Abstract
Ficus benjamina was held in light-and-temperature-controlled chambers for 12 weeks under 3 light sources of 20 μE m−2s−1 incandescent (INC) lamps, 20 μE m−2s−1 Cool White fluorescent (CWF) lamps, or 10 μE m−2s−1 INC + 10 μE m−2s−1 CWF light combination totaling 20 μE m−2s−1 photosynthetically active radiation (PAR). Plants also received 4 light durations (6, 12, 18, or 24 hr/day). Growth index was greater for plants held under INC. When plants were held under the light combination, leaf drop was reduced and plant grade was improved. Dry weight and plant grade increased and leaf drop decreased when plants were lighted for 24 hr/day. Chlorophyll content decreased under the light sources in the following order: CWF> light combination >INC.
Abstract
Studies on winter desiccation of broadleaved evergreens have raised the question of low temperature impedance of water movement in roots and stems. Temperature control of a section of stem can be readily accomplished by the use of cooling collars. Johnson (3), Handley (1), and Zimmerman (6) have brought about wilting of the leaves of various tree species by cooling parts of the stem to near or below the tissue freezing point. Presumably, the wilting was caused by restriction of water flow through the cooled section of stems. The wilted foliage recovered after the stem temperatures were allowed to rise, but no attempt has been reported to measure the minimum temperature at which water started to flow through the stem after freezing. To obtain information on this latter question was the primary objective of the study reported here.
A plant-based temperature control system for infrared heating to maintain the plant canopy at a desired temperature was evaluated under growth chamber conditions with possible projections to greenhouse environment. Benefits for using this system includes energy saving and plant protection. Infrared radiant heaters raised canopy temperatures to the optimum range which increased water use of New Guinea Impatiens over the same kind of plants grown with no radiant heat. Plant water use was 118% higher at an 18°C air temperature vs. 8°C air temperature and 33% higher at 24°C air temperature vs. 18°C air temperature. The degree of increase in plant water use was proportional to decrease (leaf air) temperature. The Penman-Monteith equation gave satisfactory results when the differential between leaf and air temperature was very low. At high (leaf-air) temperature deviation, the latent heat equation used to estimate stomatal resistance gave higher values for heated plants.
Abstract
The effects of high (86°F) and low (68°F) day temperature, and of high (2,500 to 5,000 ft-c) and low (500 to 1,200 ft-c) light intensity, on the coloration of ‘Cardinal’ and ‘Pinot noir’ grapes grown in sunlit, temperature-controlled rooms during the ripening period were investigated. Night temperature (7 PM to 7 AM) was 59°F in all treatments.
Low day temperature significantly increased the level of anthocyanin pigments in the skins of both cultivars at both high and low light intensity. Anthocyanin synthesis was almost completely inhibited in the skins of ‘Cardinal’ berries that had average daytime temperatures between 91 and 95°F.
Low light intensity greatly reduced coloration of ‘Pinot noir’ grapes at both low and high day temperatures but decreased the level of pigments in grapes grown at 86°F. It either increased or had little effect on fruit coloration of ‘Cardinal’ grapes grown at 68°F.
Abstract
Premature ripening, a physiological disorder of ‘Bartlett’ pears, was induced experimentally by use of temperature controlled limb cages. Exposure to 65° day and 45° F night temperatures for 3-31 days prior to harvest caused an early acceleration in ethylene production and occurrence of the climacteric rise in respiration. These changes were accompanied by fruit softening, increases in soluble pectin and protein N, a more rapid decline in malic acid as well as a decrease in the rate of citric acid accumulation. Treatments with gibberellic acid (GA3), 100 ppm, and succinic acid 2,2-dimethyl hydrazide (Alar), 1000 ppm, counteracted the effect of cool temperature exposure and retarded premature ripening. The disorder did not develop in fruit maintained at 75° day and 60° night temperatures during the experiment.
Temperature is most often used to control the progress of a poinsettia (Euphorbia pulcherrima Willd.) crop after flower initiation, but lack of good temperature control can make crop timing difficult. Degree-day summations are used to monitor and predict developmental stages of many crops. The objective was to determine whether degree-days can be used to predict poinsettia crop development. Dates of occurrence of first bract color and anthesis were observed for `Gutbier V-14 Glory' and `Annette Hegg Dark Red' poinsettia plants for 3 years. Total degree-day accumulation was read from an electronic instrument each day dates were recorded. There was a high level of consistency in the degree-day values, suggesting that degree-day accumulations offer a means of monitoring crop progress and of calculating temperature regimes so that plants finish on time.
Apple shoots were cultured in a MS medium with agar. Whole-plant stomatal conductance and net photosynthesis were measured in a temperature-controlled room with a modified steady state porometer coupled to an IRGA. The gas exchange cuvette was maintained at a steady 95% RH. Once a steady state conductance was reached, a light stimulus (about 350 μmol m–2 s–1) was applied to measure photosynthesis. At the end of the gas exchange measurements, shoot relative water content was determined. Rooted shoots had higher values stomatal conductance, net photosynthesis and shoot relative water content compared to shoots without roots. Both conductance and photosynthesis were correlated to shoot RWC. These results suggest that in vitro roots improve plant function, measured as conductance and photosynthesis, by allowing the plant to have a higher water status compared to shoots that lack shoots.
The contribution of in vitro-formed roots to the water status of tissue culture plants was studied by observing the stomatal responses of rooted and unrooted apple shoots. Stomatal conductance was measured on whole plants with a modified steady state porometer in a temperature-controlled room. The porometer was maintained at a steady 90% RH and conductance was measured every 30 seconds. Plants were kept in the gas exchange system for about 28 h. Steady state values of stomatal conductance for rooted and unrooted shoots were 220 (S.E= 19) and 163 (S.E=23) mmol m-2 s-1, respectively. When the plants were exposed to a light stimulus (1200 μmol m-2 s-1), rooted shoots showed an increase of about 64% in stomatal conductance. In the absence of roots, no response to light was observed. These results suggest that the presence of the roots improved, at least partially, water uptake and plant water status.
Little is known about the effect of growth temperature on Aster (Compositae, Asteraceae) flower development. In this study, we report on this effect for two aster lines, `Suntana' and `Sungal'. Growth temperature had a dramatic effect on the duration of flower development, ranging from 22 days for plants growing at 29 °C up to 32 days for plants grown at 17 °C. Flower longevity was ≈40% shorter under the higher temperature for both lines. Growth temperature also affected flowerhead form: `Suntana' flowerhead diameter was 20% larger at 17 °C than at 29 °C. The number of `Sungal' florets per flowerhead was four times greater at the lower temperature. Shading (30%) under temperature-controlled conditions had no effect on any of the parameters measured. For plants grown outdoors, our results suggest that shading plants may increase quality by reducing the growth temperature.
Schefflera arboricola was held in light- and temperature-controlled chambers for 6 months under three light intensities of 10 μmol·m–2·s–1, 20 μmol·m–2·s–1, and 80 μmol·m–2·s–1 measured as photon flux density (PFD). Plants also received three temperature regimes: 15 °C, 20 °C, and 25 °C. Reduced light intensity significantly decreased fresh and dry weight and increased chlorophyll content, but did not affect leaf thickness and palisade and spongy mesophyll parenchyma. High temperatures reduced fresh weight and significantly increased chlorophyll content and leaf thickness. The authors conclude that reduced photosynthetic energy flow at low light intensities (10 μmol·m–2·s–1, 20 μmol·m–2·s–1) could not be buffered by a downregulation of energy-consuming processes. Therefore the life span and quality of S. arboricola is reduced at such PFD values, especially at higher temperatures. Plants lose their marketability within 6 months.