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Abstract
Seedlings of ‘Pineapple’ sweet orange [Citrus sinensis (L.) Osbeck] (Swt), Cleopatra mandarin (C. reshni Hort ex Tan) (Cleo)], and trifoliate orange [Poncirus trifoliata (L.) Raf.] (Tri) were grown from seed for 10 months in 2-liter containers of native Candler fine sand in a glasshouse, watered two times per week, and fertilized weekly with a complete nutrient solution. NaCI at 0, 15, 30, or 60 mM was added to the watering solution for 2 additional months. Increases in salinity decreased hydraulic conductivity of roots, transpiration rate, leaf water potential, and root growth. The effect of salinity on mineral composition of tissues was rootstock-dependent. High salinity leaves of Tri had the highest N, K+, and Cl− but the lowest Na+, whereas Tri roots had the highest Na+ at the highest salinity. High-salinity Cleo leaves had the lowest Cl− and K. All seedlings survived −4°C for 6 hr in a controlled freeze test. Salinity decreased leaf loss, except in the deciduous Tri, in which 60 mM NaCI may have been excessive. Thus, moderate salinity treatment can reduce growth and modify water and mineral nutrient relations so as to increase cold hardiness of certain Citrus species.
Abstract
Mature fruiting and defruited ‘McIntosh’/M.26 apple (Malus domestica Borkh.) trees were exposed to natural rainfall or to no rainfall with the use of under-canopy tent-like covers. With covers present, fruit diameter tended to be less and, on one occasion, soluble solids concentration and fruit firmness increased. Trunk growth was reduced more by fruit than by covers. Trunk growth of fruiting trees did not respond to covers, whereas trunk growth of defruited trees was reduced by covers. Fruit load and reduced soil water content did not affect terminal shoot length. In one experiment, specific leaf weight (SLW) was less for fruiting trees than for defruited trees. Fruiting increased foliar N, P, Ca, and Mg and decreased K concentration. On a leaf-area basis, K was again lower in cropping trees while other nutrients remained mostly unchanged. With tent covers, trees generally had less foliar N, P, and K based on either concentration or amount per unit of leaf area. Leaf water potential was lower for trees with fruit and tended to be lower for trees with tent covers. Leaf stomatal conductance was higher for fruiting trees than for defruited trees and higher for trees without tent covers than for trees with tent covers.
Abstract
Young ‘Golden Delicious’/M7 trees were root pruned on 2 sides at 2.5, 5.0, and 10.0 cm distances from the stem which removed 10%, 28%, or 59% of their roots. Net photosynthesis (Pn) was reduced 35% and 47% and transpiration (Tr) 29% and 45% one day after root pruning of 28% and 59%, respectively, and recovery began 10 days later. Root pruning reduced leaf water potential significantly for 6 hr; recovery was apparent after one day. Root pruning severity of 10% had no effect on Pn, Tr, or water potential. Shoot growth rates decreased with increasing root pruning severity. The greatest reduction of shoot extension occurred during the 2nd and 3rd week following root pruning, with increasing growth rates observed in the 4th week. Suppression of shoot diameter increase lasted for 2 weeks. Leaves that developed following 28% or 59% root pruning were smaller than leaves of unpruned trees and had increased specific leaf weights (SLW), while previously expanded leaves were not affected. As root pruning severity increased, fresh weight of leaves and current shoots were reduced 45%; older parts of the tree were not influenced. Four weeks after root pruning there was no difference in total fresh weight of roots. The distribution of small roots from root pruned trees was increased in close proximity to the stem and decreased at distances greater than 5 cm from the stem.
Cucumber (Cucumis sativus L. cv. Fidelio) grown in sand culture in the greenhouse was trickle-irrigated with nutrient solution containing 0, 10, or 50 mm NaCl. Gas exchange of Individual leaves was measured by a portable infrared gas analyzer et saturating photosynthetic photon flux. Salt at 10 mm had no detectable effect on plant performance, but exposure to 50 mm NaCl caused net CO2 fixation to decline by 33% and 48% in the eighth and ninth oldest leaves, respectively. Stomatal conductance and transpiration rate were also reduced (≈ 50%) In these leaves. These differences, as well as lower leaf water potentials, were associated with a 60% reduction in fruit fresh weight. The relationship between net CO2 fixation and intercellular (substomatal) CO2 concentrations was determined for individual, attached leaves of plants with roots exposed to various concentrations of NaCl in hydroponics. With 50 and 100 mm NaCl, a nonstomatal contribution to the inhibition of photosynthesis at the chloroplast level was Indicated by strong inhibition of CO, fixation at a saturating CO2 concentration. Salt-induced inhibition of CO2 fixation was associated with accumulation of Na+ and Cl-, and lower K+ in the individual leaves examined.
Abstract
Pressure chamber and thermocouple psychrometer measurements of leaf water potentials in vegetative Euphorbia pulcherrima Willd. cv. Eckespoint C-l Red were evaluated. The 2 methods agreed within 0.2 MPa between −0.3 and −1.8 MPa and were equal at −1.1 MPa. Minimum daily water potential for nonstressed plants reached −0.67 MPa by 1230 hr. Abaxial water vapor conductance and water potential varied little between 1230 and 1630 hr. When drought was imposed, incipient stomatal closure occurred at −0.8 MPa with full closure observed at −1.2 MPa. Complete loss of turgor pressure occurred at water potentials between −1.2 and −1.4 MPa. The linear correlation coefficient for conductance and leaf-air temperature differential was 0.96, with leaf and air temperature equal when conductance was 0.6 cm·s−1. Xylem pressure potentials of upper leaves on drought-stressed plants declined to −1.7 MPa in 8 days and abscission of proximal leaves began. There was little change in xylem pressure potentials of upper leaves after leaf abscission began.
Abstract
After initially withholding irrigation (WI) to dry out the root zone of pear trees, regulated deficit irrigation (RDI) applied to replace 23% and 46% of evaporation over the planting square (Eps) was compared with 69% and 92% Eps applied during the WI and RDI periods, respectively (full irrigation). Irrigation was increased to 120% Eps on all treatments after rapid fruit growth commenced. Leaf water potential (ψ1) measured at dawn and midday became less negative during RDI than during WI but in both periods was more negative than the control (69%/92% Eps). On the other hand, ψ1 of treatments receiving WI and RDI became less negative than the control when all irrigation treatments were increased to 120% Eps. Withholding irrigation followed by RDI reduced vegetative growth by 52%. In contrast, however, WI did not inhibit fruit growth, while, during RDI following WI fruit, growth was stimulated. A similar but greater stimulation of fruit growth (consistent with relatively less negative ψ1) was measured on WI/RDI plants when all treatments received 120% Eps. This stimulation of fruit growth increased yields by about 20%. The results indicate fruit osmoregulate to maintain and/or increase growth at the expense of inhibited vegetative growth when WI and or RDI reduce ψ1 in spring to values approaching −0.5 MPa at dawn.
full impact of local kernel N demand on leaves. Water status of each tree was measured as midday stem water potential (i.e., bagged leaf water potential; Shackel et al., 1997 ) on each gas exchange measurement date. Starting at ≈1200 hr , two shaded
.F. García-Orellana, Y. Conejero, W. Ruiz-Sánchez, M.C. Alarcón, J.J. Torrecillas, A. 2006 Stem and leaf water potentials, gas exchange, sap flow, and trunk diameter fluctuations for detecting water stress in lemon trees Trees (Berl.) 20 1 8 Qiu, R.J. Kang, S
≈1300 and 1500 hr on each gas exchange measurement date. One shaded leaf in the lower, interior portions of each tree canopy was placed in a sealed reflective bag for at least 20 min before leaf water potential was measured with a Scholander pressure
relationship between leaf temperature and transpirational cooling ( Jackson et al., 1981 ). Under drought stress conditions, soil moisture becomes depleted, resulting in reduced leaf–water potential, stomatal conductance, and transpirational cooling, which