The relationship between initial total non-structural carbohydrate concentration (TNCi) in marigold seedlings, night temperature, and night length were evaluated. Seedlings containing an average of 7.2, 18.1, and 23.5 mg/100 mg dwt of nonstructural carbohydrate (TNC) at sunset were treated with night temperatures of low (10°C), medium (17°C), and high (24°C). Starch and soluble sugars were determined at intervals during the night. TNC concentration at the end of the night is a function of the night temperature, TNCi concentration at sunset, and the night length. A model describing the relationship of these variables and their interactions was derived to estimate TNC concentration at any time during the night. This model when solved for temperature (t) establishes a temperature that will regulate the metabolic rate so the TNC concentration is metabolized efficiently to some minimum concentration by the end of the dark period. t = (–2.93 + 1.14 TNCi + 0.74 T – TNC – 0.48 TNCi * T)/(–0.18 + 0.011 TNCi + 0.04*T), R 2 = 0.88**). Thus, by knowing TNCi (possibly by near-infrared spectroscopy), the length of the night, and, assuming some minimum concentration for TNC by the end of the dark period, the night temperature is established.
Guoqiang Hou and Jack W. Buxton
Guoqiang Hou and Jack W. Buxton
Through control of light intensity and CO, concentrations, three levels of starch (low, medium and high) in marigold seedlings existed at sunset. The range in starch concentration represented that encountered under average greenhouse conditions. For each starting starch concentration, an optimum temperature was initially determined based on first and second order reactions on the corresponding starch decline curve. Every day, during seedling growth in the greenhouse, the starch concentration at sunset was predicted based on primarily the quantity of light received throughout the day; the night temperature was adjusted to the predicted optimum night temperature setting. Based on these studies a significant improvement in seedling growth can be achieved with significantly less heating cost.
Guoqiang Hou, Jack W. Buxton and Michael Collins
Studies were conducted to determine if near infrared reflectance spectrophotometry (NIR) could be used to rapidly determine nonstructural carbohydrate (TNC) concentrations in marigold tissue. Marigold seedlings were grown in natural light growth chambers. Light intensity and CO2 concentration were adjusted to establish leaf samples with a wide range of the carbohydrate concentration. NIR spectra were collected on dry, ground samples using a reflectance scanning monochromator. Conventional laboratory analysis values for the same samples were correlated with spectral data. Calibration statistics were as follows: TNC; standard error of calibration (SEC)= 1.73, R2= 0.95, standard error of prediction or perfomance (SEP) = 1.64, R2= 0.95; Starch, SEC = 1.35, R2= 0.96, SEP = 1.37, R2= 0.94; Soluble Sugars, SEC = 0.26, R2= 0.91, SEP = 0.29, R2= 0.84. These results show that the NIR method can be used to rapidly determine concentrations of nonstructural carbohydrates in marigold leaf tissue and suggest the possibility for routine assessment of carbohydrate status for optimum management of environmental factors.
Jack W. Buxton, Wenwei Jia and Guoqiang Hou
The automatic subirrigation system consists of a capillary mat placed above a constant water level in a reservoir. The optimum mat height above the water level was established by slanting a flat surface so the difference in vertical height from one end of the surface to the other was 25 cm. A ground cover providing water movement but not root penetration was placed over the mat. The capillary mat extended beyond the lowest end of the slopped surface and into the reservoir, the mat at the lowest end of the slopped surface was at the same vertical height as the water in the reservoir and remained constantly saturated. Plug trays were placed at intervals of 2.5 cm in vertical height above the water level. An average of 96-100% germination was obtained with marigold, tomato, impatiens and pepper seed in trays placed 5-7.5 cm in vertical height above the water level. These seedlings continued to develop and reached transplanting stage quicker than other trays. The rate and % germination was less in trays placed on the surface nearer to the height of the water in the reservoir. Germination in trays above 12.5 cm was greatly reduced and seed that did germinate did not develop and eventually died.
Jack W. Buxton, Donna Switzer and Guoqiang Hou
Marigold seedlings, 3 weeks old, were grown in natural light growth chambers at 3 day/night temperature regimes, 8°N/16°D, 13°N/20°D and 18°N/24°D, in a factorial combination with ambient and 1000-1500 ppm CO2. Seedlings were harvested at regular intervals during a 24 hr period and were analyzed for soluble sugars (reducing sugars and sucrose) and starch. Neither temperature nor CO2 concentration affected the accumulation of soluble sugars or starch during the day or night. The soluble sugar concentration ranged from 3% of dry weight at sunrise to 6% at mid-day; the concentration changed little during the night. Light intensity was different during replications of the experiment. Increased light intensity appeared to cause a slight increase in the soluble sugars maintained by the seedling during the day. Accumulated starch increased 6% to 8% from sunrise to late afternoon. Preliminary results indicate that light intensity greatly affected the concentration of starch. On the higher light intensity day, starch accumulated to a maximum of 18% of dry weight; whereas on the lower light intensity day the maximum concentration was 10%. During the night following the lower light intensity day, the starch concentration decreased to approximately 3% by the end of the night; following a brighter day the starch content was 13% at the end of the night.