rehydration on Indoleacetic Acid Oxidase, Ribonuclease, Ribulosediphosphate Carboxylase, and Ketose-1-Phosphate Aldolase

1973 ◽  
Vol 26 (3) ◽  
pp. 591 ◽  
Author(s):  
B Darbyshire ◽  
BT Steer
Keyword(s):  
Water Potential ◽  
Indoleacetic Acid ◽  
Acid Oxidase ◽  
Enzyme Preparations ◽  
Water Potentials ◽  
Membrane Technique ◽  
Indoleacetic Acid Oxidase

A pressure-membrane technique has been developed to physically manipulate the water potential of in vitro enzyme preparations. Enzyme preparations were subjected to a range of water potentials using this technique.

Corrigenda - Measurement of the total water potential of aqueous solutions of polyethylene glycol - A comparison between osmometer, thermocouple psychrometer and equilibrated soil cores

Soil Research ◽  
1993 ◽  
Vol 31 (1) ◽  
pp. 1
Author(s):  
IM Wood ◽  
IK Dart ◽  
HB So
Keyword(s):  
Polyethylene Glycol ◽  
Water Potential ◽  
Close Correlation ◽  
Ease Of Use ◽  
Effect Of Temperature ◽  
Soil Cores ◽  
Total Water ◽  
Matric Potential ◽  
Thermocouple Psychrometer ◽  
Water Potentials

This study examined two polyethylene glycol (PEG) polymers (PEG 6000 and PEG 10000) and compared measurements of water potential obtained with a thermocouple osmometer and thermocouple psychrometers at three temperatures (15, 25 and 35�C) and five osmdalities (50, 100, 200, 300 and 400 g/1000 g water). These were then compared with estimates of matric potential of three soils brought to equilibrium with PEG solutions of the same osmolalities. At the same osmolality and temperature the two PEG polymers gave essentially the same water potential. There was a significant effect of temperature on water potential which corresponded closely with changes in specific gravity of the PEG solution. There was a close correlation between the measurements of water potential of the PEG solutions obtained with the osmometer and the psychrometers (R = 0.99). However, the psychrometer gave increasingly lower values than the osmometer as water potential decreased. The differences in the measurements between the two methods are thought to be the result of design and calibration differences. The ease of use of the osmometer is such that it is recommended for routine use. The water potentials of the soil cores brought to equilibrium with the PEG 10 000 solution were linearly related to the water potentials of the PEG solutions estimated from both the osmometer and psychrometers (R2 = 0.84). However, there were clear deviations from a 1:l relationship. It was concluded that the results from the soil cores could not be used to determine which of the two instruments gave the more accurate measurement of water potential of PEG solutions.

Evaluation of the hydraulic press for measurement of leaf water potentials in cassava

1983 ◽  
Vol 101 (2) ◽  
pp. 407-410 ◽  
Author(s):  
J. A. Palta
Keyword(s):  
Water Potential ◽  
Leaf Water Potential ◽  
Hydraulic Press ◽  
Pressure Chamber ◽  
Leaf Water ◽  
Moisture Loss ◽  
Total Leaf Area ◽  
Water Potentials ◽  
Wide Range ◽  
Poor Relationship

SUMMARYIn the application of the Scholander pressure chamber technique to cassava water relations studies, the leaf water potential measured on central lobules was initially compared with that measured on entire leaves (including petiole). Measurements made using both a Campbell-Brewster hydraulic press and a pressure chamber of the leaf water potential in six different cassava clones were also compared. Although the central lobules showed a greater sensitivity to moisture loss after sampling than entire leaves, their leaf water potential was in close agreement with those measured on the entire leaves (r3 = 0·96). Therefore, for routine and field estimates in cassava, measurements made on the central lobules may be used to avoid the large reduction in total leaf area. The Campbell-Brewster hydraulic press satisfactorily estimated leaf water potential in M.Col. 1684 clone, which had the longest and narrowest lobules, but in other clones the leaf water potential was overestimated at high leaf potential (> -12·5) and underestimated at low water potentials (< -12·5). Over a wide range of leaf water potentials, a poor relationship between leaf water potentials estimated with hydraulic press and with the pressure chamber was observed for cassava because press estimates are influenced by lobule length and lobule width.

Dehydration tolerance of five bur oak (Quercusmacrocarpa) seed sources from Texas, Nebraska, Minnesota, and New York

1993 ◽  
Vol 23 (3) ◽  
pp. 387-393 ◽  
Author(s):  
Michael R. Kuhns ◽  
Walter W. Stroup ◽  
G. Michael Gebre
Keyword(s):  
New York ◽  
Water Potential ◽  
Electrolyte Leakage ◽  
Dry Period ◽  
Membrane Injury ◽  
North Central ◽  
Dehydration Tolerance ◽  
Seed Sources ◽  
Water Potentials ◽  
Bur Oak

Dehydration tolerance was studied in saplings of five widely distributed sources of Quercusmacrocarpa Michx. growing together in an outdoor plot in Lincoln, Nebraska. Membrane electrolyte leakage, expressed as percent injury, was used as a measure of dehydration tolerance. Leaves were excised from several plants of each source on July 16 after a long dry period and on August 26 after a long moist period. Leaves were allowed to dry for various times in a laboratory, their water potential was measured, and membrane injury was determined. Regressions were calculated for percent injury versus leaf water potential, so sources could be compared at selected water potentials. All sources showed increased leakage at lower water potentials, with most leakage occurring below a water potential of −3 MPa. A source from Texas had the highest leakage, 23% at −6 MPa in August, while a source from a more xeric site in north central Nebraska generally had the lowest leakage. Stress preconditioning appeared to affect leakage, with leakage often significantly lower in July than in August.

Effects of water potential on germination of lettuce, sunflower, and citrus seeds

1969 ◽  
Vol 47 (11) ◽  
pp. 1761-1764 ◽  
Author(s):  
Merrill R. Kaufmann
Keyword(s):  
Polyethylene Glycol ◽  
Water Stress ◽  
Water Potential ◽  
Cellulose Acetate Membrane ◽  
Lettuce Seeds ◽  
Water Potentials ◽  
Citrus Seeds ◽  
Germinating Seeds ◽  
Polyethylene Glycol 6000 ◽  
Selection Of

The effect of nearly constant water potential on germination of citrus, sunflower, and lettuce seeds was studied. Water potential equilibration was achieved by placing soil above a cellulose acetate membrane which was in contact with a solution of polyethylene glycol-6000. Selection of solute potentials in the solution resulted in controlled water potentials in the soil over a range of 0 to −14.9 bars for citrus and 0 to −8.0 bars for sunflower and lettuce. The water stress experienced by germinating seeds in this system is largely the result of a matric effect rather than a solute effect.Citrus seeds germinated at water potentials as low as −4.7 bars and lettuce at −4.1 bars, but sunflower germinated at −8.0 bars. Sunflower germinated as rapidly at −4.1 bars as lettuce at −2.3 bars, both reaching 50% germination at about 8 days. Citrus germinated much more slowly, requiring 26 days at 0 bars.

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