Search Results

You are looking at 101 - 110 of 211 items for :

  • "relative water content" x
  • All content x
Clear All
Free access

Rajeev Arora, Dharmalingam S. Pitchay, and Bradford C. Bearce

This study evaluated the effect of reversible water stress on heat stress tolerance (HST) in greenhouse-grown geraniums. Water stress was imposed by withholding irrigation until pots reached ≈30% (by weight) of well-watered (control) plant pots, and maintaining this weight for 7 days. Control plants were watered to just below field capacity, every other day. Leaf xylem water potential (LXWP, MPa), leaf-relative water content (LRWC,%), media water content (MWC, % fresh weight), and heat stress tolerance (HST, LT50) were determined for control and stressed plants. HST (LT50), defined as temperature causing half-maximal percent injury, was based on electrolyte leakage from leaf disks subjected to 25 to 60C. Control-watering was restored in stressed plants and above measurements made after 7 days of recovery. Data indicate: 1) LXWP, LRWC, and MWC in control and stressed plants were –0.378 and –0.804 MPa, 92.31% and 78.69% and 82.86% and 15.5%, respectively; 2) HST increased significantly in stressed as compared to control plants (LT50 of 55C vs. 51C); 3) control plants were near maximally injured by 53C treatment and sustained more than 3-fold greater injury than stressed plants at 53C. In recovered plants, LXWP and RWC reversed back to control levels, paralleled by loss of higher HST.

Full access

Chenping Xu and Beiquan Mou

Protein hydrolysates (PHs) are an important group of plant biostimulants that have received increasing attention in recent years because of their positive effects on crop performance and contribution to agroecological sustainability. The aim of the study was to determine the effects of fish-derived PHs on growth, chlorophyll content and fluorescence, and leaf gas exchange of lettuce (Lactuca sativa) grown in a growth chamber. Fish-derived PHs were drench applied (300 mL of 3 mL·L−1) three times at 0, 14, and 24 days after transplanting (DAT), and lettuce were evaluated 30 DAT. Application of PHs significantly increased the lettuce leaf number per plant from 22 to 28, stem diameter from 1.37 to 1.68 cm, shoot fresh and dry weight (FW and DW) from 59 to 89 g and 5.5 to 7.7 g, and root dry weight from 0.52 to 0.80 g. It also significantly increased the leaf relative water content (RWC) from 87% to 90% and succulence from 267 to 288 g·m−2 water, but had no effect on specific leaf area (SLA). PHs significantly enhanced chlorophyll content, photosynthetic rate, stomatal conductance, and transpiration rate although they did not alter chlorophyll fluorescence. Our study indicated that plant biostimulants and fertilizer PHs improved plant performance and might have potential to be used for sustainable production of lettuce.

Free access

Kristian Borch, Carter Miller, Kathleen M. Brown, and Jonathan P. Lynch

A series of experiments was conducted to investigate the response to drought stress of marigold (Tagetes patula L. `Janie Tangerine') plants grown with reduced phosphorus. Plants were grown with convention al phosphorus fertilization (1 mm, control) or one of two levels of alumina-buffered phosphorus (Al-P), 21 or 5 μm. Plants supplied with 21 μm Al-P produced plants with equal total dry weight, more flowers and reduced leaf area compared to control plants. Whole-plant photosynthetic CO2 assimilation expressed on a leaf area basis was nearly twice as high in 21 μm Al-P plants as in controls, probably as a result of reduced intraplant shading. In plants supplied with 21 μm Al-P, smaller leaf area resulted in reduced whole-plant transpiration. Moreover, the relative water content of the growing medium was significantly lower at wilting with 21 μm Al-P than for control or 5 μm Al-P regimes. The improved water acquisition with 21 μm Al-P could be explained by increased root proliferation via longer main roots and less densely distributed lateral roots. The results indicate that optimizing phosphorus nutrition with solid-phase buffered-phosphorus fertilizer improves drought tolerance by reducing transpiration and increasing water acquisition from the medium.

Free access

Thomas E. Marler and Haluk M. Discekici

`Honey Jean #3' sweet corn was planted in one-half of a split-root culture system containing `Tainung 1' or `Known You 1' papaya seedlings to determine if papaya roots could transfer water to the corn seedlings. After the corn seedlings were established, water was withheld from both compartments (2/2) or only the compartment containing the corn seedlings (1/2). Control plants were grown with both halves well-watered. Pre-dawn relative water content (RWC) of corn leaves was measured as an indicator of drought stress. Following 11 days, root competition was relieved in half of the 1/2 plants by cutting the papaya root connection between the half with corn from the rest of the papaya culture system. RWC of 1/2 corn plants was maintained above that of 2/2 plants, but below that of control plants. After relieving root competition, the 1/2 plants in competition with papaya roots maintained higher RWC than the 1/2 plants relieved of competition. Leaf tissue of all corn plants except the control plants was necrotic by 30 days. The results indicate that development of drought stress in corn using this culture system was retarded by watering a portion of the papaya roots not associated with the corn roots. Drought stress was accelerated by relief of competition with papaya, which is evidence that water was being supplied by the papaya roots within the papaya/corn system.

Free access

Frank Williams, Alexis Barbarin, Donald Hauber, and Harish Ratnayaka

Drought is a major constraint to chili production in a variety of cropping systems worldwide. A greenhouse study was conducted to understand mechanisms underlying drought acclimation of leaf gas exchange in two popular chili cultivars, `Big Chili' and `Jalapeno'. Unstressed `Big Chili' had 27% greater net photosynthesis (P net), 60% higher stomatal conductance (g w), and 18% higher transpiration (E), but only 3% greater intercellular CO2 concentration (C i) than `Jalapeno'. Light compensation point was 43.3 and 31.6 μmol·m-2·s-1 in `Big Chili' and `Jalapeno', respectively, although light-saturated assimilation (A max) and photosystem II efficiency (F' v/F' m) were the same in the two cultivars. Maximum rubisco-mediated carboxylation, V cmax, was 66.3 and 69.1 μmol·m-2·s-1 in `Big Chili' and `Jalapeno', respectively. During drought, 50% of plants wilted to zero P net in 5 days in `Big Chili', and 7 days in `Jalapeno'. However, at wilting, relative water content was the same at 66%, with 97% less g w than unstressed plants, in each cultivar. `Jalapeno' had 9% greater F' v/F' m than `Big Chili', at wilting. Four days after rewatering, P net, g w and F' v/F' m were 27%, 47%, and 8% less in `Big Chili', but only 11%, 19%, and 4% less in `Jalapeno', than unstressed plants, respectively. `Jalapeno' shows greater acclimation of gas exchange to drought than `Big Chili' through rapid recovery of photosystem II, carbon assimilation and stomatal activity.

Free access

Suzanne S. McDonald, Douglas D. Archbold, and Cheng Lailiang

The expression gti, or tissue ionic conductance, was proposed to describe the efflux of ions from leaf disks (Whitlow et al., 1992, Plant Physiology, 98:198-205). The objective of this study was to determine the effectiveness of the gti method to screen germplasm for heat and desiccation tolerance using representative selections of 5 Fragaria species. Leaf disks were exposed to 4 levels of heat, 25, 35, 45, and 55 C, and 4 levels of desiccation. 60, 70, 80 and 100% relative water content (RWC). F. virginiana glauca was consistently ranked as the leakiest in all treatments including controls, with gti values 70 to 100% higher than in the other species. Temperatures of 25 to 45 C did not influence gti over time. A temperature of 55 C was lethal to the tissue and, thus, the ion flux was initially very high but soon diminished. At 70% RWC F. virginiana glaucu tissue was the leakiest, and F. virginiana and F. vesca tissues were somewhat leakier than those of F. × ananassa and F. chiloensis. Differences among species diminished with time in bathing solutions.

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

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

S.M. Lutfor Rahman, Eiji Nawata, and Tetsuo Sakuratani

Effects of water stress at different plant ages on SOD activities were studied in two tomato cultivars. Water stress treatment decreased the leaf water potential in all stages, but reduction of leaf water potential was more rapid and pronounced in KF than TM at all DSLs (days of seedlings). After withdrawal of water stress treatment, stressed plants of TM increased leaf water potential to the values of control level in all DSLs, but in KF, leaf water potential of stressed plants were much lower than that of control plants. Effects of water stress on relative water content (RWC) of leaves at 20 DSL showed a similar tendency to that on leaf water potential. The SOD activities in both cultivars showed significant increase by water stress treatment at all DSLs, but the increase of SOD by water stress was larger in TM than in KF. This tendency was observed at all DSLs. The results may indicate that SOD activities play an important role in drought tolerance of tomato at various plant ages and suggest a possible use of SOD activities as a criterion for tomato drought tolerance.

Free access

R.L. Geneve, S.T. Kester, and J.W. Buxton

A capillary mat-mist system was developed to provide near constant media water contents at differing quantities of mist. Media water contents were reduced by increasing the capillary mat height above a constant water table maintained at bench level. Increased tensions from 0 to 10 cm above the water table reduced water content in Oasis, rockwool, and peat-perlite by 35.4%, 27.6%, and 17.4%, respectively. There was no difference in water content for each medium when the mist quantity ranged between 600 and 1800 mL·m-2·h-1, except when the capillary mat was at 9 cm above the water table and mist volume was 300 mL·m-2·h-1. Chrysanthemum cuttings rooted best when water content was highest regardless of media. Using the peat-perlite medium, water content had the greatest impact on rooting when the mist volume was low (600 mL·m-2·h-1). Relative water content of cuttings was lowest during the first 5 days of sticking and both reduced media water content and mist quantity resulted in the lowest internal water status for the cuttings.