, Cambridge, U.K.). The water potential components of leaves were measured psychrometrically on the same date of the stomatal resistance measurements using a dew-point psychrometer (WP4; Decagon Devices, Pullman, WA). Leaf water potential (Ψ w ) was measured
. Measurement of stem water potential and leaf water potential. Midday ψ stem and ψ leaf (between 1400 and 1500 hr Mountain Standard Time) were determined simultaneously using a pressure chamber (Model 1000 with digital gauge; PMS Instrument Company, Albany
Abstract
A field experiment monitored the response of 1-, 2-, and 3-year-old strawberry (Fragaria × ananassa Duch. ‘Bounty’) plants to irrigation scheduled according to three criteria: a) daily rainfall ⩽1 mm, b) predawn leaf water potential ⩽ − 0.25 MPa, and c) soil water content ⩽50% plant-available water. All irrigated plots had significantly higher yields than nonirrigated plots (P < 0.05). The mean fruit weight was also higher in all irrigated plots, but differences were not statistically significant (P > 0.10). The irrigation treatments had no effect on the length of the harvest period. Plots watered each day that rainfall was ⩽1 mm had significantly more crown development than other irrigated and nonirrigated plots (P < 0.05). Predawn leaf water potential was the most conservative criterion for irrigation scheduling.
`Meyer' zoysiagrass (Zoysia japonica Steud.) was established on a silt loam soil in 27-cm-diameter × 92-cm-deep containers in a greenhouse to investigate the influence of irrigation frequency on turfgrass rooting and drought tolerance. Turf was irrigated daily or at the onset of leaf rolling with a water volume equal to the cumulative evapotranspiration of well-watered turf in small weighing lysimeters. After >90 days of irrigation treatments, a dry-down was imposed during which no additional water was applied for 55 days. A recovery period followed during which time turf was watered to maintain soil matric potential at greater than –30 kPa. Compared to turf irrigated daily, that watered at the onset of leaf rolling exhibited 1) 32% to 36% lower leaf water potential and 14% to 22% lower osmotic potential before the onset of drought; 2) 13% higher leaf water potential ≈40 days into dry-down; 3) more extensive rooting at 55- and 75-cm soil depths as indicated by 11% to 19% lower volumetric soil moisture content at the end of dry-down; 4) 25% to 40% lower shoot growth rate during irrigation and 13% to 33% higher shoot growth rate during dry-down; and 5) higher quality ratings during dry-down and recovery. Thus, deep, infrequent irrigation better prepares zoysiagrass for an oncoming drought than light, frequent irrigation.
Abstract
Diurnal and seasonal measurements of leaf water potential (ψ1), leaf diffusive resistance (R1), and leaf stomatal conductance (gs) of highbush blueberry (Vaccinium corymbosum L. cv. Bluecrop) were made in 1984 and 1985. Marked diurnal variation in ψ1, R1, and gs was observed. The most negative values of ψ1 were usually reached by 1000 Central Standard Time and were maintained until late afternoon. Leaf stomatal conductance values were high in early morning, remained high throughout the day, and decreased in late evening. Stomata were absent on the adaxial leaf surface, while the abaxial surface averaged 553 stomata/mm2. Unexplained seasonal changes in ψ1 and R1 were noted in 1985. Leaf water potential and R1 were significantly correlated in one year. Leaf water potential and R1 were significantly correlated with air temperature and relative humidity, respectively, in both years.
Abstract
The relationships of net photosynthesis (Pn) to soil water potential, leaf diffusive resistance, leaf water potential, and relative water content were studied with hybrid geranium (Pelargonium × hortorum Bailey cv Sprinter Scarlet) grown under conditions of greenhouse pot culture. Net photosynthesis went through 4 stages according to the effects of water stress on the plants. As water stress increased, Pn went from a steady-state maxiumum rate to slow decline, to rapid decline, to total inhibition. During rapid Pn decline, soil water potential rapidly decreased from −4 bars to −14 bars, and leaf diffusive resistance increased from 4 s cm−1 to 80s cm−1. Leaf water potential was −7 bars, and relative leaf water content was 81–87%. Leaf water potential appeared to be the best indicator of imminent Pn decline. After rewatering water-stressed plants, 3 days were required to elevate Pn to a steady-state maximum which was only 90% of initial steady-state Pn.
Two experiments were conducted to assess the ability of a water-absorbing synthetic polymer to reduce water stress injury of seedlings of Pinus pinea L. under greenhouse and field conditions. In both experiments, two rates of hydrated hydrogel, corresponding to 200 and 400 cm3 of stored water, and a control treatment without hydrophilic polymer were tested. Survival periods for the pine seedlings were 1.4 and 2.0 times longer for the 200- and 400-cm3 treatments, respectively, than for a control treatment in a greenhouse assay. In the field assay, only differences in seedling survival between both hydrogel treatments and control were measured. Leaf water potential values of control plants were significantly lower than hydrated polymer treatments in both experiments. From these results, we conclude that the use of hydrophilic polymers may be an important method of increasing the success of reforestation in semiarid regions.
Abstract
‘Golden Delicious’ apples (Malus domestica Borkh.) from trickle-irrigated plots were more mature than sprinkle-irrigated apples. Trickle-irrigated apples were higher in yellow color, soluble solids, and pH. Titratable acidity and moisture were less in fresh and stored apples that were grown with trickle irrigation. Applesauce from trickle-irrigated apples was superior in consistency and developed less free liquor (weep) than sauce from sprinkle-irrigated apples. Drip losses were greater in frozen apple slices from sprinkle-irrigated apples. Canned or frozen apple slices were firmer when produced from apples that were sprinkle-irrigated. The color of apple products from trickle-irrigated apples was superior to the products from sprinkle-irrigated apples. These differences resulted from treatments where leaf water potential differed by only 1 to 2 bars, –14 and –12 bars with trickle and –12 and –11 bars with sprinklers in 1978 and 1979.
The effect of fall irrigation level in `Mauritius' and `Floridian' lychee (Litchi chinensis Sonn.) on soil and plant water status, flowering intensity, and yield the following year was studied in a field during 2 consecutive years. At the end of the second vegetative flush after harvest (1 Oct. 1994 and 10 Oct. 1995), four irrigation treatments were initiated: 0.5, 0.25, 0.125, and 0 Class A pan evaporation coefficients designated 100%, 50%, 25%, and 0%. The three lower irrigation levels effectively stopped shoot growth, suggesting the 50% treatment to be the threshold for shoot growth cessation in both years. For both years, flowering intensity and yield in the 100% treatment were lower than those following the other three treatments. Soil and plant water-stress indicators responded to the water-stress irrigation treatments. However soil water-potential values were highly variable relative to plant water potentials. Stem water potential differed more markedly between treatments than leaf water potential. Midday stem water potential appeared to be the best water-stress indicator for irrigation control. Midday stem water potential in both years was correlated with midday vapor-pressure deficit, suggesting that the threshold for irrigation control should take into account evaporative demand.
Effects of water stress on superoxide dismutase (SOD) activities, changes in protein content, leaf water potential (Ψ l ) and growth were studied in drought-sensitive Kyokko (KK) and Ratan (RT), and drought-tolerant TM 0126 (TM) and VF-134-1-2 (VF) cultivars of tomato (Lycopersicon esculentum Mill.) in order to obtain fundamental information for breeding drought tolerant cultivars that may be adapted to water stress in many parts of the world. Growth of drought-tolerant TM and VF was greater than that of drought-sensitive KK and RT under water stress conditions. Leaf water potential (Ψ l ) decreased by water stress treatments in all the cultivars, but the reduction was much more rapid and pronounced in KK and RT than VF and TM. Ψ l of stressed cultivars decreased by 30% to 40% compared to the untreated control cultivars. The initial reduction in the range of 20% to 35% was more rapid in KK and RT than TM and VF. SOD activities were increased by water stress in all cultivars. Increase of SOD activities by water stress was much more rapid and pronounced in TM and VF than in KK and RT. Leaf protein concentration was decreased by the water stress treatments in all cultivars evaluated. In KK and RT, much more rapid reductions in protein concentration were observed than in TM and VF. The regression analysis of Ψ l and SOD suggest the possibility to using SOD activities as an additional screening criterion for tomato drought tolerance improvement.