Search Results

You are looking at 91 - 100 of 714 items for :

  • "irradiance" x
  • Refine by Access: All x
Clear All
Free access

A.M. Armitage, N.G. Seager, I.J. Warrington, D.H. Greer, and J. Reyngoud

Incremental increases in temperature from 14 to 22 to 30C resulted in linear increases in stem length and node number and decreases in stem diameter and stem strength of Oxypetalum caeruleum (D. Don.) Decne. Higher temperatures also resulted in additional flower abortion, reduced time to flowering, and fewer flowering stems per inflorescence. Reduction in the photosynthetic photon flux (PPF) from 695 to 315 μmol·s-1·m-2 had similar effects as increasing the temperature on vegetative characteristics, but had little effect on reproductive ones. The rate of stem elongation was greatest at low PPF for all temperatures and at high temperature for all PPF treatments. Net photosynthesis rose between 14 and 22C and declined at 30C for all PPF treatments. Long photoperiods (12 or 14 hours) resulted in longer internodes, longer stems, and more flowers per cyme than short photoperiods (8 or 10 hours), but photoperiod had little effect on flowering time. Treatments to reduce latex coagulant and silver thiosulfate treatments had no significant effect on vase life.

Free access

J.H. Lieth and C.C. Pasian

A mathematical description for the relationship between the rate of rose (Rosa hybrida L.) leaf net photosynthesis and photosynthetically active radiation, leaf temperature, and leaf age is developed. The model provides a tool for the prediction of these rates for leaves growing in a rose crop canopy.

Free access

James E. Faust and Royal D. Heins

Leaf unfolding rate (LUR) was determined for `Utah' African violet plants grown in growth chambers under 20 combinations of temperature and photosynthetic photon flus (PPF). A nonlinear model was used to predict LUR as a function of shoot temperature and daily integrated PPF. The maximum predicted LUR was 0.27 leaves/day, which occurred at 25C and a daily integrated PPF of 10 mol/m2 per day. The optimum temperature for leaf unfolding decreased to 23C, and the maximum rate decreased to 0.18 leaves/day as the daily integrated PPF decreased from 10 to 1 mol/m2 per day. A greenhouse experiment using 12 combinations of air temperature and daily integrated PPF was conducted to validate the LUR model. Plant temperatures used in the model predicted leaf development more accurately than did air temperatures, but using average hourly temperature data was no more accurate than using average daily temperature data.

Free access

John Clemens and R. Hugh Morton

Containerized plants of Heliconia psittacorum L.f. × H. spathocircinata Aristeguieta `Golden Torch' were grown in a greenhouse for 8 months from early summer to winter under selected combinations of N, P, and K. Fertilizer rates ranged from zero to rates that exceeded those reported in the literature by 50% to 100%. Biomass variables (vegetative and inflorescence dry weight, and leaf area) were predicted to be maximized at high N and high N to P, and N to K ratios corresponding to N-P-K application rates of 1.2, 0.5, and 0.6 kg·m-3, respectively (≈2:1:1). However, the number of shoots and flowers produced per rhizome were maximal at lower N to K ratios (1:1). Flower yield could therefore be optimized with appropriate fertilization, provided attention was paid to the N to K ratio so that the size of plants and their flowers was not compromised by efforts to increase shoot and flower number. The heavier the rhizome planted, the shorter the time for shoot emergence and flowering to occur, and the greater the number of flowers harvested. However, rhizome weight had no effect on number of shoots to emerge. The probability of shoots flowering declined markedly with order of shoot emergence, although this could be increased with appropriate mineral nutrition. The maximum number of leaves subtending the inflorescence (seven) was obtained at high N and P rates. Flower production was probably limited by declining solar radiation in autumn, and by within-plant competition for rooting space.

Free access

Daniel C. Wright

Because ASHS has adopted in their editorial policies the use of Systeme International (SI) units, it has become necessary to report light measurements in units other than footcandles. Since measurements using a radiometer can be tedious, tables providing values for different sources of light are often used to approximate required units. Using the tables provided by Thimijan and Heins [HortScience 18(6): 818-822], a Lotus 123 worksheet program was designed to interconvert photometric, radiometric, and quantum light units of measure. The worksheet is menu driven and can handle straight conversions or mixed conversions by entering requested information. Setup of the worksheet and instructions in its use will be provided at the meeting.

Free access

Allan M. Armitage

Hamelia patens Jacq. (Texas firebush) is a long-day plant for flower initiation and flower development; however, flower development is more sensitive to photoperiod than is flower initiation. The critical photoperiod for flower development at 25C is between 12 and 16 hours. Flowering was delayed under low light conditions, and plant dry weight was heavier and flowering time was earlier for plants grown at a constant 25 or 30C than at 20C. A greenhouse environment with a 16-hour photoperiod and moderately high temperature (25C) would be appropriate for production of H. patens.

Free access

Svoboda V. Pennisi, Marc W. van Iersel, and Stephanie E. Burnett

The growth of three english ivy cultivars in ebb-and-flow subirrigation systems was examined under three photosynthetic photon flux (PPF) treatments (low, medium, or high, corresponding to an average daily PPF of 3.2, 5.4, or 8.5 mol·m–2·d–1, respectively) and four fertilizer concentrations (0, 100, 200, or 300 mg·L–1 N) geared toward production of acclimatized foliage plants. Marketable quality english ivy can be subirrigated with 100 mg·L–1 N. Although 8.5 mol.m–2.d–1 produced the maximum shoot dry weight (SDW), good quality plants also were produced under 5.4 mol·m–2·d–1. `Gold Child', `Gold Dust', and `Gold Heart' english ivy produced with low fertility and low light may be better acclimatized and show superior performance in interior environments. Under light levels lower than 8.5 mol·m–2·d–1, `Gold Heart' had less variegation (12% or 21% for ivy grown under 3.2 or 5.4 mol·m–2·d–1, respectively). `Gold Dust' and `Gold Child' had 65% and 22% variegated leaf area, respectively, when grown under 5.4 mol·m–2·d–1 PPF. Under 5.4 mol·m–2·d–1 PPF, `Gold Dust' retains attractive foliage with overall perception of increased lighter-green coloration.

Free access

Mengmeng Gu, Curt R. Rom, James A. Robbins, and Hyun-Sug Choi

The genus Betula consists of approximately 50 deciduous species throughout northern hemisphere. Net CO2 assimilation ([A]) of four birch taxa (Betula alleghaniensis Britton, B. davurica Pall., B. nigra L. `Heritage', and B. papyrifera Marsh.) was measured with a portable gas exchange system, CIRAS-I. Light was increased from 0 to 2000 μmol· m-2·s-1 at increments of 25, 50, 100, 250, 500, 750, 1000, 1250, 1500, 1750, 2000 μmol·m–2·s–1 to create an [A] light-response curve. CO2 concentration was gradually increased to 1100 ppm in increments 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100 ppm to create an [A]-Ca (ambient CO2) curve. B. davurica had significantly higher potential A capacity than the other taxa under high CO2 conditions. Betula nigra `Heritage' had the highest carboxylation efficiency among four taxa. B. davurica and B. nigra `Heritage', had higher [A] when ambient CO2 is 0ppm. Betula davurica and B. nigra `Heritage', had higher light-saturated rate of gross [A] than B. alleghaniensis and B. papyrifera.

Free access

Allan M. Armitage

Plants were subjected to daily temperatures of 15, 20 or 25 °C after transplanting to 10cm containers. As temperatures decreased, plants were significantly slower to reach anthesis, however, however no significant differences in visible bud time occurred between 20–25 °C. Night break incandescent lighting or HID lamps for 2 or 4 weeks were used to illuminate plants during the daylight production cycle (0800–1700 hr). No differences in growth or flowering time between HID durations occurred, but both HID treatments resulted in larger plants and one week faster flowering compared with control and incandescent-lit plants. The effect of incandescent light, however, had no effect on flowering time but resulted in significantly taller plants. Additional photoperiod studies were conducted using continuous LD (night-break lighting), continuous SD (black cloth from 1700-0800) and a combination of LD-SD and SD-LD treatments. In all treatments, photoperiod had no significant effect on flowering time or growth, suggesting Ruellia `Rajin Cajin' is a day neutral taxon. Experiments with `Rajin Cajin' suggested in was a 6 week crop from plug to market.

Free access

Jason J. Griffin, Thomas G. Ranney, and D. Mason Pharr

Tolerance to high solar irradiation is an important aspect of stress tolerance for landscape plants, particularly for species native to understory conditions. The objective of this study was to evaluate differential tolerance to high solar irradiation and underlying photosynthetic characteristics of diverse taxa of Illicium L. grown under full sun or 50% shade. Eleven commercially available taxa of Illicium were evaluated for light tolerance by measuring light-saturated photosynthetic capacity (Amax), dark-adapted quantum efficiency of photosystem II (Fv/Fm), and relative chlorophyll content using a SPAD chlorophyll meter. Comparisons of Amax indicated that three of the 11 taxa (I. anisatum L., I. parviflorum Michx. ex Vent., and I. parviflorum `Forest Green') maintained similar rates of light-saturated carbon assimilation when grown in either shade or full sun. All other taxa experienced a significant reduction in Amax when grown in full sun. Chlorophyll fluorescence analysis demonstrated that Fv/Fm was similar between sun and shade plants for the same three taxa that were able to maintain Amax. These taxa appeared to experience less photoinhibition than the others and maintained greater maximum photochemical efficiency of absorbed light. SPAD readings were not significantly reduced in these three taxa either, whereas most other taxa experienced a significant reduction. In fact, SPAD readings were significantly higher in I. parviflorum `Forest Green' when grown under full sun, which also maintained the highest Amax of all the taxa. These results suggest that there is considerable variation in light tolerance among these taxa, with I. parviflorum `Forest Green' demonstrating superior tolerance to high light among the plants compared. A more rigorous examination of I. parviflorum `Forest Green' (high light tolerance) and I. floridanum Ellis (low-light tolerance) demonstrated that I. parviflorum `Forest Green' had a considerably higher Amax, a higher light saturation point, greater potential photosynthetic capacity, reduced susceptibility to photoinhibition as indicated by superior PSII efficiency following light exposure, greater capacity for thermal de-excitation as indicated by a higher rate of nonphotochemical quenching (NPQ) under full sun, greater apparent electron transport rate (ETR) at mid-day, and higher concentrations of the free-radical scavenger myo-inositol. All of these factors contribute potentially to a greater capacity to use light energy for carbon fixation while minimizing photodamage.