Spraying 7-year-old citrus trees with film-forming antitranspirants before transplanting increased leaf water potential, thereby reducing “transplant shock.” Leaf water potential decreased rapidly after transplanting, by as much as 21 atm in unsprayed, and as little as 6 atm in sprayed trees. There was little benefit from transplanting in late afternoon rather than the morning.
Measurements of leaf water potential for 5 plant species were made with the J-14 leaf press and a Scholander-type pressure bomb. Although a significant linear relationship was found between the readings from both instruments, the variability in the J-14 readings at a particular pressure bomb value prevents reliable predictions of the pressure bomb valve from the J-14 measurements.
The relationship between pea (Pisum sativum L.) leaf water potential (ψ) and crop color was investigated as water stress developed in the field. A technique was developed to measure pea leaflet ψ using a Scholander-type pressure chamber. The pressure chamber gave values similar to those of the screen-caged thermocouple psychrometer against which it was calibrated. The pressure chamber measured the decrease in associated with the green-to-blue change in crop color that occurs with the development of water stress. Use of crop color change offers an easily identifiable indicator of the onset of water stress that could, with further testing, be used in crop water management.
Three-year-old peach [Prunus persica (L.) Batsch] trees in a growth room under well-watered conditions were subjected to photosynthetically active radiation (PAR) levels (400-700 nm) of 444, 287, 144, 61, and 19 μmol°s−1m−2. At very low PAR levels (19 and 61 μmol°s−1m−2), the photosynthetic rate (P) declined with increasing temperature. Multiple regression analyses for the 3 highest PAR levels showed that an increase in PAR increased the optimum temperature for both P and stomatal conductance (gs). The highest leaf water potential (ψL) was found at 21°C in all 3 PAR levels. The regression equations also showed that PAR was the main determinant of P and gs, but that temperature was the main determinant of ψL.
Stomatal conductance, transpiration, and photosynthesis declined steadily with decreasing leaf water potential in seedlings of peach [Prunus persica (L.) Batsch] grown in large pots containing about 84 kg of steam-sterilized sandy loam soil under controlled environmental conditions. Growth and transpiration were reduced mainly through the effect of stomatal closure as soon as water stress commenced.
Leaf water potential (LWP). relative water content (RWC), gas exchange rates and 4th-derivative spectra were measured in water-stressed and normally Irrigated plank of Totem' strawberry (Fragaria × ananassa) grown in a growth chamber. CO2 assimilation rate (A) dropped sharply when LWP decreased from -0.5 to -1.2 MPa and almost ceased as LWP fell below -1.5 MPa. There was a significant but more gradual decline of A as RWC decreased form 90% to 55%. An exponential relationship with A was observed across a wide range of LWP and RWC (Rz= 0.64, 0.86, respectively). LWP was more closely related with transpiration and leaf and stomatal conductances than with A and water use efficiency. RWC was highly correlated with all gas exchange parameters.
Under moderate water stress, younger leaves maintain higher RWC and A than older leaves. There was no relationship between LWP and leaf age.
RWC and A were both negatively correlated with peak amplitudes of Ca 684 and Ca 697 and positively correlated with Ca 693 in their 4th-derivative spectra of chlorophyll. LWP had a negative correlation with Cb 640.
Ilex rugosa × cornuta ‘China Girl’ plants were established around structures simulating typical residential dwellings to determine tolerance to summer and winter stresses of sun and shade patterns. All plants survived the summer of 1983, when temperatures in the leaf canopy at one location reached 49°C. Leaf water potential was lowest in summer at the southeast, south, and southwest exposures, and most winter injury occurred at these same sites. Most growth and berry production occurred at cool northern exposures. No appreciable injury was caused by the 1983-84 winter, when low temperatures of -23° occurred in both December and January. However, winter burn on foliage was quite extensive in southeast and southwest locations exposed to winter sun. Temperature fluctuations of as much as 28° occurred the same day in southwest locations. Variations of as much as 18° occurred among sites at the same time of day. This new interspecific hybrid exhibited equal winter hardiness but greater heat tolerance than Ilex × meservae cultivars at the same exposures.
Leaf water potential (LWP), relative water content (RWC), gas exchange characteristics, and specific leaf weight (SLW) were measured six hours before, during, and after water stress treatment in F. chiloensis and F. ×ananassa grown in growth chambers. The leaves of both species showed significantly lower LWP and RWC as water stress developed. F. ×ananassa had consistency lower LWP under stressed and nonstressed conditions than F. chiloensis. F. ×ananassa had higher RWC under nonstressed conditions, and its RWC decreased more rapidly under water stress than F. chiloensis. In comparison to F. ×ananassa, F. chiloensis had significantly higher CO2 assimilation rate (A), leaf conductance (LC), and SLW, but not transpiration rate (Tr), under stressed and nonstressed conditions. LC was the most sensitive gas exchange characteristic to water stress and decreased first. Later, A and stomatal conductance were reduced under more severe water stress. A very high level of Tr was detected in F. ×ananassa under the most severe water stress and did not regain after stress recovery, suggesting a permanent damage to leaf. The Tr of F. chiloensis was affected less by water stress. Severe water stress resulted in higher SLW of both species.
moderating fruit size in ‘Lane Late’ navel oranges ( Goldhamer, 2007 ). The objective of our study was to measure the effects of differential levels of late-season water stress as quantified by reductions in leaf water potential from well-watered ‘Beck
higher transpiration in apple under a temperate climate. An objective of this research was to determine whether foliar particle film increased leaf water potential and/or g S in field-grown wine grapes under varying levels of vine water stress. The