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J.L. Catley

The influences of temperature and irradiance on vegetative growth of two species of Leucocoryne (Leucocoryne coquimbensis F. Phil and L. ixioides (Hook.) Lindl.) were examined in controlled environment growth rooms. The growing environments had day/night temperatures of 10/5, 15/10, or 20/15 °C, providing mean temperatures of 7.5, 12.5, or 17.5 °C, and photosynthetic photon fluxes (PPF) of 497 or 710 μmol·m-2·s-1. Leaf emergence data were recorded up to three times a week, and measurements of vegetative growth were made in the rooms twice weekly. Destructive harvests were carried out at intervals up to four weeks apart. Leaves of L. ixioides emerged first in all mean temperatures. As mean temperature decreased from 17.5 to 7.5 °C, the differences in first emergence dates became more apparent between species. Appearance of the second leaf of both species occurred in less than half the number of days the first leaf took to emerge. The time taken for further leaves to develop increased as temperature decreased, particularly for L. ixioides and at mean temperatures below 12.5 °C. Although leaves of L. ixioides emerged first, days to emergence of further leaves increased to lag behind production of L. coquimbensis leaves, particularly when mean temperatures dropped below 12.5 °C. Temperature also significantly affected growth of other plant parts. As mean temperature increased, maximum leaf, root and main bulb dry weights increased for both species, along with secondary bulb dry weights of L. coquimbensis. As irradiance increased, maximum leaf dry weights decreased and maximum bulb dry weights increased of both species, and maximum dropper dry weights of L. coquimbensis increased. Leucocoryne coquimbensis appears to have the greatest capacity to multiply vegetatively and this is enhanced by high mean temperatures. These results suggest that mean temperatures higher than those used in this study are required for sustained leaf emergence, particularly for L. ixioides although this species has the capacity to emerge at low temperatures. High mean temperatures are also likely to promote vegetative mass of all plant parts of both species, whereas higher irradiance levels than used in this study would enhance main bulb growth.

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Hiphil S. Clemente and Thomas E. Marler

Field-grown `Red Lady' papaya (Carica papaya L.) plants were used to measure foliar gas-exchange responses to rapid changes in irradiance levels to determine if papaya stomata are able to track simulated sun-to-cloud cover transitions. Natural sunlight and neutral shade cloth placed over the leaf were used to provide high photosynthetic photon flux (PPF) of about 2000 μmol·m-2·s-1 until leaves reached steady state within the cuvette, followed by three minutes with low PPF of about 325 μmol·m-2·s-1, and a return to PPF of about 2000 μmol·m-2·s-1. Net CO2 assimilation (A) declined from an initial 20 μmol·m-2·s-1 to about 9 μmol·m-2·s-1 within 20 seconds of initiating low PPF, and remained fairly stable for the duration of the three minutes of low PPF. Stomatal conductance (gs) declined within 60 seconds of initiating low PPF, from 385 to about 340 μmol·m-2·s-1 during the three minutes duration of low PPF. Following the return to high PPF, A rapidly increased to about 18 μmol·m-2·s-1, then gradually increased to the original value. After a lag of about 1 minute following the return to high PPF, gs began to increase and returned to the original value after three minutes. Container-grown `Tainung #1' papaya plants were used in a second study to determine the influence of mild drought stress on gas-exchange responses to rapid irradiance transitions. For drought-stressed plants, gs declined to a greater magnitude following the high-to-low PPF transition, and gs and A recovered more slowly following the transition from low-to-high PPF than for well-watered plants. Water use efficiency declined to a minimum immediately following the high-to-low PPF transition for both sets of plants, but recovered more rapidly for drought-stressed plants. These results indicate that papaya stomata are able to track rapid changes in irradiance, and mild drought stress enhances the tracking response.

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J.C. Vlahos

Three cultivars of Achimenes, `Flamenco', `Hilda', and `Rosenelfe', were grown for 10 weeks in nine environments: 17, 21, and 25C combined with 8, 16, or 24 hours of irradiance (213 μmol·s-1·m-2). Increase in temperature increased plant height, number of nodes, number of flowers, and shortened time to anthesis. Number of axillary shoots was enhanced at 17C. Increasing duration of illumination increased shoot dry weight and reduced plant height; a 16-hour light duration compared to 8 or 24 hours increased size and fresh and dry weight of rhizomes. `Rosenelfe' responded differently from `Flamenco' and `Hilda' to the environmental treatments. Depending on cultivar, top growth and flowering were influenced by temperature and duration of illumination, whereas rhizome growth was affected mainly by the latter.

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Ikuo Kataoka and Kenji Beppu

The contribution of the UV light component on the skin coloration was determined in `Hakuho' peach. Detached fruit partially covered with a UV-proof polyvinylchloride (PVC) film and a polyethylene film were exposed to sunlight for 4 days. Red coloration of the fruit and anthocyanin content in the skin were considerably reduced with the UV-proof PVC film. Irradiation with a UV fluorescent lamp at 3.58 W·m-2 markedly enhanced the red color development, while white fluorescent light at 120 μmol·m-2·s-1 did not affect the coloration. UV irradiation also increased the anthocyanin content in the cultured skin discs with increasing irradiance up to above 7.3 W·m-2. These results suggest that the UV component contributes significantly to the enhancement of the fruit coloration by sunlight exposure.

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John Erwin, Esther Gesick, Ben Dill, and Charles Rohwer

Photoperiod, irradiance, and/or a cool temperature effects on Chamaelobivia hybrid `Rose Quartz' flowering was studied. Two- to 3-year-old plants were grown for 4 months under natural daylight (DL; August–November) in a greenhouse maintained at 26 ± 2 °C. Plants were then placed in either of two greenhouses: a cool temperature house (5 ± 2 °C; natural daylight), or a lighting treatment house (22 °C day/18 ± 1 °C night temperature, respectively). The lighting treatment house had eight light environments: 1) short day (SD; 8 h; 0800–1600 HR); 2) SD+25–35 μmol·m-2·s-1; 3) SD+45-50 μmol·m-2·s-1; 4) SD+85-95 μmol·m-2·s-1; 5) DL plus night interruption lighting (NI; 2200–0200 HR; 2 μmol·m-2·s-1 from incandescent lamps); 6) DL+25-35 μmol·m-2·s-1 (lighted from 0800–0200 HR); 7) DL+45-50 μmol·m-2·s-1; and 8) DL+85-95 μmol·m-2·s-1. Supplemental lighting was provided using high-pressure sodium lamps. Plants were placed in the cool temperature environment for 0, 4, 8, or 12 weeks before being placed under lighting treatments. All plants received a 6-week lighting treatment and were then placed in the finishing greenhouse (22 ± 2 °C). Data were collected on the date when each flower opened (five only), the flower number per plant, and flower longevity (five only). Vernalization interacted with photoperiod to affect flowering. Unvernalized plants exhibited an obligate long-day requirement for flowering. Vernalized plants exhibited a facultative long-day requirement for flowering. The impact of vernalization, photoperiod, and irradiance on flower number, time to flower, and longevity will also be discussed.

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Terril A. Nell, Ria T. Leonard, and James E. Barrett

Production irradiance levels on growth, light compensation point (LCP), dark respiration (DR), and interior longevity of potted chrysanthemum (Demfranthema grandiflora Tzvelev. cvs. Iridon and Mountain Peak) and poinsettia (Euphorbia pulcherrima Wind. cvs. Annette Hegg Dark Red and Gutbier V-10 Amy) were determined. LCP and DR were measured at anthesis and during acclimatization to interior conditions (10 μmol·s-1·m-2). Days to flowering, inflorescence diameter, total chlorophyll, and interior longevity of chrysanthemum increased when maintained at a mean maximum photosynthetic photon flux density (PPFD) of 500 μmol·s-1·m-2 compared to plants shifted to 300 or 100 μmol·s-1·m-2 8 weeks after planting. LCP and DR were highest at anthesis and were reduced 38% and 49%, respectively, for chrysanthemum and 19% and 42%, respectively, for poinsettia within 3 days in interior conditions. Chrysanthemum plants shifted to 300 μmol·s1·m-2 during production had lower LCP and DR rates at anthesis and throughout time in interior conditions compared to plants maintained at 500 μmol·s-1·m-2. The acclimatization of chrysanthemum to reduced production PPFD is of little significance because interior longevity is reduced. No differences were found in the LCP or DR of poinsettia or chrysanthemum cultivars that differ in interior performance, demonstrating that these physiological characteristics are not good indicators of interior longevity for chrysanthemum and poinsettia.

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Rajasekaran R. Lada, F. Christine Pettipas, Steve Kyei-Boahen, Robert Gordon, and Tess Astatkie

Genotypes and environmental parameters interactively act on plants and modify their yield responses through modifying photosynthetic processes. In order to optimize yield, it is critical to understand the photosynthetic behavior of the crop as altered by genotypes and environment. Leaf gas exchange parameters of carrot (Daucus carota L.) cultivars Cascade, Carson, Oranza, and Red Core Chantenay (RCC) were examined in response to various irradiances, fertility levels, moisture regimes, and to elevated CO2 concentrations. Leaf net photosynthetic rate (PN), stomatal conductance (gs), and transpiration rate (E) were measured. Cultivars responded similarly to increasing PAR and CO2 concentrations and did not differ in photosynthetic parameters. Increasing PAR from 100 to 1000 μmol·m-2·s-1 increased PN, which did not reach saturation. The gs and E increased to a peak between 600 and 800 μmol·m-2·s-1, then rapidly declined, resulting in a sharp increase in water use efficiency (WUE). Increasing CO2 concentrations from 50 to 1050 μmol·mol-1 increased PN until saturation at 650 μmol·mol-1. The gs and E increased to a peak at 350 μmol·mol-1 and then declined. WUE increased linearly with increasing CO2. Carrots exposed to drought over a period of 5 days decreased PN and E. The PN decrease was cultivar specific. Nutrient concentrations of 0 to 400 ppm gave a similar pattern of decrease for PN, E, and gs. Treatment of 50 ppm had the highest PN, E, and gs. The WUE generally increased with increasing nutrient concentration.

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G.A. Picchioni and Héctor M. Quiroga-Garza

Two greenhouse studies were conducted to trace the fate of fertilizer N in hybrid bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy `Tifgreen'], and to estimate total plant N recovery and losses. The first experiment was performed during winter, with artificial light supplementing natural light to provide a photoperiod of 13.6 to 13.8 hours. The second experiment was conducted during summer and fall under only natural light conditions, with a progressively decreasing photoperiod of 13.7 to 11.1 hours. Urea (UR), ammonium sulfate (AS), and ammonium nitrate (AN) were labeled at 2 atom% 15N, and applied at N rates of 100 or 200 kg·ha-1 for 84 days (divided into six equal fractions and applied every 14 days). Fertilizer N source did not affect total dry matter (DM) accumulation by the plant components, but the high N rate increased clipping DM production under the longer photoperiod. Under the decreasing photoperiod, overall DM production was reduced, and clipping DM production was unaffected by increased N rate. Average N concentration of clippings varied between N sources, ranging from a high of 38.6 g·kg-1 DM with AS to a low of 34.7 g·kg-1 for UR. In Expt. 1, the greatest total plant N recovery [clippings, verdure (shoot material remaining after mowing), and thatch plus roots] occurred with AS (78.5%) and the lowest with UR (65.9%). In Expt. 2, these values declined to 53.0% and 38.0%, respectively. Urea fertilization resulted in the greatest N losses as a fraction of the N applied (33.6% to 61.5%) and AS fertilization the lowest (20.7% to 46.3%). In view of the greater N losses, UR may be a less suitable soluble N source for bermudagrass fertilization within the conditions of this study. In addition, late-season N fertilization may result in a significant waste of fertilizer N as bermudagrass progresses into autumnal dormancy when temperature, photoperiod, and irradiance decline and cause reduction in growth and N uptake.

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Ariana P. Torres and Roberto G. Lopez

seedlings requires an understanding of the effects of irradiance [photosynthetically active radiation (PAR) or photosynthetic photon flux ( PPF )] and temperature to manipulate plant growth and development ( Fausey and Cameron, 2005 ). Some desired

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Cheryl L. Reese and John E. Erwin

The interaction between day/night temperature (DT/NT) and irradiance during the photoperiod prior to the inductive night on Pharbitis nil (L.) cv. Violet flower induction was studied. Plants exposed to 12 or 18 °C NT did not flower regardless of DT. When NT was 24 or 30 °C, percent flowering plants increased progressively as DT increased from 12 to 30 °C. Percent flowering plants and total flower bud number per plant was greatest when seedlings were induced with a 24 or 30 °C DT/30 °C NT regime. DT/NT did not affect the node number to first flower. Irradiance did not affect flowering. Temperature effects on P. nil flowering could be described as a function of average daily temperature, where flowering increased as temperature rose from 22 to 30 °C.