Most systems used for controlling rootzone temperature (RZT) involve grouping plants in each treatment together in one temperature-controlling apparatus (3, 5). The power of experiments using systems with grouped plants is limited because the groups constitute single experimental units during data analysis. Some systems have overcome this problem, but reports may lack fabrication details (2) or indicate a limited RZT range was used (1, 4). We designed a precise, inexpensive system capable of achieving a wide range of RZT in which individual plants are discrete experimental units.
Hanan and Holley (6), in 1960. published on a simple air temperature control system for research purposes. However, present climate control systems have completely revolutionized the manner, quality, and efficiency of research carried out in greenhouses. Reports by Willits et al. (8, 9) showed that building a system with equipment extant in 1975 would be difficult for a practicing horticulturist. There are possibly now more than five companies in the United States marketing environmental control “computer” systems for the greenhouse industry. Within the past 10 years, interest in the potential of sophisticated climate control has been marked (1–4, 7–9).
An inexpensive, well-stirred chamber for measuring net fluxes of CO2 and H2O vapor from single leaves was constructed from readily available materials. It incorporates a fan that maximizes air turbulence and boundary-layer conductance. Leaf temperature can be maintained within ± 0.5°C of air temperature. Temperatures can be varied for experimental purposes or can be maintained constant even under varying heat loads using a temperature-controlled water circulator. When used in conjunction with such a circulator and CO2 and H2O vapor analyzers, this chamber can become an inexpensive yet useful component of a gas-exchange system.
A cooling system using the principles of heat transfer was designed to provide a temperature difference of 6C between root and shoot zones and to study the effect of this difference on growth, yield, and phenology of `TI-155' sweetpotato [Ipomoea batatas (L.) Lam.] grown using the nutrient film technique in a greenhouse. Treatments were temperature control (20C) and variable temperature (26C) in a randomized complete-block design with two replications. A modified half Hoagland's nutrient solution with a 1 N: 2.4 K ratio was used and was changed every 2 weeks. Nutrient solution pH was maintained between 5.5 and 6, and electrical conductivity, salinity, and solution temperature were monitored at regular intervals. Storage root fresh and dry weights (except for fibrous root dry weight) and foliage fresh and dry weights were not significantly influenced by root zone temperature. Leaf expansion rate and vine length were lower for root zone temperature control plants; stomatal conductance, transpiration, and leaf unfolding rates were similar for both treatments.
Tulip bulbs are produced in the Netherlands and are shipped to United States during the months of July and August in temperature-controlled shipping containers. Each shipment is often composed of a mixture of many cultivars. Mechanical failure of temperature controls may result in high temperatures that ultimately may reduce forcing quality of the bulbs. When such accidents occur, an immediate decision must be made about whether to invest more time and money on these potentially damaged bulbs. Such a decision is not easy because symptoms of heat damage are often delayed until months later. Research on a single cultivar, `Apeldoorn', has shown that heat stress can cause flower abortion and other abnormalities. However, cultivars undoubtedly vary in their response to heat stress. Thus in the 2002 and 2004 forcing seasons, ≈45 cultivars were screened for response to a standard heat stress of 4 days at 35 °C. Prior to the heat stress, bulbs were held at 17 °C or 9 °C for 4 weeks, mimicking conditions used for late and early forced bulbs, respectively. Flower and leaf height, percent flower abortion, and flowering date were evaluated. Heat stress caused flower abortion and reduced plant height in sensitive cultivars. Across all cultivars, cold storage prior to the heat stress significantly increased bulb's sensitivity to heat stress. Using percent flower abortion, cultivars were grouped into three categories: resistant, moderate, and susceptible. With this information, we hope that damage assessment may become easier and fewer bulbs wasted.
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.
`High-temperature controlled-atmosphere (high CO2/low O2) conditioning was investigated as a possible treatment to delay the incidence of internal breakdown of peaches and nectarines (Prunus persica L. Batsch) during subsequent cold storage. Maintaining an atmosphere of 5% to 15% CO2 added to air or to 1% to 5% O2 while conditioning peaches for 2 days at 20C partially prevented fruit ripening (compared to fruit conditioned in air), as measured by flesh softening and loss of green pigment, while no off-flavors were detected. Conditioning of peaches at 20C for 4 days in air or in air + 20% CO2 was detrimental to fruit quality, as indicated by flesh softening or detection of off-flavors.
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.
Four types of media [coir, 1 coir: 1 peat (by volume), peat, and sandy loam soil] were evaluated for their effects on plant growth and nitrate (NO – 3) leaching in the production of oriental lilies (Lilium L.) `Starfighter' and `Casa Blanca'. Twenty-five bulbs were planted in perforated plastic crates and placed on the ground in temperature-controlled greenhouses. The potential for NO – 3 leaching was determined by placing an ion-exchange resin (IER) bag under each crate at the beginning of the study. After plant harvest (14 to 16 weeks), resin bags were collected and analyzed for NO – 3 content. Plant tissues were dried, ground, and analyzed for N content. Results indicated that the use of coir and peat did not significantly influence plant growth (shoot dry weight) relative to the use of sandy loam soil; however, substrate type influenced the amount of NO – 3 leached through the media and N accumulation in the shoots for `Starfighter', but not `Casa Blanca'.
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.