Search Results

You are looking at 71 - 80 of 730 items for :

  • "water relations" x
  • Refine by Access: All x
Clear All
Free access

Brent M. Chapman, James E. Barrett, and Terril A. Nell

Catharanthus roseus `Cooler Peppermint' were grown under four different watering regimes [well-watered (WW), wilt plus 1 day (W+1), wilt plus 3 days (W+3), and wilt plus 1 day during the last 2 weeks only (L W+1)] and two different light levels [1100 and 750 μmol·m–2·s–1]. Stress treatments affected finished plant size and leaf area as well as stomatal conductance, water potential and time to wilt during two dry-down periods imposed at the end of an 8-week production cycle. W+3 plants were 50% smaller with 50% less leaf area compared to WW plants. During the second dry-down period, WW plants in high light wilted in 2 days vs 4 days for the W+3 plants. Similarly, WW plants in low light wilted in 3 days vs 6 days for the W+3 plants. The W+3 plants maintained significantly higher water potentials and greater stomatal conductances than the other treatments throughout both dry-down periods.

Free access

A.R. Biggs

Whole-shoot water potential, osmotic potential of the xylem fluid, and bark water potential were examined from late winter through early spring for six peach [Prunus persica (L.) Batsch.] cultivars varying in relative susceptibility to Leucostoma canker. There were significant differences among cultivars for whole-shoot water potential on all 11 dates tested in 1986, but not in 1985. The date effect was not consistent among cultivars, although when averaged across dates, the whole-shoot water potential of `Loring' was significantly more negative than that of `Candor' or `Garnet Beauty'. There were significant differences among cultivars for xylem fluid osmotic potential on one of five dates tested in 1985 and three of 11 dates tested in 1986, although cultivar differences were not consistent between years. Cultivars exhibited differences in bark water potential on three of five dates tested in 1985, with `Loring' exhibiting the least negative values when averaged across dates. There were only occasional significant correlations of the water status characteristics with relative susceptibility to Leucostoma canker or suberin accumulation. Measurements of plant water status among cultivars or genotypes in peach do not appear to be reliable indicators of susceptibility to Leucostoma spp. or wound response.

Free access

James A. Zwack, Anthony S. Aiello, William R. Graves, and Alden M. Townsend

Freeman maples (Acer ×freemanii E. Murray) are suspected to be more resistant to environmental stress than red maples (A. rubrum L.) because the lineage of Freeman maple includes silver maple (A. saccharinum L.). Little is known, however, about stress resistance of silver maple, and few data from direct comparisons of red and Freeman maples are available. Our objectives were to determine effects of root-zone heat on silver maples from northern and southern provenances, and to compare red and Freeman maple cultivars for resistance to rootzone heat stress and drought. There were no provenance-by-temperature interactions when silver maples from 33.3°N (Mississippi) and 44.4°N (Minnesota) latitude were grown with root zones at 29 and 35°C. Plants from 44.4°N latitude had 36% higher fresh mass, 43% more leaf surface area, and 35% and 59% higher, respectively, root and shoot dry masses than plants from 33.3°N latitude. Midday xylem water potential was 68% more negative for plants at 35°C than for plants at 29°C, and transpiration rate was 129% less for plants with root zones at 35°C than for those with root zones at 29°C. During preliminary work with Autumn Flame and Franksred red maple and Indian Summer and Jeffersred Freeman maples, rooted cuttings were grown in 25 and 37°C root zones under both drought and nondrought conditions. Reductions in growth at 37°C were similar for all cultivars. Results of this work could influence development, marketing, and use of Freeman maples.

Free access

Michael V. Mickelbart and Thomas E. Marler

Sapodilla [Manilkara zapota (L.) Royen], reportedly tolerant of saline conditions relative to other tropical fruit species, was studied in sand culture under greenhouse conditions to examine the physiology of sapodilla trees exposed to NaCl and to aid in determining the basis for this apparent tolerance. Treatments, consisting of a complete nutrient solution of 1 dS·m–1 (control) or this solution amended to 12 or 20 dS·m–1 with NaCl, were administered from 16 Nov. 1991 until 29 Jan. 1992. Net CO2 assimilation (A) of plants receiving NaCl gradually decreased relative to that of the control plants. At the end of 8 weeks of salinity, A of plants receiving 12 or 20 dS·m–1 was 72% or 31% of control plants, respectively. Substrate NaCl reduced apparent quantum yield, photosynthetic CO2-use efficiency, leaf osmotic potential, and predawn xylem potential of sapodilla leaves. Dark respiration and the variable: maximal chlorophyll fluorescence ratio were not influenced by NaCl. Exposure to NaCl also increased leaf tissue Na+ and Cl concentrations and the Na+: K+ ratio. These results indicate that gas exchange of sapodilla is relatively low for woody evergreen species. Moreover, sapodilla may not be as tolerant of salt stress as previously reported. The responses of sapodilla to root zone NaCl were consistent with other woody perennial glycophyte species. Photochemical efficiency of leaves on plants receiving NaCl was not different from that of leaves on control plants for >8 weeks after NaCl reduced gas exchange.

Free access

E. Jay Holcomb, Robert Berghage, and William Fonteno

The concepts of container water-holding capacity and air-filled porosity are important yet complicated for students interested in containerized crop production; however, both of these concepts can be observed and understood more completely if students develop a moisture retention curve. Our objectives were to describe an easy-to-construct and economical apparatus for creating a moisture retention curve and then to compare this curve with one generated by standard methods. The student method (column method) is constructed from plastic pipe cut into 5-cm sections. The sections of pipe are individually packed with a substrate then stacked and taped together, resulting in a 60-cm column of the substrate. The column is saturated and allowed to drain for 24 h. Then, the column is taken apart and the water content of each section determined gravimetrically. The water content of each section is graphed against height so that the result is a moisture retention curve. Data are presented to show the curve developed from the column method is similar to the curve developed by standard soil moisture tension method. The moisture retention curve can provide a better understanding of water and air holding capacities of substrates.

Free access

Rick M. Bates and Alexander X. Niemiera

Shoot and root water potentials were determined for bare-root Norway maple (Acer platanoides L.) and washington hawthorn (Crataegus phaenopyrum Med.) seedlings subjected to shoot and root exposure treatments for six cold storage durations. Shoot and root water potentials for all exposure treatments and both species decreased with increased time in storage, and the greatest degree of water stress occurred during the first six weeks of storage. Maple shoot and root water potentials for the exposed shoot treatment were the same as the whole plant covered treatment. In contrast, hawthorn shoot and root water potentials for the exposed shoot treatment were the same as values for the roots exposed treatment. Based on these data, we conclude that desiccation sensitive species such as washington hawthorn require root and shoot protection to minimize water loss.

Free access

Bingru Huang and Hongwen Gao

To investigate shoot physiological responses to drought stress of six tall fescue (Festuca arundinacea) cultivars representing several generations of turfgrass improvement, forage-type `Kentucky-31', turf-type `Phoenix', `Phoenix', and `Houndog V', and dwarf-type `Rebel Jr` and `Bonsai' were grown in well-watered or drying soil for 35 days in a greenhouse. Net photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (Tr), relative water content (RWC), and photochemical efficiency (Fv/Fm) declined during drought progression in all cultivars, but the time and the severity of reductions varied with cultivars and physiological factors. Pn, RWC, gs, and Tr decreased significantly for `Rebel Jr', `Bonsai', and `Phoenix' when soil water content declined to 20% after 9 days of treatment (DOT) and for `Falcon II', `Houndog V', and `Kentucky-31' when soil water content dropped to 10% at 15 DOT. A significant decrease in Fv/Fm was not observed in drought-stressed plants until 21 DOT for `Rebel Jr', `Bonsai', and `Phoenix' and 28 DOT for `Houndog V', `Kentucky-31', and `Falcon II'. The decline in Pn was due mostly to internal water deficit and stomatal closure under short-term or mild drought-stress conditions. After a prolonged period of drought (35 DOT), higher Pn in `Falcon II', `Houndog V', and `Kentucky-31' could be attributed to their higher Fv/Fm.

Free access

Jeffrey Melkonian and David W. Wolfe

Cucumber (Cucumis sativus L. cv. Marketmore 80) plants were exposed to a soil water deficit and subsequently rewatered. Maximum stress intensity was -1.5 MPa midday leaf water potential compared to -0.6 to -0.8 MPa in the well watered control, eight days after withholding water. Midday stomatal conductance {ks), leaf turgor potential and water potential decreased in the stress treatment compared to the control beginning at the first sampling, two days after withholding water. The decrease in all three was approximately linear with time over the stress. Decreased leaf elongation was observed at the second sampling, three days after the initial decline in ks and five days after withholding water. At similar relative water content {RWC), osmotic potentials of the stress and control treatments were the same throughout most of the stress. Further, there was no difference in osmotic potential, at the same RWC, between the stress and control treatments 12 - 16 hours after rewatering. Split-root experiments were also conducted to examine a possible role of a non-hydraulic signal from roots in drying soil in the regulation of ks and leaf elongation in cucumber. No conclusive evidence of a signal was found despite significant decreases in soil water potential of one-half of the root system of the stress plants. However, fluctuating vapor pressure gradients (vpg) may have obscured evidence of a signal.

Free access

Robert L. Heath, Michael V. Mickelbart, Mary Lu Arpaia, Claudia Fassio, and Ruby Miller

Vapor pressure deficit (VPD) is the driving force for plant water loss. However, air relative humidity (RH) can be used as a surrogate for VPD. While plants can adapt to environments with varying RH, little is known about how they respond to sudden shifts in RH. Areas of Southern California can experience drastic shifts in RH, from 60% or greater to less than 20% in just a few hours. The effect of these shifts on avocado (Persea americana Mill.) tree productivity is a major concern to growers. We studied the effect of shifts in RH on `Hass' avocado leaf stomatal conductance (g s) and branch sap flow in trees grafted on Duke 7 clonal rootstock. Under many conditions, the avocado assimilation rate is governed by g s. When g s is high in morning (>150 mmol·m-2·s-1), the water loss generally leads to some stomatal closure in the afternoon (50% or more). Conversely, low morning g s results in a higher g s rate in the afternoon (10% to 20% stomatal closure). This relationship between morning and afternoon g s is intensified by a shift from high to low RH in the afternoon. Therefore, in a drier atmosphere in the afternoon, the afternoon depression in g s is greater, leading to an impaired assimilation capacity. We hypothesize that the afternoon decrease in g s is due to low root/shoot hydraulic conductivity since soil water is readily available. While it is possible that low hydraulic conductivity on g s is exacerbated at the graft union, sap flow of grafted trees in greenhouse studies was nearly equal to trees on their own roots (ungrafted); in fact, often the depression in the afternoon was less on grafted trees. This suggests that while avocado is not suited to areas with low RH, water flow through the roots could be an additional criterion in selecting improved rootstocks.