Seasonal and Diurnal Changes in the Water Contents and Water Deficits of Bartlett Pear Leaves

Abstract

It is general knowledge that the water content of (leciduous leaves usually decreases as the season advances. It has also been noted that the water deficit fluctuations of such leaves are often more pronounced early in the growing season when these parts are young and succulent than later when they are older and harder. The seasonal changes in the actual weights of the water and dry matter components of leaves, however, are less commonly understood.Leaf samples are comparatively easy to pick, dry and weigh. For this reason, the water content of leaves is often used to indicate water changes within plants. Knight (5) found slight diurnal variations in water contents of leaves of the plants he tested in the area of southeastern England. Livingston and Brown (7) found large diurnal changes in the water contents of the desert plants with which they worked. Miller (9) made frequent periodic water content determinations on the leaves of corn and sorghums in his studies of the water relations of these crop plants.MIaximov (8), Stanescu (12), Kramer (6), and Wilson, Boggess, and Kramer (14) have also reported on the fluctuations in the water contents of plants.Stocker (13) devised a measurement of water deficits by which he related the amount of water needed to bring a leaf to full saturation, or zero deficit, to the total amount of water in the leaf at saturation. The resulting ratio figure was multiplied by 100 and expressed as a percentage. Stocker used such a measurement to obtain a comparison of the water deficits existing in the leaves taken at different periods of the day from plants growing in widely separated climatic zones. Oppenheimer and Mendel (10), Halma (3, 4), Compton (1), and Runyon (11) have reported on the use of similar measurements to determine changes in the water deficits of plants.During the past five years the Department of Horticulture of the State College of Washington has conducted a study of certain water relationships of Bartlett pear trees. A portion of this study included the measurement of the seasonal and diurnal fluctuations in the leaf water contents and water deficits and the weight changes of the leaf constituents responsible for these fluctuations.MATERIALS AND METHODS As a source of leaf materials, eight bearing Bartlett pear trees were selected for this study. These trees were located in one orchard block at the Tree Fruit Experiment Station, Wenatchee, Washington. The leaf samples were taken from non-bearing fruit spurs near the periphery of the trees. An effort was made to limit the number of leaves removed from In determining seasonal changes, the sampling dates covered six 6-day periods spaced at three-week intervals from May 15 to September 2, 1950. The samples were taken between 2:00 and 2:30 P.M. each day from four sides of each tree and at three levels-5, 10, and 15 feet from the ground. To determine diurnal changes, leaf samples were taken at 4-hour intervals during six 32-hour periods spaced throughout much of the 1950 growing season. Four leaves were selected from eac...

Development and validation of a dynamical atmosphere–vegetation–soil HTO transport and OBT formation model

“…These estimated q v , solar and long-wave radiations respectively contains uncertainty of 8% by weight and 20 W m À2 (Ackley, 1954;Kondo and Miura, 1985). Furthermore, during the exposure, radiations inside the chamber can have differed from the radiations outside, affected by the vinyl-film covering of the chamber.…”

“…Variables q v a Solar radiation b Long-wave radiation b Solar and long-wave radiation c Uncertainties þ8% À8% þ20 W m À2 À20 W m À2 þ20 W m À2 À20 W m À2 Half solar and long-wave radiation G m for c v (Ackley, 1954). G m is an average value for the whole five-day period.…”

“…where leaf water content q v by weight was also estimated to be 60% from the observation on the water content in pear leaves, including an error of AE8% derived from seasonal and daily variations in it (Ackley, 1954). Having obtained the initial P w i , initial carbohydrate amount in the structural carbon pool was calculated by w str ¼ 0.95 Â P w i , where the factor 0.95 is the relative amount of the structural carbon to the total carbon in a leaf (Fondy and Geiger, 1982).…”

SEASONAL AND DIURNAL EXPANSION AND CONTRACTION OF PINUS BANKSIANA AND PICEA GLAUCA CONES*

“…Such diurnal changes in moisture content have been reported for leaves (Ackley, 1954), buds (Kozlowski and Petersen,i960) and fruits (Bartholomew, 1926;Kozlowski, 1964Kozlowski, , 1965Kramer and Kozlowski, i960). As water is translocated into plant tissues or is lost from them by transpiration or translocation, they expand or contract accordingly.…”

Assessing crop water stress during late kharif season using Normalized Diurnal Difference Vegetation Water Content (nddVWC) of Advanced Microwave Scanning Radiometer–Earth Observing System (AMSR-E)

“…Throughout the time period VWC p was found to be higher than VWC a . In the limited soil moisture condition, the VWC a \ VWC p because of the radiation induced evapotranspiration loss of water from crop during day time and restricted water supply from soil (Ackley 1954). In the rainfed condition, as shown in the Fig.…”