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Abstract
Net CO2 assimilation rate (A) and plant water relations of peach [Prunus persica (L.) Batsch cv. Flordaking] leaves were monitored during development under field conditions. Leaf conductance to water vapor (gl) and transpiration rate (E) of unfolding and expanding leaves approached maximum values before maximum A values were achieved. Net CO2 assimilation rate and water use efficiency (WUE) were greatest for recently expanded leaves and gradually declined with age after full expansion. Leaf water potential (ψw) was similar for all leaf ages under field conditions. Leaf dry weight/cm2 and chlorophyll/cm2 increased with leaf age after expansion. Diurnal patterns of gl, E, and ψw were similar for expanded spring- and summer-flush leaves. Midday ψw of −2.4 MPa (ψp = about 0.3 MPa) did not reduce gl. Expanding shoots had higher osmotic potentials (ψπ) and thus maintained lower turgor potentials (ψp) than fully expanded shoots. Shoot and leaf elongation rates were related exponentially to ψp and were reduced drastically below ψp 1.0 and 0.7 MPa, respectively. The bulk modulus of elasticity (є) increased linearly with ψp, but there were no significant differences in є of expanding and nonexpanding shoots. As leaf water deficits developed, shoot and leaf expansion were inhibited prior to gl or A. Thus, a moderate level of water stress can reduce the rate of vegetative growth of peach trees without concomitant reductions in carbon assimilation.
Abstract
Citrus blight or young tree decline, is a wilt-like disease of unknown etiology which is characterized by restricted water movement and an upset in normal zinc distribution patterns. Diurnal leaf and fruit water potentials and leaf stomatal conductances of sweet orange Citrus sinensis (L.) Osbeck leaves on trees in various stages of decline were characterized to determine the progression of this disorder. All blight affected trees, regardless of severity of tree condition, had similar diurnal water relations. Blight affected trees have fewer and smaller leaves, less leaf area per tree, lower stomatal conductances, and lower diurnal transpiration rates than healthy trees. These differences did not result in any apparent changes in specific leaf weight, leaf osmotic potentials or in the critical leaf water deficits at which leaf turgor was lost. At equivalent transpirational fluxes, leaf water potential was much lower in blight affected trees than in healthy trees. Therefore, the water stress symptoms associated with blight are related to increased resistances in the water transport system and are not a result of lost stomatal function or changes in water relations characteristics of leaves that remain on blight affected trees.
Abbreviations: ET c , crop evapotranspiration; DOY, day of year; K c , crop coefficient; LWP, leaf water potential; RWC, leaf relative water content; VPD, air vapor pressure deficit. 1 Plant Physiologist. 2 Agronomist. 3 Agricultural Engineer. 4
Abbreviations: DAFB, days after full bloom; DC, drying cycle; E pan , potential water use measured from a Class A pan; ET, evapotranspiration; k c , crop coefficient; WU, water use; Ψ 1 , leaf water potential. 2 Senior Lecturer. 3 Professor. Current
Abstract
Spring- and summer-flush pecan [Carya illinoensis (Wangenh.) C. Koch] leaves were evaluated to determine climatological factors affecting leaf gas exchange, biophysical factors affecting growth, and to investigate the potential impact of a summer growth flush on alternate bearing. Expanding leaves had a higher osmotic potential, lower turgor pressure (ψp), poorer stomatal control, higher cuticular conductance, and a lower bulk modulus of elasticity than expanded leaves. Stomatal closure occurred at a progressively lower leaf water potential (ψw) as leaves aged. Net CO2 assimilation rate and leaf conductance to water vapor (g1) of pecan in the field did not decline in response to high atmospheric water stress and minimum midday ψw of −1.4 to −1.9 MPa when trees were supplied with adequate soil moisture. Leaf elongation rate was exponentially related to with marked reductions in growth occurring at ψp below 0.6 MPa and a complete cessation in growth below ψp = 0.3 MPa. Net CO2 assimilation rates of expanded leaves were up to 22 μmol·s−1m−2, several times higher than previously reported. Net CO2 assimilation rate was not inhibited by 41.5°C leaf temperature, 2000 μmol·s−1m−2 photosynthetic photon flux, and 3 kPa vapor pressure deficits (VPD). Transpiration rate (E) increased greatly with increasing VPD. Values of gl and E were generally higher than those reported for woody C3 perennials. The efficient water transport system of pecans under conditions of nonlimiting soil moisture may be a consequence of evolution in a floodplain ecosystem.
Abbreviations: CK, cytokinins; LWP, leaf water potential. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate
The sensitivity of leaf (ψleaf) and stem (ψstem) water potential and stomatal conductance (gs) to soil moisture availability in apple (Malus domestics Borkh.) trees and their correlation with yield components were studied in a field experiment. Two drip irrigation treatments, 440 mm (H) and 210 mm (L), were applied to a `Golden Delicious' apple orchard during cell enlargement stage (55-173 days after full bloom). Data collected included ψstem, y leaf, gs, and soil water potential at 25 (ψsoil-25) and 50 cm (ψsoil-50). No differences in midday ψleaf's were found between irrigation treatments. Stem water potential was higher in the H treatment than in the L treatment in diurnal measurements, and at midday throughout the season. Stomatal conductance of the H treatment was higher than the L treatment throughout the day. Stomatal conductance between 0930 and 1530 hr were highly correlated with ψstem. The H treatment increased the percentage of fruit >65 mm, and increased the proportion of earlier harvested fruit reaching marketable size compared to the L treatment. Fruit size in the first harvest and the total yield were highly correlated with ψstem. The degree of correlation between plant water stress indicators and yield component decreased in the following order: ψstem>ψsoil-25,>ψsoil-50>ψleaf. The data suggest that midday ψstem may serve as a preferable plant water stress indicator with respect to fruit size.
d of treatment, PI 440603 had significantly higher ψLEAF than the other three entries ( Fig. 3 ). Fig. 3. Leaf water potential responses of four kentucky bluegrass entries under increasing salt treatments and for 28 d of treatment. Error bars
in 1 m m ABA solution had higher stomatal resistance and leaf water potential than untreated seedlings after transplanting. When irrigation was withheld for 15 h after transplanting to impose water stress, the improved water status by ABA resulted in
Growth of potted Ligustrum was controlled by uniconazole at 3.0 mg a.i./pot. Uniconazole inhibited growth by inducing shorter internodes with smaller diameter and by reducing secondary branching and new leaf production. As a result, the total leaf area of the treated plants was 6396 less than the control plants. The chlorophyll content of recently expanded leaves was 27% lower in treated than in control plants, even though there were no visual differences in leaf color. Leaves of treated plants also had a 28% higher stomatal density than the control. The liquid flow conductance of Ligustrum was 3.7 × 10-14 m·s-1·Pa-1 and was similar for plants in both treatments. Differences in daily water, use between the two treatments began to appear at the same time as differences in growth. Total water use of treated plants was 13% less than that of the control. When daily water use was normalized on a-leaf-area basis, water use between treatments was similar, suggesting that differences in total water use were primarily due to differences in leaf area. For plants in both treatments, peak sap flow rates in the main trunk ranged between 60 and 100 g·h-1·m-2. Leaf conductance, transpiration rates, and water potential were also similar for treated and control plants. Chemical name used: (E)-1-(4-chlorophenyll) -4,4, -dimethyl-2-(l,2,4-triazo1-l-y1)-l-penten-3-ol (uniconazole).