Cotton (Gossypium hirsutum L.), sorghum (Sorghum bicolor L.), soybean (Glycine max L.), and sunflower (Helianthus annuus L.) plants were exposed during daylight hours to an atmosphere enriched with CO2 to 630 ppm (v:v) (HiCO2) in a glasshouse. Temperature was trolled continuously to produce a daily maximum of 35 C and a minimum of 21 C. Days were cloudless and long, May to August, in Phoenix, Ariz. Average CO2 exchange rate (CER) increased 15% for cotton, 2% for sorghum, 41% for soybean, and 7% for sunflower compared to the CER of these species at 330 ppm CO2 (LoCO2). The increase in CER was not statistically significant for sorghum and sunflower. Measurements of relative growth rate and net assimilation rate showed the growth rate of all species increased during the juvenile stage (10d‐30d) in the enriched atmosphere. and were not higher in the enriched atmosphere after the juvenile stage, but cotton and soybean plants maintained their larger size and greater absolute growth.Final dry weights of cotton and soybean increased 110 and 380%, respectively, in HiCO2 compared to LoCO2. Lint yield of cotton was increased 180% by HiCO2 on a per‐plant basis and 88% on a unit leaf area basis. Became of growth fimitations imposed by terminal flowers, the final size of sorghum and sunflower plants in HiCO2 was not significantly larger than in LoCO2 These results imply that selection for CER will not effectively increase yield of determinate species such as sunflower and sorghum, but may effectively increase yield of indeterminate species such as cotton and soybean, if a sensitive assay for CER can be found.

The effects of some environmental factors on abscission (shedding) of young cotton (Gossypium hirsutum L.) fruits were investigated because excessive shedding is sometimes a problem in cotton production. Increasing the concentration of CO2 in the atmosphere from 350 to 1,000 ppm decreased shedding, increased the glucose and fructose contents of leaves, and lowered the average node number of the first bolls. Increasing the daily photoperiod from 8 to about 14 hours had similar effects. Conversely, shedding was increased by warm nights (30 C) and by low light intensity.These results indicate that factors that decrease photosynthesis or increase respiration may delay fruiting and decrease retention of floral buds (squares) and bolls. Low light intensity could become critical with high plant populations (more than 100,000 plants/ha), cloudy weather, rank growth, or a combination of the above conditions.

Abstract. Young Gossypium hirsutum L. seedlings chilled at 5°showed a continual decrease in ATP ooncentration with time of chilling. Chilled plants returned to optimum conditions were aible to restore the initial ATP concentration when chilled only 1 day, but not when chilled 2 days. The decrease in ATP with chilling was prevented by hardening the seedlings at 150 for 2 days (14-hr-day-length) immediately before chilling. The ATP level of hardened plants was higher than of unhardened plants. When hardened plants were chilled at 50, the ATP level increased in the leaves but decreased in the roots.A mechanism of chilling injury is discussed in relation to the decrease in ATP ooncentration at low temperature. gested that the metabolic injury in chilling-susceptible tissues may be due to an inability of the relatively inflexible mitochondria to function at low temperatures. Although ATP is required in n,early every synthetic process of plant metabolism, low temperature inhibition of phosphorylation would be important only if it resulted in a depletion of ATP to the point of disrupting metabolism (through an imbalance between phosphorylation rate and ATP utilization rate). A determination of the effects of chilling on ATP concentration in a chilling-susceptible plant should give an indication of whether or not chilling slows phosphorylation more than it slows ATP utilization. This study reports changes in the ATP contents of leaves and roots of cold-hardened and non-hardened cotton seedlinigs in response to chilling at 50.