4,256 research outputs found
Why does low intensity, long-day lighting promote growth in Petunia, Impatiens, and tomato?
Numerous reports demonstrate that low intensity, long-day (LD) lighting treatments can promote growth. However,
there are conflicting suggestions as to the mechanisms involved. This study examines the responses of Petunia,
Impatiens, and tomato to LD lighting treatments and concludes that no single mechanism can explain the growth
promotion observed in each case. Petunia showed the most dramatic response to photoperiod; up to a doubling in dry
weight (DW) as a result of increasing daylength from 8 h d–1 to 16 h d–1.This could be explained by an increase in specific leaf area (SLA) comparable to that seen with shading. At low photosynthetic photon flux densities (PPFD), the increased leaf area more than compensated for any loss in photosynthetic capacity per unit leaf area. In Petunia, the response may, in part, have also been due to changes in growth habit. Impatiens and tomato showed less dramatic increases in DW as a result of LD lighting, but no consistent effects on SLA or growth habit were observed. In tomato, increased growth was accompanied by increased chlorophyll content, but this had no significant effect on
photosynthesis. In both species, increased growth may have been due to a direct effect of LD lighting on photosynthesis.
This is contrary to the generally held view that light of approx. 3 – 4 μmol m–2 s–1 is unlikely to have any significant impact on net photosynthesis. Nevertheless, we show that the relationship between PPFD and net photosynthesis is non-linear at low light levels, and therefore low intensity LD lighting can offset respiration very efficiently.
Furthermore, a small increase in photosynthesis will have a greater impact when ambient light levels are low
The effects of day and night temperature on Chrysanthemum morifolium: investigating the safe limits for temperature integration
The impact of day and night temperatures on pot chrysanthemum (cultivars ‘Covington’ and ‘Irvine’) was assessed by exposing cuttings, stuck in weeks 39, 44, and 49, to different temperature regimes in short-days. Glasshouse heating setpoints of 12°, 15°, 18°, and 21°C, were used during the day, with venting at 2°C above these set-points. Night temperatures were then automatically manipulated to ensure that all of the treatments achieved similar mean diurnal temperatures. Plants were grown according to commercial practice and the experiment was repeated over 2 years. Increasing the day temperature from approx. 19°C to 21°C, and compensating by reducing the night temperature, did not have a significant impact on flowering time, although plant height was increased.This suggests that a temperature integration strategy which involves higher vent temperatures, and exploiting solar gain to give higher than normal day temperatures, should have minimal impact on crop scheduling. However, lowering the day-time temperature to approx. 16°C, and compensating with a warmer night, delayed flowering by up to 2 weeks. Therefore, a strategy whereby, in Winter, more heat is added at night under a thermally-efficient blackout screen may result in flowering delays.Transfers between the temperature regimes showed that the flowering delays were proportional to the amount of time spent in a low day-time temperature regime. Plants flowered at the same time, irrespective of whether they were transferred on a 1-, 2-, or 4-week cycle
The effects of long-day lighting and removal of young leaves on tomato yield
While low intensity long-day (LD) lighting has been shown to enhance the growth of young plants under low light levels, its effect on the yield of a long-season glasshouse tomato crop has not been previously examined. LD were provided by the use of tungsten lamps (2.8 μmol m-2 s-1 at approx. 0.5 m from the ground) between 04.00 h to sunrise and from sunset until 20.00 h (GMT). LD lighting increased leaf chlorophyll contents, and the numbers of flowers and fruits set per truss when the plants were young. However, this treatment did not affect the total yield of tomatoes. Different leaf removal treatments were applied within each glasshouse compartment. A previous experiment had shown that reducing the leaf area index (LAI) from 5.2 to 2.6, by removing old leaves, did not affect yield. It was also thought that removal of young leaves reduced the total vegetative sink-strength and favoured assimilate partitioning into the fruit. Therefore, removal of young leaves could increase fruit yield. In the present experiments, one-third of the leaves were removed in March (those immediately below each truss) and, subsequently, every third leaf was removed at an early stage of its development. This reduced the LAI from 4.1 to 2.9 and resulted in a loss of yield from 3 – 4 weeks after leaf removal until the end of the experiment, at which point there was an 8% loss of cumulative yield due to a reduction in the average number of fruits set per truss and in mean fruit weight. We postulate that the light which would have been intercepted by young photosynthetically-efficient leaves at the top of the canopy was intercepted instead by older leaves which were less efficient, reducing overall net canopy photosynthesis
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The importance of moisture distribution for the growth and energetics of mid-latitude systems
A primitive equation model is used to study the sensitivity of baroclinic wave life cycles to the initial latitude-height distribution of humidity. Diabatic heating is parametrized only as a consequence of condensation in regions of large-scale ascent. Experiments are performed in which the initial relative humidity is a simple function of model level, and in some cases latitude bands are specified which are initially relatively dry. It is found that the presence of moisture can either increase or decrease the peak eddy kinetic energy of the developing wave, depending on the initial moisture distribution. A relative abundance of moisture at mid-latitudes tends to weaken the wave, while a relative abundance at low latitudes tends to strengthen it. This sensitivity exists because competing processes are at work. These processes are described in terms of energy box diagnostics. The most realistic case lies on the cusp of this sensitivity. Further physical parametrizations are then added, including surface fluxes and upright moist convection. These have the effect of increasing wave amplitude, but the sensitivity to initial conditions of relative humidity remains. Finally, 'control' and 'doubled CO2' life cycles are performed, with initial conditions taken from the time-mean zonal-mean output of equilibrium GCM experiments. The attenuation of the wave resulting from reduced baroclinicity is more pronounced than any effect due to changes in initial moisture
Survey of Pain Curriculum Among Entry-Level Occupational Therapy Programs in the United States
Occupational therapy practitioners address pain management across settings, populations, and the lifespan. Occupational therapy practitioners offer unique contributions to pain management through biopsychosocial approaches, targeting supported self-management and occupational engagement. Comprehensive pain education is necessary to prepare entry-level occupational therapy practitioners to address pain in practice, yet no standards exist in entry-level occupational therapy education. This survey describes the status of pain-related education in entry-level occupational therapy programs across the United States. A total of 41 entry-level occupational therapy programs completed the survey. Total instructional time for pain content was reported to be an average of 9.68 hours, ranging from 1 to 30 hours, indicating significant variability. Average lecture (4.88 hours) and lab-based (5.05 hours) time devoted to pain content were similar. More time was devoted to teaching pain interventions (4.91 hours) than pain assessments (2.82 hours). Most programs integrated pain content throughout the curriculum (73%). One program utilized a standardized pain curriculum (International Association for the Study of Pain Occupational Therapy Curriculum). Open-ended questions revealed a breadth of evidence-based resources, pain assessments, and interventions covering all domains of the biopsychosocial model of pain. The majority of faculty (61%) felt their current amount of pain education was insufficient, citing the need for increased time and educational activities for pain education across all program years. Given the essential and unique role of occupational therapy practitioners in pain management, improving pain education and practitioner competence is an important consideration across entry-level occupational therapy education. Further discussion is needed regarding educational standards and entry-level occupational therapy curricula relating to pain management
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