The effects of ambient temperatures between 15° and 43°C were determined on net photosynthesis of ‘French’ prune (Prunus domestica L. cv. Agen) trees maintained under a non-limiting soil water supply. The temperature optimum for photosynthesis was about 30° and net CO2 assimilation decreased rapidly above 35° even when water vapor pressure differences (VPD) were only 5 to 10 mb. Leaf resistance (r1) remained very low (2 to 3 sec cm-1) although leaf temperature reached 47° and the leaf water potential (ψ) decreased to -25 bars. Thus, non-stomatal photosynthetic inhibition was responsible for the 80% decline in net CO2 assimilation. Canopy wetting prevented the decline in net CO2 assimilation by reducing leaf temperature 8° (vs. control) and maintaining the ψ 14 bars higher than the non-misted control.
Relationships between midday (Ψmd) and predawn (Ψpd) leaf water potential, stomatal conductance (gs), and net CO2 assimilation rate (A) were determined at different fruit growth stages and for 2 years with different fruit loads in a `Sudanell' peach [Prunus persica (L) Batsch] plot subjected to two regulated deficit irrigation (RDI) strategies plus a control irrigation treatment. A postharvest RDI (PRDI) treatment was irrigated at 0.35 of the control after harvest. The second treatment (SPRDI) applied RDI during Stage II, the lag phase of the fruit growth curve, at 0.5 of the control and postharvest at 0.35 of the control. The control treatment and the PRDI and SPRDI when not receiving RDI were irrigated at 100% of a modified Penman crop water use calculation (ETo) in 1994, a full crop year, and 80% in 1995, a year of nearly zero crop. In 1995, with 80% of the 1994 irrigation rate and no crop, the Ψmd was higher, probably because of the lower crop load, while Ψpd was lower, probably because less water was applied to the soil. The relationship of gs and A with Ψmd during Stage II was steeper than during postharvest. Low Ψmd was not indicative of a depression in gs and A in Stage III. Osmotic leaf water potential at turgor loss (Ψπ 0) as derived from pressure-volume curves was more negative during Stage III and postharvest (about -2.9 MPa) than in Stage II (about -2.7 MPa). The Ψmd measurements together with Ψπ 0 determinations seemed to be more useful to characterize peach tree water status than Ψpd under soil water deficits because of their better relationship to midday stomatal closure.
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.
particularly appropriate for irrigation scheduling ( Hanson et al., 2000 ). Leaf water potential (Ψ l ) measured at different times of the day (predawn and during the day) is often used to determine plant water status. Leaf water potential measured at predawn
market tomatoes ( USDA, 1991 ). Predawn and midday leaf water potential (Ψ L ) and leaf relative water content (RWC) measurements were initiated on 7 July 2009 and 14 July 2010. Measurements of leaf RWC and Ψ L were conducted during the same time period
Abbreviations: BBL, `Bush Blue Lake 274'; DAP, days after planting; g,, leaf conductance; LN, `Luna'; Pn, photosynthesis; ψ L , leaf water potential. 1 Current address: Fakultas Pertanian, Universitas Sriwijaya, Palembang 30139, Indonesia. 3 Dept
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
‘Olympus’ strawberries (Fragaria × ananassa (Duch.) with and without black polyethylene mulch were compared in terms of leaflet elongation and diurnal water potential (ψ) of leaves at 2 levels of drip irrigation. Mulch increased leaflet elongation at both irrigation levels, but had no appreciable effect on soil water potential at 20 cm depth, nor on leaf ψ or leaf turgor. Leaflet elongation with black polyethylene may have been favored by the increased soil temperature throughout the upper 20 cm. At the 10-cm depth, mulched, high-moisture soil was an average of 3.0°C warmer during a diurnal cycle. Greatest warming was in late afternoon and late evening in low and high moisture soil, respectively.