Search Results
Abstract
Single stem Euphorbia pulcherrima Willd. cv. Eckespoint C-1 Red were exposed to single or repeated episodes of drought stress to leaf water potentials of −1.0 or −1.3 MPa at different times during crop development. Decreased plant height and delayed flowering generally were caused by treatments including stress prior to time of initial bract coloration. Plant quality was reduced by those treatments that inhibited bract development and caused leaf abscission. Inflorescence diameter was reduced the most by stress after bract coloration. Bract dry weight was sensitive to stress and was reduced by stress between the time of initiating long nights and bract coloration. Leaf abscission resulted from a single exposure to −1.3 MPa after flower initiation. Stress prior to start of long nights had little effect on plant development.
Abstract
Leafy cuttings of Rhododendron catawbiense Michx. ‘Roseum Elegans’ were rooted under 0%, 55%, or 95% shade in a greenhouse. Compared to the low-light treatment, higher light induced high photosynthetic rates, high sucrose and starch levels, and low leaf water potential, but these differences only persisted for the initial part of the 23-week rooting period and did not influence subsequent rooting percentage. However, in cuttings receiving 95% shade, dry weights of leaves and stems and rootball size were relatively small after 23 weeks, suggesting that growth was reduced by lack of photosynthate. The reduced size of cuttings rooted under 95% shade apparently did not affect vigor because the size of the above-ground portion of all plants was equal after 2 months of growth in a greenhouse.
practically non-existent. When red oak ( Quercus rubra ) leaf water potential was between –1.5 and –2.0 MPa, CO 2 assimilation reduction relative to control trees was 60% ( Weber and Gates, 1990 ). Subjecting rubber trees ( Hevea brasiliensis ) seedlings to
were replicated six times in a randomized complete block design with seven plants in each replicate. Predawn leaf water potential was measured using a Scholander pressure chamber (ZIZ-4; Lanzhou University, Lanzhou, China) on leaves removed from the
leaf water potential in plants exposed to drought stress ( Boyle et al., 2016 ; Comstock and Mencuccini, 1998 ). Lower Ψ L can increase stomatal sensitivity to abscisic acid ( Tardieu and Davies 1992 ). Abscisic acid–mediated reduction in g S during
chlorophyll content, g S , transpiration rate, leaf temperature, and leaf water potential ( Castrillo et al., 2001 ; Dias and Brüggemann, 2010 ; Lizana et al., 2006 ; Ninou et al., 2013 ; Wentworth et al., 2006 ). However, these traits showed variable
Abstract
Seedlings of sweet corn (Zea mays L. cv. Iochief) were grown in sand with 3 rates of N at a moderate and severe water-stress rate produced by adding polyethylene glycol (PEG 6000) to the nutrient solution. As water stress increased, dry-matter production decreased. Increasing N rate compensated in part for the loss in dry-matter production that resulted from the water stress. Leaf chlorophyll levels and stomatal density on the abaxial leaf surface increased with an increase in N, and a faster recovery of the relative water content of leaf tissue following waterstress treatment occurred. All 3 responses could have contributed to the N response in dry-matter production observed at the 2 water-stress levels. A low N rate may aid young sweet corn seedlings under severe water stress to resist drought, as indicated by a stabilization in dry-matter production in plants receiving only 8 mm N in the nutrient solution when moving from moderate to severe water stress. These plants had a higher relative water content and leaf water potential under severe water stress than plants receiving higher rates of N, which may have contributed to the ability of plants receiving a low-N rate to cope with the severe water stress.
Abstract
Tomato accessions PI 128644 (Lycopersicon peruvianum var. dentatum Mill.) and PI 406966 (L. esculentum Mill.) were identified in preliminary screening trials as being relatively nonresistant and resistant to root-zone flooding, respectively. A comparative study of these accessions was undertaken to examine adaptive responses to inundation. Root and shoot growth of both accessions were inhibited by 120 hr of flooding. Aerobic respiratory capacity of secondary roots of both accessions decreased to a similar extent after 24 hr of inundation. Flooding did not significantly affect anaerobic root respiration rate of either accession. Stomatal conductance decreased after 24 hr of flooding for both accessions, with some recovery by PI 406966 after 168 hr of treatment, coinciding with development of adventitious roots on lower stems. Few adventitious roots formed on flooded PI 128644 plants. Leaf water potential of both accessions initially increased as a result of flooding, but declined to near control level by 120 hr of treatment. Total phenol content of PI 128644 roots decreased with 72 hr of flooding, while that of PI 406966 roots was not significantly affected. Factors underlying the greater resistance of PI 406966 to flooding remain unclear, but may include a lower root respiratory requirement for O2 and greater ability to sequester or eliminate toxic substances during inundation.
Abstract
Greenhouse-grown peach [Prunus persica (L.) Batsch] seedlings and cuttings were drought-stressed by reducing soil water potential (ψsoil) from field capacity (FC) to permanent wilting point, (PWP). Mean ψsoil and leaf water potential (ψleaf) were correlated with measurements of stomatal conductance (gs), net photosynthetic (Pn) rate, and vapor pressure deficit (VPD). Decreasing Pn and gs trends were noted as ψsoil decreased. Photosynthetic rate and gs were significantly reduced at ψleaf more negative than −1.5 MPa. Values of Pn and gs were more highly correlated to ψleaf than ψsoil. A midday depression in Pn rates began 2 hr earlier and peak rates were at least 50% lower when ψsoil was more negative than −0.05 MPa. The correlation coefficient (r) between ψleaf and ψsoil and between gs and Pn rate at different ψsoil was above 0.70. The r values decreased as soil and plant water potential became more negative. Stomatal conductance peaked at optimal ψsoil (FC) 2 hr following sunrise. Photosynthetic rate peaked at a ψsoil around −0.05 MPa 4 hr after sunrise.
Abstract
Osmotic adjustment in response to onset of winter dormancy was characterized in well-watered, potted sweetgum (Liquidambar styraciflua L.) and southern magnolia (Magnolia grandiflora L.) growing outdoors in Knoxville, Tenn. Analyses of water potential isotherms indicated that adjustment occurred in both species, with osmotic potential (ψπ) at full turgor decreasing 0.8 MPa in sweetgum (by the time of first color, 27 Oct.) and 1.0 MPa in magnolia (by 1 Dec.). Osmotic adjustment occurred despite the fact that plants did not suffer osmotic stress; morning and afternoon leaf relative water content (RWC) and leaf water potential (ψ) remained high throughout the fall. Leaf conductance was halved in sweetgum and doubled in magnolia as the autumn progressed. A correlation was found in magnolia between turgid : dry weight ratio and ψπ at full turgor. Tissue elasticity decreased somewhat, as the elastic modulus increased ≈2 to 3 MPa in each species through the autumn. Water potential isotherms changed most dramatically through the autumn in magnolia. Initially, ψ was −1 MPa at 82% RWC and, by December, leaves were able to withstand ψs of −3 MPa before RWC dropped to 82%. These changes are similar to those commonly reported as responses to drought or salinity.