were calculated. From the dry weights and leaf area data, net assimilation rate (NAR), leaf area ratio (LAR), and relative growth rate (RGR) were calculated according to Evans (1972) . To calculate NAR, LAR, and RGR, plants within the initial and
Hala G. Zahreddine, Daniel K. Struve, and Salma N. Talhouk
Lenore J. Nash and William R. Graves
Abbreviations: ψ waterpotential; ϵ max , maximum bulk modulus of tissue elasticity; NAR, net assimilation rate; RGR, relative growth rate. 1 Present address: Dept. of Horticulture and Landscape Architecture, Univ. of Kentucky, Lexington, KY 40506
W.A. Erb, A.D. Draper, and H. J. Swartz
, internal leaf CO 2 concentration; LAD, leaf area duration; LAP, leaf area production; LAR, leaf area ratio; LT, leaf temperature; LW, leaf dry weight; LWR, leaf weight ratio; NAR, net assimilation rate; RGR, relative growth rate; RW, root dry weight; RWR
David R. Dreesen and Robert W. Langhans
Abbreviations: CEGR, controlled-environment growth room; HI, high irradiance levels; LAR; leaf area ratio; LI, low irradianee levels; MHI, medium-high irradiance levels; MLI, medium-low irradiance levels; MRGR, mean relative growth rate; NAR, net
Jong-Goo Kang and Marc W. van Iersel
To evaluate the effects of nutrient concentration and pH of the fertilizer solution on growth and nutrient uptake of salvia (Salvia splendens F. Sellow ex Roem. & Schult. `Scarlet Sage'), we grew plants with five different concentrations of Hoagland nutrient solution [0.125, 0.25, 0.5, 1.0, and 2.0× full strength; electrical conductivity (EC) of 0.4, 0.7, 1.1, 2.0, and 3.7 dS·m-1, respectively]. In a concurrent experiment, plants were subirrigated with modified Hoagland solution at 0.5× concentration and one of five solution pH values: 4.4, 5.4, 6.4, 7.2, and 8.0. Shoot and total dry weight and leaf area increased greatly with increasing nutrient solution concentrations from 0.125 to 1.0×, while leaf photosynthesis (Pn), transpiration, and stomatal conductance decreased with increasing nutrient solution concentrations. Treatment effects on growth apparently were caused by changes in carbon allocation within the plants. Shoot: root ratio and leaf area ratio increased with increasing fertilizer concentration. Plants flowered 8 days later at low concentrations of nutrient solution than at high concentrations. Shoot tissue concentrations of N, P, K, and B increased, while C, Al, Mo, and Na decreased with increasing concentration of the nutrient solution. The pH of the nutrient solution had no effect on the growth or gas exchange of the plants, while its effects on nutrient concentration in the shoot tissue generally were smaller than those of fertilizer concentration. These results indicate that 1.0 to 2.0× concentrations of Hoagland solution result in maximum growth, apparently because the plants produce leaf area more efficiently at high fertilizer concentrations.
Cathleen Feser, Rolston St. Hilaire, and Dawn VanLeeuwen
Mexican elder (Sambucus mexicana Presl.) is used in arid landscapes of the Southwest, but the plant is known for its unpredictable performance in those landscapes. We studied drought responses of mexican elder plants grown in an arid environment using an in-ground nursery production system. Plants were maintained as well-irrigated controls or exposed to cyclic drought and irrigated based on evapotranspiration. Drought treatment lasted 165 days. Plants exposed to drought had more negative predawn and midday water potentials than well-watered plants. The ratio of variable to maximal fluorescence (Fv/Fm) for the drought group (0.76), was near the optimum value of 0.8, suggesting that chloroplasts of drought-stressed plants maintained high levels of activity. Drought cycle, but not drought treatment affected stomatal conductance. Drought-stressed plants had lower transpiration rates than controls except at drought cycle five when transpiration rates were similar between irrigation treatments. Relative water content was higher in controls (76%) than plants exposed to drought (66%). Leaf area of well-irrigated plants was over four times higher than that of plants exposed to drought. Leaf area to root dry weight ratio of drought-stressed plants was 79% lower than control plants. Severely reduced leaf area of drought-stressed plants might be one reason why landscape personnel conclude that mexican elder plants perform poorly in arid landscapes.
Chieri Kubota and Toyoki Kozai
Growth and net photosynthetic rate of potato (Solanum tuberosum L.) `Benimaru' plantlet in vitro were studied under a conventional photomixotrophic condition [with 20 g sucrose/liter in the medium and under 70 μmol·m-2·s-1 photosynthetic photon flux (PPF)] with minimal ventilation (MV) and under photoautotrophic conditions (without sugar in the medium and under 190 μmol·m-2·s-l PPF) with enhanced natural ventilation using an air diffusive filter (DV) or with forced ventilation (FV). Fresh weight of the plantlets cultured in the FV and DV treatments was 2.4 times that of the plantlets cultured in the MV treatment. Net photosynthetic rate and dry weight per plantlet were the highest in FV followed by DV. For photoautotrophic micropropagation, FV was superior to DV.
Marc van Iersel
Transplanting often causes root damage, and rapid root growth following transplanting may help to minimize the effects of transplant shock. The objective of this study was to determine the effects of NAA and IAA on posttransplant growth of vinca (Catharanthus roseus L.). Bare-root seedlings were germinated in a peat-based growing mix and transplanted into diatomaceous earth 10 days after seeding. Immediately after transplanting, seedlings were drenched with several concentrations of IAA or NAA (62.5 mL/plant). Both auxins increased posttransplant root and shoot growth, but the response was dose-dependent. The maximum growth occurred at concentrations of 10 mg·L-1 (IAA) or 0.1 mg·L-1 (NAA). The growth-stimulating effect of these auxins decreased at higher rates and NAA was highly toxic at 100 mg·L-1, killing most of the plants. Unlike the growth of bare-root seedlings, plug seedling growth was not stimulated by drenching with NAA solutions. These results show that auxins have the ability to stimulate posttransplant growth of vinca, but their effects may depend on the application method, rate, and timing, and transplanting method. Chemical names used: 1-naphthaleneacetic acid (NAA); 1-indole-3-acetic acid (IAA).
Edward J. Nangle, David S. Gardner, James D. Metzger, Dominic P. Petrella, Tom K. Danneberger, Luis Rodriguez-Saona, and John L. Cisar
.00 mm, 850 µm, and 500 µm. The shoot:root ratio was then calculated based on dry weight ( Gwynn-Jones and Johanson, 1996 ). Relative growth rate was calculated based on the formula of Gardner et al. (1985) : where RGR is the relative growth rate, W 2
evaluated the relative growth rates to compare plant growth rate at different growth stages. To determine the plant growth rate from transplanting to harvesting, we calculated the relative growth rate between 10 and 35 d after sowing (RGR DAS35 ). However