Effects of light, CO(2) and temperature on carbohydrate metabolism in marigold (Tagetes patula)

Quantitative relationship between greenhouse environment and plant physiological responses are needed to determine optimal strategies for environmental control. In this research, seven experiments were conducted in a glass greenhouse compartment with six natural light growth chambers to (1) investigate the diurnal pattern of carbohydrate concentration under varying light intensities, CO{dollar}sb2{dollar} concentrations and day/night temperatures, (2) quantify the effects of CO{dollar}sb2{dollar} and light on carbohydrate accumulation, (3) determine effects of initial carbohydrate concentration on day time accumulation and night time utilization of starch and soluble sugar, (4) test the night temperature effect on seedling growth and (5) evaluate the near-infrared reflectance (NIR) spectroscopy method for rapid measurement of carbohydrate concentration in plant tissue.; Carbohydrate accumulation during the day was significantly affected by light intensity and CO{dollar}sb2{dollar} concentration. Starch and soluble sugar concentration increased from sunrise to late afternoon depending upon light intensity. During late afternoon as light decreased, starch and soluble sugar concentration decreased. On sunny days the peak accumulation of starch in the plant at 1000 ul/l CO{dollar}sb2{dollar} was 60-90% greater than at ambient CO{dollar}sb2;{dollar} the difference was not as great on cloudy days. Even though soluble sugar concentration was greater at 1000ul/l CO{dollar}sb2{dollar} than at ambient, the differences were not nearly as great as for starch.; The initial concentration of starch and soluble sugar at sunrise significantly affected the net additional accumulation of starch and soluble sugar. The greater the initial starch concentration above approximately 4 mg/100 mg dwt, the greater the inhibition of additional starch accumulation during the day. The inhibition was greater on a sunny day than on cloudy days.; The rate of carbohydrate metabolism at night was dependent upon the initial TNC concentration, night temperature and length of night. The greater the TNC{dollar}sb{lcub}rm i{rcub}{dollar} and night temperature the greater the rate of metabolism during the night. The model A = {dollar}-{dollar}1.571 + 0.889 TNC{dollar}sb{lcub}rm i{rcub}{dollar} + 0.139 t + 0.539 T {dollar}-{dollar} 0.007 TNC{dollar}sb{lcub}rm i{rcub} sp*{dollar}t {dollar}-{dollar} 0.036t{dollar}sp*{dollar}T describes the relationship between TNC{dollar}sb{lcub}rm i{rcub},{dollar} time after sunset (T) and night temperature (t) on starch concentration (A) at the end of the night period. Solving the equation for t gives an approximate temperature to metabolize starch (TNC{dollar}sb{lcub}rm i{rcub}){dollar} to a predetermined minimum concentration (A) by the end of the night period. The minimum concentration would be selected based on preventing inhibition of photosynthesis the next day as well as consideration of heating cost and quality of growth. A similar model was derived for soluble sugar.; Obtaining a quick and reliable measurement of carbohydrate concentration in the plant at sunset is critical for implementation of the proposed night temperature control strategy. Wet laboratory analysis is time consuming and would not be capable of determining the plant carbohydrate status at the beginning of the night. Therefore, near infrared reflectance spectroscopy (NIR) was evaluated as a more rapid method for plant carbohydrate analysis. The NIR analysis of starch, soluble sugar and TNC in marigold seedlings was highly correlated with chemical laboratory analysis.